LTC2923IDE datasheet(5/20 Pages) LINER

5 / 20 page

LTC2923

2923fa

PI FU CTIO S

VCC (Pin 1): Positive Supply Input Pin. 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.

ON (Pin 2): 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 LTC2923. If a resistive

divider connected to VCC drives the ON pin, the supplies

will automatically start up when VCC is fully powered.

TRACK1, TRACK2 (Pins 3, 4): Tracking Control Input. A

resistive voltage divider between RAMPBUF and TRACKx

determines the tracking profile of a slave supply (see

Applications Information). TRACKx pulls up to 0.8V and

the current supplied at TRACKx is mirrored at FBx. TRACKx

is capable of supplying at least 1mA when VCC = 2.9V.

Because a TRACKx pin is capable of supplying up to 30mA

under short-circuit conditions, avoid connecting TRACKx

to GND for extended periods. Limit the capacitance at each

TRACKx pin to less than 25pF. Float the TRACKx pins if

unused.

RAMPBUF (Pin 5): 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 (Pins 6, 13): Circuit Ground.

FB1, FB2 (Pins 8, 7): Feedback Control Output. FBx pulls

up on 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 force OUTx to track

RAMP. To prevent damage to the slave supply, the FBx pin

will not force the slave’s feedback node above 1.7V. In

addition, it will not actively sink current from this node

even when the LTC2923 is unpowered. Float the FB pins if

unused.

GATE (Pin 9/Pin 11): 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 MOS-

FET. A capacitor connected from GATE to GND sets the

ramp rate. An internal charge pump guarantees that GATE

will pull up to 5V above VCC 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 elec-

tronic circuit breaker in the LTC2923 pulls the GATE low

immediately with 20mA. Tie GATE to GND if unused. It is

a good practice to add a 10Ω resistor between this

capacitor and the FET’s gate to prevent high frequency FET

oscillations.

RAMP (Pin 10/Pin 12): Ramp Buffer Input. When the

RAMP pin is connected to the source of the external

N-channel FET, the slave supplies track the FET’s source

as it ramps up and down. If the GATE is fully enhanced

(GATE > RAMP + 4.9V) and (VCC – RAMP > 200mV)

indicates a shorted output, then the electronic circuit

breaker trips and GATE quickly pulls low with 20mA. The

GATE will not ramp up again until ON is pulled below 0.4V

and then above 1.23V. 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. RAMP must not

be driven above VCC (except by the GATE pin).

SDO (Pin 9, DE Package Only): Slave Supply Shutdown

Output. SDO is an open-drain output that holds the shut-

down (RUN/SS) pins of the slave supplies low until the ON

pin is pulled above 1.23V. If the slave supply is capable of

operating with an input supply that is lower than the

LTC2923’s minimum operating voltage of 2.9V, the SDO

pin can be used to hold off the slave supplies. SDO will be

pulled low again when RAMP < 100mV and ON < 1.23V.

STATUS (Pin 10, DE Package Only): 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.

MS/DE Packages

LTC2923IDE датащи(PDF) 5 Page - Linear Technology

LTC2923IDE датащи(HTML) 5 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

датащи скачать

ссылки URL