DC-to-DC Output Current Sensing

摘要

Method and circuits enable measuring output current in DC/DC converters operating in pulse frequency modulation (PFM) mode and in pulse width modulation (PWM) mode. The method is applicable to DC/DC converters using an inductor at the output. Current is sampled on one pass transistor only. The DC/DC converter disclosed turns a PMOS transistor off when the output current reaches its current limit.

主权项

1. A buck converter enabled for output current measurement comprising:
a main output stage comprising a PMOS pass transistor and an NMOS pass transistor both connected in series, wherein the PMOS pass transistor is connected to supply voltage VDD and the NMOS pass transistor is connected to ground; a coil, wherein a first terminal of the coil is connected to a mid-node between the PMOS pass transistor and the NMOS pass transistor and a second terminal of the coil is connected to an output port of the buck converter; a circuitry configured to providing a first voltage node representing an output current limit of the buck converter and to providing a second voltage node to be sampled in PFM mode, whenever either the PMOS pass device or the NMOS pass device is on; a switch, wherein a first terminal of the switch may contact multiple contact points and a second terminal of the switch is connected to a filter, wherein the switch is configured in PFM mode to either sampling the second voltage node in order to provide an average current during the output current pulse or to being connected to the supply voltage or a correspondent voltage and in PWM mode to either sampling the mid-node voltage between the PMOS pass transistor and the NMOS pass transistor or being connected to open circuit;wherein the buck converter is configured to switch the PMOS pass transistor off when an output current through the coil reaches a maximum current limit, which is indicated by the first voltage node, and then the current through the coil falls linearly until the coil is completely discharged.