Linear Technology LTC2924 Quad Supply Sequencer DC818A DC818A Fiche De Données

LTC2924

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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 <240

Ω. 

When enabled, each output is connected to an internally 

generated charge pump supply (nominally V

CC

 + 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 high with an ex-

ternal 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. 
V

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

circuits are powered from this pin. V

CC

 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 dura tion. 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 con nected 

directly to ground to disable the power good timer func-

tion. Keep the ratio C

PGT

/C

TMR

 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 V

CC

 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/R

EXT

 (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 

Applica tions 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 thresh old 

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 mul tiple LTC2924s, 

see Applications Information for connect ing the ON pin.