CN103917011B - A kind of white LED driver system with soft-start module - Google Patents

Abstract

The present invention is about a kind of white LED driver system based on electric charge pump, on the basis of common White LED Drive, uses 1X/1.5X adaptive charge pump, can substantially increase power conversion efficiency according to the change auto-changing mode of operation of input voltage；In whole power supply supply district (2.7V 5.5V), the automatic switchover of two kinds of mode of operations of 1X/1.5X can be realized, it is ensured that higher conversion efficiency；By outside pulse control signal, it is achieved the flexible to LED luminance；In conjunction with pulse amplitude modulation PAM degenerative error amplifier, the stationarity of output voltage is effectively ensured；Especially having soft start function can effectively prevent chip to be input to the surge current of outfan when starting.Whole drive system has the features such as driving force is strong, brightness regulation convenience, wide supply district, power supply conversion efficiency are high, temperature performance is stable, peripheral circuit is simple.

Description

A kind of white LED driver system with soft-start module

Technical field

The present invention relates to a kind of White LED Drive, be specifically related to a kind of white light with soft-start module based on electric charge pump LED drive circuit.

Background technology

At present, the characteristics such as white light LEDs is outstanding with its source mass, low in energy consumption, application is simple, mobile phone, MP3, PDA, DC, The LCD backlight of the portable sets such as individual's notebook is widely used；And also lead at automobile lamp, domestic lighting etc. Territory occupies one seat.The market potential that white light LEDs is huge, driven greatly LED driver to low-power consumption, Gao Ji Cheng Hua, the direction of programmable are developed.At present, the research and development of domestic power management chip are in quick developmental stage, have been achieved with Impressive achievement.So developing high-quality White LED Driver the most just become the emphasis of everybody research.

Electric charge pump is exactly to utilize electric capacity that from input, the build-up effect of electric charge is transferred to outfan electric charge, it is achieved boost function, Electric current needed for simultaneously providing for load, its topological structure determines transformation multiple and conversion efficiency, and adaptive charge pump be exactly Auto-changing between different transformation multiples.It has simple in construction, low EMI, the feature such as is easily integrated, the most widely It is applied to the every field such as White-light LED illumination, memorizer, level translator.

For white light LEDs application in the portable set LCD backlight such as mobile phone, PDA, the present application is a kind of based on electricity The white LED driver chip of lotus pump, and have that volume is little, EMI is low, transformation efficiency is high and the feature such as low cost.Can drive simultaneously Dynamic 4 main display white light LEDs and 2 secondary display screen white light LEDs, especially, defeated in order to prevent chip to be input to when starting Going out the surge current of end, the white LED driver that the application is invented has a soft-start module, and this module is prevented from surge Electric current, it is ensured that steady and drive circuit the highly effective and safe of electric current runs.

The content of invention

To achieve these goals, the present invention adopts the following technical scheme that

A kind of based on electric charge pump the white LED driver system that the present application relates to, this system includes: electric charge pump boost module, Error amplifier block, Logic control module, maximum current setting module, rheonome module, make energy control module, LED Negative pole minimum voltage selects module, oscillator module and these basic function module of reference offset module.

Wherein, electric charge pump boost module is common 1X/1.5X electric charge pump, along with the change of supply voltage, automatically operates in 1X Or under 1.5X pattern, make output voltage be more than white light LEDs normally voltage V_F, it is sufficient to drive white light LEDs.Supply voltage is relatively Time low, it is operated under 1.5X pattern, it is achieved boost function；When supply voltage is higher, work is in the 1 x mode；

In particular, the drive circuit as above that the application relates to also includes a soft-start module, and this soft-start module is used for When chip starts, prevent the surge current produced due to input and the big pressure reduction of outfan；

White LED driver system as above, is further characterized in that: this LED drive system also includes that a power supply selects mould Block, this power supply selects module the maximum in the input voltage selecting chip and output voltage, opens as power in electric charge pump Closing the maximum level of pipe control signal, effectively to drive charge pump power switch, output simultaneously enables signal, is used for controlling power The driving module of pipe.

White LED driver system as above, is further characterized in that: this LED drive system also includes a model selection mould Block, for selecting the output of module to compare with reference gate voltage limit minimum voltage, selects signal according to different situations output mode.

White LED driver system as above, is further characterized in that: this LED drive system also includes that a patten transformation makes Energy module, for providing a low power transition enabled signal, and mode select signal co-controlling electric charge pump is transformed into from 1.5X 1X pattern.

Accompanying drawing explanation

Fig. 1, system function module frame diagram

Fig. 2, White LED Drive figure based on electric charge pump

Error amplifier equivalent schematic diagram in Fig. 3, White LED Drive based on electric charge pump

Fig. 4, error amplifier circuit schematic diagram 1

Fig. 5, error amplifier circuit schematic diagram 2

Fig. 6, the equivalent framework map of soft starting circuit

Fig. 7, soft starting circuit schematic diagram

Fig. 8, power supply select module principle figure

Fig. 9, power supply select the common grid comparator circuit figure in module

Figure 10, mode selection module fundamental diagram

Figure 11, enable module fundamental diagram

Figure 12, enable module work equivalent circuit diagram

Reference

Detailed description of the invention

Fig. 1 is the overall structure figure of the white LED driver system involved by the application.

1X/1.5X CHARGE-PUMP shown in Fig. 1 is 1X/1.5X electric charge pump, along with the change of supply voltage, automatically works Under 1X or 1.5X pattern, output voltage is made to be more than white light LEDs normally voltage V_F, it is sufficient to drive white light LEDs.Power supply When voltage is relatively low, it is operated under 1.5X pattern, it is achieved boost function；When supply voltage is higher, work is in the 1 x mode.Figure SOFT-START shown in 1 is soft-start module: when chip starts, and prevents from producing due to input and the big pressure reduction of outfan Surge current；In the case of overload (output short-circuit), the every 2.1ms of soft-start module works once.EA shown in Fig. 1 is for by mistake Difference amplifier: for amplifying minimum voltage and the reference voltage difference of 0.18V of 6 LED negative pole ends, adjusted by pulse amplitude The negative feedback of system (PAM), makes the output voltage stabilization of 1.5X electric charge pump.LOGIC-CONTROL shown in Fig. 1 is logic control Module: for controlling the work that modules is coordinated.PROTECTION shown in Fig. 1 for protection module: comprise excess temperature, overvoltage, Under-voltage locking, four protection circuits of short circuit, it is ensured that chip works the most safely.CURRENT-SET shown in Fig. 1 is maximum Current settings module.Error amplifier is V the voltage clamp arranging resistance Rset_REF2, set A point by current mirror simultaneously Level；The size of Rset determines the maximum current of LED.LDO C-REGULATOR shown in Fig. 1 is LDO rheonome Part, regulates the electric current of each LED, it is achieved constant-current driving respectively, it is ensured that higher currents match degree, uniform to obtain Brightness；Main-auxiliary screen control signal controls it can realize LED11 rank brightness flop.Shown ENM/ENS CONTROL be ENM, ENS control module: process outside ENM, ENS pulse control signal, controls main-auxiliary screen switch and brightness regulation.Shown SEL-MIN Module is selected: for the voltage of 6 LED negative pole ends of detection, select minima, feed back to error for LED negative pole minimum voltage Amplifier.Shown OSC is agitator: for providing the fixed frequency of 1MHz for system.On the basis of shown REF&IBIAS Biasing module: for providing the reference voltage and bias current not affected by temperature and mains voltage variations for each module of system, protect Card system is working properly.

The specific works principle of the white LED driver system involved by the application is as shown in Figure 2:

After system electrification (switching on power), first detect ENM, ENS and control the signal level of end.If ENM and ENS is low Level, then chip is still in shutdown mode.If it is high level that ENM/ENS has one or all, chip starts to start: first Base modules is set up, and then current offset module is started working, for the operating current that other submodules offer of system is stable.Connect , soft start is started working, and in order to prevent the surge current formed due to pressure reduction bigger between IN end and OUT terminal, soft opens Output capacitance is gradually charged by dynamic model block by the slope current source of digital-to-analogue conversion, until OUT is close to IN.This process maintains about 2ms, Electric charge air pump inoperative during this period.

Starting after terminating, chip will judge to be operated under 1X or 1.5X mode of operation.When supply voltage is higher, i.e. SEL-MIN selects the minimum voltage V of 6 LED negative pole ends_SEL-MINMore than 0.1V, output mode control signal MODE_SEL is High level, chip would operate under 1X pattern；Otherwise, V_SEL-MINBeing low level less than 0.1V, MODE_SEL, chip will It is operated under 1.5X pattern.If chip operation is in the 1 x mode, along with the use of battery, supply voltage declines, works as V_SEL-MIN Dropping to below threshold voltage 0.1V, chip (namely electric charge pump) jumps to 1.5X MODE of operation, simultaneously V_SEL-MINPass through Error amplifier EA negative feedback control electric charge pump, regulated output voltage VOUT.If chip operation is under 1.5X pattern, along with Charging battery, supply voltage VIN rises；When cell voltage is higher than VOUT about 50mV and V_SEL-MINIt is increased to more than 0.1V Time, chip jumps to again 1X MODE of operation.

Can realize LED luminance 11 rank by ENM or ENS low level pulse to change, each pulse reduces the 10% of LED current, 10th pulse makes LED current be reduced to 5%；ENM or ENS keeps low level to turn off more than 2ms, the LED of main screen or secondary screen； ENM and ENS keeps low level more than 2ms simultaneously, and whole chip turns off.The high-high brightness of LED is set by non-essential resistance Rset Fixed, representative value is 20mA.

Error amplifier block operation principle and circuit diagram explanation.

Wherein, the operation principle of error amplifier block is as shown in Figure 3.Mainly it is made up of amplifier and pulse sampling circuit.Put The reference voltage V just terminating 0.18V of big device_REF1, negative terminal meets the output voltage V of SEL-MIN module_SEL-MIN, i.e. 6 LED Minimum amount of voltage that in negative pole level, such amplifier and electric charge pump just form degeneration factor, V_SEL-MINClamper is at 0.18V Left and right, is effectively ensured the stability of output voltage.Pulse sampling circuit is very simple, the metal-oxide-semiconductor group of on-off action by Become, grid pulsing oscillation pulse signal, it is possible to realize the sampling to amplifier output voltage, thus define PAM signal.

Fig. 4 show the circuit diagram 1 of error amplifier.Error amplifier EA is made up of EA1, EA2 two parts, wherein EA1 For gain stage, EA2 is output stage and pulse sampling circuit.EN_OTP is from thermal-shutdown circuit, making for error amplifier Energy signal, high level is effective；V_REF0、V_REF1From band-gap reference module, it is provided that the reference voltage of 1.25V and 0.18V；V_SEL-MIN From SEL-MIN module, it is the minimum levels of 6 LED negative pole end voltages, the stability of negative feedback control output voltage；I_CR1 From current regulating module, provide part tail current for error amplifier；END_SS is from Logic control module, for soft start The id signal terminated, Low level effective；I_SOFTFrom soft-start module, for the ramping current signal in soft start stage, control Error amplifier is in the output in soft start stage；P_S3 is from Logic control module, for the pulse control signal of S3.Two anti- Phase device and switching tube MG150, MG151, MG160, MG162, MG163 form auxiliary control circuit, signal EN_OTP control Whether EA1 processed normally works.When EN_OTP is low level, EA1 turns off；When EN_OTP is high level, circuit is just Often work.Wherein QG27, RG2, MG124 branch road and QG26, RG1, QG23, RG24 branch road be respectively amplifier EA1 and EA2 offer bias current and tail current:

$I_{\mathrm{BIAS}1}=\frac{V_{\mathrm{LB}46}-V_{T,Q27}}{\mathrm{RG}2}---(4-1)$

$I_{\mathrm{BIAS}2}=\frac{V_{\mathrm{LB}46}-V_{T,Q26}}{\mathrm{RG}1}---(4-2)$

QG34, QG24, RG17 and QG33, QG25, RG18 constitute two source followers, for the input of error amplifier Level, to promote the level of input signal in the common-mode input range of amplifier；QG32, QG22, RG15 and MG165, MG166, MG167 forms current mirror, is used for eliminating the base current of source follower QG33 and QG34；QG28, QG29 are that the first order is put The input difference pair of big device, QG30, QG31 that mirror image connects is the load of difference amplifier, and RX1, RX2 are mainly for increasing The output resistance of amplifier, to improve gain；MG126 and I_CR1Tail current is provided；QG37, QG38 that diode connects are reverse-biased, To compensate temperature to the differential impact on collector current；I_CR1It is the constant current from current regulating module, with LED luminance Difference and adjusted in concert, provide part tail current for error amplifier, and then improve the performance of error amplifier under different brightness Parameter.The output gain of first order amplifier is:

A_VD1=g_m,QG29*r_o1

Wherein,For the mutual conductance of QG29, r_o1Output resistance for difference amplifier.

QG35, QG36 and MG134, the grounded emitter amplifier of 135 compositions are second level amplifier, improve error amplifier further Gain, its gain is:

A_V2=g_m,QG35*r_o2

Wherein,For the mutual conductance of QG35,Load resistance for grounded emitter amplifier.

As it is shown in figure 5, MG164, MG91 of being controlled by END_SS and phase inverter form the control circuit in soft start stage.When When chip is in the soft start stage, END_SS is high level, and WG110 is set to high level, now slope current I_SOFTPass through The PMOS common-source amplifier of MG88, MG89, MA2 composition controls the output signal of error amplifier；After soft start terminates, END_SS is set to low level, and the PMOS common-source amplifier of MG88, MG89, MA2 composition quits work, and MG130, MG131, The third level that common-source amplifier is error amplifier of MA2 composition, its gain is:

A_V3=g_m,MG130*r_o3

Wherein, g_m,MG130For the mutual conductance of MG130,Load resistance for PMOS common-source amplifier.

QG5, MG93 and Q15, MG115 separately constitute source follower, for the output stage of error amplifier, regulation gain stage output electricity Flat, MG113 and MG108 provides bias voltage；QG2, QG12 form push-pull output stage, provide foot for power switch pipe MNS3 Enough driving signals.The switching tubes such as MG58, MG59 and logic below circuit composition control circuit and pulse signal control circuit； The MG55 pulse signal by grid, the output to error amplifier is sampled, and forms PAM signal.

Soft-start module operation principle and circuit diagram explanation.

In order to prevent chip to be input to the surge current of outfan when starting, this chip contains a soft starting circuit.Work as chip After powering on, soft start is charged to output capacitance by slope current source (not having the effect of electric charge pump), until output voltage is close Input voltage, now, chip will judge to be operated under 1X pattern or 1.5X pattern.If it is in the case of 1X pattern, soft Starting and will terminate, chip starts normally to work；Otherwise, the soft start minimum level in LED1 LED6 that always works reaches pre- If value (0.1V).If the situation having overload or output earth short circuit occurs, soft start will often be repeated once by 2ms.

Fig. 6 is the equivalent architectures figure of soft starting circuit, I_tIt is a time dependent current source slope current source, V_CGFor power The control voltage of switching tube grid.Slope current source I_tIt is copied to M2, M3 composition by the current mirror of M1, M2 composition Branch road, then the electric current flowing through M2, M3 is:

$I_{M3}=I_{M2}=\frac{{\mathrm{\β}}_2}{{\mathrm{\β}}_1}*I_{M1}=\frac{{\mathrm{\β}}_2}{{\mathrm{\β}}_1}*I_t---(4-6)$

And the expression formula of M3 leakage current is as follows:

I_M3=β₃*(V_DD-V_CG-|V_THP,M3|)² (4-7)

Formula (4-7) is substituted into formula (4-6) can get:

$V_{\mathrm{CG}}=V_{\mathrm{DD}}-\left|V_{\mathrm{THP},M3}\right|-\sqrt{\frac{{\mathrm{\β}}_2}{{\mathrm{\β}}_1*{\mathrm{\β}}_3}*I_t}---(4-8)$

By formula (4-8) it will be seen that the current source ramped up controls V_CGWith slope form decline, and then gradually make power switch tube S 1, S5 opens, thus limits chip and be input to the electric current of outfan.

As it is shown in fig. 7, slope current source essence is exactly the DAC of a current-mode, by frequency divider, (D of two divided-frequency connection triggers Device) enumerator (circle C1) of D1-D12 composition and the PMOS current source array (enclosing C2) of current mirror composition.Wherein, EN_SC, EN_2FD, EN_RP are all from Logic control module, respectively V_S1And V_S5Output enables signal (high level is effective), meter In number device, 2 frequency dividings enable signal (high level is effective), the enable signal (Low level effective) of PMOS current source array；F_RP is Slope current source starts id signal；F_ES is that soft start terminates id signal；V_S1、V_S5For soft start stage power pipe S1, The control signal of S5 grid；I_BIASBias current for 4uA；V_OSCCarry out self-oscillator, for the pulse signal of 1MHz；V_{S_SEL} Selecting module from power supply, its value is MAX (V_IN,V_OUT)。

When chip is not actuated, EN_2FD is low level, and EN_RP is high level, and EN_SC is low level；Each 2 points Frequently device is output as high level, MB1078-MB1082(P type) it is turned off；MB1128 ends, bias current I_BIASCannot flow into mould Block；MB1118 turns on, and makes MB1083 and MB1102 grid put ground and cannot turn on, and MB513, MB244 are also switched off simultaneously, Make to export V_S1、V_S5In high-impedance state.

When, after benchmark is set up and when chip operation environment is normal, chip starts soft start: EN_RP is become low level from high level, MB1128 conducting, MB1118 cut-off, bias current I_BIASFlow into MB1058, and mirror image is to current source array；Meanwhile, EN_2FD Being become high level from low level, enumerator starts counting up.Along with the counting of enumerator, MB1078-MB1082 (p-type) is believed by counting Number control is respectively turned on or ends, and the electric current flowing through MB1109 is gradually increased.Due to each PMOS of current source array in parallel Number ratio is as follows:

M₁₀₅₈:M₁₀₇₇:M₁₀₅₁:M₁₀₄₇:M₁₀₄₃:M₁₀₄₅:M₁₀₄₂=8:1:1:2:4:8:16 (4-9)

The electric current flowing through MB1109 increases with the step of 0.5uA, is converted into current analog signal from the digital signal of this enumerator.About After crossing 128us, F_RP is uprised level by low level, by logic control circuit EN_SC is set to high level, MB513, MB244 turns on, V_S1、V_S5Open with S1, S5 in higher Automatic level control electric charge pump, and passage V in time_S1、V_S5By Gradually reducing with slope form, this makes to flow through the electric current of S1, S5 in electric charge pump and is gradually increased, when effectively inhibiting chip to open Surge current；About crossing 2.048ms, F_ES and become high level from low level, soft start terminates.

Power supply selects module operation principle and circuit diagram explanation.

It is maximum that power supply selects (SOURCE-SEL) module mainly to select in the input voltage VIN of chip and output voltage VO UT Person, as the maximum level of power switch pipe control signal in electric charge pump, effectively to drive charge pump power switch, exports simultaneously Enable signal EN_LA10, for controlling the driving module of power tube.

It is VIN and more higher charge pump output voltage than supply voltage owing to power supply selects module to be used to compare supply voltage VOUT, uses common voltage comparator to be difficult to this function, so the application selects has being total to of wide common-mode input range Grid comparator.Fig. 8 show power supply and selects module principle figure, and wherein EN_UVLO is from under-voltage locking module, selects for power supply Selecting the enable signal of module, high level is effective；I_BIASBias current for 2uA；V_{S_SEL}The output valve of module is selected for power supply, Its value is equal to MAX (VIN, VOUT)；EN_LA10 power tube drives module to enable signal.

When EN_UVLO is high level, normal circuit operation.Now, its equivalent circuit as it is shown in figure 9, MG651, MG652, MG657-MG660, MXMG constitute grid comparator, an I altogether_BIASBias current is provided, then flows through the electric current of each metal-oxide-semiconductor For:

I_D,651=I_D,657=K₁*I_BIAS (4-10)

I_D,652=I_D,660=K₂*I_BIAS (4-11)

I_D,659=K₃*I_BIAS (4-12)

Wherein K₁、K₂、K₃It is respectively MG657, MG660, MG659 and the ratio of MG658 breadth length ratio, is current mirror multiple. The MG651 of diode-connected is in saturation region, and the expression formula of its leakage current is as follows:

I_D,651=β₆₅₁*(V_OUT-V_A-V_TH,651)² (4-13)

Then the expression formula of A point voltage is:

$V_A=V_{\mathrm{OUT}}-V_{\mathrm{TH},651}-\sqrt{I_{D,651/{\mathrm{\β}}_{651}}}---(4-14)$

The electric current flowing through MG657, MG660 during due to VOUT=VIN is fixed and proportional, then at the grid of MG651 and MG652 A defines a balanced voltage V_{A, OUT=IN}, B point also reaches balanced voltage V_{B, OUT=IN}.Now, by adjusting phase inverter INV7 The wide length of middle pipe, makes V_{B, OUT=IN}Just equal to the threshold voltage V of phase inverter_TH,INV。

Following for easy analysis, it is assumed that VIN fixes, VOUT changes.

When VOUT raises and is higher than VIN, formula (4-14) level understanding A point also raises and higher than its balanced voltage, it may be assumed that

V_A＞ V_{A, OUT=IN} (4-15)

Then the voltage of B point decreases lower than the threshold voltage of phase inverter INV7, it may be assumed that

V_B＜ V_TH,INV (4-16)

Phase inverter INV7 exports high level, and WG8 becomes high level, thus opens MXMG pipe, and the electric current of MG659 also flows through MG652, Then MG652 leakage current is:

I⁺ _D,652=I_D,660+I_D,659=(K₂+K₃)*I_BIAS (4-17)

The level of B point is lower, and further having locked WG7 is low level, and WG8 is high level.Now, WG9 is set to low level, EN_LA10 is high level, opens power tube MG426, switch-off power pipe MG410, makes the output V of SOURCE-SEL module_{S_SEL} Voltage equal to VOUT end.

In like manner, have when VOUT declines and is less than VIN:

V_A＜ V_{A, OUT=IN} (4-18)

V_B＞ V_TH,INV (4-19)

WG7 becomes high level, and WG8 is low level, turns off MXMG pipe, WG6 point is locked as high level, then flows through MG652's Electric current is:

I^- _D,652=I_D,660=K₂*I_BIAS (4-20)

Make WG9 is high level simultaneously, and EN_LA10 is low level, and switch-off power pipe MG426 opens power tube MG410, makes The output V of SOURCE-SEL module_{S_SEL}Voltage equal to VIN end.

When EN_UVLO is low level, illustrate that circuit is in under-voltage protection state, i.e. chip major part module from service, OUT terminal is pulled down to ground by the resistance RG37 that resistance is 5K Ω, and B point is high level, and EN_LA10 is low level, from And open power tube MG410, make the outfan V of SOURCE-SEL module_{S_SEL}Voltage equal to VIN end.

In a word, the output V of SOURCE-SEL module_{S_SEL}It is exactly to select level higher in VIN and VOUT end, for its of chip He provides power supply at module.

Mode selection module

Minimum levels is selected the output V of (SEL-MIN) module by the mode selection module moment_SEL-MIN(6 LED negative pole ends minimum Level) and reference gate voltage limit V_REF(100mV) comparing, output mode selects signal MODE_SEL.When supply voltage is higher Time, i.e. V_SEL-MIN>V_REF, MODE_SEL exports high level, and circuit would operate under 1X pattern.But along with supply voltage Reducing, output voltage declines, V_SEL-MINIt is also reduced to V_REFHereinafter, MODE_SEL is turned to low level by high level, electricity Lotus pump jumps to 1.5X MODE of operation, now V_SEL-MINIt is clamped at about 0.18V (reference error amplifier EA), MODE_SEL exports again high level, but under now electric charge pump is still operated in 1.5X pattern, and do not overturn；Only work as electricity Source voltage raises (to lithium cell charging) to higher than output voltage V_OUTDuring about 50mV (the EN-TD module with reference to below), chip is It is transformed into again 1X MODE of operation.

As shown in Figure 10, MODE-SEL module is simple two-stage open loop comparator.Wherein, EN_OTP is from overheat protector Circuit, for the enable signal of mode selection module, high level is effective；V_REFFrom reference offset module, for the benchmark of 100mV Voltage；V_SEL-MINSelect module from minimum levels, be the minimum level of 6 LED negative pole ends；I_BIASBiased electrical for 8uA Stream；MODE_SEL transports to Logic control module, for mode select signal.

When EN_OTP is high level, MG499 opens, and MG493, MG498, MG497 turn off, and comparator normally works. Now, mode selector is just equivalent to two grades of open loop comparator (two-stage calculation amplifier of not compensated), V_SEL-MINFor Positive input terminal, V_REFFor negative input end.Wherein, pipe, MG504 and MG505 are formed by MG483 and MG484 composition input difference Current mirror makees its load, and MG488 provides tail current, and they constitute first order differential amplifier, and its gain is:

A_V1=g_m,484*(r_o,484||r_o,505) (4-25)

MG503 and MG487 forms current source load amplifier, and for second level amplifier, its gain is:

A_V2=g_m,503*(r_o,503||r_o,487) (4-26)

The gain that then this comparator is total is:

A_V=A_V1*A_V2={ [g_m,484*(r_o,484||r_o,505)]*[g_m,503*(r_o,503||r_o,487)] (4-27)

Work as V_SEL-MIN>V_REF, outfan WG38 output higher level (higher than the threshold voltage of phase inverter), through two-stage phase inverter The high level digital signal MODE_SEL of outputting standard.Work as V_SEL-MIN<V_REF, WG38 level is less than the threshold value electricity of phase inverter Pressure, MODE_SEL is low level.

When EN_OTP is low level, mode selection module quits work.MG499 turns off, and MG493 opens, and WG42 is set to For high level, MG498, MG497 open, and WG38 puts ground, and MODE_SEL is low level.

Patten transformation enables EN-TD (Enable-Transform Down) module

As it was previously stated, only when supply voltage VIN rises above output voltage VO UT50mV, and MODE_SEL is high During level, electric charge pump is just from 1.5X patten transformation to 1X MODE of operation, because supply voltage now has been able to meet effect The 1X mode operating conditions that rate is higher；Otherwise, even if MODE_SEL is high level, also can be shielded. EN-TD (Enable-Transform Down) module is just to provide such a low power transition enabled signal EN_TD, and pattern Signal MODE_SEL co-controlling electric charge pump is selected to be transformed into 1X pattern from 1.5X.

Functionally see, an EN-TD module actually comparator.But it is different with common comparator, this is owing to it wants straight Connect compare be supply voltage VIN and may be higher than supply voltage charge pump output voltage VOUT, this just require comparator want There is a wide common-mode input range (selecting as module with power supply), and common comparator can not meet this requirement, and EN-TD Module is through common-gate input stage comparator and realizes the function of ultra-wide input common-mode input range.

As shown in figure 11, wherein EN_OTP is from thermal-shutdown circuit, for mode selection module for the schematic diagram of EN-TD module Enable signal, high level is effective；I_BIASBias current for 8uA；I_CR2From current regulating module, regulate EN-TD mould The switching threshold of block.

Under 1.5X mode of operation, though electric charge pump output VOUT has small ripple, but it is believed that its value immobilizes, this not shadow Ring analysis result.And supply voltage VIN is along with the charging of battery, gradually rise.

When EN_OTP is high level, module normally works, and now circuit equivalent circuit is as shown in figure 12.Wherein MG250 Bias current is provided；MG268 is common-gate input stage, is made up of the PMOS of 4 series connection, and MG252, MG272 provide biasing, So VIN is by the level of common-gate input stage regulation E point so that it is synchronize to raise；Simultaneously in order to ensure to flow through the electric current of MG272 Constant, the level of A point also keeps the rising synchronized；MG276, MG256 form first order PMOS common-source amplifier, by MG274, MG257 provides biasing；MG254 and MG260 composition second level NMOS common-source amplifier, MG248, MG261 provide biasing；Two Individual phase inverter INV1, INV2 composition output buffer stage, it is intended to improve the steep of output signal and be greatly enhanced its driving energy Power.Here, in view of when LED current is because of external world's regulation change, charge pump output voltage VOUT has little scope the most accordingly Float, influence whether that Power convert threshold value makes charge pump modes conversion not accurate enough；And with the I of LED current change_CR2Just By resistance Rc regulation A point and the common mode electrical level of B point, thus the suitable transform key adjusting supply voltage.

(1) V is worked as_IN＜ V_OUTTime, A level point is relatively low, and the level of B point is higher so that MG254 turns on and is operated in linear zone, The D level point threshold level less than phase inverter INV3, EN_TD is low level.

(2) raise along with supply voltage, work as V_IN=V_OUTTime, owing to the conducting voltage of MG268 makes E level point slightly below VIN, though A level point has increase but still relatively low, B level point is the highest so that D level point is still below the threshold of phase inverter INV3 Value level, EN_TD is still low level.

(3) V is worked as_IN＞ V_OUTDuring+50mV, the level of A point is higher, and MG276 ends, and B point is set to low level；MG254 cuts Only, MG260 is operated in linear zone, and D point is high level, and EN_TD exports high level.

When EN_OTP is low level, Module Fail.MG243 turns on, and D point is put ground, and EN_TD is low level, this Time MODE_SEL also will be shielded.

The White LED Drive of the present application can achieve the functions such as adaptive model conversion, digital dimming, soft start, There is driving force strong (can simultaneously drive 6), brightness regulation convenience, wide supply district, power supply conversion efficiency high, stability The features such as energy is stable, peripheral circuit is simple, can be widely applied in the portable set such as mobile phone, MP4.

Claims (3)

1. a white LED driver system based on electric charge pump, this drive system includes electric charge pump boost module: along with power supply The change of voltage, automatically operates under 1X or 1.5X pattern, makes output voltage be more than white light LEDs normally voltage, it is sufficient to Drive white light LEDs, when supply voltage is relatively low, be operated under 1.5X pattern, it is achieved boost function, when supply voltage is higher, work Make in the 1 x mode；Error amplifier block: for amplifying minimum voltage and the reference voltage difference of LED negative pole end, pass through arteries and veins Rush the negative feedback of amplitude modulation(PAM), make the output voltage stabilization of 1.5X electric charge pump；Logic control module: be used for controlling modules association The work adjusted；Maximum current setting module: for determining the maximum current of LED；Rheonome module: for regulating respectively The electric current of each LED, it is achieved constant-current driving, it is ensured that higher currents match degree, to obtain uniform brightness；Enable and control Module: be used for processing outside ENM, ENS pulse control signal, control main-auxiliary screen switch and brightness regulation；LED negative pole minimum electricity Pressure selects module: for detecting the voltage of LED negative pole end, selects minima, feeds back to error amplifier；Oscillator module with And reference offset module: for providing the fixed frequency of 1MHz for system and providing not by temperature and power supply electricity for each module of system The reference voltage of bucklingization impact and bias current, it is ensured that system is working properly；It is characterized in that:

This LED drive system also includes a soft-start module, and this soft-start module, for when chip starts, prevents due to defeated The surge current entering the end pressure reduction big with outfan and produce；

This LED drive system also includes that a power supply selects module, is used for selecting in the input voltage of chip and output voltage Big person, as the maximum level of power switch pipe control signal in electric charge pump, effectively to drive charge pump power switch, the most defeated Go out to enable signal, for controlling the driving module of power tube.

2. white LED driver system as claimed in claim 1, is further characterized in that: this LED drive system also includes one Mode selection module, for selecting the output of module to compare with reference gate voltage limit minimum voltage, exports mould according to different situations Formula selects signal.

3. white LED driver system as claimed in claim 1, is further characterized in that: this LED drive system also includes one Patten transformation enables module, and for providing a low power transition enabled signal, and mode select signal co-controlling electric charge pump is from 1.5X It is transformed into 1X pattern.