LTC1255
Dual 24V High-Side
MOSFET Driver
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
Fully Enhances N-Channel Power MOSFETs
12µA Standby Current
Operates at Supply Voltages from 9V to 24V
Short Circuit Protection
Easily Protected Against Supply Transients
Controlled Switching ON and OFF Times
No External Charge Pump Components
Compatible With Standard Logic Families
Available in 8-Pin SOIC
The LTC1255 dual high-side driver allows using low
cost N-channel FETs for high-side industrial and auto-
motive switching applications. An internal charge pump
boosts the gate drive voltage above the positive rail,
fully enhancing an N-channel MOS switch with no
external components. Low power operation, with 12µA
standby current, allows use in virtually all systems with
maximum efficiency.
Included on-chip is independent overcurrent sensing
to provide automatic shutdown in case of short circuits.
A time delay can be added to the current sense to
prevent false triggering on high in-rush current loads.
The LTC1255 operates from 9V to 24V supplies and is
well suited for industrial and automotive applications.
The LTC1255 is available in both an 8-pin DIP and an
8-pin SOIC.
APPLICATI
s
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S
Solenoid Drivers
DC Motor Drivers
Stepper Motor Drivers
Lamp Drivers/Dimmers
Relay Drivers
Low Frequency H-Bridge
P-Channel Switch Replacement
TYPICAL APPLICATI
Dual 24V High-Side Switch with Overcurrent Protection
24V
+
0.036Ω
10µF
V
S
DS1
IRLR024
12V
DS2
IRLR024
12V
G1 LTC1255 G2
IN1
GND
IN2
0.036Ω
SUPPLY CURRENT (µA)
24V/0.5A
SOLENOID
FROM
1N4001
µP,
ETC.
FROM
µP,
ETC.
1N4001
24V/0.5A
SOLENOID
LTC1255 • TA01
U
Standby Supply Current
50
45
40
35
30
25
20
15
10
5
0
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
V
IN1
= V
IN2
= 0V
T
A
= 25°C
LTC1255 • TA02
UO
UO
1
LTC1255
ABSOLUTE
AXI U
RATI GS
Operating Temperature Range
LTC1255C............................................... 0°C to 70°C
LTC1255I ........................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Supply Voltage ......................................... – 0.3V to 30V
Transient Supply Voltage (< 10ms) ......................... 40V
Input Voltage ..................... (V
S
+ 0.3V) to (GND – 0.3V)
Gate Voltage ...................... (V
S
+ 20V) to (GND – 0.3V)
Current (Any Pin)................................................. 50mA
PACKAGE/ORDER I FOR ATIO
TOP VIEW
DS1 1
GATE 1 2
GND 3
IN1 4
8
7
6
5
DS2
GATE 2
V
S
IN2
ORDER PART
NUMBER
DS1 1
LTC1255CN8
LTC1255IN8
N8 PACKAGE
8-LEAD PLASTIC DIP
T
JMAX
= 100°C,
θ
JA
= 130°C/ W
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
PARAMETER
Quiescent Current OFF
V
S
= 9V to 24V, T
A
= 25°C, unless otherwise noted.
MIN
TYP
12
12
12
160
350
600
q
q
CONDITIONS
V
S
= 10V, V
IN
= 0V (Note 1)
V
S
= 18V, V
IN
= 0V (Note 1)
V
S
= 24V, V
IN
= 0V (Note 1)
V
S
= 10V, V
GATE
= 22V, V
IN
= 5V (Note 2)
V
S
= 18V, V
GATE
= 30V, V
IN
= 5V (Note 2)
V
S
= 24V, V
GATE
= 36V, V
IN
= 5V (Note 2)
Quiescent Current ON
V
INH
V
INL
I
IN
C
IN
V
SEN
I
SEN
V
GATE
– V
S
I
GATE
Input High Voltage
Input Low Voltage
Input Current
Input Capacitance
Drain Sense Threshold Voltage
Drain Sense Input Current
Gate Voltage Above Supply
Gate Output Drive Current
0V
≤
V
IN
≤
V
S
0V
≤
V
SEN
≤
V
S
V
S
= 9V
V
S
= 18V, V
GATE
= 30V
V
S
= 24V, V
GATE
= 36V
2
U
U
W
W W
U
W
TOP VIEW
8
7
6
5
DS2
GATE 2
V
S
IN2
ORDER PART
NUMBER
LTC1255CS8
LTC1255IS8
S8 PART MARKING
1255
1255I
GATE 1 2
GND 3
IN1 4
S8 PACKAGE
8-LEAD PLASTIC SOIC
T
JMAX
= 100°C,
θ
JA
= 150°C/ W
MAX
40
40
40
400
800
1200
0.8
±1
UNITS
µA
µA
µA
µA
µA
µA
V
V
µA
pF
mV
mV
µA
V
µA
µA
2
q
q
q
q
q
q
80
75
7.5
5
5
5
100
100
10.5
20
23
120
125
±0.1
12
LTC1255
ELECTRICAL CHARACTERISTICS
SYMBOL
t
ON
PARAMETER
Turn-ON Time
V
S
= 9V to 24V, T
A
= 25°C, unless otherwise noted.
MIN
30
75
40
75
50
10
10
10
5
5
5
TYP
100
250
120
250
180
24
21
19
16
16
16
MAX
300
750
400
750
500
60
60
60
30
30
30
UNITS
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
CONDITIONS
V
S
= 10V, C
GATE
= 1000pF (Note 3)
Time for V
GATE
> V
S
+ 2V
Time for V
GATE
> V
S
+ 5V
V
S
= 18V, C
GATE
= 1000pF (Note 3)
Time for V
GATE
> V
S
+ 5V
Time for V
GATE
> V
S
+ 10V
V
S
= 24V, C
GATE
= 1000pF (Note 3)
Time for V
GATE
> V
S
+ 10V
V
S
= 10V, C
GATE
= 1000pF, (Note 3, 4)
V
S
= 18V, C
GATE
= 1000pF, (Note 3, 4)
V
S
= 24V, C
GATE
= 1000pF, (Note 3, 4)
V
S
= 10V, C
GATE
= 1000pF, (Note 3, 4)
V
S
= 18V, C
GATE
= 1000pF, (Note 3, 4)
V
S
= 24V, C
GATE
= 1000pF, (Note 3, 4)
t
OFF
Turn-OFF Time
t
SC
Short-Circuit Turn-OFF Time
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Quiescent current OFF is for both channels in OFF condition.
Note 2:
Quiescent current ON is per driver and is measured independently.
The gate voltage is clamped to 12V above the rail to simulate the effects of
protection clamps connected across the GATE-SOURCE of the power
MOSFET.
Note 3:
Zener diode clamps must be connected across the GATE-SOURCE
of the power MOSFET to limit V
GS
. 1N5242A (through hole) or
MMBZ5242A (surface mount) 12V Zener diodes are recommended. All
Turn-ON and Turn-OFF tests are performed with a 12V Zener clamp in
series with a small-signal diode connected between V
S
and the GATE
output to simulate the effects of a 12V protection Zener clamp connected
across the GATE-SOURCE of the power MOSFET.
Note 4:
Time for V
GATE
to drop below 1V.
TYPICAL PERFOR A CE CHARACTERISTICS
Standby Supply Current
50
45
40
V
IN1
= V
IN2
= 0V
T
A
= 25°C
SUPPLY CURRENT (mA)
SUPPLY CURRENT (µA)
35
30
25
20
15
10
5
0
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
1.2
1.0
0.8
0.6
0.4
0.2
0
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
V
GATE
– V
S
(V)
U W
LTC1255 • TPC01
Supply Current per Driver (ON)
2.0
1.8
1.6
1.4
ONE INPUT = 0N
OTHER INPUT = OFF
T
A
= 25°C
20
18
16
14
12
10
8
6
4
2
0
Gate Voltage Above Supply
V
CLAMP
= 12V
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
LTC1255 • TPC02
LTC1255 • TPC03
3
LTC1255
TYPICAL PERFOR A CE CHARACTERISTICS
Input Threshold Voltage
2.4
125
DRAIN SENSE THRESHOLD VOLTAGE (V)
2.2
INPUT THRESHOLD VOLTAGE (V)
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
V
ON
V
OFF
110
105
100
95
90
85
80
75
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
GATE CLAMP CURRENT (µA)
2.0
Turn-ON Time
1000
900
800
TURN-OFF TIME (µs)
C
GATE
= 1000pF
T
A
= 25°C
TURN-OFF TIME (µs)
TURN-ON TIME (µs)
700
600
500
400
300
200
100
0
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
V
GS
= 2V
V
GS
= 5V
Standby Supply Current
50
STANDBY SUPPLY CURRENT (µA)
45
40
35
30
25
20
15
10
5
0
–50
–25
V
S
= 18V
V
S
= 24V
V
S
= 10V
SUPPLY CURRENT (mA)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
75
100
0
–50
V
S
= 18V
V
S
= 10V
–25
25
50
0
TEMPERATURE (°C)
75
100
V
S
= 24V
INPUT THRESHOLD VOLTAGE (V)
25
50
0
TEMPERATURE (°C)
4
U W
LTC1255 • TPC04
Drain Sense Threshold Voltage
50
T
A
= 25°C
120
115
Gate Clamp Current
45
40
35
30
25
20
15
10
5
0
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
V
CLAMP
= 12V
T
A
= 25°C
LTC1255 • TPC05
LTC1255 • TA06
Turn-OFF Time
50
45
40
35
30
25
20
15
10
5
0
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
C
GATE
= 1000pF
TIME FOR V
GATE
< 1V
50
45
40
35
30
25
20
15
10
5
0
Short-Circuit Turn-OFF Delay Time
C
GATE
= 1000pF
TIME FOR V
GATE
< 1V
0
5
15
20
10
SUPPLY VOLTAGE (V)
25
30
LTC1255 • TA07
LTC1255 • TA08
LTC1255 • TA09
Supply Current per Channel (ON)
2.0
1.8
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
Input ON Threshold
V
S
= 10V
V
S
= 24V
0.4
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
LTC1255 • TA10
LTC1255 • TA11
LTC1255 • TA12
LTC1255
PI FU CTIO S
Input Pin
The LTC1255 input pin is active high and activates all of
the protection and charge pump circuitry when switched
ON. The LTC1255 logic and shutdown inputs are high
impedance CMOS gates with ESD protection diodes to
ground and supply and therefore should not be forced
beyond the power supply rails. The input pin should be
held low during the application of power to properly set
the input latch.
Gate Drive Pin
The gate drive pin is either driven to ground when the
switch is turned OFF or driven above the supply rail
when the switch is turned ON. This pin is of relatively
high impedance when driven above the rail (the equiva-
lent of a few hundred kΩ). Care should be taken to
minimize any loading of this pin by parasitic resistance
to ground or supply.
Supply Pin
The supply pin of the LTC1255 serves two vital pur-
poses. The first is obvious; it powers the input, gate
drive, regulation and protection circuitry. The second
purpose is less obvious; it provides a Kelvin connection
to the top of the drain sense resistor for the internal
100mV reference.
The LTC1255 is designed to be continuously powered
so that the gate of the MOSFET is actively driven at all
times. If it is necessary to remove power from the
supply pin and then reapply it, the input pin should be
cycled (low to high) a few milliseconds
after
the power
is reapplied to reset the input latch and protection
circuitry. Also, the input pin should be isolated from the
controlling logic by a 10k resistor if there is a possibility
that the input pin will be held high after the supply has
been removed.
Drain Sense Pin
The drain sense pin is compared against the supply pin
voltage. If the voltage at this pin is more than 100mV
below the supply pin, the input latch will be reset and
the MOSFET gate will be quickly discharged. Cycle the
input to reset the short-circuit latch and turn the MOSFET
back on.
This pin is also a high impedance CMOS gate with ESD
protection and therefore should not be forced outside
of the power supply rails. To defeat the overcurrent
protection, short the drain sense pin to the supply pin.
Some loads, such as large supply capacitors, lamps or
motors require high in-rush currents. An RC time delay
can be added between the sense resistor and the drain
sense pin to ensure that the drain sense circuitry does
not false trigger during startup. This time constant can
be set from a few microseconds to many seconds.
However, very long delays may put the MOSFET at risk
of being destroyed by a short-circuit condition (see
Applications Information section).
The supply pin of the LTC1255 should never be forced
below ground as this may result in permanent damage
to the device.
A 100Ω resistor should be inserted in
series with the ground pin if negative supply voltage
transients are anticipated.
OPERATIO
The LTC1255 is a dual 24V MOSFET driver with built-in
protection and gate charge pump. The LTC1255 consists
of the following functional blocks:
TTL and CMOS Compatible Inputs and Latches
The LTC1255 inputs have been designed to accommo-
date a wide range of logic families. Both input thresh-
U
U
U
U
olds are set at about 1.3V with approximately 100mV of
hysteresis. A low standby current regulator provides
continuous bias for the TTL-to-CMOS converter.
The input/protection latch should be set after initial
power-up, or after reapplication of power, by cycling
the input low to high.
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