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PDF AN709 Data sheet ( Hoja de datos )
| Número de pieza | AN709 | |
| Descripción | Designing with the Si9976DY N-Channel Half-Bridge Driver and LITTLE FOOT Dual MOSFETs | |
| Fabricantes | Vishay Siliconix | |
| Logotipo |  |
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AN709
Vishay Siliconix
Designing with the Si9976DY N-Channel Half-Bridge Driver and
LITTLE FOOTR Dual MOSFETs
Wharton McDaniel
INTRODUCTION
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.
SI9976DY OVERVIEW
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, VCC, 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).
V+
Bootstrap
V+3 Regulator
VDD4
Low Voltage
Regulator
VCC 7
8
FAULT
Under Voltage
Lockout 2
Charge
Pump
Short Ckt &
UVL Detect
VDD
Under Voltage
Lockout 1
IN 5
0.01 mF
EN 6
10
GND
R
SQ
Enable Latch
Substrate
250 ns
Delay
300 ns
Delay
2 CAP
CBoot
12 G1
13 S1
Half-Bridge
Output
9 G2
Document Number: 70582
15-Jun-00
Figure 1. Si9976DY Functional Block Diagram
GND
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1
1 page  
AN709
Vishay Siliconix
Si9976
Si9976
Dual
Dual
DIR
IN LITTLE
LITTLE
IN
FOOT
FOOT
MOSFET
MOSFET
EN EN
PWM
DIR
Figure 7a. Sign-Magnitude Control
Si9976
IN
EN
Dual
LITTLE
FOOT
MOSFET
Dual
LITTLE
FOOT
MOSFET
Si9976
IN
EN
PWM
Figure 7b. Sign-Magnitude Control for Low-Side MOSFET PWM
There are a couple of things to be aware of in this mode of
operation. Application of the PWM signal to the EN input when
the IN input is held low will create an erroneous Fault signal
which is the inverse of the PWM signal. This can be eliminated
by applying the inverse of the PWM signal to the IN input as
shown in Figure 7b. Secondly, care must be taken to ensure
that the bootstrap capacitor has been charged prior to a
high-side turn on. As low-side on-times decrease, this
becomes of greater concern. Minimum low-side on-times must
be observed to ensure that the high-side will turn on.
Remember that this minimum time can be reduced by adding
an external bootstrap diode (see Figure 8). When this is done,
it increases the load on VDD and therefore on the decoupling
capacitor. The value of the VDD decoupling capacitor should
be doubled to prevent an undervoltage condition from
occurring.
CURRENT SENSING
If current sensing is required, a fractional W resistor can be
inserted in between the low-side MOSFET source connection
and ground. External op amps or comparators can then be
used to implement current limit or some other current control.
A Schottky diode must be connected from the half-bridge
output to ground to protect output from negative voltage
spikes. In addition to causing potential damage to the Si9976,
negative spikes can cause an erroneous latching FAULT. The
sensing resistor provides a small amount of isolation of the
MOSFET decoupling capacitors from ground. Make sure that
decoupling capacitors on MOSFETs are connected directly
across the MOSFET pair, high-side drain to low-side source to
maximize their effectiveness at reducing noise (see Figure 7).
CBOOT
BRAKING
Braking is accomplished by turning on both upper or both lower
MOSFETs in the H-bridge so the motor windings are shorted
together. If the upper MOSFETs are used for this function, be
certain that the bootstrap capacitors are charged prior to
turning them on.
IN4148
or
Equivalent
2 x CDD
CAP
S1
Si9976
VDD
Document Number: 70582
15-Jun-00
Figure 6. External Bootstrap Diode
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5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet AN709.PDF ] | |
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