LTC1255CS8 Linear Technology, LTC1255CS8 Datasheet - Page 9

• Manufacturer Part Number: LTC1255CS8
• Description: IC MOSFET DVR HI-SIDE DUAL 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC1255CS8

• Configuration: High-Side
• Input Type: Non-Inverting
• Delay Time: 180µs
• Number Of Configurations: 2
• Number Of Outputs: 2
• Voltage - Supply: 9 V ~ 24 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Peak: -
• High Side Voltage - Max (bootstrap): -

APPLICATIO S I FOR ATIO
Current Limited Power Supplies
The LTC1255 requires at least 3.5V at the supply pin to
ensure proper operation. It is therefore necessary that
the supply to the LTC1255 be held higher than 3.5V at
all times, even when the output of the switch is short
circuited to ground. The output voltage of a current
limited regulator may drop very quickly during short
circuit and pull the supply pin of the LTC1255 below
3.5V before the shutdown circuitry has had time to
respond and remove drive from the gate of the power
MOSFET. A supply filter should be added as shown in
Figure 7 which holds the supply pin of the LTC1255
high long enough for the overcurrent shutdown cir-
cuitry to respond and fully discharge the gate.
Linear regulators with small output capacitors are the
most difficult to protect as they can “switch” from a
voltage mode to a current limited mode very quickly.
15V
18V
+
Figure 7. Supply Filter for Current Limited Supplies
10 F
IN1
+
1/2 LTC1255
REGULATOR
GND
V
47 F*
12V/2A
Figure 6. Using a Speed-Up Diode
S
DS1
G1
*SUPPLY FILTER COMPONENT
IN1
U U
1/2 LTC1255
GND
V
S
10 *
0.01 F
C
0.01 F
DS1
DELAY
G1
R
1N4148
100k
DELAY
1N4148
W
100k
+
+
LTC1255 • F07
LTC1255 • F06
100 F
12V
12V
10 F
LOAD
U
MTP12N06E
R
0.1
IRF530
R
0.036
SHORT
CIRCUIT
SENSE
SENSE
The large output capacitors on many switching regula-
tors, on the other hand, may be able to hold the supply
pin of the LTC1255 above 3.5V sufficiently long that this
extra filtering is not required.
Because the LTC1255 is micropower in both the standby
and ON state, the voltage drop across the supply filter
is very small (typically < 6mV) and does not signifi-
cantly alter the accuracy of the drain sense threshold
voltage which is typically 100mV.
AUTOMOTIVE APPLICATIONS
Reverse Battery Protection
The LTC1255 can be protected against reverse battery
conditions by connecting a resistor in series with the
ground lead as shown in Figure 8. The resistor limits the
supply current to less than 120mA with – 12V applied.
Since the LTC1255 draws very little current while in
normal operation, the drop across the ground resistor
is minimal. The 5V P (or controlling logic) is protected
by the 10k resistors in series with the input.
Transient Overvoltage Protection
A common scheme used to limit overvoltage transients
on a 14V nominal automotive power bus is to clamp the
supply to the module containing the high-side MOSFET
switches with a large transient suppressor diode, D1 in
Figure 9. This diode limits the supply voltage to 40V
under worse case conditions. The LTC1255 is designed
to survive short (10ms) 40V transients and return to
normal operation after the transient has passed.
CONTROL
LOGIC
p OR
5V
Figure 8. Reverse Battery Protection
14V
10k
IN1
1/2 LTC1255
GND
V
S
100
DS1
G1
28V
+
10 F
LTC1255 • F08
LTC1255
12V
LOAD
MTP12N06E
R
0.036
SENSE
9