CMOS CURRENT MODE
PWM CONTROLLERS
TC18C46
TC28C46
TC38C46
PIN DESCRIPTION
Pin No.
Symbol
Description
1
CURRENT LIMIT, SOFT START
Pin for setting the peak current limit threshold of sense inputs pin 3 and pin 4. A
second function of this pin is for Soft-Start programming with a capacitor between this
pin and ground, pin 12.
2
3
4
5
VREF
Pin is an output for the reference supply voltage of 5.1 volts. This reference can supply
a minimum of 20mA of output current.
– CURRENT SENSE
+ CURRENT SENSE
+ ERROR AMP
Pin is the current sense inverting input for sensing peak current of the pass transistor
through the series current monitor resistor.
Pin is the non-inverting input for sensing peak current of the pass transistor. The
positive end of the current sense resistor is connected here.
Pin is the non-inverting input for sensing voltage feedback from output for voltage
regulation.
6
7
8
– ERROR AMP
COMPENSATION
CT
Pin is the inverting input for sensing the reference voltage to regulate the output.
Pin for compensating the feedback loop response.
Pin is the input for timing capacitor, CT, to set oscillator frequency in conjunction with
9 resistor RT, input. A second function is for setting the crossover dead time of the
outputs, pins 11 and 14.
9
RT
Pin is the input for the timing resistor, RT, to set oscillator frequency by setting the
(constant) current charge rate for capacitor CT.
10
11
12
13
14
15
16
SYNC
OUTA
GND
VDD
Pin is the input or output for the oscillator synchronization pulse.
Pin is the output drive of phase A to drive push pull transistor A.
Pin is the ground return path for all input and output signals.
Pin is the supply power input terminal for the output drivers.
Pin is the output drive of phase B to drive push pull transistor B.
Pin is voltage bias supply input for all circuits except the output drivers
OUTB
VIN
SHUT
Pin is an input for shutdown when a 350mV threshold is exceeded: both output drives
will then be terminated.
4-110
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