LTC1155CS8 Linear Technology, LTC1155CS8 Datasheet - Page 8

• Manufacturer Part Number: LTC1155CS8
• Description: IC MOSFET DVR HI-SIDE DUAL 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC1155CS8

• Configuration: High-Side
• Input Type: Non-Inverting
• Delay Time: 450µs
• Number Of Configurations: 2
• Number Of Outputs: 2
• Voltage - Supply: 4.5 V ~ 18 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): -

LTC1155
A
sense pin and dramatically reducing the amount of time
the MOSFET is in an overload condition. The drain sense
resistor value is selected to limit the maximum DC current
to 4A. Above 28A, the delay time drops to 10 s.
Switched Supply Applications
Large inductive loads, such as solenoids, relays and
motors store energy which must be directed back to either
the power supply or to ground when the supply voltage is
interrupted (see Figure 4). In normal operation, when the
switch is turned OFF, the energy stored in the inductor is
harmlessly absorbed by the MOSFET; i.e., the current
flows out of the supply through the MOSFET until the
inductor current falls to zero.
8
PPLICATI
+
IN1
IN1
Figure 3. Using a Speed-Up Diode
LTC1155
LTC1155
O
Figure 4. Switched Supply
GND
V
GND
V
S
S
U
GND
GND
V
S
+
S
DS1
= 5.0V
DS1
G1
G1
I FOR ATIO
C
U
S
C
0.22 F
C
DLY
DLY
1N4148
W
R
270k
R
D1
DLY
DLY
LOAD
1155 F03
IRLZ34
1155 F04
R
0.025
IRLZ34
R
0.025
L
SEN
SEN
U
LOAD
If the MOSFET is turned ON and the power supply (battery)
removed, the inductor current is delivered by the supply
capacitor. The supply capacitor must be large enough to
deliver the energy demanded by the discharging inductor.
If the storage capacitor is too small, the supply lead of the
LTC1155 may be pulled below ground, permanently
destroying the device.
Consider the case of a load inductance of 1mH which is
supporting 3A when the 6V power supply connection is
interrupted. A supply capacitor of at least 250 F is
required to prevent the supply lead of the LTC1155 from
being pulled below ground (along with any other circuitry
tied to the supply).
Any wire between the power MOSFET source and the load
will add a small amount of parasitic inductance in series
with the load (approximately 0.4 H/foot). Bypass the
power supply lead of the LTC1155 with a minimum of
10 F to ensure that this parasitic load inductance is
discharged safely, even if the load is otherwise resistive.
Large Inductive Loads
Large inductive loads (>0.1mH) may require diodes con-
nected directly across the inductor to safely divert the
stored energy to ground. Many inductive loads have these
diodes included. If not, a diode of the proper current rating
should be connected across the load to safely divert the
stored energy.
Reverse-Battery Protection
The LTC1155 can be protected against reverse-battery
conditions by connecting a resistor in series with the
ground lead as shown in Figure 5. The resistor limits the
supply current to less than 50mA with –12V applied. Since
the LTC1155 draws very little current while in normal
operation, the drop across the ground resistor is minimal.
The TTL or CMOS driving logic is protected against
reverse-battery conditions by the 100k input current lim-
iting resistor. The addition of 100k resistance in series
with the input pin will not affect the turn ON and turn OFF
times which are dominated by the controlled gate charge
and discharge periods.