lx1563 Microsemi Corporation, lx1563 Datasheet - Page 16

• Manufacturer Part Number: lx1563
• Description: Second-generation Power Factor Controller
• Manufacturer: Microsemi Corporation

LX1562/1563
16
CURRENT DETECT LOGIC
upper 7.8V clamp prevents input overvoltage breakdown dur-
ing switch off time, while during the on time the lower 0.7V
clamp prevents substrate injection. An internal current limit
resistor protects the lower clamp transistor in case the “I
is accidently shorted to ground.
START-UP TIMER
A start-up timer circuit eliminates the need for an external os-
cillator when used in stand alone applications. The timer, as
shown in Figure 30, provides a means to automatically start the
pre converter if the latch output Q comes up in a wrong (HI)
state. The timer capacitor ramps up and resets the latch to a
low state, turning the output driver on.
L1
I
DEF
5
300
1.72V
(continued)
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
S
E C O N D
FIGURE 30 — START-UP TIMER & CURRENT DETECT LOGIC CIRCUITRY
V
REF
P
-G
R O D U C T I O N
V
E N E R AT I O N
TIMER
I C D E S C R I P T I O N
C.S.
C.S. Latch
DET
” pin
P
Delay
O W E R
S
1µs
R
D
OUTPUT DRIVER STAGE
The LX1562/63 output driver is designed for direct driving of
an external power MOSFET. It is a totem pole stage with
±500mA peak current capability. This typically results in a
130ns rise and fall times into a 1000pF capacitive load. Addi-
tionally the output is held low during the undervoltage condi-
tion to ensure that the MOSFET remains in the off state until
supply voltage reaches the start-up threshold.
ways lower than 13.8V (typ.) when supply voltage variation
exceeds more than rated V
nal MOSFET. This eliminates an external zener diode and extra
power dissipation associated with it that otherwise is required
for reliable circuit operation.
A T A
F
Internal voltage clamping ensures that output driver is al-
A C T O R
Q
Q
S
C
H E E T
O N T R O L L E R
HI
C.S.
GS
threshold (typ 20V) of the exter-
V
M0
OUT
C.S.
L1
7
4
Copyright © 1996
Rev. 1.3a
8/30