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參數(shù)資料
| 型號(hào)： | LM9061 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Power MOSFET Driver with Lossless Protection |
| 中文描述： | 功率MOSFET驅(qū)動(dòng)器，帶有無(wú)損保護(hù) |
| 文件頁(yè)數(shù)： | 9/14頁(yè) |
| 文件大小： | 234K |
| 代理商： | LM9061 |
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Application Hints
(Continued)
a manner that there is virtually no current flowing into the
non-inverting input of the comparator. Therefore, only I
REF
flows through resistor R
THRESHOLD
. All of the input bias
current, 20
m
A maximum, for the comparator input stage
(twice the I
SENSE
specification of 10
m
A maximum, defined
for equal potentials on each of the comparator inputs) how-
ever flows into the inverting input through resistor R
SENSE
.
At the comparator threshold, the current through R
SENSE
will be no more than the I
SENSE
specification of 10
m
A.
To tailor the V
DS (MAX)
threshold for any particular applica-
tion, the resistor R
THRESHOLD
can be selected per the fol-
lowing formula:
V
DS (MAX)
e
V
REF
c
R
THR
R
REF
where R
REF
e
15.4 k
X
, I
SENSE
is the input bias current to
the protection comparator, R
SENSE
is the resistor connect-
ed to pin 1 and V
OS
is the offset voltage of the protection
comparator (typically in the range of
g
10 mV).
The resistor R
SENSE
is optional, but is strongly recommend-
ed to provide transient protection for the Sense pin, espe-
cially when driving inductive type loads. A minimum value of
1 k
X
will protect the pin from transients ranging from
b
25V
to
a
60V. This resistor should be equal to, or less than, the
resistor used for R
THRESHOLD
. Never set R
SENSE
to a value
larger than R
THRESHOLD
. When the protection comparator
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 compara-
tor. 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).
b
(I
SENSE
c
R
SENSE
)
a
V
OS
In automotive applications the load supply may be the bat-
tery of the vehicle whereas the V
CC
supply for the LM9061
is a switched ignition supply. When the V
CC
supply is
switched OFF there is always a concern for the amount of
current drained from the battery. The only current drain un-
der this condition is a leakage current into the Threshold pin
which is less than 10
m
A.
A bypass capacitor across R
REF
is optional and is used to
help keep the reference voltage constant in applications
where the V
CC
supply is subject to high levels of transient
noise. This bypass capacitor should be no larger than
0.1
m
F, 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 ca-
pacitor discharged. Should a surge of load current trip the
protection comparator high, the discharge transistor turns
OFF and an internal 10
m
A current source begins linearly
charging the delay capacitor.
If the surge current, with excessive V
DS
voltage, lasts long
enough for the capacitor to charge to the timing comparator
threshold of typically 5.5V, the output of the comparator will
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
DELAY
and
can be found from:
T
DELAY
e
(V
TIMER
c
C
DELAY
)
I
DELAY
where typically V
TIMER
e
5.5V and I
DELAY
e
10
m
A.
Charging of the delay capacitor is clamped at approximately
7.5V which is the internal bias voltage for the 10
m
A current
source.
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
DS
, is equal to the full load supply voltage be-
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.
TL/H/12317–12
FIGURE 4. Delay Timer
9
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