CN104167807A

CN104167807A - RTC power source circuit of digital wireless terminal

Info

Publication number: CN104167807A
Application number: CN201410375319.2A
Authority: CN
Inventors: 童奉群; 付文良
Original assignee: KIRISUN COMMUNICATION CO Ltd
Current assignee: Fujian Kirisun Communications Co ltd
Priority date: 2014-08-01
Filing date: 2014-08-01
Publication date: 2014-11-26
Anticipated expiration: 2034-08-01
Also published as: CN104167807B

Abstract

The invention provides an RTC power source circuit of a digital wireless terminal. The RTC power source circuit of the digital wireless terminal comprises a main power source, a backup battery, a main power source loop, a backup battery charging loop, a backup battery discharging loop and an isolating circuit. The output end of the main power source is connected to the input end of the isolating circuit through the main power source loop, and is connected to the input end of the isolating circuit sequentially through the backup battery charging loop, the backup battery and the backup battery discharging loop. The output end of the isolating circuit is connected to a power source pin of an RTC module. The RTC power source circuit of the digital wireless terminal is simple, unique, low in cost, easy to implement and capable of prolonging service life of the backup battery arranged in a terminal device and improving stability and reliability of the RTC circuit of a system under various power source conditions.

Description

RTC clock power supply circuit of digital wireless terminal

Technical Field

The invention relates to the field of professional wireless communication, in particular to an RTC clock power supply circuit of a digital wireless terminal.

Background

With the digital transformation of professional wireless communication devices, a large number of digital communication terminal devices are on the market. However, various terminal devices are mixed with fishes and dragons, the performance is uneven, and particularly, some detailed functions are not satisfactory.

Most of the novel professional digital wireless communication terminal equipment adopts an embedded operating system platform, uses a large-scale high-speed multi-core processor and is configured with a color display screen, so that the RTC (real-time clock) function is basically supported. Especially for the handheld terminal device, there are high requirements for the real-time of the display interface, including the clock precision, the RTC clock holding time after the main battery is powered off, and the like.

The embedded processor adopted by the terminal equipment is generally provided with a built-in independent RTC module which provides an independent backup power interface. In circuit design, a small-capacity button battery is generally used to supply power to a power supply terminal of the RTC module to maintain the RTC clock running normally and to hold other important data that helps the processor start.

The circuit design requires that stable working voltage can be provided for the RTC module under the condition that a main power supply of the terminal equipment normally exists, so that the equipment can be normally started, energy needs to be supplemented for a backup battery, and the RTC module can be maintained to work as long as possible by discharging the backup battery alone under the condition that the main power supply is disconnected.

In the circuit design of the terminal equipment, the design of a backup power supply circuit of a real-time clock (RTC) is easy to be ignored, and a common simple design method is to directly hang the anode and the cathode of a small button battery between an RTC power supply interface of a processor and the ground or to connect a circuit too simply. The simplified design of the RTC clock circuit brings some hidden troubles to the quality of the terminal.

An independent RTC module circuit, an independent backup power port and an independent reference clock are generally arranged in the embedded processor and are not influenced by the reset of the processor. The RTC module circuit has certain requirements on a backup power supply, and when the voltage is too high or too low, the operation of an RTC internal clock can be influenced. The standby power supply of the RTC module also provides power for a starting data standby memory circuit of the processor, the load current of a power supply port of the RTC module has larger fluctuation under different load conditions of starting, shutting down, carrying a battery, not carrying the battery and the like of the terminal equipment, and if the voltage adaptive range is not well controlled, the terminal equipment is easy to lose efficacy under certain extreme conditions, the display clock is abnormal, and even the starting of the terminal equipment fails.

Because the internal space of the handheld terminal device is generally waiting to be compact, the size of the packaged element is strictly limited, and a small button battery is mostly selected as a backup battery of the RTC module. For the small-capacity backup battery, the incorrect or unreasonable charging and discharging circuit design can seriously affect the use effect of the battery, shorten the discharging time of the battery, cause the equipment to be shut down for a long time and placed or lose real-time clock data easily when the battery is replaced, or cause the display to have low time precision and large error. The service life of the backup battery can be shortened, the backup battery is rapidly disabled, the terminal equipment can not keep correct time display at last, and the time for turning off or replacing the main battery at each time is immediately reset to zero. In an extreme case, when the terminal device is turned on, if the backup power supply voltage is abnormal, the processor may not be started.

Disclosure of Invention

The invention aims to provide an RTC clock power supply circuit of a digital wireless terminal, which prolongs the discharge time of a backup battery, prolongs the service life of the backup battery and improves the stable reliability of the RTC clock circuit of a system real-time clock under various power supply conditions.

The purpose of the invention is realized by the following technical scheme.

An RTC clock power supply circuit of a digital wireless terminal, comprising: the system comprises a main power supply, a backup battery, a main power supply loop, a backup battery charging loop, a backup battery discharging loop and an isolating circuit;

the output end of the main power supply is connected to the input end of the isolation circuit through a main power supply loop, and is connected to the input end of the isolation circuit through a backup battery charging loop, a backup battery and a backup battery discharging loop in sequence; the output end of the isolation circuit is connected to a power pin of the RTC module;

the main power supply loop is used for carrying out voltage reduction conversion on the output voltage of the main power supply and providing a stable voltage to supply power to the RTC module through the isolation circuit;

the backup battery charging loop is used for carrying out voltage reduction transformation on the output voltage of the main power supply and providing a path of stable voltage to supplement electric energy for the backup battery so that the backup battery is always kept close to a full voltage state; the system is also used for reversely isolating the backup battery when the main power supply is disconnected;

the backup battery discharging loop is used for providing a path of voltage to supply power to the RTC module through the isolation circuit after the output of the backup battery is subjected to current limiting and voltage reduction;

the isolation circuit is used for cutting off a discharge loop of the backup battery, conducting a main power supply loop and supplying power to the RTC module by the main power supply when the main power supply loop has voltage output and the backup battery is fully charged; and when the main power supply loop does not output, controlling the backup battery discharge loop to supply power to the RTC module, and isolating and cutting off reverse leakage current from the backup battery to the main power supply loop.

Preferably, the main power supply includes: the main battery and the first stage power LDO;

one end of the first-stage power LDO is connected with the main battery, and the other end of the first-stage power LDO is simultaneously connected with the main power supply loop and the backup battery charging loop;

the first-stage power LDO is used for reducing the rated voltage of the main battery of 7.5V to 3.6V and then is used as the output voltage of the main power supply.

Preferably, the main power supply loop includes a second stage power supply LDO, an input end of which is connected to the output end of the main power supply, and an output end of which is connected to the input end of the isolation circuit, and is configured to reduce the output voltage of the main power supply from 3.6V to 1.2V and supply the reduced voltage to the RTC module via the isolation circuit.

Preferably, the backup battery charging loop comprises a first isolation diode and a charging current-limiting resistor which are connected in series, the anode of the first isolation diode is connected with the output end of the main power supply, and the charging current-limiting resistor is simultaneously connected with the backup battery.

Preferably, the first isolation diode is embodied as a schottky diode.

Preferably, the backup battery discharge circuit includes: and two ends of the discharging current-limiting voltage-reducing resistor are respectively connected with the backup battery and the isolating circuit.

Preferably, the isolation circuit includes: a second isolation diode and a third isolation diode;

the positive pole of the second isolation diode is connected with the output end of the main power supply loop, the negative pole of the second isolation diode is connected with a power supply pin of the RTC module, the positive pole of the third isolation diode is connected with the backup battery discharge loop, and the negative pole of the third isolation diode is connected with the power supply pin of the RTC module.

Preferably, the isolation circuit includes: a second isolation diode, an N-channel MOSFET, and a third resistor;

the anode of the second isolation diode is connected with the discharge loop of the backup battery, and the cathode of the second isolation diode is connected with a power pin of the RTC module; the source electrode of the N-channel MOSFET is connected with a main power supply loop, the drain electrode of the N-channel MOSFET is connected with a power supply pin of the RTC module, and the grid electrode of the N-channel MOSFET is connected with one end of a third resistor; the other end of the third resistor is connected with the output end of the main power supply.

Compared with the prior art, the invention has the beneficial effects that:

the invention is simple and unique, has low cost and easy implementation, can prolong the service life of a backup battery arranged in the terminal equipment and improve the stable reliability of the RTC circuit of the real-time clock of the system under various power supply conditions.

Drawings

FIG. 1 is a schematic diagram of an RTC clock power supply circuit of the present invention;

FIG. 2 is a circuit diagram of an RTC clock power supply according to a first embodiment of the present invention;

fig. 3 is a circuit diagram of an RTC clock power supply according to a second embodiment of the present invention.

Detailed Description

The core idea of the invention is as follows: an external backup power circuit is designed for an RTC module in the terminal equipment, reasonable circuit forms and circuit parameters are selected according to the requirements of RTC module circuit hardware on a power supply, the voltage change range is controlled, the distribution switching of a main power supply and a backup power supply is controlled, reasonable charging and discharging current is controlled, the optimal working state of a backup battery is kept, the discharging time of the backup battery is prolonged, the service life of the backup battery is prolonged, and the real-time display function of the terminal equipment is more stable and reliable.

Referring to fig. 1, taking a terminal device using a TI OMAP processor as an example, a real-time clock (RTC) circuit module is embedded in the processor, and the RTC module provides an independent power pin for accessing a backup power. The nominal voltage of the power supply terminal of the RTC module is 1.2V, and the voltage variation range allowed by the actual operation of the RTC circuit is 0.5V-1.3V. If the voltage exceeds 1.3V, the RTC clock stops working; if the voltage is too low, the error of the RTC clock will be increased, and the time-lapse precision is affected.

In this case, the main power supply of the handheld terminal device uses a large-capacity rechargeable battery of thousands of milliampere hours, which is called the main power supply. The backup battery uses button battery, and the capacity is about 0.1mAh to 1.0 mAh.

According to the scheme, a main battery of the terminal equipment directly provides main power supply voltage and is not controlled by a power switch of the equipment, as long as the main battery is installed on the terminal equipment, even if the equipment is shut down, the output of a main power supply loop can be still kept, and the RTC module is maintained to work independently. When the terminal equipment is not provided with a main battery, the RTC module is required to be capable of keeping independent work.

The circuit within the solid line box in fig. 1 is divided into two large current paths:

route (i): and in the main power supply loop, the voltage of the main battery is subjected to voltage reduction and conversion, and a stable voltage is provided and directly supplied to the RTC module through the isolation circuit.

Route (ii): and the backup battery loop comprises charging and discharging of the backup battery and supplies power to the RTC module through the current-limiting resistor and the isolation circuit.

Wherein, the backup battery loop of the path (II) is divided into a charging loop and a discharging loop, and the charging loop and the discharging loop are arranged in front and at back:

A. the first half section is a charging loop, the voltage of the main battery is subjected to voltage reduction and conversion, and a path of stable voltage is provided to continuously and slowly supplement electric energy for the backup battery, so that the backup battery is always kept close to a full voltage state; this loop controls the charging current while avoiding reverse leakage from the backup battery when the main power supply is off.

B. The second half section is a discharge loop, and the backup battery supplies power to the RTC module circuit after discharging through the current-limiting resistor and voltage reduction. This loop controls the discharge current, controls a reasonable voltage drop, and is capable of isolating and switching the main power supply.

The output voltage of the path (II) and the voltage directly output by the main power supply in the path (I) are switched by the isolation circuit, and one path is selected to supply power to the RTC module.

The main power supply loop and the backup battery loop are two current paths independent of each other.

When the main battery is installed on the terminal equipment, namely the main power supply loop has output and the backup battery is fully charged, the main power supply loop is preferentially used to supply power to the RTC module when the backup battery discharge loop is cut off through the selection of the isolation circuit.

When the terminal equipment is not provided with a main battery, namely the main power supply does not output, the RTC module is powered by the backup battery discharge loop. And meanwhile, the reverse leakage current of the backup battery to the main power supply loop is isolated and cut off.

The charging current of the main battery to the backup battery is controlled to be about 5uA by adjusting the parameters of the current limiting resistor according to the battery capacity.

The discharge current of the backup battery is controlled to be about 5uA by adjusting the parameters of the current limiting resistor according to the capacity of the battery.

The discharge time of the backup battery is required to reach more than 24 hours under the state that the terminal equipment is shut down or a main battery is not installed, namely a main power supply is not provided.

The time display part is used for assisting in explaining an application form, is irrelevant to the principle of the method, and is not detailed later.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example one

The detailed circuit is shown in fig. 2, wherein U3 is an embedded processor of the terminal device, and the RTC module unit is built in, and has an independent power interface. X1 is the independent clock of the RTC module, typically 32.768 KHz. The main power supply comprises a main battery BATT and a first stage power supply LDO (U1).

U1 is a first-stage step-down voltage regulator, a low dropout power supply conversion chip LDO, the rated voltage of a main battery is reduced to 3.6V, the rated voltage is used as the output voltage of a main power supply, one path of the output voltage is supplied to a rear-stage LDO and then is reduced to 1.2V, and then the output voltage is directly supplied to an RTC module; while the other path is used to charge the backup battery.

U2 is second step-down regulator, and low dropout power supply changes chip LDO, falls 3.6V of main power supply output to 1.2V again, supplies RTC module, ensures that the maximum voltage of RTC VDD end does not exceed 1.3V.

D1 is an isolation diode using schottky barrier diode (schottky barrier diode) with low junction voltage, and has a small forward voltage difference of about 0.1-0.2V depending on the current. The reverse isolation for the charging loop of the backup battery can isolate the discharge current of the backup battery BT1 from returning to U1 and U2 and avoid current leakage when the terminal is not provided with a battery, namely, the terminal is not provided with a main power supply.

R1 is the charging current limiting resistor of the backup battery BT1, and proper parameters are selected to control the charging current to be in the range of 1uA-10 uA.

R2 is the discharge current-limiting voltage-reducing resistor of the backup battery BT1, the discharge current is controlled within the range of 1uA-10uA by selecting proper parameters, and meanwhile, the maximum voltage drop is controlled to be 1.8V, so that the maximum voltage of the positive end of D2 is about 1.2V.

D2 and D3 are isolated diodes using schottky barrier diode (schottky barrier diode) with small forward voltage difference.

D2 is used for switching the backup battery circuit, and when the terminal equipment is provided with a main battery, namely the main power supply has output, the main power supply is preferentially used, and the backup battery discharging circuit is disconnected, so that the backup battery BT1 is prevented from discharging.

The function of the D3 is to disconnect the main power supply loop when the main battery is not installed in the terminal device, i.e. the main power supply does not output, so that the current at the RTC VDD terminal does not return to the U2, thereby avoiding current leakage.

After 1.2V output by the second LDO (U2) of the main power supply loop passes through D3, the voltage is reduced by about 0.2V, and the voltage reaching the VDD terminal of RTC is about 1.0V.

When the backup battery BT1 is fully charged (3.0V), the discharge loop is subjected to current limiting and voltage reduction through the resistor R2, the appropriate R2 parameter is adjusted, and the maximum voltage reaching the positive end of the D2 is controlled to be about 1.2V. In actual use, the discharge voltage of the backup battery is gradually reduced.

The discharge loop of the backup battery has three working states:

A. if the terminal equipment is normally started, the main power supply loop has output, because the processor is started, the power supply load current of the RTC circuit is larger, the voltage drop of the diode D3 is about 0.2V, the voltage reaching the RTC VDD is 1.0V, the voltage of two ends of the anode and the cathode of the diode D2 is the same, the diode D is in a cut-off state, the discharge loop of the backup battery is disconnected, and the battery cannot discharge. The RTC module is powered by the main power supply loop at the moment.

B. If the terminal device is in the power-off state, the main power loop still has output, but the processor is in the sleep state, the power supply of the RTC circuit will decrease to the minimum holding current, the voltage drop of the diode D3 is about 0.1V, and the voltage reaching the RTC VDD is about 1.1V. The voltage of the positive electrode of the diode D2 is lower than that of the negative electrode, the diode D2 is in a cut-off state, the discharge circuit of the backup battery is disconnected, and the battery cannot discharge. The RTC module is powered by the main power supply loop at the moment.

C. If the terminal equipment is not equipped with a battery, the main power supply loop has no voltage output, and D2 remains on because of the forward bias. Only the backup battery discharge loop is maintained to work independently at the moment. The backup battery slowly discharges, passes through the R2 current-limiting voltage-reducing circuit, passes through the diode D2, and reaches the RTC VDD end to be supplied to the RTC module. In this state, the voltage of the discharged backup battery BT1 gradually decreases after a period of time, the discharge current also gradually decreases, and the voltage at the RTC VDD terminal also decreases accordingly. The normal work of the RTC module can be maintained until the voltage of the RTC VDD is reduced to 0.5V.

Carry out two

The detailed circuit is shown in fig. 3, wherein U3 is an embedded processor of the terminal device, and the RTC module unit is built in, and has an independent power interface. X1 is the independent clock of the RTC module, typically 32.768 KHz. The main power supply comprises a main battery BATT and a first stage power supply LDO (U1).

The power conversion chip U2 is a second-stage low dropout regulator LDO, reduces the 3.6V output by the main power supply to 1.2V again, and supplies the RTC module to ensure that the maximum voltage at the RTC VDD end does not exceed 1.3V.

R1 is a charging current-limiting resistor of the backup battery BT1, and proper parameters are selected to control the charging current to be in the range of 1uA-10 uA.

R2 is a discharge current-limiting voltage-reducing resistor of the backup battery BT1, proper parameters are selected to control the discharge current to be in the range of 1uA-10uA, and meanwhile, the maximum voltage drop is controlled to be about 1.8V, so that the maximum voltage of the positive end of D2 is about 1.2V.

D2, Q1 and R3 belong to the isolated circuit part.

D2 is an isolated diode using schottky barrier diode with low junction voltage with forward voltage difference of about 0.1-0.2V. D2 is used for switching the backup battery circuit, and when the terminal is provided with a main battery, namely the main power supply has output, the main power supply is preferentially used, and the backup battery discharging circuit is disconnected, so that the backup battery BT1 is prevented from discharging.

Q1 is N channel type MOSFET, and is used for the isolator of main power supply circuit, and the MOS pipe has more excellent conduction performance than the schottky pipe, and the voltage drop is nearly 0, belongs to voltage drive formula device, and the high level switches on. When the terminal is provided with a battery, namely the main power supply has an output, a high level is provided for the grid electrode of the MOS transistor Q1 through R3, so that Q1 is conducted, and the stable output voltage of the LDO (U2) reaches the voltage of the RTC VDD end and is still about 1.2V.

The Q1 is used as a switch of the main power supply loop, instead of the function of D3 in fig. 2 (a), it is used to prevent the current at the VDD terminal of the RTC from returning to U2 when the terminal is not equipped with a battery, i.e. there is no main power supply, so as to avoid current leakage.

When the backup battery BT1 is fully charged (3.0V), the current is limited and reduced through the resistor R2, the appropriate R2 parameter is adjusted, and the maximum voltage reaching the positive end of the D2 is controlled to be about 1.2V. In actual use, the discharge voltage of the backup battery is gradually reduced.

The discharge loop of the backup battery has three working states:

C. If the terminal equipment is not equipped with a battery, the main power supply loop has no voltage output, and D2 remains on because of the forward bias. Only the backup battery discharge loop is maintained to work independently at the moment. The backup battery slowly discharges, passes through the R2 current-limiting voltage-reducing circuit, passes through the diode D2, and reaches the RTC VDD end to be supplied to the RTC module. In this state, the voltage of the discharged backup battery BT1 gradually decreases after a period of time, the discharge current also gradually decreases, and the voltage at the RTC VDD terminal also decreases accordingly. Before the RTC VDD terminal drops to 0.5V, the normal operation of the RTC module can be maintained.

The difference between the second embodiment and the first embodiment is in the isolation circuit portion. Wherein,

in the first embodiment, D3 uses schottky diode as the isolation element, the circuit is simple, and the disadvantage is that there is a certain voltage drop.

In the second embodiment, a MOS transistor Q1 is used as an isolation element, and Q1 is equivalent to D3 in the first embodiment, and also serves as an isolation and switch of the main power circuit.

When the terminal equipment is provided with a battery, a high-level turn-on voltage is supplied to the grid electrode of the MOS transistor Q1 through R3, and Q1 is conducted. The main power supply supplies power to the RTC module;

when the terminal equipment is not provided with a battery, namely a main power supply, the MOS transistor Q1 can be quickly turned off through the R3, so that the current at the RTC VDD end cannot return to the U2, the current leakage is avoided, and the maintenance time of a backup battery is further prolonged.

The second embodiment has the advantage that the MOS transistor has a lower conduction voltage drop, which is almost 0, compared with the schottky diode, and can ensure that the voltage at the RTC VDD terminal can be stably maintained at about 1.2V in the normal operation state when the terminal device is installed with a battery and is powered on, thereby providing more reliable voltage for the RTC module.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. An RTC clock power supply circuit of a digital wireless terminal, comprising: the system comprises a main power supply, a backup battery, a main power supply loop, a backup battery charging loop, a backup battery discharging loop and an isolating circuit;

2. The RTC clock power supply circuit of a digital wireless terminal of claim 1, wherein the primary power supply comprises: the main battery and the first stage power LDO;

3. The RTC clock power supply circuit of the digital wireless terminal as claimed in claim 1, wherein the primary power supply loop comprises a second stage power LDO, the input terminal of which is connected to the output terminal of the primary power supply, and the output terminal of which is connected to the input terminal of the isolation circuit, for reducing the output voltage of the primary power supply from 3.6V to 1.2V and supplying the reduced voltage to the RTC module via the isolation circuit.

4. The RTC clock power supply circuit of a digital wireless terminal according to claim 1, wherein said backup battery charging loop comprises a first isolation diode and a charging current limiting resistor connected in series, the anode of said first isolation diode being connected to the output of the main power supply, the charging current limiting resistor being connected to the backup battery at the same time.

5. The RTC clock supply circuit for a digital wireless terminal as claimed in claim 4, wherein said first isolation diode is embodied as a Schottky tube.

6. The RTC clock power supply circuit of a digital wireless terminal of claim 1, wherein the backup battery discharge loop comprises: and two ends of the discharging current-limiting voltage-reducing resistor are respectively connected with the backup battery and the isolating circuit.

7. The RTC clock supply circuit of a digital wireless terminal according to any of claims 1 to 6, characterized in that the isolation circuit comprises: a second isolation diode and a third isolation diode;

8. The RTC clock supply circuit of a digital wireless terminal according to any of claims 1 to 6, characterized in that the isolation circuit comprises: a second isolation diode, an N-channel MOSFET, and a third resistor;