Datasheet

LT1910
10
1910fa
APPLICATIONS INFORMATION
Low Voltage/Wide Supply Range Operation
When the supply is less than 12V, the LT1910’s charge
pump does not produce suffi cient gate voltage to fully
enhance the standard N-channel MOSFET. For these ap-
plications, a logic-level MOSFET can be used to extend
the operating supply down to 8V. If the MOSFET has a
maximum V
GS
rating of 15V or greater, then the LT1910
can also operate up to a supply voltage of 60V (absolute
maximum rating of the V
+
pin).
Protecting Against Supply Transients
The LT1910 is 100% tested and guaranteed to be safe
from damage with 60V applied between the V
+
and GND
pins. However, when this voltage is exceeded, even for a
few microseconds, the result can be catastrophic. For this
reason it is imperative that the LT1910 is not exposed to
supply transients above 60V. A transient suppressor, such
as Diodes Inc.’s SMAJ48A, should be added between the
V
+
and GND pins for such applications.
For proper current sense operation, the V
+
pin is required
to be connected to the positive side of the drain-sense
resistor (see Drain-Sense Confi guration). Therefore, the
supply should be adequately decoupled at the node where
the V
+
pin and drain sense resistor meet. Several hundred
microfarads may be required when operating with a high
current switch.
When the operating voltage approaches the 60V absolute
maximum rating of the LT1910, local supply decoupling
between the V
+
and GND pins is highly recommended. An
RC snubber with a transient suppressor are an absolute
necessity. Note however that resistance should not be
added in series with the V
+
pin because it will cause an
error in the current-sense threshold.
Low Side Driving
Although the LT1910 is primarily targeted at high side
(grounded load) switch applications, it can also be used
for low side (supply connected load) switch applications.
Figures 8a and 8b illustrate the LT1910 driving low side
power MOSFETs. Because the LT1910 charge pump tries
to pump the gate of the N-channel MOSFET above the
supply, a clamp Zener is required to prevent the V
GS
(ab-
solute maximum) of the MOSFET from being exceeded.
FAULT
IN
V
+
SENSE
3
4
8
6
LT1910
R1
5.1k
12V TO 48V
5V
FAULT OUTPUT
INPUT
0V
GND
Q1
IRFZ44
15V
1N4744
1910 F08a
C1
100μF
100V
C
T
1μF
R
S
0.01Ω
(PTC)
4A
LOAD
+
GATETIMER
5
1
2
FAULT
IN
TIMER
V
+
SENSE
GATE
3
4
2
8
6
5
LT1910
R1
5.1k
5V
FAULT OUTPUT
INPUT
GND
Q1
IRF630
15V
1N4744
1910 F08b
C1
10μF
50V
C
T
1μF
1
R
S
0.02Ω
HV
LOAD
51Ω
2N2222
8V TO 24V HV
–
+
+
LT1006
51Ω
Figure 8a. Low Side Driver with Load Current Sensing
Figure 8b. Low Side Driver for Source Current Sensing