Detailed Operating Description

The LM5112 is a high speed , high peak current (7A) single

channel MOSFET driver. The high peak output current of the

LM5112 will switch power MOSFET’s on and off with short

rise and fall times, thereby reducing switching losses con-

siderably. The LM5112 includes both inverting and non-

inverting inputs that give the user flexibility to drive the

MOSFET with either active low or active high logic signals.

The driver output stage consists of a compound structure

with MOS and bipolar transistor operating in parallel to opti-

mize current capability over a wide output voltage and oper-

ating temperature range. The bipolar device provides high

peak current at the critical Miller plateau region of the MOS-

FET V

swing. The totem pole output drives the MOSFET gate be-

tween the gate drive supply voltage V

ground potential at the V

The control inputs of the driver are high impedance CMOS

buffers with TTL compatible threshold voltages. The nega-

tive supply of the input buffer is connected to the input

ground pin IN_REF. An internal level shifting circuit connects

the logic input buffers to the totem pole output drivers. The

level shift circuit and separate input/output ground pins pro-

vide the option of single supply or split supply configurations.

When driving the MOSFET gates from a single positive

supply, the IN_REF and V

power ground.

The isolated input and output stage grounds provide the

capability to drive the MOSFET to a negative V

a more robust and reliable off state. In split supply configu-

ration, the IN_REF pin is connected to the ground of the

controller which drives the LM5112 inputs. The V

connected to a negative bias supply that can range from the

IN_REF potential to as low as 14 V below the Vcc gate drive

supply. For reliable operation, the maximum voltage differ-

ence between V

14V.

The minimum recommended operating voltage between Vcc

and IN_REF is 3.5V. An Under Voltage Lock Out (UVLO)

circuit is included in the LM5112 which senses the voltage

difference between V

When the V

the driver is disabled and the output pin is held in the low

state. The UVLO hysteresis prevents chattering during

brown-out conditions; the driver will resume normal opera-

tion when the V

3.0V.

20066803

FIGURE 2. Simplified Application Block Diagram

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