BQ25713 datasheet(92/111 Pages) TI2

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To calculate top MOSFET gate drive loss (PGate_top):

PGate_top =VIN· QGate_top · fS

(17)

• QGate_top is the top MOSFET gate charge which can be found in MOSFET datasheet;

• Note here VIN is used instead of real gate drive voltage 6 V because, the gate drive 6 V is generated based

on LDO from VIN under buck mode, the total gate drive related loss are all considered when VIN is used for

gate drive loss calculation .

The bottom-side MOSFET loss also includes conduction loss and switching loss:

Pbottom =Pcon_bottom+Psw_bottom

(18)

Pcon_bottom =(1 - D) · IL_RMS 2 · RDS(on)_bottom;

(19)

Psw_bottom =PRR_bottom+PDead_bottom+PGate_bottom;

(20)

The first item Pcon_bottom represents the conduction loss which is straight forward. The second term Psw_bottom

represents the multiple switching loss items in bottom MOSFET including reverse recovery losses (PRR_bottom),

Dead time body diode conduction loss (PDead_bottom) and gate drive loss (PGate_bottom). The detail calculation can

be found below:

PRR_bottom=VIN · Qrr · fS

(21)

• Qrr is the bottom MOSFET reverse recovery charge which can be found in MOSFET data sheet;

PDead_bottom=VF · Ivalley · fS · tdead_rise+VF · Ipeak · fS · tdead_fall

(22)

• VF is the body diode forward conduction voltage drop;

• tdead_rise is the SW rising edge deadtime between top and bottom MOSFETs which is around 40 ns;

• tdead_fall is the SW falling edge deadtime between top and bottom MOSFETs which is around 30 ns;

PGate_bottom can follow the same method as top MOSFET gate drive loss calculation approach refer to Equation

17.

P-channel MOSFETs is used for battery charging BATFET. The gate drivers are internally integrated into the IC

with 10 V of gate drive voltage. 20 V or higher voltage rating MOSFETs are preferred for 1- to 4-cell battery

application, 30 V or higher voltage rating MOSFETs are preferred for 5-cell battery application, the Ciss of

P-channel MOSFET should be chosen less than 5 nF.

BQ25730

SLUSE65A – FEBRUARY 2021 – REVISED JANUARY 2024

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BQ25713 Datasheet(PDF) 92 Page - Texas Instruments