ISL89166, ISL89167, ISL89168

9

FN7720.0

January 14, 2011

Power Dissipation of the Driver

The power dissipation of the ISL89166, ISL89167, ISL89168 is

dominated by the losses associated with the gate charge of the

driven bridge FETs and the switching frequency. The internal bias

current also contributes to the total dissipation but is usually not

significant as compared to the gate charge losses.

Figure 19 illustrates how the gate charge varies with the gate

voltage in a typical power MOSFET. In this example, the total gate

charge that a driver must source to turn-on the MOSFET and

must sink to turn-off the MOSFET.

Equation 1 shows calculating the power dissipation of the driver:

Where:

freq = Switching frequency,

Note that the gate power dissipation is proportionally shared with

the external gate resistor. When sizing an external gate resistor,

do not overlook the power dissipated by this resistor.

Typical Application Circuit

FIGURE 17. SETTING DELAYS A RESISTOR

INx

OUTx

RDTx

ISL89166

FIGURE 18. SETTING DELAYS WITH A RCD NETWORK

INx

D

OUTx

ISL89160

12

10

8

6

4

2

0

02468 10 12 14 16 18 20 22 24

FIGURE 19. MOSFET GATE CHARGE vs GATE VOLTAGE

(EQ. 1)

()

+

------------------------------------------

() V

DD

•

+

•

•

•

•

=

PWM

LR

LL

LL

Red dashed lines

emphasize the

resonant switching

delay of the low-

side bridge FETs

ZVS Full Bridge

T1A

T1B

T2

U1B

U2A

U2B

LL

LR

SQR

SQR

R

ISL89162

U1A

½ ISL89166

½ ISL89166

LL: lower left

LR: lower right

UL: upper left

UR: upper right

GLL: gate lower left