BICMOS PWM CONTROLLERS
1
2
3
4
5
6
7
8
TC25C25
TC35C25
OUTPUT SECTION
OSCILLATOR SYNCHRONIZATION WITH
SEPARATE RC TIMER
The output stage of the TC35C25 is comprised of two
pairs of complimentary CMOS drivers operating in a push-
pull mode. Each output is capable of sinking or sourcing
nearly 500mA of peak current. They are also capable of
absorbing just as much "kick-back" current without latching.
Synchronization can also be done by having a separate
RC timing circuit on the slave oscillator that is slightly lower
frequency than the master oscillator. The sync input will not
be in a high impedance state so the number of slave
oscillators is limited. This method of synchronization is
useful when slave oscillator is located in a different location.
When a separate RC timer is used in the slave controller,
ground loop noise pickup in the oscillator is minimized.
SOFT START
A soft restart recovery rate may be selected by placing
a capacitor from SOFT START (pin 8) to ground. The
calculationfortherecoverytimingisapproximately60msec/
µF.
SOFT START will mediate the start-up from under
voltage recovery, power-on, or SHUTDOWN.
6
R
T
R
T
MASTER
TCx5C25
5
C
GND
12
OSC OUT
4
T
SHUTDOWN
C
T
There is a minimum delay, non-latching shutdown fea-
ture on the TC35C25 PWM controller. Both outputs may be
turnedoffbyapplyingapositivevoltagetoSHUTDOWN(pin
10). Typical shutdown threshold is 2.4V. Returning the pin
back to ground will reinitialize the soft start cycle.
3
6
V
R
C
SYNC
REF
T
R
T
SLAVE
TCx5C25
GND
12
5
OSCILLATOR SECTION
T
C
T
A tri-state feature has been added to accommodate
systems which require multiple controllers to be run in a
"master/slave"configuration. Thetimingresistorpin(RT, pin
6) may be tied to VREF to place the sync pin (SYNC, pin 3)
in a high impedance state. This will allow the chip to be
clocked from an external source.
SLAVE TC > MASTER TC
The sync output (OSC OUT, pin 4) of the TC35C25 can
drive several sync inputs configured in this manner.
OSCILLATOR SYNCHRONIZATION
Synchronization of two TC35C25's can be done by
making one PWM Controller as the master oscillator to
synchronize the slave as follows:
6
R
T
R
T
MASTER
TCx5C25
5
C
GND
12
OSC OUT
4
T
C
T
16
3
6
5
V
R
C
SYNC
REF
T
SLAVE
TCx5C25
GND
12
T
TELCOM SEMICONDUCTOR, INC.
4-115
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
