LM9061MXSLASHNOPB datasheet(12/33 Pages) TI1

12 / 33 page

LM9061, LM9061-Q1

SNOS738H – APRIL 1995 – REVISED JANAURY 2015

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Feature Description (continued)

Figure 12. Basic Application Circuit

7.3.2 Basic Operation

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

potential at pin 5. Once the gate voltage exceeds the gate-source threshold voltage of the MOSFET, VGS(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 VGS to 15 V.

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

the VCC supply pin. The VCC pin should be bypassed with a capacitor with a value of at least 10 times the Gate

capacitance, and no less than 0.1

μF. The output current into the Gate will typically be 30 mA with VCC at 14 V

and the Gate at 0 V. As the Gate voltage rises to VCC, the output current will decrease. When the Gate voltage

reaches VCC, the output current will typically be 1 mA with VCC at 14 V.

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 VGS(ON) threshold of the MOSFET, the source

voltage starts following the gate voltage and ramps toward ground. Eventually the source voltage equals 0 V 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 Lossless Overcurrent Protection).

7.3.3 Turn On and Turn Off Characteristics

The actual rate of change of the voltage applied to the gate of the power device is directly dependent on the

input capacitances of the MOSFET used. These times are important to know if the power to the load is to be

applied repetitively as is the case with pulse width modulation drive. Of concern are the capacitances from gate

to drain, CGD, and from gate to source, CGS. Figure 13 details the turn ON and turn OFF intervals in a typical

application. An inductive load is assumed to illustrate the output transient voltage to be expected. At time t1, the

ON/OFF input goes high. The output, which drives the gate of the MOSFET, immediately pulls the gate voltage

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LM9061MX/NOPB Datasheet(PDF) 12 Page - Texas Instruments