LTC2924 Linear Technology, LTC2924 Datasheet - Page 5

• Manufacturer Part Number: LTC2924
• Description: Quad Power Supply Sequencer
• Manufacturer: Linear Technology

PI FU CTIO S
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 V
an internal 10µA (typ) current source.
 F  A  U  L  T (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.
 D  O  N  E (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  D  O  N  E pin.
V
circuits are powered from this pin. V
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.
CC
U
(Pin 11): LTC2924 Power Supply Input. All internal
U
U
CC
should be con-
CC
+ 5V) via
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
connected directly to ground to disable the power good
timer function.
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. If
an internal fault condition occurs, TMR will indicate so by
going to V
connect any other circuits to the TMR pin.
HYS/CFG (Pin 15): Hysteresis Current Setting and Cascade
Configuration. Connecting a resistor between this pin and
GND programs a 0.5/R
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 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.
CC
until the fault condition is cleared. Do not
EXT
(typ) hysteresis current which
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