LTC2925
4
2925fd
For more information www.linear.com/LTC2925
Typical perForMance characTerisTics
I
CC
vs V
CC
V
GATE
vs V
CC
V
GATE
vs I
GATE
I
GATE
Fast Pull-Down vs
Temperature
V
RAMPBUF(OL)
vs Temperature
elecTrical characTerisTics
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All currents into the device pins are positive; all currents out of
device pins are negative. All voltages are referenced to ground unless
otherwise specified.
Note 3: The GATE pin is internally limited to a minimum of 11.5V. Driving
this pin to voltages beyond the clamp may damage the part.
2.5
I
CC
(mA)
12
10
8
6
4
2
0
3
3.5 4 4.5
2925 G01
V
CC
(V)
5 5.5
I
TRACKx
= I
FBx
= 1mA
I
RAMPBUF
= 3mA
I
TRACKx
= I
FBx
= 0mA
I
RAMPBUF
= 0mA
V
CC
(V)
2
8
V
GATE
(V)
9
10
12
11
3 4
2925 G02
5 6
I
GATE
(µA)
0
0
V
GATE
(V)
5
10
15
5 10
V
CC
= 2.9V
V
CC
= 5.5V
2925 G03
15
TEMPERATURE (°C)
–50 –25
I
GATE
(mA)
50 75
2925 G04
0 25 100
50
45
40
35
30
25
V
CC
= 5.5V
V
CC
= 2.9V
V
GATE
= 5V
TEMPERATURE (°C)
–50
V
RAMPBUF(OL)
(mV)
25
75
2925 G05
–25 0 50
70
65
60
55
50
45
40
35
30
100
V
CC
= 2.9V
V
CC
= 5.5V
V
RAMPBUF(OH)
vs Temperature
TEMPERATURE (°C)
–50
80
90
100
25 75
2925 G06
70
60
–25 0
50 100
50
40
V
RAMPBUF(OH)
(mV)
110
V
CC
= 2.9V
V
CC
= 5.5V
Specifications are at T
A
= 25°C
LTC2925
5
2925fd
For more information www.linear.com/LTC2925
Typical perForMance characTerisTics
Specifications are at T
A
= 25°C
V
SDx(OL)
vs V
CC
V
TRACK
vs Temperature Tracking Cell Error vs I
TRACKx
V
CC
(V)
0
0
V
SDx(OL)
(V)
0.2
0.4
0.6
0.8
1.0
1
2 3 4
2925 G07
5
I
SDx
= 10µA
I
SDx
= 5mA
TEMPERATURE (°C)
–50
V
TRACKx
(V)
0.805
0.800
0.795
0.790
0 50–25 25 75
2925 G08
100
V
CC
= 5.5V
I
TRACKx
= 10µA
V
CC
= 2.9V
I
TRACKx
= 1mA
V
CC
= 5.5V
I
TRACKx
= 1mA
V
CC
= 2.9V
I
TRACKx
= 10µA
I
TRACKx
(mA)
0
3
4
5
4
2925 G09
2
1
0
1 2 30.5 4.51.5 2.5 3.5 5
V
TRACKx
0.8V
I
FBx
I
TRACKx
–1 (%)
pin FuncTions
GN/UF Packages
V
CC
(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. V
CC
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 V
CC
.
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 immediately to
protect the FET. If unused, tie SENSEN and SENSEP to V
CC
.
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, ramping the
supplies down. Pulling the ON pin below 0.4V resets the
electronic circuit breaker in the LTC2925. If a resistive
divider connected to V
CC
drives the ON pin, the supplies will
automatically start up when V
CC
is fully powered.
SDTMR (Pin 5/Pin 2): Shutdown Timer. A capacitor from
SDTMR to GND sets the delay time between the ON pin
transitioning high (which releases the SDx pins) and the sup
-
plies 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.
LTC2925
6
2925fd
For more information www.linear.com/LTC2925
pin FuncTions
GN/UF Packages
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/Pin 7): Circuit Ground.
Exposed Pad (Pin 25): Exposed pad may be left open or
connected to GND.
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 profile of OUTx (see Applications Information).
TRACKx pulls up to 0.8V and the current supplied at
TRACKx is mirrored at FBx. The TRACKx pin is capable
of supplying at least 1mA when V
CC
= 2.9V. It may be
capable of supplying up to 30mA when the supply is at
5.5V, so care should be taken not to short this pin for
extended periods. Limit the capacitance at the TRACKx
pin to less than 25pF. Float the TRACKx pins if unused.
FB1, FB2, FB3 (Pins 16, 13, 11/Pins 13, 10, 8): Feed-
back Control Output. FBx connects to the feedback node
of slave supplies. Tracking is achieved by mirroring the
current from TRACKx into FBx. If the appropriate resistive
divider connects RAMPBUF and TRACKx, the FBx current
will for
ce OUTx to track RAMP. The LTC2925 is capable of
controlling slave supplies with feedback voltages between
0V and 1.6V. To prevent damage to the slave supply, the
FBx pin will not force the slaves feedback node above
2.5V. In addition, it will not actively sink current from this
node even when the LTC2925 is unpowered. Float the FBx
pins if unused.
REMOTE (Pin 17/Pin 14): Remote Sense Switch. A 15Ω
switch connects REMOTE to RAMP when the GATE is fully
enhanced (GATE > RAMP + 4.9V). Otherwise, it presents
a high impedance. When the slave supplies track the
master supply, REMOTE can be used to compensate for
the voltage drop across the external sense resistor and
N-channel FET. A resistor between the output and the sense
nodes of the master supply provides feedback before the
external FET is fully enhanced. If an external FET is not
used, float REMOTE.
RAMP (Pin 18/Pin 15): Ramp Buffer Input. When the
RAMP pin is connected to the source of the external N-
channel FET, the slave supplies track the FETs source as
it ramps up and down. Alternatively, when no external FET
is used, the RAMP pin can be tied directly to the GATE pin.
In this configuration, the supplies track the capacitor on
the GATE pin as it is charged and discharged by the 10µA
current source controlled by the ON pin. When the GATE
is fully enhanced (GATE > RAMP + 4.9V) the open-drain
STATUS pin goes high impedance and the remote sense
switch connects the RAMP pin to the REMOTE pin.
GATE (Pin 19/Pin 16): Gate Drive for External N-Channel
FET. When the ON pin is high, an internal 10µA current
source charges the gate of the external N-channel MOSFET.
A capacitor connected from GATE to GND sets the ramp
rate. It is a good practice to add a 10Ω resistor between
this capacitor and the FETs gate to prevent high frequency
FET oscillations. An internal charge pump guarantees that
GATE will pull up to 5V above V
CC
ensuring that logic-
level N-channel FETs are fully enhanced. When the ON
pin is pulled low, the GATE pin is pulled to GND with a
10µA current source. Under a short-circuit condition, the
electronic circuit breaker in the LTC2925 pulls the GATE
low immediately with 20mA. Tie GATE to GND if unused.
FAULT (Pin 20/Pin 17): Circuit Breaker and Power Good
Timer Fault Output. FAULT is an open-drain output that
pulls low when the electronic circuit breaker is activated
or a power good timeout fault is detected. FAULT is reset
by pulling ON below 0.4V. To allow retry, tie FAULT to ON.
STATUS (Pin 21/Pin 18): Power Good Status Indicator. The
STATUS pin is an open-drain output that pulls low until
GATE has been fully charged at which time all supplies
will have reached their final operating voltage.
PGI (Pin 22/Pin 19): Power Good Timer Input. PGI con
-
nects to the RST pin of the downstream supply monitor. If
PGI has not transitioned high within a power good timer
cycle (see PGTMR), the F
AULT pin will be pulled low and
the supplies will be turned off by pulling the GATE pin
low with 20mA. PGI is pulled up with 10µA. An internal
Schottky diode allows PGI to be pulled safely above V
CC
.
Float PGI when it is unused.

LTC2925IUF#PBF

Mfr. #:
Manufacturer:
Analog Devices Inc.
Description:
Power Management Specialized - PMIC Pwr Supply Sequence/Tracking Controller
Lifecycle:
New from this manufacturer.
Delivery:
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