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IR3088A Datasheet PDF : 33 Pages
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IR3088A
IR3088A THEORY OF OPERATION
Block Diagram
The Block diagram of the IR3088A is shown in figure 6, and specific features are discussed in the following sections.
RMPIN+
RMPIN-
EAIN
BIASIN
PWMRMP
SCOMP
ISHARE
LGND
VRHOT
HOTSET
RAMP
COMPARATOR
CLOCK
PULSE
GENERATOR
PWM
COMPARATOR
-
SYSTEM
REFERENCE
VOLTAGE
+
ENABLE
PWM
LATCH
S
RESET
DOMINANT
R
RAMP
SLOPE
ADJUST
RAMP
DISCHARGE
CLAMP
-
+
GATE
NON-OVERLAP
COMPARATORS
SHARE
ADJUST
ERROR
AMP
+
10K
20mV
+
-
VRHOT
COMPARATOR
+ VOLTAGE
PROPORTIONAL
TO ABSOLUTE
-
TEMPERATURE
X
0.91
0% DUTY
CYCLE
COMPARATOR
+
FAULT
COMPARATOR
2V
INTERNAL
CIRCUIT
BIAS
CURRENT
SENSE
AMP
X34
VCCH
GATEH
VCCL
GATEL
PGND
VCC
DACIN
CSIN+
CSIN-
PHSFLT
Figure 6. IR3088A Block Diagram
Tri-State Gate Drivers
The gate drivers can deliver up to 3A peak current. An adaptive non-overlap circuit monitors the voltage on the
GATEH and GATEL pins to prevent MOSFET shoot-through current while minimizing body diode conduction.
An Enable signal is provided by the Control IC to the Phase IC without the addition of a dedicated signal line. The
Error Amplifier output of the Control IC drives low in response to any fault condition such as input under voltage or
output overload. The IR3088A 0% duty cycle comparator detects this and drives both gate outputs low. This tri-state
operation prevents negative inductor current and negative output voltage during power-down.
The Gate Drivers revert to a high impedance “off” state if VCCL and VCCH supply voltages are below the normal
operating range. An 80kΩ resistor is connected across the GATEH/GATEL and PGND pins to prevent the
GATEH/GATEL voltage from rising due to leakage or other cause under these conditions.
Thermal Monitoring (VRHOT)
The IR3088A senses its own die temperature and produces a voltage at the input of the VRHOT comparator that is
proportional to temperature. An external resistor divider connected from VBIAS to the HOTSET pin and ground can
be used to program the thermal trip point of the VRHOT comparator. The VRHOT pin is an open-collector output and
should be pulled up to a voltage source through a resistor. If the thermal trip point is reached the VRHOT output
drives low.
Page 11 of 33
1/15/05
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