ADM1041A datasheet(17/56 Pages) AD

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ADM1041A

Rev. 0 | Page 17 of 56

Mnemonic

Description

DC_OK

The DC_OK function advises the system on the status of the power supply. When it is false, the system is

assured of at least 1 ms of operation if ac power is lost for any reason. Other turn-off modes provide more

warning time. This pin is an open-drain output. It can be configured as a P-channel pull-up or an N-channel

pull-down. It may also be configured as positive or negative (inverted) logic.

AC_OK

The AC_OK function advises the system whether or not sufficient bulk voltage is present to allow reliable

operation. The system may choose to shut down if this pin is false. The power supply normally tries to

maintain normal operation as long as possible, although DC_OK goes false when only a millisecond or so of

operation time is left. This pin is an open-drain output. It can be configured as a P-channel pull-up or an N-

channel pull-down. It may also be configured as positive or negative (inverted) logic.

DC_OK on delay

The DC_OK output is kept false for typically 100 ms to 900 ms during power-up.

DC_OK off delay

When the system is to be shut down in response to PSON going low, or in response to an OCP or OTP event, a

signal is first sent to the DC_OK output to go false as a warning that power is about to be lost. PEN is signaled

false typically 2 ms later (configurable).

Debounce Digital Noise

Filter

All of the inputs to the logic core are first debounced or digitally filtered to improve noise immunity. The

debounce period for OV events is in the order of 16 μs, for UV events it is 450 μs, and for PSON it is typically

80 ms (configurable).

ACSENSE1

A voltage from the secondary of the power transformer, which can provide an analog of the bulk supply, is

rectified and lightly filtered and measured by the ac sense function. At start-up, if this voltage is adequate,

this function signals the end-user system that it is okay to start. If a brown-out occurs or ac power is removed,

this function can provide early warning that power is about to be lost and allow the system to shut down in

an orderly manner. While ACSENSE is low, UVB is enabled, which means undervoltage protection is not

initiated. If ac power is so low that the converter cannot continue to operate, other protection circuits on the

primary side normally shut down the converter. When an adequate voltage level is resumed, a power-up

cycle is initiated.

Pulse OK

As well as providing ACSENSE, the preceding connection to the transformer is used to gate the operation of

the OrFET circuit. If the output of the transformer is good, the OrFET circuit allows gate drive to the OrFET.

AC Hysteresis

ACSENSE Hysteresis. Configurable voltage on the ACSENSE input allows the ACSENSE upper and lower

threshold to be adjusted to suit different amounts of low frequency ripple present on the bulk capacitor.

ACSENSE2

An alternate form of ac sense can be accepted by the ADM1041A. This may in the form of an opto-coupled

signal from the primary side where the actual level sensing might be done. As with the above, while ac is low

and UVB is disabled, AC_OK is false and DC_OK is true. Any brownout protection that might be required on

the primary is done on the primary side.

Soft-Start

At start-up, the voltage reference to the voltage error amplifier is brought up slowly in approximately 127

steps to provide a controlled rate of rise of the output voltage.

VDD–OVP

An OVP fault on the auxiliary supply to the ADM1041A causes a standard OVP operation (see the OVP

function in this table).

VDD–UVL

A UVL fault on the auxiliary supply to the IC causes a standard UVP operation (see the UVP function in this

table).

Auto Restart Mode

In this mode, the housekeeping circuit attempts to restart the supply after an undervoltage event at about 1

second intervals. No other fault can initiate auto-restart.

VREF–MON

The internal precision reference is monitored by a separate reference for overvoltage and allows truly

redundant OVP. The externally available reference is also monitored for an undervoltage that would indicate

a short on the pin.

GND–MON

The internal ground is constantly monitored against the VS- pin. If the chip ground goes positive with respect

to this pin, it indicates that the chip ground is open-circuit either inside the ADM1041A or the external wiring.

The ADM1041A would be latched off, similar to an OV event.

ADM1041A Datasheet(PDF) 17 Page - Analog Devices

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