Design Description

This circuit uses a four-channel buffered voltage output DAC to voltage margin a switch-mode power supply (SMPS). A voltage margining circuit is used to trim, scale, or test the output of a power converter. Adjustable power supplies, such as low dropout regulators (LDOs), DC/DC converters, or SMPS provide a feedback (FB) input that is used to control the desired output. A precision smart DAC, such as the DAC53204 or DAC53004, provides linear control of the power supply output when the DAC is supplied and the output is powered on. Most DACs include an internal pull-down resistor at the voltage output when the DAC is supplied but the output is in power down mode. Also, when most DACs are completely powered off, the ESD cells on the output pin conduct current if the output is pulled away from ground which is the case in voltage margining circuits. The DAC53204 or DAC53004 provides a high impedance (Hi-Z) output when the DAC is powered off or when the output channel is in power down mode, meaning that the DACs draw very little current through the FB pin of the SMPS and the output is set at the nominal voltage. The DAC53204 and DAC53004 have a general-purpose input (GPI) pin that allows the DAC output to be toggled between a high and low voltage output. This allows the SMPS to be toggled within ±10% of the nominal output value. All register settings can be saved using the non-volatile memory (NVM) on the DAC53204 and DAC53004 meaning that the devices can be used without a processor, even after a power cycle. This circuit can be used in applications such as Communications Equipment, Enterprise Systems, Test and Measurement, and general-purpose power-supply modules.