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[FAQ]: Can an Ideal Diode Controller used as load switch with external MOSFET?

Part Number: LM74700-Q1
Other Parts Discussed in Thread: LM5050-1, LM5050-2, , LM5060-Q1

Can Ideal Diode controller or ORing Controller used to control MOSFET as a high side switch or load switch?

RELATED PRODUCTS: LM74700-Q1, LM5050-1 and LM5050-2

  • Background:
    Ideal Diode controllers drive a single N-Channel MOSFET to emulate an ideal diode. When the MOSFET is turned off, the power path is not blocked in the forward path due to the forward conduction of the MOSFET’s body diode. One question which arises naturally is that, can the MOSFET orientation be changed to high side switch or load switch as shown in Figure 1, where power path is cut off when MOSFET is turned off.

    Figure 1: Ideal Diode Controller NOT suitable for Load Switch or High Side Switch

    Capability to drive the MOSFETs connected as high side switch or load switch is based on the gate drive topology of the ideal diode controller or ORing 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 are 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 Q2 cannot be turned off because source and drain are swapped, 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

    Ideal Diode Controllers LM74700-Q1, LM5050-1 and LM5050-2 cannot be used to drive a MOSFET in a load switch application. For low current load application, it is recommended to use integrated FET load switches or high side switches.
    For higher current requirement, recommend to use LM5060-Q1 for load switch or other hot-swap controllers in high side switch application.