TC96C55 Datasheet, PDF (8/9 Pages) TelCom Semiconductor, Inc – 3A OUTPUT PROGRAMMABLE POWER OSCILLATOR

3A OUTPUT PROGRAMMABLE
POWER OSCILLATOR
TC96C555
APPLICATIONS (Cont.)
Maximum Frequency
RCHG = 13K, Rdis = 6.8K
900
700
500
400
300
200
100
10
20 30 40 50 60 80 100
C in pF
100K
Minimum Frequency
RCHG = 200K, Rdis = 100K
10K
1K
100
10
1
0.1
10pF 100pF .001µF .01µF .1µF 1µF
C in pF
Figure 4. Typical Maximum and Minimum
Operating Frequency vs. Capacitor
+12V
This circuit will convert a 6 to 15V input to a 5V output of
200 milliamps. Normal operating frequency is 50kHz. Peak
to peak ripple is 50 millivolts. A change from 100mA to
200mA produces a 50mV peak change in V_OUT, with recov-
ery in 200µs.
The TC96C555 is used here as a duty cycle modulator
in a buck output circuit. The source current is modulated to
control the duty cycle. Sink current is fixed at 100µA with a
resistor (R4) of 10K. Transistor Q1, (2N2907A), is used for
current modulation into TC96C555 Pin 4, the charge current
program input. Shunt regulator TL431 is used for voltage
sense and regulation feedback. The TL431 has an internal
reference of 2.495V. Terminal R is compared with this
reference to control conduction of cathode C to anode A. R2
and R3 are selected to give proper bias current to the TL431.
C2 and R7 are for loop compensation and are optimized for
a recovery time of 200µs. The TC96C555 outputs, Pin 7 and
6, are tied together so that when output is HIGH, current
conducts from V_DD Pin 8 to output Pin 7 to charge the
inductor, L1. When output is OFF or LOW, energy stored in
L1 will continue to conduct through TC96C555 Pin 6 to the
lower internal MOSFET and out to Pin 5, the ground return.
This circuit does not have current limiting. A fuse is recom-
mended for protection. Figure 6 shows the duty cycle as a
function of the source current. Figure 8 shows the frequency
vs control voltage.
R1
10K
Q1
2N2907A
R2
560Ω
C4
.1µF
C5
100µF
8
4 _VR1 ^VDD
3
VREF
OUT ⁷
R4
10K
1 _VR2
C6
OUT
6
4.7µF
2
VIN
TC96C555
GND
C1
470pF
5
R3, 390Ω
L1, 3mH
C3
100µF
C2
.1µF
C
AR
TL431
100K
R7
VOUT
10K
R5
10K
R6
4-166
Figure 5. +5V Buck Regulator Power Supply with 82% Efficiency at 200mA Output
TELCOM SEMICONDUCTOR, INC.