www.ti.com

FUNCTIONAL DESCRIPTION

POWER SUPPLY SEQUENCING

POWER SUPPLY ENABLES

VOLTAGE REFERENCE

UCD9080

SLVS692A – SEPTEMBER 2006 – REVISED DECEMBER 2006

The UCD9080 can be configured to sequence the power rails using the enable signals or the general-purpose

outputs in one of three ways:

The first way is to specify a delay time after a sequence event. A sequence event includes a device reset

(including power-on-reset), a RESET command, or a resequence action. The enable/GPO is asserted after the

sequence event plus specified delay.

The second way is to specify a delay time after another (parent) rail has achieved regulation (Vrail is within

specified under and overvoltage settings). The enable/GPO is asserted after the (parent) rail is in regulation plus

specified delay.

The third way is to specify a (parent) rail voltage. The enable/GPO is asserted after the (parent) rail voltage is

greater than or equal to the specified voltage.

Of course, a rail does not have to be sequenced. This could be used in the case of a backplane voltage which is

not under the control of the UCD9080, but is being monitored.

The UCD9080 can sequence and enable/disable up to 8 power supplies through the ENx (EN1 to EN8) signals

on the device. These signals can be configured for either active high or active low, to support power supplies

that use either polarity.

The enable signals for up to 8 power supplies can be sequenced by the UCD9080 as described below. Note that

requires the GPO1 signal, then this signal is not available for power supply enable sequencing.

The enable signals on the UCD9080 are not intended to drive the gate of N-channel MOSFET. These pins are

LVCMOS level only, providing the capability of driving either logic high or low (3.3 V or 0 V).

Note that while the UCD9080 is not operating, the state of the enable signals is not defined. If these signals

need to be defaulted to the disabled state, according to the power supply definition, then they should be pulled

up or down accordingly on the board.

section. The voltage reference can either be an internally generated 2.5-V reference or an external 3.3-V

UCD9080.

Depending on the voltage reference that is being used, the accuracy of reading voltages is affected. The internal

reference is not as accurate as the external reference and affects the accuracy of the sampled voltages of the

monitored rails. See the Electrical Characteristics for information on voltage reading accuracy for use with each

of the references.

The section on Configuring the UCD9080 details how to select the internal or external voltage reference.

9

Submit Documentation Feedback