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LTC2928I

Multichannel Power Supply Sequencer and Supervisor

Linear Technology 

LTC2928

Pin Functions

OV: Overvoltage Output. Pulls low when any positive supply

exceeds its configured overvoltage threshold. OV remains

low until all positive supplies have remained below the

overvoltage threshold for a time equal to the configured

RST delay time. To generate an overvoltage fault, con-

nect OV to FLT. The OV output has a weak pull-up to VCC

and may be pulled above VCC using an external pull-up.

OV may be left unconnected if unused. See Applications

Information for details.

OVA: Over Voltage Adjust Input. After configuring the un-

dervoltage thresholds, bias this input to set the overvoltage

threshold for all positive supplies. Leave the pin floating

to set an overvoltage threshold approximately 32% above

the undervoltage threshold. Tie OVA to VCC to move the

overvoltage threshold above 1V. Consult the Applications

Information for details on OVA biasing.

PTMR: Power Good Timer. Attach an external capacitor to

ground to set the maximum time allowed for all supplies

to reach their configured undervoltage threshold during

sequence-up phase (or all supplies below their sequence-

down threshold during sequence-down phase). The timer

is started when the first enable (EN) is raised (or lowered).

The power good timing scale factor is 4000ms/µF. A 0.1µF

capacitor generates a 400ms delay time. If any supply is

late, a sequence fault is generated. FLT pulls low and all

supply enable outputs are pulled low. Disable the power

good timer by grounding PTMR. Consult Applications

Information for more details.

RDIS: Reset Disable Three State Input. Typically used for

supply margining applications. Pull RDIS high or low to

force RST high. Leave the RDIS input open to allow RST

to operate normally.

REF: Reference Output. REF is used to offset negative

supplies connected through resistance to V1. The refer-

ence will move during sequence-up and sequence-down

operation to effect the selected thresholds. The buffered

reference sources 1mA and sinks up to 200µA of current.

The reference drives a bypass capacitor of up to 1000pF

without oscillation.

RST: Reset Output. If any supply is below its undervolt-

age threshold, RST pulls low. RST pulls high after all

supplies are above their undervoltage threshold for the

configured delay time (configure delay time using the

RTMR pin). The RST output has a weak pull-up to VCC

and may be pulled above VCC using an external pull-up.

RST is guaranteed low with VCC down to 0.5V. Configure

the RST to FLT relationship using the MS1, MS2 inputs.

See Applications Information for details. Leave the RST

output open if unused.

RTMR: Reset Timer. Attach an external capacitor to

ground to set a reset delay time of 4000ms/µF. Floating

RTMR generates a minimum delay of approximately 50µs.

A 0.047µF capacitor will generate a 190ms delay time.

RT1-RT4: Resistive Time Position Configuration Inputs.

Place a single resistor from VCC to each input to select one

of eight time positions in which to turn-on or turn-off each

enable output (see Application Information for RT table).

Each RT input numerically corresponds to a respective

EN output and monitor input. During sequencing-up, an

enable output (EN) pulls high at the start of its chosen time

position. During sequencing-down, an enable output (EN)

pulls low at the start of its chosen time position (sequence-

down position is the reverse of sequence-up). To remove

a monitor channel from participation, command any en-

able off by pulling its corresponding RT input to ground.

Prior to sequencing, any enable may be commanded on

by pulling its corresponding RT input to VCC. Maximum

capacitive load is 150pF.

SQT1, SQT2: Sequencing Threshold Three State Configura-

tion Inputs. Select sequencing thresholds as a percentage

of the 0.5V supply monitor threshold for positive supplies

and as a percentage of REF for negative supplies. For

sequencing-up choose from 33%, 67% or 100%. For

sequencing-down choose from 100%, 67%, 33% or 10%.

See Applications Information for configuration table.

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For more information www.linear.com/LTC2928

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