LTC1647-2IS8 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1647-2IS8' PDF : 20 Pages View PDF
BLOCK DIAGRA S
VCC1 1
SENSE 1 15
ON1 2
FAULT 1 3
+– 50mV
+
–
1.21V
+
–
2.45V
UVL
LTC1647-1/LTC1647-2/LTC1647-3
LTC1647-3
CHANNEL ONE
50µs
FILTER
FAULT
CP
10µA
50µA
13 GATE 1
GND 8
REFERENCE 1.21V
CHARGE
PUMP
CP
VCC
SELECTION
VCC2 16
SENSE 2 14
ON2 4
FAULT 2 5
CHANNEL TWO
(DUPLICATE OF CHANNEL ONE)
12 GATE 2
1647-1/2/3 BD3
APPLICATIO S I FOR ATIO
VCC Selection Circuit
The LTC1647-3 features separate supply inputs (VCC1 and
VCC2) for each channel. The reference and charge pump
circuit draw supply current from the higher of the two
supplies. An internal VCC 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 VCC.
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.
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 resis-
tor R1 as shown in Figure 1. The circuit breaker threshold,
VCB, is 50mV and it exhibits a response time, tFAULT, of
approximately 300ns. If the voltage between VCC and
SENSE exceeds VCB for more than tFAULT, 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 tRESET (50µs). A timing diagram of these
events is shown in Figure 2.
The value of the sense resistor R1 is given by
R1 = VCB/ITRIP(Ω)
where VCB is the circuit breaker trip voltage (50mV) and
ITRIP is the value of the load current at which the circuit
breaker trips. Kelvin-sense layout techniques between the
sense resistor and the VCC and SENSE pins are highly
recommended for proper operation.
9
Share Link: 
