BQ25708 datasheet(76/94 Pages) TI2

76 / 94 page

to choose a higher voltage rating or nominal capacitance value in order to get the required capacitance value at

the operating point. Considering the 25-V 0603 package MLCC capacitance derating under 21-V to 23-V output

voltage, the recommended practical capacitors configuration at VSYS output terminal can also be found in

Table 10-2. Tantalum capacitors (POSCAP) can avoid dc-bias effect and temperature variation effect which are

recommended to be used along VSYS output distribution line to meet total minimum effective output capacitance

requirement.

Table 10-2. Minimum Output Capacitance Requirement

OUTPUT CAPACITORS VS TOTAL INPUT

POWER

65W

90W

130W

Minimum Effective Output Capacitance

50 μF

Minimum output capacitors at charger VSYS

output terminal

7*10 μF (0603 25 V MLCC)

9*10 μF (0603 25 V MLCC)

Additional output capacitors along VSYS

distribution line

2*22 μF (25 V~35 V

POSCAP)

2*22 μF (25 V~35 V

POSCAP)

2*22 μF (25 V~35 V

POSCAP)

10.2.2.5 Power MOSFETs Selection

Four external N-channel MOSFETs are used for a synchronous switching battery charger. The gate drivers are

internally integrated into the IC with 6 V of gate drive voltage. 30 V or higher voltage rating MOSFETs are

preferred for 19 V - 20 V input voltage.

Figure-of-merit (FOM) is usually used for selecting proper MOSFET based on a tradeoff between the conduction

loss and switching loss. For the top side MOSFET, FOM is defined as the product of a MOSFET's on-resistance,

RDS(ON), and the gate-to-drain charge, QGD. For the bottom side MOSFET, FOM is defined as the product of the

MOSFET's on-resistance, RDS(ON), and the total gate charge, QG.

FOMtop = RDS(on) x QGD; FOMbottom = RDS(on) x QG

(6)

The lower the FOM value, the lower the total power loss. Usually lower RDS(ON) has higher cost with the same

package size.

The top-side MOSFET loss includes conduction loss and switching loss. It is a function of duty cycle (D=VOUT/

VIN), charging current (ICHG), MOSFET's on-resistance (RDS(ON)), input voltage (VIN), switching frequency (fS),

turn on time (ton) and turn off time (toff):

top

CHG

DS(on)

CHG

off

= D

+ t

)

(7)

The first item represents the conduction loss. Usually MOSFET RDS(ON) increases by 50% with 100°C junction

temperature rise. The second term represents the switching loss. The MOSFET turn-on and turn-off times are

given by:

off

, t

(8)

where Qsw is the switching charge, Ion is the turn-on gate driving current and Ioff is the turn-off gate driving

current. If the switching charge is not given in MOSFET datasheet, it can be estimated by gate-to-drain charge

(QGD) and gate-to-source charge (QGS):

= Q

(9)

Gate driving current can be estimated by REGN voltage (VREGN), MOSFET plateau voltage (Vplt), total turn-on

gate resistance (Ron) and turn-off gate resistance (Roff) of the gate driver:

BQ25713, BQ25713B

SLUSD83C – JUNE 2018 – REVISED MAY 2023

www.ti.com

Submit Document Feedback

Product Folder Links: BQ25713 BQ25713B

BQ25708 Folha de dados(PDF) 76 Page - Texas Instruments

BQ25708 Folha de dados(HTML) 76 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94

Folha de dados Download

Ligação URL