LTC2925I View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2925I' PDF : 26 Pages View PDF
LTC2925
TYPICAL PERFORMANCE CHARACTERISTICS Specifications are at TA = 25°C
VSDx(OL) vs VCC
1.0
0.8
0.6
0.4
0.2
0
0
ISDx = 5mA
ISDx = 10μA
1
2
3
4
5
VCC (V)
2925 G07
VTRACK vs Temperature
0.805
VCC = 5.5V
ITRACKx = 1mA
VCC = 5.5V
ITRACKx = 10μA
0.800
0.795
VCC = 2.9V
ITRACKx = 1mA
VCC = 2.9V
ITRACKx = 10μA
0.790
–50
–25 0 25 50
TEMPERATURE (°C)
75 100
2925 G08
Tracking Cell Error vs ITRACKx
5
4
3
2
1
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
ITRACKx (mA)
2925 G09
PIN FUNCTIONS GN/UF Packages
VCC (Pin 1/Pin 22): Positive Supply Input. The operating
supply input range is 2.9V to 5.5V. An undervoltage lockout
circuit resets the part when the supply is below 2.5V. VCC
should be bypassed to GND with a 0.1μF capacitor.
SENSEP (Pin 2/Pin 23): Circuit Breaker Positive Sense
Input. SENSEP and SENSEN measure the voltage across
the sense resistor and trigger the circuit breaker function
when the current exceeds the level programmed by the
sense resistor for longer than a short-circuit timer cycle (see
SCTMR). If unused, tie SENSEN and SENSEP to VCC.
SENSEN (Pin 3/Pin 24): Circuit Breaker Negative Sense
Input. SENSEN connects to the low side of the current
sense resistor. SENSEP and SENSEN monitor the current
through the external FET by measuring the voltage across
the sense resistor. The circuit breaker turns off the FET
when the sense voltage exceeds 50mV for longer than a
short circuit timer cycle (see SCTMR). If the short-circuit
timer times out, the GATE pin will be pulled low im-
mediately to protect the FET. If unused, tie SENSEN and
SENSEP to VCC.
ON (Pin 4/Pin 1): On Control Input. The ON pin has a
threshold of 1.23V with 75mV of hysteresis. An active high
will cause 10μA to flow from the GATE pin, ramping up the
supplies. An active low pulls 10μA from the GATE pin, ramp-
ing the supplies down. Pulling the ON pin below 0.4V resets
the electronic circuit breaker in the LTC2925. If a resistive
divider connected to VCC drives the ON pin, the supplies will
automatically start up when VCC is fully powered.
SDTMR (Pin 5/Pin 2): Shutdown Timer. A capacitor from
SDTMR to GND sets the delay time between the ON pin tran-
sitioning high (which releases the SDx pins) and the supplies
beginning to ramp-up. Float SDTMR when it is unused.
SD1, SD2, SD3 (Pins 6, 7, 8/Pins 3, 4, 5): Outputs for
Slave Supply Shutdowns. The SDx pins are open-drain
outputs that hold the shutdown (RUN/SS) pins of the slave
supplies low until the ON pin is pulled above 1.23V. The
SDx pins will be pulled low again when RAMP <100mV and
ON <1.23V. If a slave supply is capable of operating with
an input supply that is lower than the LTC2925’s minimum
operating voltage of 2.9V, the SDx pins can be used to hold
off the slave supplies. Each SDx pin is capable of sinking
greater than 1mA with supplies as low as 2.3V.
RAMPBUF (Pin 9/Pin 6): Ramp Buffer Output. Provides a
low impedance buffered version of the signal on the RAMP
pin. This buffered output drives the resistive dividers that
connect to the TRACKx pins. Limit the capacitance at the
RAMPBUF pin to less than 100pF.
GND (Pin 10/Pins 7, 25): Circuit Ground.
TRACK1, TRACK2, TRACK3 (Pins 15, 14, 12/Pins 12, 11,
9): Tracking Control Input Pin. A resistive divider between
RAMPBUF, TRACKx and GND determines the tracking
2925fc
5
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