lt3572 Linear Technology Corporation, lt3572 Datasheet - Page 7

• Manufacturer Part Number: lt3572
• Description: Dual Full-bridge Piezo Driver With 900ma Boost Converter
• Manufacturer: Linear Technology Corporation

OPERATION
Switching Regulator
The LT3572 uses a constant frequency, current mode,
control scheme to provide excellent line and load regulation
for the output drivers. Operation can be best understood
by referring to the Block Diagram in Figure 1. A pulse
from the oscillator sets the RS fl ip-fl op, A4, and turns on
the internal NPN bipolar power switch, Q1. Current in Q1
and the external inductor, L1, begins to increase. When
this current exceeds a level determined by the voltage at
the output of the error amplifi er A1, comparator A2 resets
A4, turning Q1 off. The current in L1 fl ows through the
external Schottky diode D1 and begins to decrease. The
cycle begins again at the next pulse from the oscillator.
In this way, the voltage at the output of the error amplifi er
controls the current through the indictor to the output. The
soft-start capacitor, C2, clamps the output of the error
amplifi er causing the current limit to slowly increase. This
helps reduce overshoot on the output and helps minimize
inrush current on the input.
Output Drivers
The function of the driver section is to level shift the input
of the PWM pins to the voltage of the V
ers operate in an H-bridge fashion, where the OUTA and
OUTB pins are the same polarity as the PWMA and PWMB
pins respectively and the ⎯ O ⎯ U ⎯ T ⎯ A and ⎯ O ⎯ U ⎯ T ⎯ B are inverted
from PWMA and PWMB respectively. The OUT pins will
be high impedance until the FB pin is within 95% of its
regulated voltage. The OUT pins will follow PWMA and
PWMB as long as FB stays within 85% of the regulated
voltage. If FB drops below 85%, the OUT pins will go high
impedance.
OUT
LT3572
pin. The driv-
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