UCC27321 , UCC27322

UCC37321, UCC37322

SLUS504G – SEPTEMBER 2002 – REVISED MAY 2013

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The switching load presented by a power MOSFETcan be converted to an equivalent capacitance by examining

the gate charge required to switch the device. This gate charge includes the effects of the input capacitance plus

the added charge needed to swing the drain of the device between the ON and OFF states. Most manufacturers

provide specifications that provide the typical and maximum gate charge, in nC, to switch the device under

specified conditions. Using the gate charge Qg, one can determine the power that must be dissipated when

charging a capacitor. This is done by using the equivalence Qg = CeffV to provide the following equation for

power:

This equation allows a power designer to calculate the bias power required to drive a specific MOSFET gate at a

specific bias voltage.

Enable

UCC37321/2 provides an Enable input for improved control of the driver operation. This input also incorporates

logic compatible thresholds with hysteresis. It is internally pulled up to VDD with 100-k

Ω resistor for active high

operation. When ENBL is high, the device is enabled and when ENBL is low, the device is disabled. The default

state of the ENBL pin is to enable the device and therefore can be left open for standard operation. The output

state when the device is disabled is low regardless of the input state. See the truth table below for the operation

using enable logic.

ENBL input is compatible with both logic signals and slow changing analog signals. It can be directly driven or a

power-up delay can be programmed with a capacitor between ENBL and AGND.

Table 1. Input/Output Table

ENBL

IN

OUT

0

0

0

0

1

0

INVERTING

UCC37321

1

0

1

1

1

0

0

0

0

NON--

0

1

0

INVERTING

1

0

0

UCC37322

1

1

1

10

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Product Folder Links: UCC27321 UCC27322 UCC37321 UCC37322