SIP42101 Vishay Intertechnology, SIP42101 Datasheet - Page 5

• Manufacturer Part Number: SIP42101
• Description: dual MOSFET drivers
• Manufacturer: Vishay Intertechnology

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DETAILED OPERATION
PWM
The PWM pin controls the switching of the external MOSFETs.
The driver logic operates in a noninverting configuration. The
PWM input stage should be driven by a signal with fast
transition times, like those provided by a PWM controller or
logic gate, (<200 ns). The PWM input functions as a logic input
and is not intended for applications where a slow changing
input voltage is used to generate a switching output when the
input switching threshold voltage is reached.
Low-Side Driver
The supplies for the low-side driver are V
shutdown, OUT
High-Side Driver
The high-side driver is isolated from the substrate to create a
floating high-side driver so that an n-channel MOSFET can be
used for the high-side switch. The supplies for the high-side
driver are BOOT and LX. The voltage is supplied by a floating
bootstrap capacitor, which is continually recharged by the
switching action of the output. During shutdown OUT
low.
Bootstrap Circuit
The internal bootstrap diode and a bootstrap capacitor form a
charge pump that supplies voltage to the BOOT pin. An
Document Number: 73176
S-50265—Rev. B, 21-Feb-05
FUNCTIONAL BLOCK DIAGRAM
BRAKE
GND
PWM
V
SD
DD
L
is held low.
UVLO
OTP
DD
and GND. During
H
New Product
is held
Figure 1.
integrated bootstrap diode replaces the external Schottky
diode needed for the bootstrap circuit; only a capacitor is
necessary to complete the bootstrap circuit. The bootstrap
capacitor is sized according to,
where Q
high-side MOSFET and DV
allowed in the bootstrapped supply voltage when the high-side
MOSFET is driven high. The bootstrap capacitor value is
typically 0.1 mF to 1 mF. The bootstrap capacitor voltage rating
must be greater than V
and ringing.
Shoot-Through Protection
The external MOSFETs are prevented from conducting at the
same time during transitions. Break-before-make circuits
monitor the voltages on the LX pin and the OUT
control the switching as follows: When the signal on PWM goes
low, OUT
the voltage on LX falls below 1 V by the inductor action, the
low-side driver is enabled and OUT
delay. When the signal on PWM goes high, OUT
after an internal propagation delay. After the voltage on OUT
drops below 1 V the high-side driver is enabled and OUT
go high after an internal propagation delay. If LX does not drop
below 1 V within 400 ns after OUT
high until the next PWM transition.
GATE
H
will go low after an internal propagation delay. After
C
BOOT
is the gate charge needed to turn on the
= (Q
+
−
DD
GATE
+ 5 V to withstand transient spikes
V
V
DD
BBM
BOOT − LX
/DV
BOOT − LX
Vishay Siliconix
H
goes low, OUT
L
is the amount of droop
goes high after some
) x 10
SiP42101
BOOT
OUT
OUT
LX
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H
L
L
will go low
L
L
is forced
pin and
H
will
5
L