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[FAQ]: Can LM5050-1, LM74700-Q1 or TPS241x controllers drive two back-back MOSFETs

Part Number: LM5050-1
Other Parts Discussed in Thread: LM74700-Q1, TPS2410, TPS2411, LM5050-2, TPS2412, TPS2413, TPS2419, LM74800-Q1

Can LM5050-1, LM74700-Q1 or TPS241x controllers drive two N-Channel MOSFETs connected back-back configuration?

RELATED PRODUCTS: LM74700-Q1, LM5050-1, LM5050-2, TPS2410, TPS2411, TPS2412 and TPS2413

  • Background:
    Ideal Diode controllers mostly are required to drive a single N-Channel MOSFET to emulate an ideal diode. However when the MOSFET is turned off using EN control, reverse current is blocked, but the power path is not blocked in the forward path due to the forward conduction of the MOSFET’s body diode. Applications which require to cut-off the power path require additional MOSFET Q2 connected back-back with the ideal diode MOSFET Q1 as shown in Figure 1.

    Figure 1: Ideal Diode Controllers NOT suitable to drive two Back-Back MOSFETs

    A common question that arises is can LM74700-Q1 or LM5050-1 or TPS241x drive two back-back connected MOSFETs as shown in Figure 1. Capability to drive two MOSFETs connected back-back is based on the gate drive topology of the ideal diode controller or OR-ing controller. Controllers such as LM74700-Q1, LM5050-1, and LM5050-2 are used in reverse battery protection applications as well as ORing applications. The gate drive of these controllers is similar and turns off the MOSFET by shorting gate to source (IN pin or ‘A’ pin or ANODE) as shown in figure 2 which sets VGS to 0V. The MOSFET Q1 is turned off because VGS = 0V, but for Q2 MOSFET, VGD = 0V and VGS is not 0V. Thus Q2 remains ON, acts as voltage follower with VOUT = (VBAT - 0.7 - VGS (TH)).

    Figure 2: LM5050 Functional Block Diagram

    Next, TPS2410, TPS2411, TPS2412, TPS2413 and TPS2419 are mainly used as ORing controllers and not recommended for reverse battery protection application because of the voltage rating limitation with maximum 16.5V. Gate drive circuit of TPS241x family of ORing controllers turn off the MOSFET by pulling GATE to GND. It is possible to control back-back connected MOSFETs as shown in Figure 3, because both the MOSFETs can be turned OFF with VGS <0V. Hence TPS241x are suitable for driving two back-back connected MOSFETs.

    Refer to FAQ for difference in Ideal Diode Controller and ORing Controller.

    Figure 3: TPS2411/10 Bidirectional MOSFET Control

    Recommended solution is to use industry first dual gate drive ideal diode controllers such as LM74800-Q1 or LM74810-Q1 to drive two back-back MOSFETs.
    Additionally TPS2410, TPS2411 and TPS2419 are suitable to drive two back-back connected MOSFETs for <16V power rails.