lm9061mx National Semiconductor Corporation, lm9061mx Datasheet - Page 14

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

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Application Information
go high to set a flip-flop and immediately latch the MOSFET
OFF. It will not re-start until the ON/OFF Input is toggled low
then high.
The delay time interval is set by the selection of C
can be found from:
where typically V
MINIMUM DELAY TIME
A minimum delay time interval is required in all applications
due to the nature of the protection circuitry. At the instant the
MOSFET is commanded ON, the voltage across the
MOSFET, V
cause the source is held at ground by the load. This condi-
tion will immediately trip the protection comparator. Without
a minimum delay time set, the timing comparator will trip and
force the MOSFET to latch-OFF thereby never allowing the
load to be energized.
To prevent this situation a delay capacitor is required at pin
8. The selection of a minimum capacitor value to ensure
proper start-up depends primarily on the load characteristics
and how much time is required for the MOSFET to raise the
load voltage to the point where the Sense input is more
positive than the Threshold input (T
mentation is required if a specific minimum delay time char-
acteristic is desired. Therefore:
DS
, is equal to the full load supply voltage be-
TIMER
= 5.5V and I
START-UP
DELAY
(Continued)
= 10 µA.
). Some experi-
DELAY
FIGURE 4. Delay Timer
and
14
Charging of the delay capacitor is clamped at approximately
7.5V which is the internal bias voltage for the 10 µA current
source.
In the absence of a specific delay time requirement, a value
for C
OVER VOLTAGE PROTECTION
The LM9061 will remain operational with up to +26V on V
If V
turn off the MOSFET to protect the load from excessive
voltage. When V
range the device will return to normal operation without
requiring toggling the ON/OFF input. This feature will allow
MOSFET operation to continue in applications that are sub-
ject to periodic voltage transients, such as automotive appli-
cations.
For circuits where the load is sensitive to high voltages, the
circuit shown in Figure 5 can be used. The addition of a
zener on the Sense input (pin 1) will provide a maximum
voltage reference for the Protection Comparator. The Sense
resistor is required in this application to limit the zener cur-
rent. When the device is ON, and the load supply attempts to
rise higher than (V
comparator will trip, and the Delay Timer will start. If the high
supply voltage condition lasts long enough for the Delay
Timer to time out, the MOSFET will be latched off. The
ON/OFF input will need to be toggled to restart the MOSFET.
CC
DELAY
increases to more than typically +30V the LM9061 will
of 0.1 µF is recommended.
CC
ZENER
has returned to the normal operating
+ V
THRESHOLD
), the Protection
01231712
CC
.