lm9061mx National Semiconductor Corporation, lm9061mx Datasheet - Page 13

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

Application Information
To tailor the V
tion, the resistor R
ing formula:
where R
protection comparator, R
pin 1 and V
parator (typically in the range of
The resistor R
mended to provide transient protection for the Sense pin,
especially when driving inductive type loads. A minimum
value of 1 kΩ will protect the pin from transients ranging from
−25V to +60V. This resistor should be equal to, or less than,
the resistor used for R
value larger than R
parator output goes high , the total bias current for the input
stage transfers from the Sense pin to the Threshold pin,
thereby changing the voltages present at the inputs to the
comparator. For consistent switching of the comparator right
at the desired threshold point, the voltage drop that occurs at
the non-inverting input (Threshold) should equal, or exceed,
the rise in voltage at the inverting input (Sense).
In automotive applications the load supply may be the bat-
tery of the vehicle whereas the V
a switched ignition supply. When the V
OFF there is always a concern for the amount of current
REF
= 15.4 kΩ, I
OS
DS (MAX)
SENSE
is the offset voltage of the protection com-
THRESHOLD
THRESHOLD
is optional, but is strongly recom-
THRESHOLD
threshold for any particular applica-
SENSE
SENSE
can be selected per the follow-
is the input bias current to the
. When the protection com-
is the resistor connected to
CC
±
10 mV).
. Never set R
supply for the LM9061 is
CC
FIGURE 3. Protection Comparator Biasing
supply is switched
(Continued)
SENSE
to a
13
drained from the battery. The only current drain under this
condition is a leakage current into the Threshold pin which is
less than 10 µA.
A bypass capacitor across R
help keep the reference voltage constant in applications
where the V
noise. This bypass capacitor should be no larger than
0.1 µF, and is not needed for most applications.
DELAY TIMER
To allow the MOSFET to conduct currents beyond the pro-
tection threshold for a brief period of time, a delay timer
function is provided. This timer delays the actual latching
OFF of the MOSFET for a programmable interval. This fea-
ture is important to drive loads which require a surge of
current in excess of the normal ON current upon start up, or
at any point in time, such as lamps and motors. Figure 4
details the delay timer circuitry. A capacitor connected from
the Delay pin 8, to ground sets the delay time interval. With
the MOSFET turned ON and all conditions normal, the out-
put of the protection comparator is low and this keeps the
discharge transistor ON. This transistor keeps the delay
capacitor discharged. Should a surge of load current trip the
protection comparator high, the discharge transistor turns
OFF and an internal 10 µA current source begins linearly
charging the delay capacitor.
If the surge current, with excessive V
enough for the capacitor to charge to the timing comparator
threshold of typically 5.5V, the output of the comparator will
CC
supply is subject to high levels of transient
REF
is optional and is used to
DS
voltage, lasts long
01231711
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