LTC2924I データシートの表示（PDF） - Linear Technology

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LTC2924I

Quad Power Supply Sequencer

Linear Technology 

LTC2924

Pin Functions

IN1-IN4 (Pins 1, 2, 3, 4): Sequenced Power Supply Moni-

tor Input. Connect this pin to an external resistive divider

between each sequenced power supply and GND. During

Power On sequencing, 0.61V (typ) at this pin indicates

that the sequenced power supply (enabled with each of

the OUT1-OUT4 pins) has reached the desired Power On

sequence voltage. A hysteresis current (programmed by

the HYS pin) is sourced out of each of the IN1-IN4 pins

after the 0.61V threshold is detected. During the Power Off

sequence, 0.61V at this pin indicates that the sequenced

power supply has reached the desired Power Off voltage.

The hysteresis current is removed after the 0.61V thresh­

old is detected.

OUT1-OUT4 (Pins 5, 6, 7, 8): Sequenced Power Supply

Enable. Connect this pin to the shutdown pin or an external

series N-channel MOSFET gate for each power supply being

sequenced. (A low at this pin means the sequenced power

supply is commanded to turn off.) When disabled, each

output is connected to GND with a resistance of <240Ω.

When enabled, each output is connected to an internally

generated charge pump supply (nominally VCC + 5V) via

an internal 10µA (typ) current source.

FAULT (Pin 9): Fault Pin. Pull this pin high with an external

10k resistor. The LTC2924 will pull this pin low if a fault

condition is detected (see Applications Information for

details). Pulling this pin low externally causes a simulta­

neous unsequenced Power Off.

DONE (Pin 10): Done Pin. Pull this pin to VCC with an

external 10k resistor. This open-drain output pulls low at

the completion of the Power-On sequence. At the end of

the Power Off sequence, the LTC2924 floats this pin. For

cascading multiple LTC2924s, see Application Information

for connecting the DONE pin.

VCC (Pin 11): LTC2924 Power Supply Input. All internal

circuits are powered from this pin. VCC should be con-

nected to a low noise power supply voltage and should

be bypassed with at least a 0.1µF capacitor to the GND

pin in close proximity to the LTC2924.

PGT (Pin 12): Power Good Timer. The PGT pin sets the time

allowed for a power supply to turn on after being enabled

with the OUT1-OUT4 pins. Connecting a capacitor between

this pin and ground programs a 200mS/µF dura­tion. The

PGT pin is reset before each of the OUT1-OUT4 pins are

asserted. If the voltage at the PGT pin reaches 1V, a fault

condition is asserted. The PGT pin must be conn­ ected

directly to ground to disable the power good timer func-

tion. Keep the ratio CPGT/CTMR between 1 and 100.

GND (Pin 13): Ground. All internal circuits are returned to

the GND pin. Connect this pin to the ground of the power

supplies that are being sequenced.

TMR (Pin 14): Timer. A capacitor connected between

this pin and ground sets the time delay between a supply

ready (IN1-IN4) signal and the enabling of the next power

supply in the sequence (OUT1-OUT4), with a 200mS/µF

duration. The TMR pin may be left floating if no delay is

required between supplies being sequenced on or off. The

PGT pin should be grounded if the TMR pin is left floating.

If an internal fault condition occurs, TMR will indicate so

by going to VCC until the fault condition is cleared. Do not

connect any other circuits to the TMR pin.

HYS/CFG (Pin 15): Hysteresis Current Setting and Cas­

cade Configuration. Connecting a resistor between this

pin and GND programs a 0.5/REXT (typ) hysteresis cur-

rent which is sourced out of each IN and ON pin. When

multiple LTC2924s are cascaded, the HYS/CFG pin is also

used to configure the position of the first LTC2924. See

Applica­tions Information for details.

ON (Pin 16): On Pin. Commands the LTC2924 to sequence

the power supplies up (Power On sequence) or down

(Power Off sequence). Typically connected to a system

controller. Hysteresis current is applied to this pin when

above 0.61V (typ). This pin has a precision 0.61V thresh­old

and can be used to sense a nonsequenced power supply’s

voltage to start the Power On sequence. See Applications

Information for details. For cascading mul­tiple LTC2924s,

see Applications Information for connect­ing the ON pin.

2924fc

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For more information www.linear.com/LTC2924

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