HIP2103, HIP2104

FN8276 Rev 0.00

Page 14 of 21

November 27, 2013

Selecting the Boot Capacitor Value

The boot capacitor value is chosen not only to supply the internal

bias current of the high-side driver but also, and more

significantly, to provide the gate charge of the driven FET without

causing the boot voltage to sag excessively. In practice, the boot

capacitor should have a total charge that is about 20 times the

gate charge of the driven power FET for approximately a 5% drop

in voltage after charge has been transferred from the boot

capacitor to the gate capacitance.

The following parameters are required to calculate the value of

the boot capacitor for a specific amount of voltage droop when

using the HIP2103, HIP2104. In the following example, some

values used are specific to the HIP2103, HIP2104 and others are

arbitrary. The values should be changed to comply with the

actual application.

The following equations calculates the total charge required for

the Period:

Qc = Qg40_12V + Period x (IHB + VHO/RGS + Igate_leak)

Cboot = 0.324µF

If the gate to source resistor is removed (RGS is usually not

needed or recommended), then:

Cboot = 0.124µF

This is the nominal value of VDD for

the HIP2104

High side driver bias voltage

referenced to VHS

Period = 100µs

This is the longest expected switching

period

RGS = 10kΩ

Gate-source resistor

Ripple = 5%

Desired ripple voltage on the boot cap

Igate_leak = 100nA

Gate leakage current (from vendor

datasheet)

Qg40_12V = 45nC

From Figure 20

FIGURE 20. TYPICAL MOSFET GATE CHARGE vs GATE VOLTAGE

4

2

0

6

8

10

12

14

16

0

5

10

15

20

25

30

35

45

50

60

Qg, GATE CHARGE (nC)

Vds = 40V

Vds = 80V

Typical Applications

FIGURE 21. HALF BRIDGE MOTOR DRIVE TOPOLOGY

uController

HIP2104

VBAT

VCen

VCC

VDD

HI

LI

E

P

A

D

LO

HS

HO

HB

VDen

VSS

DC

MOTOR

50Vmax