LT1910ES8#TRPBF - Linear Technology

LT1910

1910fa

TYPICAL APPLICATION

DESCRIPTION

Protected High Side

MOSFET Driver

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.

When the internal drain comparator senses that the switch

current has exceeded the preset level, the switch is turned

off and a fault ﬂ ag 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 ﬂ ag becomes inactive

once the switch restarts successfully.

The LT1910 has been speciﬁ cally 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.

The LT1910 is available in the SO-8 package.

Fault Protected High Side Switch

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

FEATURES

APPLICATIONS

n 8V to 48V Power Supply Range

n Protected from –15V to 60V Supply Transients

n Short-Circuit Protected

n Automatic Restart Timer

n Open-Collector Fault Flag

n Fully Enhances N-Channel MOSFET Switches

n 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

n Industrial Control

n Avionics Systems

n Automotive Switches

n Stepper Motor and DC Motor Control

n Electronic Circuit Breaker

Switch Drop vs Load Current

FAULT

TIMER

V+

SENSE

GATE

LT1910

5.1k

24V5V

FAULT OUTPUT

OFF ON

GND

IRFZ34

1910 TA01

10μF

50V

0.1μF

0.01Ω

LOAD

LOAD CURRENT (A)

TOTAL DROP (V)

0.30

0.40

0.50

1910 TA02

0.20

0.10

0.25

0.35

0.45

0.15

0.05

01235

LT1910

1910fa

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

(Note 1)

TOP VIEW

V+

SENSE

GATE

GND

TIMER

FAULT

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 1910E 8-Lead Plastic SO –40°C to 85°C

LT1910IS8#PBF LT1910IS8#TRPBF 1910I 8-Lead Plastic SO –40°C to 125°C

LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE

LT1910ES8 LT1910ES8#TR 1910E 8-Lead Plastic SO –40°C to 85°C

LT1910IS8 LT1910IS8#TR 1910I 8-Lead Plastic SO –40°C to 125°C

Consult LTC Marketing for parts speciﬁ ed 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 speciﬁ cations, go to: http://www.linear.com/tapeandreel/

PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

The l denotes the speciﬁ cations which apply over the full operating

temperature range, otherwise speciﬁ cations are at TA = 25°C. V+ = 12V to 48V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

ISSupply Current (Off State) V+ = 48V, VIN = 0.8V 1.2 1.9 2.5 mA

ΔIS(ON) Delta Supply Current (On State) VIN = 2V, Measure Increase in IS0.8 1.2 mA

VINH Input High Voltage E-Grade

I-Grade

3.5

VINL Input Low Voltage E-Grade

I-Grade

0.8

0.7

IIN Input Current VIN = 2V

VIN = 5V

110

185

μA

CIN Input Capacitance (Note 3) 5pF

VT(TH) Timer Threshold Voltage VIN = 2V, Adjust VTl2.6 2.9 3.2 V

VT(CL) Timer Clamp Voltage VIN = 0.8V 3.2 3.5 3.8 V

ITTimer Charge Current VIN = VT = 2V 9 14 20 μA

VSENSE Drain-Sense Threshold Voltage Temperature

Coefﬁ cient (Note 3)

50 65

0.33

80 mV

%/°C

LT1910

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ELECTRICAL CHARACTERISTICS

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 speciﬁ cations

from 0°C to 70°C. Speciﬁ cations over the –40°C to 85°C operating

temperature range are assured by design, characterization and correlation

The l denotes the speciﬁ cations which apply over the full operating

temperature range, otherwise speciﬁ cations are at TA = 25°C. V+ = 12V to 48V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

ISENSE Drain Sense Input Current V+ = 48V, VSENSE = 65mV 0.5 1.5 μA

VGATE – V+Gate Voltage Above Supply V+ = 8V

V+ = 12V l

4.5

8.5

V+ = 24V

E-Grade

I-Grade

V+ = 48V

E-Grade

I-Grade

VF(TH) FAULT Output High Threshold Voltage

FAULT Output Low Threshold Voltage

VIN = 2V, IF = 1mA, Adjust VT3.1

3.0

3.4

3.3

3.7

3.6

VFOL FAULT Output Low Voltage IF = 1mA l0.07 0.4 V

tON Turn-On Time V+ = 24V, VGATE = 32V, CGATE = 1nF 100 220 400 μs

tOFF Turn-Off Time V+ = 24V, VGATE = 2V, CGATE = 1nF 25 100 μs

tOFF(CL) Current Limit Turn-Off Time V+ = 24V, (V+ – VSENSE)→0.1V, CGATE = 1nF 20 50 μs

with statistical process controls. The LT1910I is guaranteed to meet

performance speciﬁ cations 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 Supply Current vs Temperature

Input Voltage vs Temperature

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

2.4

2.8

3.2

3.6

1910 G01

2.0

1.6

2.2

2.6

3.0

3.4

1.8

1.4

1.2 10 20 30 50

ON STATE

OFF STATE

TA = 25°C

TEMPERATURE (°C)

–50

SUPPLY CURRENT (mA)

1.0

2.0

3.0

2.5

–25 025 50

1910 G02

4.0

5.0

0.5

1.5

3.5

4.5

125100

V+ = 48V

ON STATE

OFF STATE

TEMPERATURE (°C)

–50

INPUT VOLTAGE (V)

1.0

1.2

1.4

1.6

2.0

–25 02550

1910 G03

75 125100

1.8

0.8

VINH

VINL

LT1910

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TYPICAL PERFORMANCE CHARACTERISTICS

Timer Charge Current

vs Tempeature

Drain Sense Threshold Voltage

vs Temperature

MOSFET Gate Voltage Above V+

(VGATE – V+) vs Supply Voltage

MOSFET Gate Drive Current

vs VGATE – V+Fault Threshold Voltage

vs Temperature

Fault Output Low Voltage

vs Temperature

Input Current vs Temperature

Timer Threshold Voltage

vs Temperature

Timer Clamp Voltage

vs Temperature

TEMPERATURE (°C)

–50

INPUT CURRENT (μA)

120

–25 025 50

1910 G04

160

200

100

140

180

125100

VIN = 5V

VIN = 2V

TEMPERATURE (°C)

–50

TIMER THRESHOLD VOLTAGE (V)

2.7

2.8

2.9

3.0

3.2

–25 02550

1910 G05

75 125100

3.1

2.6

VIN = 2V

TEMPERATURE (°C)

–50

TIMER CLAMP VOLTAGE (V)

3.3

3.4

3.5

3.6

3.8

–25 025 50

1910 G06

75 125

100

3.7

3.2

VIN ≤ 0.8V

TEMPERATURE (°C)

–50

TIMER CHARGE CURRENT (μA)

–25 02550

1910 G07

75 125100

VIN = VT = 2V

TEMPERATURE (°C)

–50

DRAIN SENSE THRESHOLD VOLTAGE (mV)

–25 025 50

1910 G08

125100

V+ = 24V

SUPPLY VOLTAGE (V)

MOSFET GATE VOLTAGE ABOVE V+ (VGATE – V+) (V)

LTC1266 • F04

10 20 30 503551525 45

TA = 125°C

TA = –40°C

TA = 25°C

VGATE – V+ (V)

024

MOSFET GATE DRIVE CURRENT (μA)

100

6 8 10 12 14 16

1910 G10

0.1

V+ = 8V V+ = 12V V+ ≥ 24V

TA = 25°C

TEMPERATURE (oC)

–50

FAULT OUTPUT LOW VOLTAGE (V)

0.04

0.08

0.12

0.10

–25 025 50

1910 G012

0.16

0.20

0.02

0.06

0.14

0.18

125100

IF = 1mA

TEMPERATURE (°C)

–50

FAULT THRESHOLD VOLTAGE (V)

3.2

3.3

3.4

3.5

3.7

–25 02550

1910 G11

75 125100

3.6

3.0

3.1

VIN = 2V

IF = 1mA

FAULT HIGH THRESHOLD

FAULT LOW THRESHOLD

LT1910

1910fa

TYPICAL PERFORMANCE CHARACTERISTICS

Turn-On Time vs Temperature Turn-Off Time vs Temperature

Automatic Restart Period

vs Temperature

TEMPERATURE (oC)

–50

TURN-ON TIME (Ms)

150

200

250

300

400

–25 02550

1910 G13

75 125100

350

100

V+ = 24V

VGATE = 32V

CGATE = 1nF

TEMPERATURE (oC)

–50

TURN-OFF TIME (Ms)

–25 025 50

1910 G014

100

125100

V+ = 24V

VGATE = 2V

CGATE = 1nF

NORMAL

CURRENT LIMIT

TEMPERATURE (°C)

–30

100

1000

–10 10 30 50 9070

1910 G15

AUTOMATIC RESTART PERIOD (ms)

–50 130110

V+ = 24V

CT = 3.3μF

CT = 0.33μF

CT = 0.1μF

CT = 1μF

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. When-

ever 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 cur-

rent 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 typical 1mA pull-up at low status

and less than 2mA under worst-case conditions.

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 sup-

ply 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 rela-

tively 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 coefﬁ cient (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

does not false trigger during start-up (see Applications

LT1910

1910fa

PIN FUNCTIONS

BLOCK DIAGRAM

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 cur-

rent 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.

–

3.3V

TIMER

14μA

V+

2.9V

1.4V

75k

FAULT

–

1.4V

250Ω

1910 BD

GATE

SENSE

V+

65mV

–

OSCILLATOR

AND

CHARGE PUMP

–

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.

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 gener-

ate 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

LT1910

1910fa

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).

3.4V

1910 F01

GATE

TIMER

FAULT

OVERCURRENTNORMAL NORMALOFF

3.5V

2.9V

V+12V

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

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).

Drain-Sense Conﬁ guration

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 conﬁ guration for

the LT1910. Note that the SENSE pin goes to the drain

end of the sense resistor, while the V+ pin is connected

51k

100k

LOGIC

INPUT

12V TO 48V

LT1910

GND

POWER GROUND

LOGIC GROUND

11910 F02

FAULT

TIMER

V+

SENSE

GATE

LT1910

5.1k

24V

FAULT OUTPUT

INPUT

GND

IRFZ34

24V

SOLENOID

1910 F03

100μF

50V

1μF

0.02Ω

(PTC)

Figure 2. Isolating the Input Figure 3. Drain-Sense Conﬁ guration

LT1910

1910fa

to the supply at the same point as the positive end of the

sense resistor.

The drain-sense threshold voltage has a positive tempera-

ture coefﬁ cient, allowing PTC sense resistors to be used

(see Printed Circuit Board Shunts). The selection of RS

should be based on the minimum threshold voltage:

S = 50mV/ISET

Thus the 0.02Ω drain-sense resistor in Figure 3 will yield

a minimum trip current of 2.5A. This simple conﬁ guration

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 follow-

ing 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

APPLICATIONS INFORMATION

FAULT pin from resetting HIGH until the IN pin has been

recycled. CT is used to prevent the FAULT pin from glitch-

ing 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.

TIMER

FAULT

FAULT OUTPUT

5.1k

ON = 5V

OFF = 0V LT1910

GND

1910 F04

2k CT

1μF

CMOS

LOGIC

V+

SENSE

LT1910

GND

IRFZ34

15V

1N4744

CLOAD

50μF

50V

1910 F05

0.01Ω

RD (≤10k)

1N4148

24V

CURRENT LIMIT

DELAY NETWORK

1N4148

100k

∂V/∂t CONTROL NETWORK

GATE 5

Figure 4. Latch-Off Conﬁ guration (Autorestart Defeated) Figure 5. Control and Current Limit Delay

LT1910

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APPLICATIONS INFORMATION

The turn-on current spike into CLOAD is estimated by:

ICVV

PEAK LOAD GTH

=•–

•11

where VTH is the MOSFET gate threshold voltage. VG is

obtained by plotting the equation:

GATE GATE

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.

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

GATE VOLTAGE (V)

GATE DRIVE CURRENT (μA)

300

400

500

30 50

1910 F06

200

100

010 20 40

600

700

800

V+ = 48V

IGATE =

VGATE/105

V+ = 24V

V+ = 12V

V+ = 8V

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.

MOSFET DRAIN CURRENT (1 = SET CURRENT)

0.01

TRIP DELAY TIME (1 = RDCD)

0.1

10 100

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 coefﬁ cient of

0.39%/°C. Since the LT1910 drain-sense threshold has a

similar temperature coefﬁ cient (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

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.

LT1910

1910fa

APPLICATIONS INFORMATION

Low Voltage/Wide Supply Range Operation

When the supply is less than 12V, the LT1910’s charge

pump does not produce sufﬁ cient gate voltage to fully

enhance the standard N-channel MOSFET. For these ap-

plications, 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).

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 Conﬁ guration). 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.

Low Side Driving

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 (ab-

solute maximum) of the MOSFET from being exceeded.

FAULT

V+

SENSE

LT1910

5.1k

12V TO 48V

FAULT OUTPUT

INPUT

GND

IRFZ44

15V

1N4744

1910 F08a

100μF

100V

1μF

0.01Ω

(PTC)

LOAD

GATETIMER 5

FAULT

TIMER

V+

SENSE

GATE

LT1910

5.1k

FAULT OUTPUT

INPUT

GND

IRF630

15V

1N4744

1910 F08b

10μF

50V

1μF

0.02Ω

LOAD

51Ω

2N2222

8V TO 24V HV

–

LT1006

51Ω

Figure 8a. Low Side Driver with Load Current Sensing

Figure 8b. Low Side Driver for Source Current Sensing

LT1910

1910fa

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

PACKAGE DESCRIPTION

APPLICATIONS INFORMATION

The LT1910 gate drive is current limited for this purpose

so that no resistance is needed between the GATE pin

and Zener.

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 ampliﬁ er (must common mode to ground) is

used to level shift the voltage across RS up to the drain-

sense 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.

S8 Package

8-Lead Plastic Small Outline (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1610)

.016 – .050

(0.406 – 1.270)

.010 – .020

(0.254 – 0.508)s 45o

0o– 8o TYP

.008 – .010

(0.203 – 0.254)

SO8 0303

.053 – .069

(1.346 – 1.752)

.014 – .019

(0.355 – 0.483)

TYP

.004 – .010

(0.101 – 0.254)

.050

(1.270)

BSC

1234

.150 – .157

(3.810 – 3.988)

NOTE 3

8765

.189 – .197

(4.801 – 5.004)

NOTE 3

.228 – .244

(5.791 – 6.197)

.245

MIN .160 p.005

RECOMMENDED SOLDER PAD LAYOUT

.045 p.005

.050 BSC

.030 p.005

TYP

INCHES

(MILLIMETERS)

NOTE:

1. DIMENSIONS IN

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)

LT1910

1910fa

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

LT 0409 REV A • PRINTED IN USA

RELATED PARTS

TYPICAL APPLICATION

Protected 1A Automotive Solenoid Driver with Overvoltage Shutdown

FAULT

TIMER

V+

SENSE

GATE

LT1910

5.1k

FAULT OUTPUT

INPUT

POWER

GROUND

8V TO 24V OPERATING

32V TO 60V SHUTDOWN

GND

MTD3055EL

24V

SOLENOID

1910 TA03

10μF

100V

1μF

5.1k

1N4148

2N3904

0.03Ω

(PTC)

10k

30V

1N6011B

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