JP5890982B2 - Overcurrent protection circuit and step-down switching power supply using the same - Google Patents

Overcurrent protection circuit and step-down switching power supply using the same Download PDF

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JP5890982B2
JP5890982B2 JP2011182499A JP2011182499A JP5890982B2 JP 5890982 B2 JP5890982 B2 JP 5890982B2 JP 2011182499 A JP2011182499 A JP 2011182499A JP 2011182499 A JP2011182499 A JP 2011182499A JP 5890982 B2 JP5890982 B2 JP 5890982B2
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原　英夫
英夫 原
吉生 東田
吉生 東田
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
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    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
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    • H02H3/087—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current for dc applications
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
    • H02H3/093—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current with timing means
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    • G10L25/00—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00
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    • G10L25/21—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00 characterised by the type of extracted parameters the extracted parameters being power information

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Description

本発明は、過電流保護回路及びこれを用いた降圧型スイッチング電源装置に関する。   The present invention relates to an overcurrent protection circuit and a step-down switching power supply device using the same.

従来より、同期整流方式の降圧型スイッチング電源装置には、過電流検出時に出力トランジスタ（上側トランジスタ）と同期整流トランジスタ（下側トランジスタ）を強制的にオフとして出力動作をシャットダウンさせる過電流保護回路が設けられている。このように、出力トランジスタと同期整流トランジスタをいずれも強制オフする構成であれば、過電流の発生原因（コントローラＩＣ外部の状態）に関わらず、過電流の流れ得る経路を遮断して、システムを安全な状態に保つことができる。   Conventionally, a synchronous rectification step-down switching power supply device has an overcurrent protection circuit that forcibly turns off an output transistor (upper transistor) and a synchronous rectification transistor (lower transistor) when an overcurrent is detected, thereby shutting down an output operation. Is provided. As described above, if both the output transistor and the synchronous rectification transistor are forcibly turned off, the path through which the overcurrent can flow is cut off regardless of the cause of the overcurrent (the state outside the controller IC). It can be kept safe.

なお、上記に関連する従来技術の一例としては、特許文献１や特許文献２を挙げることができる。   In addition, Patent Document 1 and Patent Document 2 can be cited as examples of related art related to the above.

特開２００８−２８９３０８号公報JP 2008-289308 A 特開２００２−１５３０４７号公報JP 2002-153047 A

しかしながら、上記従来の降圧型スイッチング電源装置において、出力段のコイルは、過電流検出時に出力トランジスタと同期整流トランジスタが強制的にオフされた後にも、接地端から同期整流トランジスタのボディダイオードを介して出力端に向けた電流を流し続ける。そのため、例えば、ボディダイオードの順方向降下電圧を０．７Ｖとし、ボディダイオードに流れる電流の最大値を１０Ａとした場合、ボディダイオードでは７Ｗもの大電力が消費されることになるので、大きな発熱を生じて降圧型スイッチング電源装置（またはこれを搭載したアプリケーション）の熱破壊を招くおそれがあった。   However, in the above-described conventional step-down switching power supply, the output stage coil is connected to the grounding end via the body diode of the synchronous rectification transistor even after the output transistor and the synchronous rectification transistor are forcibly turned off when an overcurrent is detected. Continue to flow current toward the output terminal. Therefore, for example, when the forward drop voltage of the body diode is 0.7 V and the maximum value of the current flowing through the body diode is 10 A, the body diode consumes a large amount of power of 7 W. This may cause thermal destruction of the step-down switching power supply device (or an application equipped with the same).

なお、上記で例示した同期整流方式の降圧型スイッチング電源装置に限らず、非同期整流方式の降圧型スイッチング電源装置についても同様の課題が存在する。   Similar problems exist not only in the synchronous rectification step-down switching power supply device exemplified above but also in the asynchronous rectification step-down switching power supply device.

本発明は、本願の発明者らにより見出された上記の問題点に鑑み、過電流保護動作時の発熱を抑えられる過電流保護回路、及び、これを用いた降圧型スイッチング電源装置を提供することを目的とする。   In view of the above-described problems found by the inventors of the present application, the present invention provides an overcurrent protection circuit capable of suppressing heat generation during an overcurrent protection operation, and a step-down switching power supply device using the same. For the purpose.

上記目的を達成するために、本発明に係る過電流保護回路は、降圧型スイッチング電源装置の出力電流が第１過電流保護値を上回ってから出力トランジスタを強制オフするまでの間に前記出力電流を前記第１過電流保護値よりも低い第２過電流保護値まで引き下げる過電流保護動作部を有する構成（第１の構成）とされている。   In order to achieve the above object, the overcurrent protection circuit according to the present invention includes the output current from the time when the output current of the step-down switching power supply device exceeds the first overcurrent protection value until the output transistor is forcibly turned off. Is configured to have an overcurrent protection operation unit (first configuration) that lowers to a second overcurrent protection value lower than the first overcurrent protection value.

なお、上記第１の構成から成る過電流保護回路において、前記過電流保護動作部は、前記第２過電流保護値を複数段階に引き下げる構成（第２の構成）にするとよい。   In the overcurrent protection circuit having the first configuration, the overcurrent protection operation unit may be configured to reduce the second overcurrent protection value in a plurality of stages (second configuration).

また、上記第１または第２の構成から成る過電流保護回路において、前記過電流保護動作部は、前記出力電流が前記第１過電流保護値を上回った直後に前記出力電流を前記第２過電流保護値まで引き下げる構成（第３の構成）にするとよい。   Further, in the overcurrent protection circuit having the first or second configuration, the overcurrent protection operation unit supplies the output current to the second overcurrent immediately after the output current exceeds the first overcurrent protection value. A configuration (third configuration) may be employed that lowers the current protection value.

また、上記第１〜第３いずれかの構成から成る過電流保護回路において、前記過電流保護動作部は、前記出力電流が前記第１過電流保護値を上回ってから第１時間が経過するまでの間、前記出力電流の上限値を前記第１過電流保護値にクランプし、前記第１時間が経過してからさらに第２時間が経過するまでの間、前記出力電流の上限値を前記第２過電流保護値にクランプし、前記第２時間が経過した時点で前記出力トランジスタを強制的にオフとする構成（第４の構成）にするとよい。   Further, in the overcurrent protection circuit having any one of the first to third configurations, the overcurrent protection operation unit is operable until a first time elapses after the output current exceeds the first overcurrent protection value. The upper limit value of the output current is clamped to the first overcurrent protection value, and the upper limit value of the output current is set to the first overtime until the second time elapses after the first time elapses. It is preferable that the output transistor is clamped to 2 overcurrent protection value and the output transistor is forcibly turned off when the second time has elapsed (fourth configuration).

また、上記第４の構成から成る過電流保護回路において、前記過電流保護動作部は、前記第１時間及び前記第２時間を計時するタイマを含む構成（第５の構成）にするとよい。   In the overcurrent protection circuit having the fourth configuration, the overcurrent protection operation unit may include a timer (fifth configuration) including a timer for measuring the first time and the second time.

また、上記第１〜第５いずれかの構成から成る過電流保護回路は、前記出力電流を監視する電流監視部と、前記第１過電流保護値と前記第２過電流保護値を設定する保護値設定部と、を有し、前記過電流保護動作部は、前記電流監視部の出力と前記保護値設定部の出力を比較して過電流保護動作を行う構成（第６の構成）にするとよい。   The overcurrent protection circuit having any one of the first to fifth configurations includes a current monitoring unit that monitors the output current, and a protection that sets the first overcurrent protection value and the second overcurrent protection value. A value setting unit, and the overcurrent protection operation unit compares the output of the current monitoring unit and the output of the protection value setting unit to perform an overcurrent protection operation (sixth configuration). Good.

また、本発明に係る降圧型スイッチング電源装置は、上記第１〜第６いずれかの構成から成る過電流保護回路を有する構成（第７の構成）とされている。   The step-down switching power supply according to the present invention has a configuration (seventh configuration) having an overcurrent protection circuit having any one of the first to sixth configurations.

なお、上記第７の構成から成る降圧型スイッチング電源装置は、整流素子として同期整流トランジスタを有する構成（第８の構成）にするとよい。   Note that the step-down switching power supply device having the seventh configuration may have a configuration (eighth configuration) having a synchronous rectification transistor as a rectifying element.

また、上記第８の構成から成る降圧型スイッチング電源装置において、前記過電流保護動作部は、前記出力トランジスタを強制オフする際、前記同期整流トランジスタも同時に強制オフする構成（第９の構成）にするとよい。   Further, in the step-down switching power supply device having the eighth configuration, when the overcurrent protection operation unit forcibly turns off the output transistor, the synchronous rectification transistor is also forcibly turned off at the same time (ninth configuration). Good.

また、上記第７の構成から成る降圧型スイッチング電源装置は、整流素子として整流ダイオードを有する構成（第１０の構成）にするとよい。   The step-down switching power supply device having the seventh configuration may have a configuration (tenth configuration) having a rectifier diode as a rectifier element.

本発明によれば、過電流保護動作時の発熱を抑えられる過電流保護回路、及び、これを用いた降圧型スイッチング電源装置を提供することが可能となる。   According to the present invention, it is possible to provide an overcurrent protection circuit capable of suppressing heat generation during an overcurrent protection operation, and a step-down switching power supply device using the same.

降圧型スイッチング電源装置の一構成例を示す図The figure which shows the example of 1 structure of a step-down switching power supply device 過電流保護回路１５の一構成例を示す図The figure which shows the example of 1 structure of the overcurrent protection circuit 15 過電流保護動作の第１例を示すタイムチャートTime chart showing the first example of overcurrent protection operation 過電流保護動作の第２例を示すタイムチャートTime chart showing second example of overcurrent protection operation 過電流保護動作の第３例を示すタイムチャートTime chart showing third example of overcurrent protection operation 降圧型スイッチング電源装置の一変形例を示す図The figure which shows the modification of a step-down switching power supply device

＜降圧型スイッチング電源装置＞
図１は、降圧型スイッチング電源装置の一構成例を示す図である。本構成例の降圧型スイッチング電源装置１は、半導体装置１０と、半導体装置１０に外付けされる種々のディスクリート部品（コイルＬ１、キャパシタＣ１、抵抗Ｒ１及びＲ２）と、を有する。 <Step-down switching power supply>
FIG. 1 is a diagram illustrating a configuration example of a step-down switching power supply device. The step-down switching power supply device 1 of this configuration example includes a semiconductor device 10 and various discrete components (coil L1, capacitor C1, resistors R1 and R2) attached to the semiconductor device 10.

半導体装置１０は、外部との電気的な接続を確立するために、少なくとも外部端子Ｘ１〜Ｘ３を有する。半導体装置１０の外部において、外部端子（電源端子）Ｘ１は、入力電圧Ｖｉｎの印加端に接続されている。外部端子（スイッチ端子）Ｘ２は、コイルＬ１の第１端に接続されている。コイルＬ１の第２端、キャパシタＣ１の第１端、及び、抵抗Ｒ１の第１端は、いずれも出力電圧Ｖｏｕｔの印加端に接続されている。キャパシタＣ１の第２端は、接地端に接続されている。抵抗Ｒ１の第２端、及び、抵抗Ｒ２の第１端は、いずれも半導体装置１０の外部端子（帰還端子）Ｘ３に接続されている。抵抗Ｒ２の第２端は接地端に接続されている。抵抗Ｒ１及びＲ２は、互いの接続ノードから出力電圧Ｖｏｕｔを分圧した帰還電圧Ｖｆｂを出力する帰還電圧生成部として機能する。コイルＬ１及びキャパシタＣ１は、外部端子Ｘ２に現れる矩形波状のスイッチ電圧Ｖｓｗを平滑化して出力電圧Ｖｏｕｔを生成する出力平滑部として機能する。   The semiconductor device 10 has at least external terminals X1 to X3 in order to establish an electrical connection with the outside. Outside the semiconductor device 10, the external terminal (power supply terminal) X1 is connected to the application terminal of the input voltage Vin. The external terminal (switch terminal) X2 is connected to the first end of the coil L1. The second end of the coil L1, the first end of the capacitor C1, and the first end of the resistor R1 are all connected to the application end of the output voltage Vout. The second end of the capacitor C1 is connected to the ground end. Both the second end of the resistor R1 and the first end of the resistor R2 are connected to the external terminal (feedback terminal) X3 of the semiconductor device 10. A second terminal of the resistor R2 is connected to the ground terminal. The resistors R1 and R2 function as a feedback voltage generation unit that outputs a feedback voltage Vfb obtained by dividing the output voltage Vout from the connection node. The coil L1 and the capacitor C1 function as an output smoothing unit that smoothes the rectangular wave switch voltage Vsw appearing at the external terminal X2 to generate the output voltage Vout.

半導体装置１０は、トランジスタ１１と、トランジスタ１２と、ドライバ１３と、コントローラ１４と、過電流保護回路１５と、を集積化したいわゆるスイッチング電源コントローラＩＣである。   The semiconductor device 10 is a so-called switching power supply controller IC in which a transistor 11, a transistor 12, a driver 13, a controller 14, and an overcurrent protection circuit 15 are integrated.

トランジスタ１１は、外部端子Ｘ１と外部端子Ｘ２との間に接続され、ドライバ１３から入力されるゲート信号Ｇ１に応じてオン／オフ制御される出力トランジスタ（上側トランジスタ）である。トランジスタ１１をＮＭＯＳＦＥＴ［N-channel type metal oxide semiconductor field effect transistor］で形成した場合、トランジスタ１１には、図示の向きでボディダイオードＤ１が寄生する。   The transistor 11 is an output transistor (upper transistor) that is connected between the external terminal X1 and the external terminal X2 and is ON / OFF controlled according to the gate signal G1 input from the driver 13. When the transistor 11 is formed of an NMOSFET (N-channel type metal oxide semiconductor field effect transistor), a body diode D1 is parasitic on the transistor 11 in the illustrated direction.

トランジスタ１２は、外部端子Ｘ２と接地端との間に接続され、ドライバ１３から入力されるゲート信号Ｇ２に応じてオン／オフ制御される同期整流トランジスタ（下側トランジスタ）である。なお、トランジスタ１２をＮＭＯＳＦＥＴで形成した場合、トランジスタ１２には、図示の向きでボディダイオードＤ２が寄生する。   The transistor 12 is a synchronous rectification transistor (lower transistor) that is connected between the external terminal X2 and the ground terminal and is on / off controlled in accordance with the gate signal G2 input from the driver 13. When the transistor 12 is formed of an NMOSFET, the body diode D2 is parasitic on the transistor 12 in the illustrated direction.

ドライバ１３は、コントローラ１４から入力されるスイッチ制御信号Ｓ０に応じてゲート信号Ｇ１及びＧ２を生成し、所定の駆動周波数（例えば５００ｋＨｚ）でトランジスタ１１及び１２を相補的（排他的）にスイッチング制御する。なお、本明細書中で用いられる「相補的（排他的）」という文言は、トランジスタ１１及び１２のオン／オフが完全に逆転している場合だけでなく、貫通電流防止の観点からトランジスタ１１及び１２のオン／オフ遷移タイミングに所定の遅延が与えられている場合（同時オフ期間が設けられている場合）も含む。トランジスタ１１及び１２が相補的（排他的）にオン／オフされることにより、外部端子Ｘ２には矩形波状のスイッチ電圧Ｖｓｗが生成される。   The driver 13 generates gate signals G1 and G2 according to the switch control signal S0 input from the controller 14, and performs switching control of the transistors 11 and 12 in a complementary (exclusive) manner at a predetermined drive frequency (for example, 500 kHz). . Note that the term “complementary (exclusive)” used in this specification is not limited to the case where the on / off states of the transistors 11 and 12 are completely reversed. This includes a case where a predetermined delay is given to the 12 on / off transition timings (when a simultaneous off period is provided). When the transistors 11 and 12 are turned on and off in a complementary manner (exclusively), a rectangular wave switch voltage Vsw is generated at the external terminal X2.

コントローラ１４は、外部端子Ｘ３に入力される帰還電圧Ｖｆｂが所定の目標値と一致するようにスイッチ制御信号Ｓ０を生成する。なお、コントローラ１４によるトランジスタ１１及び１２の駆動方式としては、ＰＷＭ［pulse width modulation］駆動方式やＰＦＭ［pulse frequency modulation］駆動方式など、いかなる方式を採用しても構わない。   The controller 14 generates the switch control signal S0 so that the feedback voltage Vfb input to the external terminal X3 matches a predetermined target value. As a driving method of the transistors 11 and 12 by the controller 14, any method such as a PWM [pulse width modulation] driving method or a PFM [pulse frequency modulation] driving method may be adopted.

過電流保護回路１５は、降圧型スイッチング電源装置１に流れる出力電流Ｉｏｕｔが過電流状態であるか否かを監視し、その監視結果に応じたクランプ制御信号Ｓ１とシャットダウン制御信号Ｓ２をコントローラ１４に出力する。   The overcurrent protection circuit 15 monitors whether or not the output current Iout flowing through the step-down switching power supply device 1 is in an overcurrent state, and sends a clamp control signal S1 and a shutdown control signal S2 to the controller 14 according to the monitoring result. Output.

＜過電流保護回路＞
図２は、過電流保護回路１５の一構成例を示す図である。本構成例の過電流保護回路１５は、電流監視部１５１と、保護値設定部１５２と、過電流保護動作部１５３を有する。 <Overcurrent protection circuit>
FIG. 2 is a diagram illustrating a configuration example of the overcurrent protection circuit 15. The overcurrent protection circuit 15 of this configuration example includes a current monitoring unit 151, a protection value setting unit 152, and an overcurrent protection operation unit 153.

電流監視部１５１は、出力電流Ｉｏｕｔを監視して、出力電流Ｉｏｕｔの電流値に応じた電流検出信号（電圧信号または電流信号）を過電流保護動作部１５３に出力する。出力電流Ｉｏｕｔの電流値を監視する手法としては、トランジスタ１１での電圧降下量を監視する手法や、出力電流Ｉｏｕｔの導通経路上に設けられたセンス抵抗での電圧降下量を監視する手法などが考えられる。   The current monitoring unit 151 monitors the output current Iout and outputs a current detection signal (voltage signal or current signal) corresponding to the current value of the output current Iout to the overcurrent protection operation unit 153. As a method for monitoring the current value of the output current Iout, there are a method for monitoring a voltage drop amount in the transistor 11, a method for monitoring a voltage drop amount in a sense resistor provided on the conduction path of the output current Iout, and the like. Conceivable.

保護値設定部１５２は、電流検出信号と比較参照される過電流保護値Ｉ１及びＩ２（ただしＩ１＞Ｉ２）を設定する。   The protection value setting unit 152 sets overcurrent protection values I1 and I2 (where I1> I2) that are compared and referenced with the current detection signal.

過電流保護動作部１５３は、電流監視部１５１の出力と保護値設定部１５２の出力とを比較して過電流保護動作を行う。なお、過電流保護動作部１５３は、過電流の誤検出を防止するためのマスク時間Ｔ（＝Ｔ１＋Ｔ２）を計時するタイマ１５４を含んでおり、出力電流Ｉｏｕｔが過電流保護値Ｉ１を上回っている状態がマスク時間Ｔにわたって継続したときに、トランジスタ１１及び１２を強制オフして出力動作をシャットダウンさせる。   The overcurrent protection operation unit 153 performs an overcurrent protection operation by comparing the output of the current monitoring unit 151 and the output of the protection value setting unit 152. The overcurrent protection operation unit 153 includes a timer 154 that measures a mask time T (= T1 + T2) for preventing erroneous detection of overcurrent, and the output current Iout exceeds the overcurrent protection value I1. When the state continues for the mask time T, the transistors 11 and 12 are forcibly turned off to shut down the output operation.

＜過電流保護動作＞
図３は、過電流保護動作の第１例を示すタイムチャートであり、上から順に、出力電流Ｉｏｕｔ及びコイル電流ＩＬの電流波形、並びに、出力電圧Ｖｏｕｔの電圧波形が描写されている。なお、実線は本発明の挙動を示しており、破線は従来の挙動を示している。 <Overcurrent protection operation>
FIG. 3 is a time chart showing a first example of the overcurrent protection operation, in which the current waveforms of the output current Iout and the coil current IL and the voltage waveform of the output voltage Vout are depicted in order from the top. In addition, the continuous line has shown the behavior of this invention, and the broken line has shown the conventional behavior.

何らかの異常によって出力電流Ｉｏｕｔが過電流状態に陥り、時刻ｔ１において出力電流Ｉｏｕｔが過電流保護値Ｉ１を上回ると、過電流保護動作部１５３は、タイマ１５４を用いてマスク時間Ｔ（例えば１μｓ）の計時を開始する。   If the output current Iout falls into an overcurrent state due to some abnormality, and the output current Iout exceeds the overcurrent protection value I1 at time t1, the overcurrent protection operation unit 153 uses the timer 154 for the mask time T (for example, 1 μs). Start timing.

時刻ｔ１から時間Ｔ１（例えば５００ｎｓ）が経過するまでの間、過電流保護動作部１５３は、出力電流Ｉｏｕｔの上限値を過電流保護値Ｉ１にクランプするようにクランプ制御信号Ｓ１を生成する。クランプ制御信号Ｓ１の入力を受けたコントローラ１４は、出力電流Ｉｏｕｔの上限値を過電流保護値Ｉ１にクランプするようにスイッチ制御信号Ｓ０を生成する。なお、出力電流Ｉｏｕｔの上限値が過電流保護値Ｉ１にクランプされたことに伴い、出力電圧Ｖｏｕｔは目標値から低下する。   Until time T1 (for example, 500 ns) elapses from time t1, the overcurrent protection operation unit 153 generates the clamp control signal S1 so as to clamp the upper limit value of the output current Iout to the overcurrent protection value I1. Upon receiving the clamp control signal S1, the controller 14 generates the switch control signal S0 so as to clamp the upper limit value of the output current Iout to the overcurrent protection value I1. As the upper limit value of the output current Iout is clamped to the overcurrent protection value I1, the output voltage Vout decreases from the target value.

時刻ｔ１から時間Ｔ１が経過して時刻ｔ２に至ると、過電流保護動作部１５３は、保護値設定部１５２に対して過電流保護値Ｉ１を過電流保護値Ｉ２とするように指示を送る。そして、時刻ｔ２からさらに時間Ｔ２（例えば５００ｎｓ）が経過するまでの間、過電流保護動作部１５３は、出力電流Ｉｏｕｔの上限値を過電流保護値Ｉ２にクランプするようにクランプ制御信号Ｓ１を生成する。クランプ制御信号Ｓ１の入力を受けたコントローラ１４は、出力電流Ｉｏｕｔの上限値を過電流保護値Ｉ２にクランプするようにスイッチ制御信号Ｓ０を生成する。なお、出力電流Ｉｏｕｔの上限値が過電流保護値Ｉ２へ引き下げられたことに伴い、出力電圧Ｖｏｕｔは目標値からさらに低下する。   When the time T1 elapses from the time t1 and reaches the time t2, the overcurrent protection operation unit 153 sends an instruction to the protection value setting unit 152 so that the overcurrent protection value I1 becomes the overcurrent protection value I2. The overcurrent protection operation unit 153 generates the clamp control signal S1 so as to clamp the upper limit value of the output current Iout to the overcurrent protection value I2 until the time T2 (for example, 500 ns) elapses from the time t2. To do. Upon receiving the clamp control signal S1, the controller 14 generates the switch control signal S0 so as to clamp the upper limit value of the output current Iout to the overcurrent protection value I2. As the upper limit value of the output current Iout is lowered to the overcurrent protection value I2, the output voltage Vout further decreases from the target value.

時刻ｔ２から時間Ｔ２が経過して時刻ｔ３に至ると、過電流保護動作部１５２は、トランジスタ１１及び１２を強制オフするようにシャットダウン信号Ｓ２を生成する。シャットダウン信号Ｓ２の入力を受けたコントローラ１４は、トランジスタ１１及び１２を強制オフするようにスイッチ制御信号Ｓ０を生成する。その結果、降圧型スイッチング電源装置１の出力動作はシャットダウンされる。   When the time T2 elapses from the time t2 and reaches the time t3, the overcurrent protection operation unit 152 generates the shutdown signal S2 so as to forcibly turn off the transistors 11 and 12. Upon receiving the shutdown signal S2, the controller 14 generates a switch control signal S0 so as to forcibly turn off the transistors 11 and 12. As a result, the output operation of the step-down switching power supply device 1 is shut down.

このとき、出力段のコイルＬ１は、トランジスタ１１及び１２が強制的にオフされた後にも、接地端からトランジスタ１２のボディダイオードＤ２を介して出力端に向けた電流を流し続ける。ただし、図３で示したように、過電流保護動作部１５３は、時刻ｔ１において出力電流Ｉｏｕｔが過電流保護値Ｉ１を上回ってから、時刻ｔ３においてトランジスタ１１及び１２を強制オフするまでの間に、出力電流Ｉｏｕｔを過電流保護値Ｉ１よりも低い過電流保護値Ｉ２まで引き下げる構成とされている。   At this time, the coil L1 in the output stage continues to flow a current from the ground terminal to the output terminal via the body diode D2 of the transistor 12 even after the transistors 11 and 12 are forcibly turned off. However, as illustrated in FIG. 3, the overcurrent protection operation unit 153 performs the interval between the time when the output current Iout exceeds the overcurrent protection value I1 at time t1 and the time when the transistors 11 and 12 are forcibly turned off at time t3. The output current Iout is reduced to an overcurrent protection value I2 lower than the overcurrent protection value I1.

このような構成とすることにより、ボディダイオードＤ２での消費電力を低減することができるので、過電流保護動作時の発熱を抑えて、降圧型スイッチング電源装置１（またはこれを搭載したアプリケーション）の熱破壊を回避することが可能となる。   With such a configuration, the power consumption of the body diode D2 can be reduced, so that heat generation during the overcurrent protection operation is suppressed, and the step-down switching power supply device 1 (or an application in which the step-down switching power supply 1 is installed) It becomes possible to avoid thermal destruction.

なお、過電流保護動作の第１例（図３）では、過電流保護値Ｉ２が一つだけ設定された構成を例に挙げて説明を行ったが、本発明の構成はこれに限定されるものではなく、過電流保護動作の第２例（図４）で示したように、過電流保護動作部１５３は、過電流保護値Ｉ２を複数段階（Ｉ２ａ、Ｉ２ｂ）で引き下げる構成としてもよい。   In the first example of the overcurrent protection operation (FIG. 3), the configuration in which only one overcurrent protection value I2 is set has been described as an example. However, the configuration of the present invention is limited to this. Instead, as shown in the second example of the overcurrent protection operation (FIG. 4), the overcurrent protection operation unit 153 may be configured to lower the overcurrent protection value I2 in a plurality of stages (I2a, I2b).

また、過電流保護動作の第１例（図３）や第２例（図４）では、出力電流Ｉｏｕｔが過電流保護値Ｉ１を上回ってから時間Ｔ１が経過した後に過電流保護値Ｉ１を過電流保護値Ｉ２に引き下げる構成を例に挙げて説明を行ったが、本発明の構成はこれに限定されるものではなく、過電流保護動作の第３例（図５）で示したように、過電流保護動作部１５３は、出力電流Ｉｏｕｔが過電流保護値Ｉ１を上回った直後に出力電流Ｉｏｕｔを過電流保護値Ｉ２まで引き下げる構成（時間Ｔ１をゼロ値に設定した構成）としても構わない。   In the first example (FIG. 3) and the second example (FIG. 4) of the overcurrent protection operation, the overcurrent protection value I1 is exceeded after the time T1 has elapsed after the output current Iout exceeds the overcurrent protection value I1. The description has been given by taking as an example the configuration for reducing the current protection value I2, but the configuration of the present invention is not limited to this, and as shown in the third example of the overcurrent protection operation (FIG. 5), The overcurrent protection operation unit 153 may be configured to reduce the output current Iout to the overcurrent protection value I2 immediately after the output current Iout exceeds the overcurrent protection value I1 (configuration in which the time T1 is set to a zero value).

このように、過電流保護動作の第２例（図４）や第３例（図５）を採用すれば、過電流保護動作の第１例（図３）と同様の効果を享受し得るほか、トランジスタ１１及び１２の強制オフ後に生じる発熱のみならず、トランジスタ１１及び１２のスイッチング動作が継続されるマスク時間Ｔに生じる発熱についても、できる限り抑制することが可能となる。   As described above, if the second example (FIG. 4) or the third example (FIG. 5) of the overcurrent protection operation is adopted, the same effect as the first example (FIG. 3) of the overcurrent protection operation can be enjoyed. Not only the heat generated after the transistors 11 and 12 are forcibly turned off, but also the heat generated during the mask time T during which the switching operation of the transistors 11 and 12 is continued can be suppressed as much as possible.

＜電流クランプ手法＞
まず、第１の電流クランプ手法（コンパレータモード）について説明する。第１の電流クランプ手法では、トランジスタ１１またはトランジスタ１２（いずれもオン抵抗値：Ｒｏｎ）でのドロップ電圧Ｖｄｒｏｐ（＝Ｒｏｎ×Ｉｏｕｔ）と、過電流保護値Ｉ１に相当する閾値電圧が比較され、その比較結果に基づいてクランプ制御信号Ｓ１が生成される。クランプ制御信号Ｓ１の入力を受けたコントローラ１４では、出力電流Ｉｏｕｔの上限値を過電流保護値Ｉ１にクランプするようにスイッチ制御信号Ｓ０が生成される。 <Current clamp method>
First, the first current clamp method (comparator mode) will be described. In the first current clamping method, the drop voltage Vdrop (= Ron × Iout) in the transistor 11 or the transistor 12 (both of which has an on-resistance value: Ron) is compared with the threshold voltage corresponding to the overcurrent protection value I1. A clamp control signal S1 is generated based on the comparison result. Upon receiving the clamp control signal S1, the controller 14 generates the switch control signal S0 so as to clamp the upper limit value of the output current Iout to the overcurrent protection value I1.

次に、第２の電流クランプ手法（カレントモード）について説明する。第２の電流クランプ手法では、トランジスタ１１に流れる出力電流Ｉｏｕｔが電圧信号（クランプ制御信号Ｓ１）として取り出され、この電圧信号がコントローラ１４内のカレントスロープ生成部（図１では不図示）に送出される。カレントスロープ生成部では、上記の電圧信号が電流に再変換され、この電流に基づいてスロープ電圧Ｖｓｌｐの角度（立上り速度）が可変制御される。コントローラ１４では、帰還電圧Ｖｆｂに応じて生成された誤差電圧Ｖｅｒｒ（＝帰還電圧Ｖｆｂと参照電圧Ｖｒｅｆとの差分電圧）と上記のスロープ電圧Ｖｓｌｐが比較され、その比較結果に基づいてトランジスタ１１のオンデューティが決定される。具体的に述べると、カレントスロープ生成部では、トランジスタ１１に流れる出力電流Ｉｏｕｔが過電流保護値Ｉ１に近いほどトランジスタ１１のオンデューティが小さくなるように、スロープ電圧Ｖｓｌｐの角度が周期的に可変制御されるので、出力電流Ｉｏｕｔの上限値を過電流保護値Ｉ１にクランプするようにスイッチ制御信号Ｓ０が生成される。   Next, the second current clamping method (current mode) will be described. In the second current clamping method, the output current Iout flowing through the transistor 11 is taken out as a voltage signal (clamp control signal S1), and this voltage signal is sent to a current slope generator (not shown in FIG. 1) in the controller 14. The In the current slope generator, the voltage signal is converted back into a current, and the angle (rising speed) of the slope voltage Vslp is variably controlled based on the current. The controller 14 compares the error voltage Verr (= difference voltage between the feedback voltage Vfb and the reference voltage Vref) generated according to the feedback voltage Vfb with the slope voltage Vslp, and the transistor 11 is turned on based on the comparison result. Duty is determined. Specifically, in the current slope generation unit, the angle of the slope voltage Vslp is periodically variably controlled so that the on-duty of the transistor 11 becomes smaller as the output current Iout flowing through the transistor 11 approaches the overcurrent protection value I1. Therefore, the switch control signal S0 is generated so as to clamp the upper limit value of the output current Iout to the overcurrent protection value I1.

＜その他の変形例＞
また、上記の実施形態では、同期整流方式の降圧型スイッチング電源装置を例に挙げて説明を行ったが、本発明の適用対象はこれに限定されるものではなく、例えば、図６（降圧型スイッチング電源装置の一変形例）で示すように、同期整流トランジスタ１２に代えて整流ダイオード１６を有する非同期整流方式の降圧型スイッチング電源装置にも本発明を適用することが可能である。 <Other variations>
In the above embodiment, the synchronous rectification step-down switching power supply device has been described as an example. However, the application target of the present invention is not limited to this, and for example, FIG. As shown in a modification of the switching power supply device, the present invention can also be applied to an asynchronous rectification step-down switching power supply device having a rectifier diode 16 instead of the synchronous rectification transistor 12.

このように、本明細書中に開示されている種々の技術的特徴は、上記実施形態のほか、その技術的創作の主旨を逸脱しない範囲で種々の変更を加えることが可能である。例えばバイポーラトランジスタとＭＯＳ電界効果トランジスタとの相互置換や、各種信号の論理レベル反転は任意である。すなわち、上記実施形態は、全ての点で例示であって、制限的なものではないと考えられるべきであり、本発明の技術的範囲は、上記実施形態の説明ではなく、特許請求の範囲によって示されるものであり、特許請求の範囲と均等の意味及び範囲内に属する全ての変更が含まれると理解されるべきである。   As described above, various technical features disclosed in the present specification can be variously modified within the scope of the technical creation in addition to the above-described embodiment. For example, mutual replacement of a bipolar transistor and a MOS field effect transistor and inversion of logic levels of various signals are arbitrary. That is, the above-described embodiment is an example in all respects and should not be considered as limiting, and the technical scope of the present invention is not the description of the above-described embodiment, but the claims. It should be understood that all modifications that come within the meaning and range of equivalents of the claims are included.

本発明は、降圧型スイッチング電源装置の安全性を高めるための技術として利用することが可能である。   The present invention can be used as a technique for increasing the safety of a step-down switching power supply device.

１ 降圧型スイッチング電源装置
１０ 半導体装置
１１ 出力トランジスタ
１２ 同期整流トランジスタ
１３ ドライバ
１４ コントローラ
１５ 過電流保護回路
１５１ 電流監視部
１５２ 保護値設定部
１５３ 過電流保護動作部
１５４ タイマ
１６ 整流ダイオード
Ｌ１ コイル
Ｃ１ キャパシタ
Ｒ１、Ｒ２ 抵抗 DESCRIPTION OF SYMBOLS 1 Step-down switching power supply device 10 Semiconductor device 11 Output transistor 12 Synchronous rectification transistor 13 Driver 14 Controller 15 Overcurrent protection circuit 151 Current monitoring part 152 Protection value setting part 153 Overcurrent protection operation part 154 Timer 16 Rectification diode L1 Coil C1 Capacitor R1 , R2 resistance

Claims (10)

電源電圧を受ける電源端子と、電圧を出力する出力端子を有する降圧型スイッチング電源装置において、
前記電源端子と前記出力端子の間に接続される出力トランジスタと、
前記出力端子と接地端の間に接続される整流素子と、
を含み、
第１端が前記出力端子と接続され、第２端が出力電圧の印加端に接続されるコイルと、
前記コイルの前記第２端と前記接地端の間に接続される出力キャパシタと、
前記コイルに流れる出力電流が第１過電流保護値を上回ったとき前記出力トランジスタを強制オフするに際し、まず前記コイルに流れる前記出力電流を前記第１過電流保護値よりも低い第２過電流保護値まで引き下げ、さらに所定時間経過後前記出力トランジスタを強制オフする過電流保護動作部を有することを特徴とする過電流保護回路。 In a step-down switching power supply device having a power supply terminal that receives a power supply voltage and an output terminal that outputs the voltage ,
An output transistor connected between the power supply terminal and the output terminal;
A rectifying element connected between the output terminal and a ground terminal;
Including
A coil having a first end connected to the output terminal and a second end connected to an output voltage application end;
An output capacitor connected between the second end of the coil and the ground end;
When the output transistor is forcibly turned off when the output current flowing through the coil exceeds the first overcurrent protection value , first, the output current flowing through the coil is reduced to a second overcurrent protection lower than the first overcurrent protection value. An overcurrent protection circuit comprising: an overcurrent protection operation unit that is lowered to a value and forcibly turns off the output transistor after a predetermined time has elapsed . 前記過電流保護動作部は、前記第２過電流保護値を複数段階に引き下げることを特徴とする請求項１に記載の過電流保護回路。   The overcurrent protection circuit according to claim 1, wherein the overcurrent protection operation unit lowers the second overcurrent protection value in a plurality of stages. 前記過電流保護動作部は、前記出力電流が前記第１過電流保護値を上回った直後に前記出力電流を前記第２過電流保護値まで引き下げることを特徴とする請求項１または請求項２に記載の過電流保護回路。   3. The overcurrent protection operation unit according to claim 1, wherein the output current is reduced to the second overcurrent protection value immediately after the output current exceeds the first overcurrent protection value. The overcurrent protection circuit described. 前記過電流保護動作部は、
前記出力電流が前記第１過電流保護値を上回ってから第１時間が経過するまでの間、前記出力電流の上限値を前記第１過電流保護値にクランプし、
前記第１時間が経過してからさらに前記所定時間である第２時間が経過するまでの間、前記出力電流の上限値を前記第２過電流保護値にクランプし、
前記第２時間が経過した時点で前記出力トランジスタを強制的にオフとする、
ことを特徴とする請求項１〜請求項３のいずれか一項に記載の過電流保護回路。 The overcurrent protection operation unit is
Until the first time elapses after the output current exceeds the first overcurrent protection value, the upper limit value of the output current is clamped to the first overcurrent protection value,
The upper limit value of the output current is clamped to the second overcurrent protection value until the second time, which is the predetermined time, elapses after the first time elapses,
Forcibly turning off the output transistor when the second time has elapsed;
The overcurrent protection circuit according to claim 1, wherein the overcurrent protection circuit is provided. 前記過電流保護動作部は、前記第１時間及び前記第２時間を計時するタイマを含むことを特徴とする請求項４に記載の過電流保護回路。   The overcurrent protection circuit according to claim 4, wherein the overcurrent protection operation unit includes a timer that counts the first time and the second time. 前記出力電流を監視する電流監視部と、
前記第１過電流保護値と前記第２過電流保護値を設定する保護値設定部と、
を有し、
前記過電流保護動作部は、前記電流監視部の出力と前記保護値設定部の出力を比較して過電流保護動作を行うことを特徴とする請求項１〜請求項５のいずれか一項に記載の過電流保護回路。 A current monitoring unit for monitoring the output current;
A protection value setting unit for setting the first overcurrent protection value and the second overcurrent protection value;
Have
The overcurrent protection operation unit performs an overcurrent protection operation by comparing the output of the current monitoring unit and the output of the protection value setting unit. The overcurrent protection circuit described. 請求項１〜請求項６のいずれか一項に記載の過電流保護回路を有することを特徴とする降圧型スイッチング電源装置。   A step-down switching power supply comprising the overcurrent protection circuit according to any one of claims 1 to 6. 前記整流素子として同期整流トランジスタを有することを特徴とする請求項７に記載の降圧型スイッチング電源装置。 The step-down switching power supply device according to claim 7, further comprising a synchronous rectifier transistor as the rectifier element. 前記過電流保護動作部は、前記出力トランジスタを強制オフする際、前記同期整流トランジスタも同時に強制オフすることを特徴とする請求項８に記載の降圧型スイッチング電源装置。   9. The step-down switching power supply apparatus according to claim 8, wherein the overcurrent protection operation unit forcibly turns off the synchronous rectification transistor simultaneously when the output transistor is forcibly turned off. 前記整流素子として整流ダイオードを有することを特徴とする請求項７に記載の降圧型スイッチング電源装置。 8. The step-down switching power supply device according to claim 7, further comprising a rectifier diode as the rectifier element.
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