BQ25708 datasheet(26/94 Pages) TI2

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Table 9-2. MOSFET Operation (continued)

MODE

BUCK

BUCK-BOOST

BOOST

Switching

9.3.5.1 Inductance Detection Through IADPT Pin

The charger reads the inductance value through the resistance tied to IADPT pin before the converter starts up.

The resistances recommended for 1uH, 2.2uH and 3.3uH inductance are 93kΩ, 137kΩ and 169kΩ, respectively.

A surface mount chip resistor with ±3% or better tolerance must to be used for an accurate inductance detection.

Table 9-3. Inductor Detection Through IADPT Resistance

INDUCTOR IN USE

RESISTOR ON IADPT PIN

1 µH

93 kΩ

2.2 µH

137 kΩ

3.3 µH

169 kΩ

9.3.5.2 Continuous Conduction Mode (CCM)

With sufficient charge or system current, the inductor current does not cross 0 A, which is defined as CCM. The

controller starts a new cycle with ramp coming up from 200 mV. As long as the error amplifier output voltage

is above the ramp voltage, the high-side MOSFET (HSFET) stays on. When the ramp voltage exceeds error

amplifier output voltage, HSFET turns off and low-side MOSFET (LSFET) turns on. At the end of the cycle,

ramp gets reset and LSFET turns off, ready for the next cycle. There is always break-before-make logic during

transition to prevent cross-conduction and shoot-through. During the dead time when both MOSFETs are off, the

body-diode of the low-side power MOSFET conducts the inductor current.

During CCM, the inductor current always flows and creates a fixed two-pole system. Having the LSFET turn-on

when the HSFET is off keeps the power dissipation low and allows safe charging at high currents.

9.3.5.3 Pulse Frequency Modulation (PFM)

In order to improve converter light-load efficiency, BQ25713/BQ25713B switches to PFM operation at light

load. The effective switching frequency will decrease accordingly when system load decreases. The minimum

frequency can be limit to 25 kHz when the OOA feature is enabled (ChargeOption0() bit[10]=1).

9.3.6 Current and Power Monitor

9.3.6.1 High-Accuracy Current Sense Amplifier (IADPT and IBAT)

As an industry standard, a high-accuracy current sense amplifier (CSA) is used to monitor the charger input

current during forward charging mode, or output current during OTG mode (IADPT) and the battery charge/

discharge current (IBAT). IADPT voltage is 20× or 40× the differential voltage across ACP and ACN. IBAT

voltage is 8x/16× (during charging), or 8×/16× (during discharging) of the differential across SRP and SRN. After

input voltage or battery voltage is above UVLO, IADPT output becomes valid. To lower the voltage on current

monitoring, a resistor divider from CSA output to GND can be used and accuracy over temperature can still be

achieved.

• V(IADPT) = 20 or 40 × (V(ACP) – V(ACN)) during forward mode, or 20 or 40 × (V(ACN) – V(ACP)) during reverse

OTG mode.

• V(IBAT) = 8 or 16 × (V(SRP) – V(SRN)) for battery charging current.

• V(IBAT) = 8 or 16 × (V(SRN) – V(SRP)) for battery discharging current.

A maximum 100-pF capacitor is recommended to connect on the output for decoupling high-frequency noise.

An additional RC filter is optional, if additional filtering is desired. Note that adding filtering also adds additional

response delay. The CSA output voltage is clamped at 3.3 V.

9.3.6.2 High-Accuracy Power Sense Amplifier (PSYS)

The charger monitors total system power. During forward mode, the input adapter powers system. During

reverse OTG mode, the battery powers the system and VBUS output. The ratio of PSYS pin output current and

total system power, KPSYS, can be programmed in REG0x31[1] with default 1 μA/W. The input and charge sense

BQ25713, BQ25713B

SLUSD83C – JUNE 2018 – REVISED MAY 2023

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