Linear Technology DC102 Demo Manual page 4

DEMO MANUAL DC102
50V N-CHANNEL HALF BRIDGE
U
OPERATION
generator to INTOP (E5) and INBOTTOM (E6). These
inputs to the LT1336 are TTL/CMOS compatible and can
withstand input voltages as high as V
channels are noninverting. The internal logic of the LT1336
prevents the top MOSFETs and bottom MOSFETs from
turning on simultaneously under any input conditions. For
instance, when both inputs are high both outputs are
actively held low.
The LT1336 incorporates a small switching regulator to
charge the floating high-side driver supply above the high
voltage rail. This regulator can provide enough charge to
the floating supply capacitor to allow the top driver to drive
several power MOSFETs in parallel at 100kHz, its maxi-
I 1
SENSE
6V
+
2
V
3k
3
INTOP
5V
3k
INBOTTOM 4
5V
UVOUT
5
SGND
6
PGND 7
BGATEFB 8
4
. Both driver
IN
Functional Diagram for the LT1336
+
V
+
–
480mV
TRIP = 10.6V
BIAS
mum operating frequency. The regulator voltage across
V – V
BOOST TSOURCE
niques with internal charge pumps, the built-in regulator
enables the half-bridge to operate from PWM to DC
without discontinuities.
In conventional half-bridge drivers using bootstrapping
techniques and internal charge pumps, approaching DC
may cause some serious problems. When the duty cycle
approaches 100%, the output pulse width becomes too
narrow for the floating capacitor to recharge. This capaci-
tor is being continuously depleted by the gate charging
currents of the top MOSFETs. The internal charge pump is
too weak to provide the currents needed to replenish the
TOP UV
TRIP = 8.7V
DETECT
BOTTOM
UV LOCK
is 10.6V. Unlike bootstrapping tech-
2.9V
2.5V
16 SW
15 SWGND
14
BOOST
13
TGATEDR
12 TGATEFB
11 T SOURCE
+
10
PV
9 BGATEDR
DC102 FD