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ADM1041A

Secondary-Side Controller with Current Share and Housekeeping

Analog Devices 

GENERAL DESCRIPTION

The ADM1041A is a secondary-side and management IC spec-

ifically designed to minimize external component counts and to

eliminate the need for manual calibration or adjustment on the

secondary-side controller. The principle application of this IC is

to provide voltage control, current share, and housekeeping

functions for single output in N+1 server power supplies.

The ADM1041A is manufactured with a 5 V CMOS process

and combines digital and analog circuitry. An internal

EEPROM provides added flexibility for trimming timing and

voltage and selecting various functions. Programming is done

via an SMBus serial port that also allows communication

capability with a microprocessor or microcontroller.

The usual configuration using this IC is on a one-per-output

voltage rail. Output from the IC can be wire-OR’ed together or

bused in parallel and read by a microprocessor. A key feature on

this IC is support for an OrFET circuit when higher efficiency

or power density is required.

SAMPLE APPLICATION CIRCUIT DESCRIPTION

Figure 1 shows a sample application circuit using the

ADM1041A. The primary side is not detailed and the focus is

on the secondary side of the power supply.

The ADM1041A controls the output voltage from the power

supply to the designed programmed value. This programmed

value is determined during power supply design and is digitally

adjusted via the serial interface. Digital adjustment of the

current sense and current limit is also calibrated via the serial

interface, as are all of the internal timing specifications.

The control loop consists of a number of elements, notably the

inputs to the loop and the output of the loop. The ADM1041A

takes the loop inputs and determines what, if any, adjustments

are needed to maintain a stable output. To maintain a stable

loop, the ADM1041A uses three main inputs:

• Remote voltage sense

• Load current sense

• Current sharing information

In this example, a resistor divider senses the output current as a

voltage drop across a sense resistor (RS) and feeds a portion

into the ADM1041A. Remote local voltage sense is monitored

via VS+ and VS− pins. Finally, current sharing information is fed

back via the share bus. These three elements are summed

together to generate a control signal (VCMP), which closes the

loop via an optocoupler to the primary side PWM controller.

ADM1041A

Another key feature of the ADM1041A is its control of an

OrFET. The OrFET causes lower power dissipation across the

OR'ing diode. The main function of the OrFET is to disconnect

the power supply from the load in the event of a fault occurring

during steady state operation, for example, if a filter capacitor or

rectifier fails and causes a short. This eliminates the risk of

bringing down the load voltage that is supplied by the redun-

dant configuration of other power supplies. In the case of a

short, a reverse voltage is generated across the OrFET. This

reverse voltage is detected by the ADM1041A and the OrFET is

shut down via the FG pin. This intervention prevents any

interruption on the power supply bus. The ADM1041A can

then be interrogated via the serial interface to determine why

the power supply has shut down.

This application circuit also demonstrates how temperature can

be monitored within a power supply. A thermistor is connected

between the VDD and MON2 pins. The thermistor’s voltage

varies with temperature. The MON2 input can be programmed

to trip a flag at a voltage corresponding to an overheating power

supply. The resulting action may be to turn on an additional

cooling fan to help regulate the temperature within the power

supply.

PWM +

PRIMARY

DRIVER

RSENSE

LOAD

OPTO-

COUPLER

AC PULSE

SENSE

DIFF CURRENT

SENSE

OrFET

CONTROL

ERROR

AMP

SOFT

START

CURRENT

SHARE

VOLT, TEMP MONITOR

AND FAULT DETECTION

ADM1041A

DIFF LOAD AND LOCAL

VOLTAGE SENSE

EEPROM AND

RAM AND TRIM

SMBus

SHARE

BUS

(μC OR STANDALONE

OPERATION)

μC

Figure 2. Application Block Diagram

Differences Between the ADM1041A and ADM1041

For all new designs, it is recommended to use the ADM1041A.

The parts differ as follows:

• The ADM1041 allows the internal VREF voltage reference to

be accessed at Pin 18. This is not accessible using the

ADM1041A.

• The ADM1041A has longer VDDOK debounce and VDDOV

debounce than the ADM1041.

• The GND_OK Disable bit (Register 11h) does not disable

when using the ADM1041. It does disable when using the

ADM1041A.

Rev. 0 | Page 3 of 56

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