AN709
Vishay Siliconix
Document Number: 70582
15-Jun-00
www.vishay.com FaxBack 408-970-5600
1
Designing with the Si9976DY N-Channel Half-Bridge Driver and
LITTLE FOOT Dual MOSFETs
Wharton McDaniel
C0078C0084 C0079 C0084 C0079C0078
The Si9976DY is a fully integrated half-bridge driver IC which
was designed to work with the LITTLE FOOT family of power
MOSFET products in 20- to 40-V systems. The Si9976DY
provides the gate drive for both the low- and high-side MOSFETs
while the Si9945 (SO-8, 3.3 A) or Si4946EY (SO-8, 4.5 A) dual
n-channel LITTLE FOOT MOSFETs provide power handling
capability without the need of a heatsink. All of these devices are
supplied in surface-mount packages. The combination of the
Si9976DY and one of the dual n-channel MOSFETs creates a
powerful and flexible solution for power switching in dc motor
drives.
C0079
The Si9976DY is an integrated driver for an n-channel
MOSFET half-bridge (see Figure 1). Schmitt trigger inputs
provide logic signal compatibility and hysteresis for noise
immunity. Low impedance outputs are provided to drive both
the low- and high-side MOSFETs of the half-bridge. The
addition of a bootstrap capacitor allows the internal circuitry to
level shift both the power supply and the logic signals that are
required for the high-side n-channel MOSFET gate drive. A
charge pump has been included to replace the leakage current
in the high-side driver, which allows static (dc) operation.
A separate voltage input, V
CC
, powers the FAULT output to
allow easy interfacing to the user’s system. Protection circuits
include an undervoltage lockout to assure safe gate-drive
levels, timing delays to prevent cross-conduction, and a
monitor for short circuits on the half-bridge output (S1). An
internal voltage regulator drops the input voltage (V+) to a
nominal 16 V for the low-side circuitry, which allows the
Si9976DY to operate over an input voltage range of 20 to 40 V.
The device is specified over the industrial temperature range
(–40 to +85 C).
Figure 1. Si9976DY Functional Block Diagram
Charge
Pump
V+
IN
EN
GND
V
DD
V
CC
FAULT
Under Voltage
Lockout 1
250 ns
Delay
300 ns
Delay
Enable Latch
R
SQ
Low Voltage
Regulator
Under Voltage
Lockout 2
Short Ckt &
UVL Detect
V
DD
CAP
S
1
G
2
G
1
Substrate
V+
C
Boot
GND
0.01 F
3
4
7
8
5
6
10
2
13
12
9
LITTLE FOOT
Bootstrap
Regulator
Half-Bridge
Output