LX1552 Microsemi Corporation, LX1552 Datasheet - Page 17

• Manufacturer Part Number: LX1552
• Description: ULTRA-LOW START-UP CURRENT/ CURRENT-MODE PWM
• Manufacturer: Microsemi Corporation

Copyright © 1994
Rev. 1.0a 1/01
From V
2N222A
R
R
d
i
Due to inherent instability of fixed frequency current mode converters running above 50% duty cycle, slope compensation should be
added to either the current sense pin or the error amplifier. Figure 34 shows a typical slope compensation technique. Pin numbers
inside parenthesis refer to 14-pin package.
High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be
connected to pin 5 in a single point ground. The transistor and 5k potentiometer are used to sample the oscillator waveform and apply an
adjustable ramp to pin 3.
O
R
C
SLOPE
F
ERROR AMP
ADJUST
C
T
4.7K
4.7K
8(14)
R
R
1K
4(7)
2(3)
1(1)
T
F
ADJUST
100K
ERROR
2N2222
OSCILLATOR
AMP
I
5V
SENSE
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
T Y P I C A L A P P L I C A T I O N C I R C U I T S
2.5V
5K
U
LTRA
UVLO
P
-L
R O D U C T I O N
R
FIGURE 35. — OPEN LOOP LABORATORY FIXTURE
T
OW
2R
5(9)
R
S
FIGURE 34. — SLOPE COMPENSATION
1
2
3
4
TART
GOOD LOGIC
COMP
V
I
R
SENSE
S
LX155x
T
FB
C
R
1V
T
V
-U
REF
LX155x
P
REF
5V
C
URRENT
COMP
C.S.
C
GROUND
T
OUTPUT
V
V
D
REF
CC
, C
LATCH
PWM
A T A
8
7
6
5
URRENT
INTERNAL
BIAS
0.1µF
S
-M
H E E T
ODE
0.1µF
PWM
(continued)
A
7(12)
1K
7(11)
6(10)
5(8)
3(5)
V
CC
LX1552/3/4/5
C
R
DC BUS
V
V
OUTPUT
GROUND
R
REF
CC
Q1
S
V
O
17