TC28C46EOE TELCOM [TelCom Semiconductor, Inc], TC28C46EOE Datasheet - Page 7

• Manufacturer Part Number: TC28C46EOE
• Description: CMOS CURRENT MODE PWM CONTROLLER
• Manufacturer: TELCOM [TelCom Semiconductor, Inc]

Under Voltage Lockout
troller outputs OFF (LOW) if the supply voltage is below 7V.
Threshold hysteresis is 0.8V and guarantees clean, jitter-
free turn-ON and turn-OFF points. The hysteresis also
reduces capacitive filtering requirements at the PWM con-
troller supply input (pin 15).
Circuit Synchronization
ated in parallel with a common load. Paralleled converters
will equally share the load current. Voltage-mode control-
lers unequally share the load current, decreasing system
reliability.
together for parallel operation. Circuits can operate from a
master PWM controller internal oscillator with an external
driver (Figure 4). Devices can also be slaved to an exter-
nal oscillator (Figure 5). Disable internal slave device os-
cillators by grounding pin 8. Slave controllers derive an
oscillator from the bidirectional synchronization output sig-
nal at pin 10.
sync output and input. This is accomplished by making the
output driver "weak." This is advantageous in that it elimi-
nates an additional pin from the package but does not
enable the device to directly drive another device. In order
to make it an effective driver, a buffer is required (Figure 4).
In order to use pin 10 as a sync input, it is necessary to
overcome the internal driver. This requires a pulse with an
amplitude equal to V
undervoltage lockout to be disabled, a CMOS or open-
collector TTL driver should be used.
CMOS CURRENT MODE
PWM CONTROLLERS
SENSE AMPLIFIER
The under voltage lockout circuit forces the PWM con-
Current-mode-controlled power supplies can be oper-
Two or more of these PWM controllers can be slaved
Pin 10 is bidirectional in that it is intended to be both a
TELCOM SEMICONDUCTOR, INC.
3.15 CURRENT–
Figure 3. Transformer Isolated Current Sense
TCX8C46
+
–
S
. Since V
4
3
V S =
+
–
I S • RS
V S
N
S
must be above 7V for the
N
1
I S
*PULSE WIDTH OF
OSCILLATOR
OSCILLATOR IS = T D
EXTERNAL*
Figure 4. Master/Slave Parallel Operation
Figure 5. External Clock Synchronization
9
8
9
8
MASTER
SLAVE
R T
C T
R T
C T
V DD
V REF
TC4427
1/2
2
10
10
TCx8C46
TCx8C46
V DD
SYNC
SYNC
SYNC
SYNC
V REF
V REF
15
10
10
15
2
2
1/2 TC4427
TCx8C46
TCx8C46
R T
R T
V DD
TC18C46
TC28C46
TC38C46
9
9
C T
C T
CMPTR
CMPTR
7
7
8
4-107
1
2
3
4
5
6
7
8