Datasheet

LTC1647-1/
LTC1647-2/LTC1647-3
10
1647fa
BLOCK DIAGRAMS
14
–
+
50μs
FILTER
–
+
1.21V
50mV
CHANNEL ONE
CHANNEL TWO
(DUPLICATE OF CHANNEL ONE)
10μA
CP
+
–
50μA
FAULT
2.45V
UVL
CHARGE
PUMP
REFERENCE 1.21V
SENSE2
4ON2
5FAULT2
1647-1/2/3 BD3
16V
CC2
12 GATE2
8GND
CP
V
CC
SELECTION
15SENSE1
13 GATE1
3FAULT1
2ON1
1V
CC1
LTC1647-3
V
CC
Selection Circuit
The LTC1647-3 features separate supply inputs (V
CC1
and V
CC2
) for each channel. The reference and charge
pump circuit draw supply current from the higher of the
two supplies. An internal V
CC
selection circuit detects and
makes the power connection automatically. This allows
a 3V channel to have standard MOSFET gate overdrive
when the other channel is 5V. An internal Zener clamps
GATE about 15V above V
CC
.
If both supplies are connected together (internally for
LTC1647-1 and LTC1647-2 or externally for LTC1647-3),
the reference and charge pump circuit draw equal current
from both pins.
APPLICATIONS INFORMATION
Electronic Circuit Breaker
Each channel of the LTC1647 features an electronic circuit
breaker to protect against excessive load current and short-
circuits. Load current is monitored by sense resistor R1 as
shown in Figure 1. The circuit breaker threshold, V
CB
, is
50mV and it exhibits a response time, t
FAULT
, of approximately
300ns. If the voltage between V
CC
and SENSE exceeds V
CB
for more than t
FAULT
, the circuit breaker trips and immediately
pulls GATE low with a 50mA current sink. The MOSFET turns
off and FAULT pulls low. The circuit breaker is cleared by
pulling the ON pin low for a period of at least t
RESET
(50μs).
A timing diagram of these events is shown in Figure 2.
The value of the sense resistor R1 is given by:
R1 = V
CB
/I
TRIP
(Ω)