Datasheet

LM9061

SNOS738F –APRIL 1995–REVISED APRIL 1995

www.ti.com

APPLICATION INFORMATION

BASIC OPERATION

The LM9061 contains a charge pump circuit that generates a voltage in excess of the applied supply voltage to

provide gate drive voltage to power MOSFET transistors. Any size of N-channel power MOSFET, including

multiple parallel connected MOSFETs for very high current applications, can be used to apply power to a ground

referenced load circuit in what is referred to as “high side drive” applications. Figure 15 shows the basic

application of the LM9061.

Figure 15. Basic Application Circuit

When commanded ON by a logic “1” input to pin 7 the gate drive output, pin 4, rises quickly to the V

supply

potential at pin 5. Once the gate voltage exceeds the gate-source threshold voltage of the MOSFET, V

GS(ON)

(the source is connected to ground through the load) the MOSFET turns ON and connects the supply voltage to

the load. With the source at near the supply potential, the charge pump continues to provide a gate voltage

greater than the supply to keep the MOSFET turned ON. To protect the gate of the MOSFET, the output voltage

of the LM9061 is clamped to limit the maximum V

to 15V.

It is important to remember that during the Turn-ON of the MOSFET the output current to the Gate is drawn from

the V

supply pin. The V

pin should be bypassed with a capacitor with a value of at least ten times the Gate

capacitance, and no less than 0.1 µF. The output current into the Gate will typically be 30 mA with V

at 14V

and the Gate at 0V. As the Gate voltage rises to V

, the output current will decrease. When the Gate voltage

reaches V

, the output current will typically be 1 mA with V

at 14V.

A logic “0” on pin 7 turns the MOSFET OFF. When commanded OFF a 110 µA current sink is connected to the

output pin. This current discharges the gate capacitances of the MOSFET linearly. When the gate voltage equals

the source voltage (which is near the supply voltage) plus the V

GS(ON)

threshold of the MOSFET, the source

voltage starts following the gate voltage and ramps toward ground. Eventually the source voltage equals 0V and

the gate continues to ramp to zero thus turning OFF the power device. This gradual Turn-OFF characteristic,

instead of an abrupt removal of the gate drive, can, in some applications, minimize the power dissipation in the

MOSFET or reduce the duration of negative transients, as is the case when driving inductive loads. In the event

of an overstress condition on the power device, the turn OFF characteristic is even more gradual as the output

sinking current is only 10 µA (see MOSFET PROTECTION CIRCUITRY section).

Product Folder Links: LM9061