lm9061mx National Semiconductor Corporation, lm9061mx Datasheet - Page 15

• Manufacturer Part Number: lm9061mx
• Description: Power Mosfet Driver With Lossless Protection
• Manufacturer: National Semiconductor Corporation

Application Information
REVERSE BATTERY
The LM9061 is not protected against reverse polarity supply
connections. If the V
respect to ground, the current from the V
limited to 20 mA. The addition of a diode in series with the
V
tract significantly from the charge pump gate overdrive out-
put voltage.
LOW BATTERY
An additional feature the LM9061 is an Under-Voltage Shut-
OFF function (UVSO). The typical UVSO threshold is 6.2V,
and does not have hysteresis. When V
guaranteed minimum operating voltage of 7.0V, and the
UVSO threshold, the operation of the MOSFET gate drive,
the delay timer, and the protection circuitry is not guaran-
teed. Operation in this region should be avoided. When V
falls below the UVSO threshold the charge pump will be
disabled and the gate will be discharged at the Normal-OFF
current sink rate, typically 110 µA.
Figure 6 shows the LM9061 used as an electronic circuit
breaker. This circuit provides low voltage shutdown, over-
voltage latch-OFF, and over-current latch-OFF.
The low voltage shutdown uses the ’On’ and ’Off’ voltage
thresholds, and the typical 1.2V of hysteresis, to disable the
LM9061 if V
ating voltage. The low voltage shutdown is accomplished
with a voltage divider biased off V
formed by R1 (30 kΩ), R2 (82 kΩ), and the internal pull-down
resistor of the ON/OFF pin (30 kΩ typical). In normal opera-
tion, V
7.0V, and the On/Off pin will be biased above the ’Off’
CC
input is recommended. This diode drop does not sub-
CC
FIGURE 5. Adding Over-Voltage Protection
will be above the minimum operating voltage of
CC
falls near, or below, the 7.0V minimum oper-
CC
supply should be taken negative with
CC
. The voltage divider is
CC
(Continued)
CC
is between the
pin should be
01231713
CC
15
threshold of 1.5V maximum (1.8V typical). When V
7.0V the On/Off pin voltage will fall below the ’Off’ threshold
voltage and the LM9061 will be turned off.
In the event of a latch-OFF shutdown, the circuit can be reset
by shutting the main supply off, then back on. An optional,
normally open, switch (Clear) from the ON/OFF pin to
ground, will allow a “push button clear” of the circuit after
latching OFF.
This voltage divider arrangement requires a mechanism to
raise the ON/OFF pin above the ’On’ threshold of 3.5V
minimum (3.1V typical) when V
This can be accomplished with a second, normally open,
switch from the ON/OFF pin across R2 (Set), so that closing
the switch will short R2 and the voltage at the ON/OFF pin
will be typically one-half of V
operating voltage of 7.0V this will bias the ON/OFF pin to
about 3.5V causing the LM9061 to turn on. When V
above typically 16.5V the resistor divider will have the ON/
OFF pin biased above 3.5V and shorting of the resistor R2
will not be needed.
While the scaling of the external resistor values between
V
resistor, can be used to increase the startup voltage, it is
important that the resistor ratio always has the ON/OFF pin
biased below the ’Off’ threshold (1.5V) when V
the minimum operating voltage of 7.0V.
The accuracy of this voltage divider arrangement is affected
by normal manufacturing variations of the ’On’ and ’Off’
voltage thresholds and the value of internal resistor at the
ON/OFF pin. If any application needs to detect with greater
precision when V
monitor should be used to drive the ON/OFF pin. The exter-
nal voltage monitor would also eliminate both the need for
the switch to short R2 to start the LM9061, as well as R2.
CC
and the ON/OFF input pin, against the internal 30 kΩ
FIGURE 6. Electronic Circuit Breaker
CC
is near to 7.0V, an external voltage
CC
. When V
CC
is less than typically 16V.
CC
is at the minimum
CC
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falls below
01231714
CC
falls to
CC
is