LT1910 - Protected High Side MOSFET Driver

LT1910
Protected High Side
MOSFET Driver
FEATURES
DESCRIPTION
8V to 48V Power Supply Range
Protected from –15V to 60V Supply Transients
Short-Circuit Protected
Automatic Restart Timer
Open-Collector Fault Flag
Fully Enhances N-Channel MOSFET Switches
Programmable Current Limit, Delay Time and
Autorestart Period
n Voltage Limited Gate Drive
n Defaults to Off State with Open Input
n Available in SO-8 Package
The LT®1910 is a high side gate driver that allows the use of
low cost N-channel power MOSFETs for high side switching
applications. It contains a completely self-contained charge
pump to fully enhance an N-channel MOSFET switch with
no external components.
n
n
n
n
n
n
n
APPLICATIONS
When the internal drain comparator senses that the switch
current has exceeded the preset level, the switch is turned
off and a fault flag is asserted. The switch remains off for
a period of time set by an external timing capacitor and
then automatically attempts to restart. If the fault still
exists, this cycle repeats until the fault is removed, thus
protecting the MOSFET. The fault flag becomes inactive
once the switch restarts successfully.
n
n
n
The LT1910 has been specifically designed for harsh
operating environments such as industrial, avionics and
automotive applications where poor supply regulation and/
or transients may be present. The device will not sustain
damage from supply transients of –15V to 60V.
n
n
Industrial Control
Avionics Systems
Automotive Switches
Stepper Motor and DC Motor Control
Electronic Circuit Breaker
The LT1910 is available in the SO-8 package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
TYPICAL APPLICATION
Fault Protected High Side Switch
5V
24V
OFF ON
LT1910
FAULT
V+
IN
IRFZ34
GATE
GND
0.40
0.01Ω
SENSE
TIMER
0.1µF
0.50
0.45
+
10µF
50V
LOAD
TOTAL DROP (V)
5.1k
FAULT OUTPUT
Switch Drop vs Load Current
0.35
0.30
0.25
0.20
0.15
0.10
1910 TA01
0.05
0
0
1
3
2
LOAD CURRENT (A)
4
5
1910 TA02
1910fc
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1
LT1910
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Supply Voltage (Pin 8)................................ –15V to 60V
Input Voltage (Pin 4)...................... (GND – 0.3V) to 15V
GATE Voltage (Pin 5)................................................. 75V
SENSE Voltage (Pin 6)......................................... V+ ±5V
FAULT Voltage (Pin 3)............................................... 36V
Current (Pins 1, 2, 4, 5, 6, 8)................................. 40mA
Operating Temperature Range (Note 2)
LT1910E................................................ –40°C to 85°C
LT1910I............................................... –40°C to 125°C
Junction Temperature Range................. –40°C to 125°C
Storage Temperature Range.................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
TOP VIEW
GND 1
8
V+
TIMER 2
7
NC
FAULT 3
6
SENSE
IN 4
5
GATE
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 150°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT1910ES8#PBF
LT1910ES8#TRPBF
1910
8-Lead Plastic SO
–40°C to 85°C
LT1910IS8#PBF
LT1910IS8#TRPBF
1910
8-Lead Plastic SO
–40°C to 125°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT1910ES8
LT1910ES8#TR
1910
8-Lead Plastic SO
–40°C to 85°C
LT1910IS8
LT1910IS8#TR
1910
8-Lead Plastic SO
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
+
temperature range, otherwise specifications are at TA = 25°C. V = 12V to 48V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
IS
Supply Current (Off State)
V+ = 48V, V
1.2
1.9
2.5
mA
0.8
1.2
mA
IN = 0.8V
UNITS
∆IS(ON)
Delta Supply Current (On State)
VIN = 2V, Measure Increase in IS
VINH
Input High Voltage
E-Grade
I-Grade
l
l
VINL
Input Low Voltage
E-Grade
I-Grade
l
l
IIN
Input Current
VIN = 2V
VIN = 5V
l
l
15
55
30
110
l
2.6
2.9
3.2
3.2
3.5
3.8
V
9
14
20
µA
50
65
0.33
80
mV
%/°C
CIN
Input Capacitance (Note 3)
VT(TH)
Timer Threshold Voltage
VIN = 2V, Adjust VT
V
V
0.8
0.7
V
V
50
185
µA
µA
5
VT(CL)
Timer Clamp Voltage
VIN = 0.8V
IT
Timer Charge Current
VIN = VT = 2V
VSENSE
Drain-Sense Threshold Voltage Temperature
Coefficient (Note 3)
2
2
3.5
pF
V
1910fc
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LT1910
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
+
temperature range, otherwise specifications are at TA = 25°C. V = 12V to 48V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
ISENSE
Drain Sense Input Current
V+ = 48V, VSENSE = 65mV
Gate Voltage Above Supply
V+ = 8V
V+ = 12V
l
V+ = 24V
E-Grade
I-Grade
V+ = 48V
E-Grade
I-Grade
VGATE
– V+
MIN
VF(TH)
FAULT Output High Threshold Voltage
FAULT Output Low Threshold Voltage
VIN = 2V, IF = 1mA, Adjust VT
VFOL
FAULT Output Low Voltage
IF = 1mA
Turn-On Time
V+ = 24V, V
GATE = 32V, CGATE = 1nF
tOFF
Turn-Off Time
V+ = 24V, V
GATE = 2V, CGATE = 1nF
tOFF(CL)
Current Limit Turn-Off Time
V+ = 24V, (V+ – VSENSE)→0.1V, CGATE = 1nF
tON
TYP
MAX
0.5
1.5
µA
4
7
4.5
8.5
6
10
V
V
l
l
10
10
12
12
14
15
V
V
l
l
10
10
12
12
14
15
V
V
3.1
3.0
3.4
3.3
3.7
3.6
V
V
0.07
0.4
V
220
400
µs
25
100
µs
20
50
µs
l
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT1910E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
100
UNITS
with statistical process controls. The LT1910I is guaranteed to meet
performance specifications over the full –40°C to 125°C operating
temperature range.
Note 3: Guaranteed but not tested.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Supply Voltage
3.6
Supply Current vs Temperature
5.0
TA = 25°C
3.4
4.5
1.8
2.6
2.4
2.2
OFF STATE
2.0
1.8
3.5
3.0
INPUT VOLTAGE (V)
ON STATE
2.8
ON STATE
2.5
OFF STATE
2.0
1.5
1.0
1.6
0
10
30
40
20
SUPPLY VOLTAGE (V)
50
1910 G01
0
–50
1.6
VINH
1.4
VINL
1.2
1.0
0.5
1.4
1.2
V = 48V
4.0
3.0
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
3.2
Input Voltage vs Temperature
2.0
+
–25
25
50
75
0
TEMPERATURE (°C)
100
125
1910 G02
0.8
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
1910 G03
1910fc
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3
LT1910
TYPICAL PERFORMANCE CHARACTERISTICS
Timer Threshold Voltage
vs Temperature
Input Current vs Temperature
3.2
TIMER THRESHOLD VOLTAGE (V)
180
VIN = 5V
100
80
60
40
VIN = 2V
20
0
–50
–25
100
25
50
75
0
TEMPERATURE (°C)
3.0
2.9
2.8
2.7
2.6
–50
125
–25
75
0
25
50
TEMPERATURE (°C)
1910 G04
90
DRAIN SENSE THRESHOLD VOLTAGE (mV)
TIMER CHARGE CURRENT (µA)
18
16
14
12
10
8
–50
75
0
25
50
TEMPERATURE (°C)
–25
100
85
V+ = 24V
80
75
70
65
60
55
50
45
40
–50
125
–25
25
50
75
0
TEMPERATURE (°C)
MOSFET Gate Drive Current
vs VGATE – V+
0.1
0
2
4
V+ = 12V V+ ≥ 24V
6
8
10
VGATE – V+ (V)
12
14
16
1910 G10
4
3.7
FAULT THRESHOLD VOLTAGE (V)
MOSFET GATE DRIVE CURRENT (µA)
10
V+ = 8V
3.5
3.4
3.3
–25
0
25
50
75
TEMPERATURE (°C)
100
100
125
3.6
16
MOSFET Gate Voltage Above V+
(VGATE – V+) vs Supply Voltage
14
TA = 25°C
TA = 125°C
12
TA = –40°C
10
8
6
4
2
0
5
0
10 15 20 25 30 35 40 45 50
SUPPLY VOLTAGE (V)
LTC1266 • F04
Fault Output Low Voltage
vs Temperature
0.20
VIN = 2V
IF = 1mA
3.5
FAULT HIGH THRESHOLD
3.4
3.3
3.2
FAULT LOW THRESHOLD
3.1
3.0
–50
–25
0
25
50
75
TEMPERATURE (°C)
125
1910 G06
Fault Threshold Voltage
vs Temperature
TA = 25°C
1
3.6
1910 G08
1910 G07
100
3.7
3.2
–50
125
Drain Sense Threshold Voltage
vs Temperature
VIN = VT = 2V
VIN ≤ 0.8V
1910 G05
Timer Charge Current
vs Temperature
20
100
MOSFET GATE VOLTAGE ABOVE V+ (VGATE – V+) (V)
140
120
3.1
100
125
1910 G11
FAULT OUTPUT LOW VOLTAGE (V)
INPUT CURRENT (µA)
160
3.8
VIN = 2V
TIMER CLAMP VOLTAGE (V)
200
Timer Clamp Voltage
vs Temperature
0.18
IF = 1mA
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0
–50
–25
25
50
75
0
TEMPERATURE (°C)
100
125
1910 G012
1910fc
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LT1910
TYPICAL PERFORMANCE CHARACTERISTICS
Turn-On Time vs Temperature
100
400
250
200
70
60
50
40
30
NORMAL
20
150
CURRENT LIMIT
10
75
0
25
50
TEMPERATURE (°C)
100
125
AUTOMATIC RESTART PERIOD (ms)
TURN-OFF TIME (µs)
TURN-ON TIME (µs)
300
–25
1000
V+ = 24V
90 VGATE = 2V
CGATE = 1nF
80
V+ = 24V
VGATE = 32V
350 CGATE = 1nF
100
–50
Automatic Restart Period
vs Temperature
Turn-Off Time vs Temperature
0
–50
–25
25
50
75
0
TEMPERATURE (°C)
100
125
1910 G014
1910 G13
V+ = 24V
CT = 3.3µF
CT = 1µF
100
CT = 0.33µF
CT = 0.1µF
10
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
1910 G15
PIN FUNCTIONS
GND (Pin 1): Common Ground.
TIMER (Pin 2): A timing capacitor, CT , from the TIMER
pin to ground sets the restart time following overcurrent
detection. Upon detection of an overcurrent condition, CT
is rapidly discharged to less than 1V and then recharged
by a 14µA nominal current source back to the 2.9V timer
threshold, whereupon the restart is attempted. Whenever
TIMER pulls below 2.9V, the GATE pin pulls low to turn off
the external switch. This cycle repeats until the overcurrent
condition goes away and the switch restarts successfully.
During normal operation the pin clamps at 3.5V nominal.
FAULT (Pin 3): The FAULT pin monitors the TIMER pin
voltage and indicates the overcurrent condition. Whenever
the TIMER pin is pulled below 3.3V at the onset of a current limit condition, the FAULT pin pulls active LOW. The
FAULT pin resets HIGH immediately when the TIMER pin
ramps above 3.4V during autorestart. The FAULT pin is an
open-collector output, thus requiring an external pull-up
resistor and is intended for logic interface. The resistor
should be selected with a maximum of 1mA pull-up at
low status.
IN (Pin 4): The IN pin threshold is TTL/CMOS compatible
and has approximately 200mV of hysteresis. When the
IN pin is pulled active HIGH above 2V, an internal charge
pump is activated to pull up the GATE pin. The IN pin can
be pulled as high as 15V regardless of whether the supply is on or off. If the IN pin is left open, an internal 75k
pull-down resistor pulls the pin below 0.8V to ensure that
the GATE pin is inactive LOW.
GATE (Pin 5): The GATE pin drives the power MOSFET
gate. When the IN pin is greater than 2V, the GATE pin is
pumped approximately 12V above the supply. It has relatively high impedance (the equivalence of a few hundred
kΩ) when pumped above the rail. Care should be taken
to minimize any loading by parasitic resistance to ground
or supply. The GATE pin pulls LOW when the TIMER pin
falls below 2.9V.
SENSE (Pin 6): The SENSE pin connects to the input of
a supply-referenced comparator with a 65mV nominal
offset. When the SENSE pin is taken more than 65mV
below supply, the MOSFET gate is driven LOW and the
timing capacitor is discharged. The SENSE pin threshold
has a 0.33%/°C temperature coefficient (TC), which closely
matches the TC of the drain-sense resistor formed from
the copper trace of the PCB.
For loads requiring high inrush current, an RC timing delay
can be added between the drain-sense resistor and the
SENSE pin to ensure that the current-sense comparator
1910fc
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5
LT1910
PIN FUNCTIONS
does not false trigger during start-up (see Applications
Information). A maximum of 10kΩ can be inserted between
a drain-sense resistor and the SENSE pin. If current sensing
is not required, the SENSE pin is tied to supply.
V+ (Pin 8): In addition to providing the operating current for the LT1910, the V+ pin also serves as the Kelvin
connection for the current-sense comparator. The V+ pin
must be connected to the positive side of the drain-sense
resistor for proper current-sensing operation.
BLOCK DIAGRAM
V+
14µA
3.3V
–
FAULT
+
V+
TIMER
2.9V
+
+
–
–
+
–
65mV
SENSE
+
1.4V
IN
75k
–
+
GATE
1.4V
OSCILLATOR
AND
CHARGE PUMP
–
75k
250Ω
1910 BD
OPERATION (Refer to the Block Diagram)
The LT1910 GATE pin has two states, off and on. In the off
state it is held LOW, while in the on state it is pumped to
12V above the supply by a self-contained 750kHz charge
pump. The off state is activated when either the IN pin is
below 0.8V or the TIMER pin is below 2.9V. Conversely,
for the on state to be activated, the IN pin must be above
2V and the TIMER pin must be above 2.9V.
The IN pin has approximately 200mV of hysteresis. If it is
left open, the IN pin is held LOW by a 75k resistor. Under
normal conditions, the TIMER pin is held a diode drop
above 2.9V by a 14µA pull-up current source. Thus the
TIMER pin automatically reverts the GATE pin to the on
state if the IN pin is above 2V.
6
The SENSE pin normally connects to the drain of the power
MOSFET, which returns through a low value drain-sense
resistor to supply. In order for the sense comparator to
accurately sense the MOSFET drain current, the V+ pin
must be connected directly to the positive side of the
drain-sense resistor. When the GATE pin is on and the
MOSFET drain current exceeds the level required to generate a 65mV drop across the drain-sense resistor, the sense
comparator activates a pull-down NPN which rapidly pulls
the TIMER pin below 2.9V. This in turn causes the timer
comparator to override the IN pin and set the GATE pin
to the off state, thus protecting the power MOSFET. When
the TIMER pin is pulled below 3.3V, the fault comparator
1910fc
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LT1910
OPERATION
also activates the open-collector NPN to pull the FAULT
pin LOW, indicating an overcurrent condition.
When the MOSFET gate voltage is discharged to less than
1.4V, the TIMER pin is released. The 14µA current source
then slowly charges the timing capacitor back to 2.9V
where the charge pump again starts to drive the GATE pin
HIGH. If a fault condition still exists, the sense comparator
threshold will again be exceeded and the timer cycle will
repeat until the fault is removed. The FAULT pin becomes
inactive HIGH if the TIMER pin charges up successfully
above 3.4V (see Figure 1).
OFF
NORMAL
OVERCURRENT
NORMAL
IN
0V
GATE
TIMER
V+
12V
0V
3.5V
2.9V
3.4V
0V
5V
FAULT
0V
1910 F01
Figure 1. Timing Diagram
APPLICATIONS INFORMATION
Input/Supply Sequencing
There are no input/supply sequencing requirements for
the LT1910. The IN pin may be taken up to 15V with the
supply at 0V. When the supply is turned on with the IN
pin set HIGH, the MOSFET turn-on will be inhibited until
the timing capacitor charges up to 2.9V (i.e., for one
restart cycle).
Isolating the Inputs
Operation in harsh environments may require isolation to
prevent ground transients from damaging control logic.
The LT1910 easily interfaces to low cost optoisolators. The
network shown in Figure 2 ensures that the input will be
pulled above 2V, but not exceed the absolute maximum
rating for supply voltages of 12V to 48V over the entire
2k
The LT1910 uses supply referenced current sensing. One
input of the current-sense comparator is connected to a
drain-sense pin, while the second input is offset 65mV
below the supply inside the device. For this reason, Pin 8
of the LT1910 must be treated not only as a supply pin,
but also as the reference input for the current-sense
comparator.
Figure 3 shows the proper drain-sense configuration for
the LT1910. Note that the SENSE pin goes to the drain
end of the sense resistor, while the V+ pin is connected
5V
100k
4
R1
5.1k 3
RS
0.02Ω
(PTC)
LT1910
8
FAULT
V+
4
6
IN
SENSE
2
5
TIMER GATE
FAULT OUTPUT
LT1910
LOGIC GROUND
Drain-Sense Configuration
24V
12V TO 48V
LOGIC
INPUT
temperature range. The optoisolator must have less than
20µA of dark current (leakage) at hot in order to maintain
the off state (see Figure 2).
INPUT
IN
Q1
IRFZ34
GND
51k
GND
1
1
1910 F02
POWER GROUND
Figure 2. Isolating the Input
CT
1µF
+
C1
100µF
50V
0V
24V
2A
SOLENOID
1910 F03
Figure 3. Drain-Sense Configuration
1910fc
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7
LT1910
APPLICATIONS INFORMATION
to the supply at the same point as the positive end of the
sense resistor.
The drain-sense threshold voltage has a positive temperature coefficient, allowing PTC sense resistors to be used
(see Printed Circuit Board Shunts). The selection of RS
should be based on the minimum threshold voltage:
RS = 50mV/ISET
Thus the 0.02Ω drain-sense resistor in Figure 3 will yield
a minimum trip current of 2.5A. This simple configuration
is appropriate for resistive or inductive loads that do not
generate large current transients at turn-on.
Automatic Restart Period
The timing capacitor, CT , shown in Figure 3 determines
the length of time the power MOSFET is held off following a current limit trip. Curves are given in the Typical
Performance Characteristics to show the restart period
for various values of CT . For example, CT = 0.33µF yields
a 50ms restart period.
Defeating Automatic Restart
Some applications are required to remain off after a fault
occurs. When the LT1910 is being driven from CMOS logic,
this can be easily implemented by connecting resistor R2
between the IN and TIMER pins as shown in Figure 4. R2
supplies the sustaining current for an internal SCR which
latches the TIMER pin LOW under a fault condition. The
FAULT pin is set active LOW when the TIMER pin falls below
3.3V. This keeps the MOSFET gate from turning on and the
FAULT pin from resetting HIGH until the IN pin has been
recycled. CT is used to prevent the FAULT pin from glitching whenever the IN pin recycles to turn on the MOSFET
unsuccessfully under an existing fault condition.
Inductive vs Capacitive Loads
Turning on an inductive load produces a relatively benign
ramp in MOSFET current. However, when an inductive
load is turned off, the current stored in the inductor needs
somewhere to decay. A clamp diode connected directly
across each inductive load normally serves this purpose.
If a diode is not employed, the LT1910 clamps the MOSFET
gate 0.7V below ground. This causes the MOSFET to resume
conduction during the current decay with (V+ + VGS + 0.7V)
across it, resulting in high dissipation peaks.
Capacitive loads exhibit the opposite behavior. Any load
that includes a decoupling capacitor will generate a current
equal to CLOAD • (∂V/∂t) during capacitor in-rush. With
large electrolytic capacitors, the resulting current spike
can play havoc with the power supply and false trip the
current-sense comparator.
Turn-on ∂V/∂t is controlled by the addition of the simple
network shown in Figure 5. This network takes advantage of
the fact that the MOSFET acts as a source follower during
turn-on. Thus the ∂V/∂t on the source can be controlled
by controlling the ∂V/∂t on the gate.
CURRENT LIMIT
DELAY NETWORK
V+
5V
FAULT OUTPUT
5V
ON = 5V
CMOS
LOGIC OFF = 0V
R2
2k
SENSE
R1
5.1k
3
4
2
8
1N4148
RS
0.01Ω
6
RD (≤10k)
LT1910
∂V/∂t CONTROL NETWORK
1N4148
FAULT
IN LT1910
TIMER
GND
CT
1µF
CD
24V
GATE
GND
1
1
C2
50µF
50V
5
+
R1
100k
R2
100k
C1
+
Q1
IRFZ34
15V
1N4744
1910 F05
1910 F04
Figure 4. Latch-Off Configuration (Autorestart Defeated)
8
CLOAD
Figure 5. Control and Current Limit Delay
1910fc
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LT1910
APPLICATIONS INFORMATION
The turn-on current spike into CLOAD is estimated by:
IPEAK = CLOAD •
VG – VTH
R1• C1
RD and CD delay the overcurrent trip for drain currents up
to approximately 10 • ISET , above which the diode conducts
and provides immediate turn-off (see Figure 7). To ensure
proper operation of the timer, CD must be ≤CT .
where VTH is the MOSFET gate threshold voltage. VG is
obtained by plotting the equation:
VGATE
R1
on the graph of Gate Drive Current (IGATE) vs Gate Voltage
(VGATE) as shown in Figure 6. The value of VGATE at the
intersection of the curves for a given supply is VG. For
example, if V+ = 24V and R1 = 100k, then VG = 18.3V. For
VTH = 2V, C1 = 0.1µF and CLOAD = 1000µF, the estimated
IPEAK = 1.6A. The diode and the second resistor in the
network ensure fast current limit turn-off.
When turning off a capacitive load, the source of the
MOSFET can “hang up” if the load resistance does not
discharge CLOAD as fast as the gate is being pulled down.
If this is the case, a 15V Zener may be added from gate to
source to prevent VGS(MAX) from being exceeded.
800
GATE DRIVE CURRENT (µA)
700
600
V+ = 48V
V+ = 24V
500
V+ = 12V
400
+
V = 8V
300
IGATE =
VGATE/105
200
100
0
TRIP DELAY TIME (1 = RDCD)
IGATE =
10
1
0.1
0.01
1
10
100
MOSFET DRAIN CURRENT (1 = SET CURRENT)
1910 F07
Figure 7. Current Limit Delay Time
Printed Circuit Board Shunts
The sheet resistance of 1oz copper clad is approximately
5 • 10–4Ω/square with a temperature coefficient of
0.39%/°C. Since the LT1910 drain-sense threshold has a
similar temperature coefficient (0.33%/°C), this offers the
possibility of nearly zero TC current sensing using the “free”
drain-sense resistor made out of PC trace material.
A conservative approach is to use 0.02" of width for each
1A of current for 1oz copper. Combining the LT1910 drain
sense threshold with the 1oz copper resistance results in
a simple expression for width and length:
Width (1oz Cu) = 0.02" • ISET
0
10
20
40
30
GATE VOLTAGE (V)
50
60
1910 F06
Figure 6. Gate Drive Current vs Gate Voltage
Adding Current Limit Delay
When capacitive loads are being switched or in very noisy
environments, it is desirable to add delay in the drain
current-sense path to prevent false tripping (inductive
loads normally do not need delay). This is accomplished
by the current limit delay network shown in Figure 5.
Length (1oz Cu) = 2"
The width for 2oz copper would be halved while the length
would remain the same.
Bends may be incorporated into the resistor to reduce
space; each bend is equivalent to approximately 0.6 • the
width of a straight length. Kelvin connection should be
employed by running a separate trace from the ends of
the resistor back to the LT1910’s V+ and SENSE pins. See
Application Note 53 for further information on printed
circuit board shunts.
1910fc
For more information www.linear.com/LT1910
9
LT1910
APPLICATIONS INFORMATION
Low Voltage/Wide Supply Range Operation
Low Side Driving
When the supply is less than 12V, the LT1910’s charge
pump does not produce sufficient gate voltage to fully
enhance the standard N-channel MOSFET. For these applications, a logic-level MOSFET can be used to extend
the operating supply down to 8V. If the MOSFET has a
maximum VGS 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).
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 VGS (absolute maximum) of the MOSFET from being exceeded.
The LT1910 gate drive is current limited for this purpose
so that no resistance is needed between the GATE pin
and Zener.
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 Configuration). 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.
10
Current sensing for protecting low side drivers can be done
in several ways. In the Figure 8a circuit, the supply voltage
for the load is assumed to be within the supply operating
range of the LT1910. This allows the load to be returned
to supply through current-sense resistor, RS, providing
normal operation of the LT1910 protection circuitry.
If the load cannot be returned to supply through RS, or
the load supply voltage is higher than the LT1910 supply,
the current sense must be moved to the source of the
low side MOSFET.
Figure 8b shows an approach to source sensing. An
operational amplifier (must common mode to ground) is
used to level shift the voltage across RS up to the drainsense pin. This approach allows the use of a small sense
resistor which could be made from PC trace material. The
LT1910 restart timer functions the same as in the high side
switch application.
1910fc
For more information www.linear.com/LT1910
LT1910
APPLICATIONS INFORMATION
12V TO 48V
5V
FAULT OUTPUT
R1
5.1k 3
4
INPUT
V+
FAULT
IN
SENSE
LT1910
2
TIMER GATE
GND
6
+
4A
LOAD
C1
100µF
100V
5
Q1
IRFZ44
15V
1N4744
1
CT
1µF
RS
0.01Ω
(PTC)
8
0V
1910 F08a
Figure 8a. Low Side Driver with Load Current Sensing
5V
FAULT OUTPUT
INPUT
8V TO 24V
R1
5.1k 3
LT1910
8
FAULT
V+
4
6
IN
SENSE
2
5
TIMER GATE
HV
HV
LOAD
51Ω
Q1
IRF630
15V
1N4744
GND
1
+
2N2222
CT
1µF
C1
10µF
50V
RS
0.02Ω
LT1006
+
–
51Ω
1910 F08b
Figure 8b. Low Side Driver for Source Current Sensing
1910fc
For more information www.linear.com/LT1910
11
LT1910
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610 Rev G)
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
.050 BSC
8
.245
MIN
.160 ±.005
.010 – .020
× 45°
(0.254 – 0.508)
NOTE:
1. DIMENSIONS IN
.053 – .069
(1.346 – 1.752)
0°– 8° TYP
.014 – .019
(0.355 – 0.483)
TYP
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE
12
5
.150 – .157
(3.810 – 3.988)
NOTE 3
1
RECOMMENDED SOLDER PAD LAYOUT
.016 – .050
(0.406 – 1.270)
6
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
.008 – .010
(0.203 – 0.254)
7
2
3
4
.004 – .010
(0.101 – 0.254)
.050
(1.270)
BSC
SO8 REV G 0212
1910fc
For more information www.linear.com/LT1910
LT1910
REVISION HISTORY
(Revision history begins at Rev B)
REV
DATE
DESCRIPTION
PAGE NUMBER
B
7/14
Updated FAULT pin description
5
C
6/15
Changed top mark
2
1910fc
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
For more
information
www.linear.com/LT1910
13
LT1910
TYPICAL APPLICATION
Protected 1A Automotive Solenoid Driver with Overvoltage Shutdown
8V TO 24V OPERATING
32V TO 60V SHUTDOWN
5V
FAULT OUTPUT
R1
5.1k 3
INPUT
30V
1N6011B
R2
10k
R3
5.1k
Q1
MTD3055EL
GND
1N4148
2N3904
RS
0.03Ω
(PTC)
LT1910
8
FAULT
V+
4
6
IN
SENSE
2
5
TIMER GATE
1
CT
1µF
+
POWER
GROUND
C1
10µF
100V
24V
1A
SOLENOID
1910 TA03
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14 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LT1910
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LT1910
1910fc
LT 0615 REV C • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2009