0V

VIN

6 V

9 V

15 V

GATE DRIVER

ENABLE

7

LM74700-Q1

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SNOSD17 – OCTOBER 2017

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7.3 Feature Description

7.3.1 Input Voltage

The ANODE pin is used to power the LM74700-Q1's internal circuitry, typically drawing 30 µA when enabled and

3 µA when disabled. If the ANODE pin voltage is greater then specified minimum operating voltage, the

LM74700-Q1 operates in either shutdown mode or conduction mode in accordance with the EN pin voltage. The

voltage from ANODE to GND is designed to vary from 65 V to –65 V, allowing the LM74700-Q1 to withstand

negative voltage transients or inputs from an AC source.

7.3.2 Charge Pump

The charge pump supplies the voltage necessary to drive the external N-channel MOSFET. An external

capacitor is placed between VCAP and ANODE to provide energy allowing the external MOSFET to be turned on

quickly. In order for the charge pump to supply current to the external capacitor, the ANODE to GND voltage

must be greater than the specified minimum operating voltage, and the EN pin must be above the specified input

high threshold. If both of these conditions are not achieved, the charge pump remains disabled. To ensure that

the external MOSFET can be driven above its specified threshold voltage, the VCAP to ANODE voltage must be

above the undervoltage lockout threshold, typically 6 V, before the internal gate driver is enabled. To remove any

chatter on the gate drive approximately 600 mV of hysteresis is added to the VCAP undervoltage lockout. The

charge pump remains enabled until the VCAP to ANODE voltage reaches 15 V, typically, at which point the

charge pump is disabled decreasing the current draw on the ANODE pin. The charge pump remains disabled

until the VCAP to ANODE voltage is below to 9 V typically at which point the charge pump is enabled. The

voltage between VCAP and ANODE continue to charge and discharge between 9 V and 15 V as shown in

Figure 1. By enabling and disabling the charge pump, the ANODE pin current of the LM74700-Q1 is greatly

reduced. The ANODE pin typically sinks 1.5 mA when the charge pump is enabled . When the charge pump is

disabled the ANODE pin typically sinks 30 µA.

Figure 1. Charge Pump Operation