TC28C43EOE TELCOM [TelCom Semiconductor, Inc], TC28C43EOE Datasheet - Page 5

• Manufacturer Part Number: TC28C43EOE
• Description: BiCMOS CURRENT MODE PWM CONTROLLERS
• Manufacturer: TELCOM [TelCom Semiconductor, Inc]

BiCMOS CURRENT MODE
PWM CONTROLLERS
Dead Time
the primary consideration is the value of C
required to discharge the capacitor is approximately 1000
C
Undervoltage Lockout Range
ranges of input voltage is not required. The range from
starting V
approximately 9.5% of the starting voltage. The typical start-
up voltage is 8.4V and dropout voltage is 7.6V. This range
is used most in DC-to-DC converter applications.
Duty Cycle Limit
maximum of 99%. The oscillator is running at the same
frequency as the output.
V IN
T
R S
.
The value of R
The TCx8C43 PWM Controller is used where wide
The TCx8C43 PWM Controller has a duty cycle limit
TELCOM SEMICONDUCTOR, INC.
R
C
UNDERVOLTAGE LOCKOUT RANGE
in
voltage threshold to under voltage threshold is
TCx8C43
V ON = 8.4V
V OFF = 7.6V
I SENSE
GND
CURRENT SENSE CIRCUIT
5
9
T
PEAK CURRENT (I S ) FORMULA:
has an effect on the discharge rate but
ERROR AMP
–
0.4V
+
I S =
0.95V
170 A
COMPARATOR
1mA
R S
2R
PWM
+
–
I S
R
7.6V
8.4 V
TCx8C43
LIMIT BUFFER
T
+
–
. The time
1.4V
V DD
BENCH TEST OPERATIONAL SIMULATION
fullpower and fed back to the I
simulates the dI/dT current ramp which would flow through
the primary of the transformer. The output voltage of the
power supply is simulated by feeding some of the reference
voltage into V
mined the operating characteristics of the current mode
controller.
RS. A small RC filter may be required to suppress switching
transient. This voltage enters PWM Controller at I
pin 5. A voltage of 0.4 V is added before this is fed into PWM
Comparator (+) input. The PWM Comparator (–) input
senses the voltage feedback error amp output with a limit
buffer that limits this voltage to 1.4V maximum. This limit
buffer limits the peak current across RS to a maximum of
0.95V. In normal operation, the error amplifier controls the
current limit threshold.
above 1 volt or pulling CMPTR, pin 1 to GND. This will set the
PWM latch so that the output will remain low until the next
clock pulse after the shutdown condition is removed.
SHUTDOWN
5.1k
5k
The timing ramp (R
Current is sensed through voltage drop across resistor
Shutdown can be accomplished by either pulling I
TO CURRENT
SENSE RESISTOR
FB
14
. The combination of the two levels deter-
SHUTDOWN METHODS
5
TCx38C43
V REF
I SENSE
T
SHUTDOWN
/C
T
) is buffered by the emitter
SENSE
input. This ramp
TC18C43
TC28C43
TC38C43
9
1
TCx38C43
CMPTR
ANALOG
GND
SENSE
SENSE
4-97
,
1
2
3
4
5
6
7
8