LTC1255CS8 Linear Technology, LTC1255CS8 Datasheet - Page 7

• 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
MOSFET AND LOAD PROTECTION
The LTC1255 protects the power MOSFET switch by
removing drive from the gate as soon as an overcurrent
condition is detected. Resistive and inductive loads can be
protected with no external time delay in series with the
drain sense pin. Lamp loads, however, require that the
overcurrent protection be delayed long enough to start the
lamp but short enough to ensure the safety of the MOSFET.
Resistive Loads
Loads that are primarily resistive should be protected with
as short a delay as possible to minimize the amount of time
that the MOSFET is subjected to an overload condition.
The drain sense circuitry has a built-in delay of approxi-
mately 10 s to eliminate false triggering by power supply
or load transient conditions. This delay is sufficient to
“mask” short load current transients and the starting of a
small capacitor (< 1 F) in parallel with the load. The drain
sense pin can therefore be connected directly to the drain
current sense resistor as shown in Figure 1.
Inductive Loads
Loads that are primarily inductive, such as relays, sole-
noids and stepper motor windings, should be protected
with as short a delay as possible to minimize the amount
of time that the MOSFET is subjected to an overload
condition. The built-in 10 s delay will ensure that the
overcurrent protection is not false triggered by a supply or
load transient. No external delay components are required
as shown in Figure 2.
18V
Figure 1. Protecting Resistive Loads
IN1
1/2 LTC1255
GND
V
S
U U
DS1
G1
+
10 F
12V
LTC1255 • F01
C
LOAD
1 F
W
IRFZ24
R
0.036
R
18
SENSE
LOAD
U
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, as shown in
Figure 2, to safely divert the stored energy.
Capacitive Loads
Large capacitive loads, such as complex electrical sys-
tems with large bypass capacitors, should be powered
using the circuit shown in Figure 3. The gate drive to the
power MOSFET is passed through an RC delay network,
R1 and C1, which greatly reduces the turn-on ramp rate of
the switch. And since the MOSFET source voltage follows
the gate voltage, the load is powered smoothly and slowly
from ground. This dramatically reduces the startup cur-
rent flowing into the supply capacitor(s) which, in turn,
reduces supply transients and allows for slower activation
15V
IN1
12V
1/2 LTC1255
Figure 3. Powering Large Capacitive Loads
GND
V
Figure 2. Protecting Inductive Loads
S
IN1
1/2 LTC1255
DS1
G1
GND
V
S
DS1
G1
100k
C
0.01 F
R1
DELAY
+
1N4148
D1
100 F
R
100k
DELAY
1N5400
LTC1255 • F02
C1
0.33 F
12V
100k
R2
+
LTC1255 • F03
IRFZ24
LTC1255
R
0.036
470 F
12V
SENSE
12V, 1A
SOLENOID
+
MTP3055E
R
0.036
SENSE
C
100 F
LOAD
7