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TPS546A24A: Sinking Current

Part Number: TPS546A24A
Other Parts Discussed in Thread: TPS546B24A, TPS546D24A

Hello E2E,

Is it possible to get the TPS546A/B/D24A device family to sink current?  What would be needed to achieve this if it all possible?




  • Hi Russell,

    The TPS546A24A can handle sinking current. Do you happen to know the approximate level of current sinking that is needed?


    Alec Biesterfeld


    The TPS546A24A, TPS546B24A, and TPS546D24A are all fully synchronous BUCK converters, they will support negative output currents.  When sinking an output current, the output energy will be boosted from VOUT back to PVIN, so it is important to make sure that either:

    The PVIN supply is also capable of regulating its output voltage under negative current.  (Most lab bench supplies and many isolated off-line supplies are NOT capable of regulating output voltage under negative current)

    The total current out of the PVIN supply is never negative.  If the source of the current into the output voltage is not coming from the same supply voltage, this may require adding a "dummy load" to the input supply to prevent a net-negative supply current, which can raise PVIN above its absolute maximum voltage.

    The TPS546A24A and TPS546B24A both have a non-programmable -10A valley current limit, which will limit their average negative current limit slightly less negative than that, depending on the ripple current.  The negative current limit does not trigger shut-down, but turns off the low-side FET, driving inductor current through the body diode of the high-side FET to limit inductor current until VOUT OV FAULT is triggered, which will trigger turn-on of the low-side FET and shutdown.

    The TPS546D24A has a non-programmable -20A valley current limit.

    If you need more sinking current capability, the TPS546A24A, TPS546B24A, and TPS546D24A all support current sharing and READ_IOUT telemetry for negative current levels down to their negative current limits (-10A and -20A respectively) so a 4-phase TPS546D24A stack can regulate and report negative currents upto -80A.

    Note:  the TPS546x24A family reports negative currents using Signed Linear 11 data format, which uses a 2s compliment mantissa value. Linear11 to decimal translation calculators which do not support signed values will report even very low negative currents as very large positive currents.

    Soft-Start / TON_RISE

    In order to support pre-biased output voltages with minimal sinking of output current, the TPS546x24A devices limit the complementary FET ON-time during the first 128 cycles of soft-start, this limits the converter's sinking current capability, but the TPS546x24A will begin switching and sinking current after the end of TON_RISE even if VOUT is greater than the target regulation voltage.

    OVP Active during disable

    The TPS546x24A family's over voltage protection is active even if the output voltage is disabled, a pull-up on the output voltage when conversion is disabled can trigger OVP and force the TPS546x24A to sink current until the output voltage is pulled below 0.4V.