Analog Devices Inc. ADM1041AARQZ-REEL

Secondary-Side Controller with Current Share and Housekeeping
Power Supply Monitor & Load Sh
Secondary Side PWM Cntrlr HOUSEKEEPING 24-Pin QSOP T/R
Telecom Circuit, 1-Func, CMOS, PDSO24
IC SECONDARY SIDE CTRLR 24QSOP
The ADM1041 is a secondary-side and management IC specifically 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 ADM1041 is manufactured with a 5 V CMOS process and combines digital and analog circuitry. An internal EEPROM provides added flexibility in the trimming of timing and voltage and selection of various functions. Programming is done via an Sm Bus serial port that also allows communication capability with a microprocessor or micro controller. The usual configuration using this IC is on a one per output basis. Outputs from the IC can be wire-ORed 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 ADM1041. The primary side is not detailed and the focus is on the secondary side of the power supply. The ADM1041 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 ADM1041 takes the loop inputs and determines what, if any, adjustments are needed to maintain a stable output. To maintain a stable loop, the ADM1041 uses three main inputs: x Remote voltage sense x Load current sense x 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 ADM1041. 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. Another key feature of the ADM1041 is its control of an OrFET. The OrFET causes lower power dissipation across the ORing 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 redundant 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 ADM1041 and the OrFET is shut down via the FG pin. This intervention prevents any interruption on the power supply bus. The ADM1041 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 V DD and MON2 pins. The thermistorR^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.