LTC2923_15 Datasheet, PDF (1/20 Pages) Linear Technology – Power Supply Tracking Controller

FEATURES
■ _{Flexible Power Supply Tracking}
■ _{Tracks Both Up and Down}
■ _{Power Supply Sequencing}
■ _{Supply Stability is Not Affected}
■ _{Controls Two Supplies Without Series FETs}
■ _{Controls a Third Supply With a Series FET}
■ _{Adjustable Ramp Rates}
■ _{Electronic Circuit Breaker}
■ _{Available in 10-Lead MS and 12-Lead}
(4mm × 3mm) DFN Packages
U
APPLICATIO S
■ _{VCORE and VI/O Supply Tracking}
■ _{Microprocessor, DSP and FPGA Supplies}
■ _Servers
■ _{Communication Systems}
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Patents Pending.
LTC2923
Power Supply
Tracking Controller
DESCRIPTIO
The LTC^®2923 provides a simple solution to power supply
tracking and sequencing requirements. By selecting a few
resistors, the supplies can be configured to ramp-up and
ramp-down together or with voltage offsets, time delays
or different ramp rates.
By introducing currents into the feedback nodes of two
independent switching regulators, the LTC2923 causes
their outputs to track without inserting any pass element
losses. Because the currents are controlled in an open-
loop manner, the LTC2923 does not affect the transient
response or stability of the supplies. Furthermore, it
presents a high impedance when power-up is complete,
effectively removing it from the DC/DC circuit.
For systems that require a third supply, one supply can be
controlled with a series FET. This optional series FET can
also control a supply that does not allow direct access to
its feedback resistors (e.g., a power module) or a supply
whose output cannot be forced to ground (e.g., a 3-termi-
nal linear regulator). When the FET is used, an electronic
circuit breaker provides protection from short-circuit
conditions.
TYPICAL APPLICATIO
V_IN
3.3V
Q1
3.3V
10nF
138k
100k
16.5k
13k ^887k
412k
V_CC GATE RAMP
ON
FB1
LTC2923
RAMPBUF
STATUS
TRACK1
SDO
TRACK2
FB2
GND
V_IN
IN
DC/DC
FB = 1.235V OUT
1.8V
35.7k ^16.5k
V_IN
IN
DC/DC
FB = 0.8V OUT
2.5V
887k
412k
2923 TA01
1V/DIV
3.3V
2.5V
1.8V
3.3V
2.5V
1.8V
1ms/DIV
2923 TA02
1V/DIV
1ms/DIV
2923 F08b
2923fa
1