Datasheet

LTC1644
10
1644f
BLOCK DIAGRA
W
When the TIMER pin is high, the circuit breaker function is
enabled. If the voltage across the sense resistor exceeds
55mV but is less than 150mV, the circuit breaker is tripped
after a 45µs time delay. In the event the sense resistor
voltage exceeds 150mV, the circuit breaker trips immedi-
ately and the chip latches off. To disable the current limit,
3V
SENSE
and 3V
IN
can be shorted together.
3V
IN
(Pin 17): 3.3V Supply Sense Input. An undervoltage
lockout circuit prevents the switches from turning on
when the voltage at the 3V
IN
pin is less than 2.48V. If no
3.3V input supply is available, connect two series diodes
between 5V
IN
and 3V
IN
(tie anode of first diode to 5V
IN
and
cathode of second diode to 3V
IN
, see Figure 11).
PI FU CTIO S
UUU
3V
OUT
(Pin 18): Analog Input used to monitor the 3.3V
output supply voltage. The PWRGD pin cannot pull low
until the 3V
OUT
pin voltage exceeds 2.9V. If no 3.3V input
supply is available, tie the 3V
OUT
pin to the 5V
OUT
pin.
V
EEOUT
(Pin 19): –12V Supply Output. A 1Ω switch is
connected between V
EEIN
and V
EEOUT
. V
EEOUT
must ex-
ceed –10.5V before the PWRGD pin pulls low unless the
V
EE
PWRGD function is disabled by grounding the V
EEIN
pin.
12V
OUT
(Pin 20): 12V Supply Output. A 0.5Ω switch is
connected between 12V
IN
and 12V
OUT
. 12V
OUT
must
exceed 11.1V before the PWRGD pin can pull low.
Q6
V
EEIN
2
TIMER
4
V
EEOUT
19
3V
OUT
18
5V
OUT
3
–
+
+–
Q9
NOTE: V
12VIN
– V
TIMER
< 1V = TIMER HI, V
12VIN
– V
TIMER
> 1V = TIMER LOW
Q8
Q2
Q3
225µA
65µA
GATE
5V
OUT
TIMER
51mV, TIMER LO
150mV, TIMER HI
55mV
12V
IN
15
5V
SENSE
14
12V
IN
1
12V
OUT
20
5V
IN
13
–
+
+–
+–
2.5V
UVL
8.3V
UVL
–
+
+–
3V
OUT
55mV
CP3
REF
3V
SENSE
16
3V
IN
17
RESETOUT
10
–
+
–
+
+–
+–
2.5V
UVL
Q4
1V
Q12
CP4
REF
–
+
+
–
CP7
REF
–
+
CP5
REF
–
+
RESETIN 9
PWRGD 7
Q10
FAULT 6
Q11
OFF/ON 5
Q5Q7
21µA
12V
IN
GND
8
DRIVE
11
PRECHARGE
1644 BD
12
LOGIC
Q1
TIMER
51mV, TIMER LO
150mV, TIMER HI
CP1
A1
CP2
A2
A3