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