LM74700MDDFREP datasheet(12/32 Pages) TI

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8.3 Feature Description

8.3.1 Input Voltage

The ANODE pin is used to power the LM74700-EP's internal circuitry, typically drawing 80 µA when enabled

and 1 µA when disabled. If the ANODE pin voltage is greater than the POR Rising threshold, then LM74700-EP

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-EP to withstand negative voltage

transients.

8.3.2 Charge Pump

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

pump capacitor is placed between VCAP and ANODE pins to provide energy to turn on the external MOSFET.

In order for the charge pump to supply current to the external capacitor the EN pin voltage must be above

the specified input high threshold, V(EN_IH). When enabled the charge pump sources a charging current of

300-µA typical. If EN pins is pulled low, then 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 6.5 V, before the internal gate driver is enabled. Use Equation 1 to

calculate the initial gate driver enable delay.

T(DRV_EN) = 75 µs + C(VCAP) × V(VCAP_UVLOR)

300 µA

(1)

where

• C(VCAP) is the charge pump capacitance connected across ANODE and VCAP pins

• V(VCAP_UVLOR) = 6.5 V (typical)

To remove any chatter on the gate drive, approximately 800 mV of hysteresis is added to the VCAP

undervoltage lockout. The charge pump remains enabled until the VCAP to ANODE voltage reaches 12.4 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 11.6-V typically, at which point the charge

pump is enabled. The voltage between VCAP and ANODE continue to charge and discharge between 11.6 V

and 12.4 V as shown in Figure 8-1. By enabling and disabling the charge pump, the operating quiescent current

of the LM74700-EP is reduced. When the charge pump is disabled it sinks to 5-µA typical.

LM74700-EP

SNOSDD6 – SEPTEMBER 2021

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LM74700MDDFREP Datasheet(PDF) 12 Page - Texas Instruments