BQ25708 datasheet(24/94 Pages) TI2

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9.3 Feature Description

9.3.1 Power-Up from Battery Without DC Source

If only battery is present and the voltage is above VVBAT_UVLOZ, the BATFET turns on and connects battery to

system. By default, the charger is in low power mode (REG0x01[7] = 1) with lowest quiescent current. The LDO

stays off. When device moves to performance mode (REG0x01[7] = 0), The host can enable IBAT buffer through

I2C to monitor discharge current. The PSYS, PROCHOT or independent comparator also can be enabled by

the host through the I2C commands. In performance mode, the REGN LDO is always available to provide an

accurate reference for the other features.

9.3.2 Vmin Active Protection (VAP) when Battery only Mode

In VAP mode operation, the buck-boost charger delivers the energy from the battery to charge the voltage of the

input decoupling capacitors (VBUS) as high as possible (like 20V). The system peak power pulse for a 2S1P or

1S2P system can be as high as 100W if the SoC and motherboard systems spikes coincide. These spikes are

expected to be very rare, but possible. During these high power spikes, the charger is expected to supplement

the battery (drawing the power from the charger’s input decoupling capacitors) to prevent the system voltage

from drooping. VAP allows the SoC to set much higher peak power levels to the SoC, thus provides for much

better Turbo performance.

Follows the steps below to enter VAP operation.:

1. Set the voltage limit to charge VBUS in REG0x07/06().

2. Set the current limit to charge VBUS in REG0x09/08() and REG0x39[7:2].

3. Set the system voltage regulation point in REG0x0D[5:0], when the input cap supplements battery, the

VSYS_MIN regulation loop will maintain VSYS at this regulation point.

4. Set the PROCHOT_VSYS_TH1 threshold to trigger the VAP discharging VBUS in REG0x36[7:4].

5. Set the PROCHOT_VSYS_TH2 threshold to assert /PROCHOT active low signal to throttle SoC in

REG0x36[3:2].

6. Enable the VAP mode by setting REG0x34[5] = 0, REG0x35[4] = 0, and pulling the OTG/VAP pin to high.

To exit VAP mode, the host should write either REG0x34[5] = 1 or pull low the OTG/VAP pin to low.

Any regular fault conditions of the charger in VAP mode will reset REG0x34[5] = 1, and the charger will exit VAP

mode automatically.

9.3.3 Power-Up From DC Source

When an input source plugs in, the charger checks the input source voltage to turn on LDO and all the bias

circuits. It sets the input current limit before the converter starts.

The power-up sequence from DC source is as follows:

1. 50 ms after VBUS above VVBUS_CONVEN, enable 6 V LDO and CHRG_OK goes HIGH

2. VBUS qualification is executed 50 ms after VBUS first rises above VVBUS_UVLOZ. If

VVBUS_UVLOZ < VBUS < VVBUS_CONVEN then charger fails VBUS qualification, and the charger will re-qualify

VBUS every 2s.

3. Input voltage and current limit setup

4. Battery CELL configuration

5. 150 ms after VBUS above VVBUS_CONVEN, converter powers up.

9.3.3.1 CHRG_OK Indicator

CHRG_OK is an active HIGH open drain indicator. It indicates the charger is in normal operation when the

following conditions are valid:

• VBUS is above VVBUS_CONVEN

• VBUS is below VACOV

• No MOSFET/inductor, or over-voltage, over-current, thermal shutdown fault

BQ25713, BQ25713B

SLUSD83C – JUNE 2018 – REVISED MAY 2023

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