CMOS CURRENT MODE
PWM CONTROLLER
TC170
SWITCH
CURRENT
×
3.15 CURRENT-SENSE
AMPLIFIER
4
3
RS
7
VDD
100
µ
A
ERROR
AMPLIFIER
5
6
+
–
V1
+
–
LIMIT
BUFFER
AMPLIFIER
Q4
+
–
PWM COMPARATOR
–
+
+
S
–
FROM
UNDERVOLTAGE
LOCKOUT
S
PWM LATCH
5.1V
VREF
2
R1
1
V1
Q
R
1
10
2
"A" = 1
OUTPUT
OFF (LOW)
0.75V
3
4
5
6
R2
Q3
350mV
–
LOCK-UP
AMPLIFIER
Q1
+
POSITIVE
FEEDBACK
Q2
SHUTDOWN
COMPARATOR
+
–
6k
16
350mV
TC170
IL
3.5k
Figure 1.
R1 and R2 Set Maximum Peak Output Current
I
×
3.15 CURRENT-
SENSE AMPLIFIER
RS
VOUT
×
3.15 CURRENT-
SENSE
AMPLIFIER
+
–
TC170
I
4
C
3
*OPTIONAL RC FILTER
R*
RS
+
–
TC170
4
3
7
(A) Ground Reference
(B) Above-Ground Resistive Sensing
Figure 2.
Resistive Sensing
8
4-123
TELCOM SEMICONDUCTOR, INC.