Rainbow Electronics MAX9937 User Manual

19-4233; Rev 0; 8/08

Automotive Current-Sense Amplifier

with Reverse-Battery Protection

General Description

The MAX9937 is a tiny automotive grade current-sense
amplifier designed for unidirectional high-side current­sense applications. This device addresses major areas
of concern for automotive applications including load­dump protection up to +40V, reverse-battery protec­tion, and filtering for EMI and transient performance.

The MAX9937 also features a low input offset voltage of
±1.2mV (max) at +25°C with a low temperature drift of
just 1µV/°C (typ).

The MAX9937 is available in a 5-pin SC70 package and
is rated over the -40°C to +125°C temperature range.

Applications

Automotive Battery Current Sense

Fuse Box Current Sense

ECU Current Monitor

Pin Configuration appears at end of data sheet.

Features

♦ Reverse Battery and Load-Dump Protection

-20V to +40V

♦ +4V to +28V Input Common-Mode Range

♦ Flexible EMI Filtering

♦ Low V

♦ Low V

: ±1.2mV (max)

OS

Drift: 1µV/°C (typ)

OS

♦ 20µA Supply Current

♦ 350kHz, 3dB Small Signal Bandwidth

Ordering Information

PART TEMP RANGE

MAX9937AXK+T -40°C to +125°C 5 SC70 +ATB

+

Denotes a lead-free/RoHS-compliant package.

T = Tape and reel.

PIN-

PACKAGE

MARK

Typical Application Circuit

MAX9937

TOP

R

SENSE

RS+

R

RSP

499Ω

RSP

GND

V

= 4V

BAT

TO 28V

MAX9937

R

V

OUT

OUT

V

SENSE

=

R

RSP

GAIN =

________________________________________________________________

R

OUT

10kΩ

OUT

RS-

R

RSN

499Ω

RSN

BIAS

BLOCK

V

CC

MICROCONTROLLER

ADC

LOAD

5V

Maxim Integrated Products

1

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

MAX9937

Automotive Current-Sense Amplifier
with Reverse-Battery Protection

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= 5V, V

BAT

= V

RS+

= 12V, V

SENSE

= (V

RS+

- V

RS-

) = 0, R

RSP

= R

RSN

= 500Ω, R

OUT

= 10kΩ, TA= -40°C to +125°C. Typical

values are at T

A

= +25°C, unless otherwise noted. See the

Typical Application Circuit

.) (Note 2)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

RSP, RSN to GND Voltage Continuous ..................-0.3V to +30V

RSP, RSN to GND Load-Dump Voltage Duration

(V

BAT

= 40V) with

Typical Application Circuit

.......................1s

RSP, RSN to GND Reverse-Battery Voltage Duration

(V

BAT

= -20V) with

Typical Application Circuit

........Continuous

Differential Input Voltage (RSP - RSN)................................±0.3V

V

CC

to GND...........................................................-0.3V to +6.0V

OUT to GND ...............................................-0.3V to (V

CC

+ 0.3V)

Output Short Circuit to Ground ..................................Continuous

Continuous Input Current into RSN, RSP* ........................±50mA

Continuous Input Current into OUT*.................................±25mA

Thermal Limits (Note 1)
5 SC70 Multiple-Layer PCB

Continuous Power Dissipation (T

A

= +70°C)

(derate 3.1mW/°C above +70°C)............................246.9mW

θ

JA

...............................................................................324°C/W

θ

JC

...............................................................................115°C/W

Operating Temperature Range .........................-40°C to +125°C

Junction Temperature......................................................+150°C

Lead Temperature (soldering, 10s) .................................+300°C

Lead Temperature (reflow) ..............................................+260°C

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a 4-layer

board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial

.

*

Junction temperature rating due to power dissipation must also be observed.

DC CHARACTERISTICS

Input Common-Mode Voltage
Range

Supply Voltage Range V

Input Offset Voltage (Note 3) V

Common-Mode Rejection Ratio CMRR V

Power-Supply Rejection Ratio PSRR VCC = +2.7V to +5.5V 90 120 dB

Quiescent Supply Current I

Input Bias Current (Note 4) IB+, I

Input Bias Current Mismatch ΔIB / I

Input Current in Shutdown I

Voltage Gain Gain = R

Voltage Gain Error (Notes 3, 5)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

RSP

V

V

RSP

RSN

CC

OS

CC

+ I

,

Inferred from CMRR test 4 28 V

Inferred from PSRR test 2.7 5.5 V

TA = +25°C ±0.3 ±1.2

TA = -40°C to +125°C ±1.6

= +4V to +28V

BAT

VCC = 5V 20 55 µA

TA = +25°C 0.8 2 5.6

B-

TA = -40°C to +125°C 0.65 6.5

2 x (IB+ - IB-)/(IB++IB-)

B

TA = +25°C, V

RSN

TA = -40°C to +125°C, VCC = 0 10

OUT/RRSP

TA = +25°C ±0.2 ±1.5

= -40°C to +125°C ±2.0

T

A

TA = +25°C 100 120

= +125°C 90

T

A

TA = +25°C ±1 ±12 %

T

= -40°C to

A

+125°C

= 0 0.01 1

CC

20 V/V

±15 %

mV

dB

µA

µA

%

MAX9937

Automotive Current-Sense Amplifier

with Reverse-Battery Protection

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 5V, V

BAT

= V

RS+

= 12V, V

SENSE

= (V

RS+

- V

RS-

) = 0, R

RSP

= R

RSN

= 500Ω, R

OUT

= 10kΩ, TA= -40°C to +125°C. Typical

values are at T

A

= +25°C, unless otherwise noted. See the

Typical Application Circuit

.) (Note 2)

Note 2: All devices are 100% production tested at T

A

= +25°C. Temperature limits are guaranteed by design.

Note 3: Gain and offset voltage are calculated based on two point measurements: V

SENSE1

= 5mV and V

SENSE2

= 200mV.

Note 4: Input bias current I

B+

and IB-refers to the internal op amp’s inputs (inverting and noninverting) so that IB-= I

RSN

and

I

B+

= I

RSP

- I

OUT

.

Note 5: The gain is set by the external resistors R

RSP

and R

OUT

. See the

Typical Application Circuit.

Note 6: V

RSP

= V

BAT

- V

SENSE

- VOS- (R

RSN

x IB-).

Maximum Output Current I

Output-Voltage Compliance
(Note 6)

Output-Voltage High V

Output-Voltage Low V

AC CHARACTERISTICS

3dB Large-Signal Bandwidth BW V

3dB Small-Signal Bandwidth 350 kHz

Settling Time to 1% t

Input-Voltage Noise e

Input Current Noise I

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

R

II

BB

++-

I

=

B

Δ ||

2

III

=

BBB

OUT

OH

OL

S

n

n

= 500Ω, R

RSN

V

V

V
V

V

SENSE

= 4V, V

BAT

= 4V, V

BAT

= V

OH

= 4V, V

BAT

SENSE

= 500mV, ΔI

- V

BAT

= 137.5mV

f = 1kHz 28 nV/√Hz
f = 1kHz 1 pA/√Hz

+

-

-

= 0, V

RSP

OUT

= 0.1V, ΔI

SENSE

= +500mV,

SENSE

OUT

= -100mV 2 20 mV

SENSE

+ 225mV

DC

= 0 2 7.5 22 mA

OUT

≤ 1% -0.1

V

-

≤ 2% -0.1

OUT

RSP

0.15

0.4 1.2 V

P-P

250 kHz

V

V

5µs

CC

0.1

RSP

0.8

+

-

V

MAX9937

Automotive Current-Sense Amplifier
with Reverse-Battery Protection

4 _______________________________________________________________________________________

Typical Operating Characteristics

(VCC= 5V, V

BAT

= V

RSP

= 12V, V

SENSE

= V

RS+

- V

RS-

= 0, R

RSP

= R

RSN

= 500Ω, R

OUT

= 10kΩ, TA= +25°C, unless otherwise noted.

See the

Typical Application Circuit

.)

0

200

100

400

300

500

600

-40 400 80 120 160

OFFSET VOLTAGE vs. TEMPERATURE

MAX9937 toc02

TEMPERATURE (°C)

OFFSET VOLTAGE (μV)

100

400

300

200

600

500

700

800

412168 202428

OFFSET VOLTAGE

vs. COMMON-MODE VOLTAGE

MAX9937 toc03

COMMON-MODE VOLTAGE (V)

OFFSET VOLTAGE (μV)

TA = +25°C

TA = +125°C

TA = -40°C

0

-700

-500

-400

-300

-200

-100

0

3.0 3.5 4.0 4.5 5.0

OFFSET VOLTAGE

vs. POWER-SUPPLY VOLTAGE

MAX9937 toc04

POWER-SUPPLY VOLTAGE (V)

OFFSET VOLTAGE (μV)

-600

TA = +125°C

TA = -40°C

TA = +25°C

AC COMMON-MODE REJECTION RATIO

C

IN

= 220nF

MAX9937 toc05

FREQUENCY (Hz)

CMRR (dBV)

100k10k1k10010

-100

-80

-60

-40

-20

0

-120
11M

C

LOAD

= 10pF

C

LOAD

= 1nF

C

LOAD

= 100pF

AC POWER-SUPPLY REJECTION RATIO

C

IN

= 220nF

MAX9937 toc06

FREQUENCY (Hz)

PSRR (dBV)

100k10k1k10010

-120

-100

-80

-60

-40

-20

0

-140
11M

C

LOAD

= 100pF

C

LOAD

= 10pF

C

LOAD

= 1nF

0

10

5

20

15

30

25

35

25 100 175 250 325 400 475 550

OFFSET VOLTAGE HISTOGRAM

MAX9937 toc01

OFFSET VOLTAGE (μV)

FREQUENCY (%)

MAX9937

Automotive Current-Sense Amplifier

with Reverse-Battery Protection

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(VCC= 5V, V

BAT

= V

RSP

= 12V, V

SENSE

= V

RS+

- V

RS-

= 0, R

RSP

= R

RSN

= 500Ω, R

OUT

= 10kΩ, TA= +25°C, unless otherwise noted.

See the

Typical Application Circuit

.)

0

5

15

10

25

20

30

-0.115

-0.110

-0.105

-0.100

-0.095

-0.090

-0.085

GAIN ERROR HISTOGRAM

MAX9937 toc07

GAIN ERROR (%)

FREQUENCY (%)

-0.1

-0.2

-0.3

0

0.1

0.2

0.3

0.4

0.5

0.6

-40 400 80 120 160

GAIN ERROR vs. TEMPERATURE

MAX9937 toc08

TEMPERATURE (°C)

GAIN ERROR (%)

-0.8

-0.2

-0.4

-0.6

0

0.2

0.4

0.6

0.8

1.0

4128 16202428

GAIN ERROR vs. COMMON-MODE VOLTAGE

MAX9937 toc09

COMMON-MODE VOLTAGE (V)

GAIN ERROR (%)

TA = +25°C

TA = +125°C

TA = -40°C

0

1.0

0.5

2.0

1.5

2.5

3.0

-40 400 80 120 160

INPUT BIAS CURRENT vs. TEMPERATURE

MAX9937 toc10

TEMPERATURE (°C)

INPUT BIAS CURRENT (μA)

-1.00

0

-0.50

0.50

1.50

1.00

2.00

-40 400 80 120 160

INPUT BIAS CURRENT MISMATCH

vs. TEMPERATURE

MAX9937 toc11

TEMPERATURE (°C)

INPUT BIAS CURRENT MISMATCH (%)

2.00

2.04

2.12

2.08

2.16

2.20

412168 202428

INPUT BIAS CURRENT

vs. COMMON-MODE VOLTAGE

MAX9937 toc12

COMMON-MODE VOLTAGE (V)

INPUT BIAS CURRENT (μA)

MAX9937

Automotive Current-Sense Amplifier
with Reverse-Battery Protection

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VCC= 5V, V

BAT

= V

RSP

= 12V, V

SENSE

= V

RS+

- V

RS-

= 0, R

RSP

= R

RSN

= 500Ω, R

OUT

= 10kΩ, TA= +25°C, unless otherwise noted.

See the

Typical Application Circuit

.)

16.0

17.0

16.5

19.0

18.5

18.0

17.5

19.5

20.0

-40 400 80 120 160

SUPPLY CURRENT vs. TEMPERATURE

MAX9937 toc17

TEMPERATURE (°C)

SUPPLY CURRENT (μA)

GAIN vs. FREQUENCY REFERENCED

TO DC GAIN (C

IN

= 220nF)

MAX9937 toc18

FREQUENCY (Hz)

GAIN (dB)

100k10k1k100

-30

-20

-10

0

10

-40
10 1M

C

LOAD

= 100nF

C

LOAD

= 10pF

C

LOAD

= 1nF

0

0.4

1.2

0.8

1.6

2.0

412168 202428

INPUT BIAS CURRENT MISMATCH

vs. COMMON-MODE VOLTAGE

MAX9937 toc13

COMMON-MODE VOLTAGE (V)

INPUT BIAS CURRENT MISMATCH (%)

0

1.0

0.5

2.0

1.5

2.5

3.0

3.0 4.03.5 4.5 5.0

INPUT BIAS CURRENT
vs. SUPPLY VOLTAGE

MAX9937 toc14

SUPPLY VOLTAGE (V)

INPUT BIAS CURRENT (μA)

80

1.2

1.6

0.8

0.4

0

3.0 4.03.5 4.5 5.0

INPUT BIAS CURRENT MISMATCH

vs. SUPPLY VOLTAGE

MAX9937 toc15

SUPPLY VOLTAGE (V)

INPUT BIAS CURRENT MISMATCH (%)

15

17

16

18

19

3.0 3.83.63.2 3.4 4.0 4.2 4.4 4.6 4.8 5.0

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX9937 toc16

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (μA)

MAX9937

Automotive Current-Sense Amplifier

with Reverse-Battery Protection

_______________________________________________________________________________________ 7

Typical Operating Characteristics (continued)

(VCC= 5V, V

BAT

= V

RSP

= 12V, V

SENSE

= V

RS+

- V

RS-

= 0, R

RSP

= R

RSN

= 500Ω, R

OUT

= 10kΩ, TA= +25°C, unless otherwise noted.

See the

Typical Application Circuit

.)

4μs/div

OUTPUT SLEW RATE

V

SENSE

= -5mV TO +5mV

OUT
50mV/div

IN
10mV/div

MAX9937 toc19

+5

-5

0V

4μs/div

OUTPUT SLEW RATE

V

SENSE

= 5mV TO 200mV

OUT
2V/div

IN
100mV/div

MAX9937 toc20

100ms/div

LOAD-DUMP PROTECTION

OUT
1V/div

V

CM

10V/div

MAX9937 toc21

4μs/div

REVERSE-BATTERY PROTECTION

OUT
2V/div

V

CM

10V/div

MAX9937 toc22

RSP

5V/div

OUTPUT-VOLTAGE NONLINEARITY

vs. SENSE VOLTAGE

MAX9937 toc23

SENSE VOLTAGE (mV)

% OF FULL-SCALE

10080604020

-0.05

0

0.05

0.10

0.15

0.20

-0.10
1 120 140 160 180 200

TA = +25°C

TA = +125°C

TA = -40°C

2.00

1.00

0

3.00

4.00

5.00

6.00

7.00

8.00

9.00

-40 400 80 120 160

MAXIMUM OUTPUT CURRENT

vs. TEMPERATURE

MAX9937 toc24

TEMPERATURE (°C)

OUTPUT CURRENT (mA)

V

BAT

= 28V

V

BAT

= 12V

V

BAT

= 4V

MAX9937

Detailed Description

The MAX9937 unidirectional high-side, current-sense
amplifier features a 4V to 28V input common-mode volt­age range that is independent of supply voltage (VCC=

2.7V to 5.5V). The MAX9937 monitors the current through
a current-sense resistor by converting the sense voltage
to a current output (OUT). Gain is set by the ratio of an
output resistor (R

OUT

) and an input resistor (R

RSP

). High­side current monitoring with the MAX9937 does not inter­fere with the ground path of the load, making it useful for
a variety of automotive battery/ECU monitoring.

Robust input ESD structure allows input common-mode
voltages to exceed the 28V maximum operating input
range for short durations, making the MAX9937 ideal
for applications that need to withstand short-duration
load-dump conditions. The MAX9937 is able to with­stand reverse-battery conditions by a suitable choice of
input resistors (R

RSN

, R

RSP

). See the

Input Common-

Mode Voltages > 28V and < 0V

section

.

Current-Sense Amplifier Operation

The MAX9937 current-sense amplifier operation is best
understood as a specialized op-amp circuit with a
p-channel FET in the feedback path. The op amp
forces a current through an external gain resistor at
RSP (R

RSP

, see the

Typical Application Circuit

) so that
its voltage drop equals the voltage drop across the
external sense resistor, R

SENSE

, making the voltage at
RSP the same as RSN. An external resistor at RSN
(R

RSN

) has the same value as R

RSP

to minimize input

offset voltage due to input bias currents.

The current through R

RSP

is now sourced by the high-

voltage p-channel FET into an external resistor (R

OUT

)
at OUT. This produces an output voltage whose magni­tude is given by the following equations:

The gain accuracy is primarily determined by the
matching of the two gain resistors, R

RSP

and R

OUT

. The

voltage gain error of the MAX9937 is less than 1.5%.

Total gain = 20V/V with R

OUT

= 10kΩ

and R

RSP

= 500Ω.

Low temperature drift of input bias currents and input
offset currents minimizes their impact on total input off­set voltage of the current-sense amplifier.

Applications Information

Choosing R

SENSE

To measure lower currents more accurately, use a high
value for R

SENSE

. The high value develops a higher
sense voltage that reduces the effect of offset voltage
errors of the internal op amp. In applications monitoring
very high currents, however, R

SENSE

must be able to

dissipate the I

2

R losses. If the resistor’s rated power
dissipation is exceeded, its value may drift or it may fail
altogether, causing large differential voltages to devel­op between RSP and RSN.

To minimize the effect of input offset voltage by produc­tion calibration, see the

Skewed Input Offset Voltage for

Production Calibration

section. This can help reduce
the size of the sense resistor in high-current applica­tions, as well as measure wide-dynamic-range currents
without sacrificing accuracy.

If I

SENSE

has a large high-frequency component, mini-

mize the inductance of R

SENSE

and use input differen-

tial filters (see the

Flexible EMI Filtering

section)

.

Low-inductance metal-film resistors are best suited for
these applications.

Calculation of Total Input Offset Voltage

Because of the use of op-amp style architecture, calcu­lation of total input offset voltage involves the same
methodology as is used for any standard op-amp cir­cuit. Interaction of the input bias currents and tolerance
of the external resistors, combined with the core input
offset voltage of the op amp, are important to consider.
Finally, RSS (root-sum-of-squares) calculation for all
these uncorrelated sources of error gives the final input
offset voltage.

Automotive Current-Sense Amplifier
with Reverse-Battery Protection

8 _______________________________________________________________________________________

Pin Description

PIN NAME FUNCTION

1V

2 GND Ground

3 OUT Current Output

4 RSN

5 RSP

CC

Power Supply. Bypass to GND with a

0.1µF capacitor.

Load-Side Connection Through
External R

Supply-Side Connection Through
External R

RSN

RSP

Resistor

Resistor

VIR

VV

=×

SENSE LOAD SENSE

R

=×

OUT SENSE

R

OUT

RSP

()()()()VVIRIR

OS FINAL OS B RS B RS−

22 2 2

=+× +×

ΔΔ

In this case, RRS= R

RSP

= R

RSN

, ΔRRSdepends on the
tolerance of the RRSresistors used, and ΔIB= input off­set current of the amplifier.

The temperature drift of these parameters similarly add
up to give a final result.

Shown below is an example calculation of VOSat
+25°C:

With VOS= ±1.2mV (max), IB= 5.6µA (max), ΔIB=
±12% (max) of 5.6µA (max) = ±0.67µA (max), and R

RS

= 500Ω with ±1% tolerance (i.e., ΔRRS= ±5Ω max)

V

OS-FINAL

= 1.25mV (max).

Flexible EMI Filtering

Real-world applications of current-sense amplifiers
need to measure currents precisely in the presence of
a wide variety of input transients. For example, fast
load-current transients when measuring at the input of a
switching buck regulator can cause high-frequency dif­ferential sense voltages to occur at inputs of the
MAX9937, although the signal of interest is the average
DC value. Alternately, parasitic voltage pickup on a dis­connected or long cable can cause common-mode
voltage transients to occur at inputs of the MAX9937,
which are required to be rejected effectively.

The MAX9937 allows two methods of filtering to help
improve performance in the presence of input common­mode voltage and input differential-voltage transients
(see Figure 1).

The capacitor CINbetween RS+ and RSN helps filter
against input differential voltages, and prevents them
from reaching the MAX9937. The corner frequency of
this filter is determined by the choice of R

RSN

and CIN.

Similarly, capacitor C

OUT

from OUT to ground helps fil­ter the output voltage, thus providing not only differen­tial filtering, but also filtering for input common-mode
transients that have made it past the MAX9937. The
corner frequency of this filter is similarly determined by
choice of R

OUT

and C

OUT

. Note: The MAX9937 is a
current-output device, and has the ability to drive an
infinite amount of load capacitance.

MAX9937

Automotive Current-Sense Amplifier

with Reverse-Battery Protection

_______________________________________________________________________________________ 9

Figure 1. Typical Application Circuit with Optional External Filtering

R

SENSE

RS+

CIN*

OUT

220nF

C

*

OUT

1nF

V

BAT

TO 28V

GAIN =

GND

= 4V

MAX9937

R

V

OUT

OUT

=

R

V

RSP

SENSE

*FILTER CAPACITORS ARE OPTIONAL.

R

RSP

499Ω

R

OUT

10kΩ

RSP

RS-

R

RSN

499Ω

RSN

BIAS

BLOCK

V

CC

MICROCONTROLLER

LOAD

5V

ADC

f

CIN

−

=

1

RC

2π

×

RSN IN

f

C OUT

−

=

2π

1

R COUT

×

OUT

MAX9937

Automotive Current-Sense Amplifier
with Reverse-Battery Protection

10 ______________________________________________________________________________________

At frequencies below the output corner frequency, the
MAX9937 itself provides excellent 100dB (DC) com­mon-mode rejection. At higher frequencies, as the
CMRR of the MAX9937 degrades, the output filter
formed by R

OUT

and C

OUT

helps boost the common-

mode rejection of the circuit.

Input Common-Mode Voltages

> 28V and < 0V

Short-duration overvoltages on the battery line are iso­lated from the RSP and RSN pins of the MAX9937 by
the use of input resistors R

RSP

and R

RSN

. The input
ESD clamp structure is designed so that the device can
withstand short-duration (< 1s) overvoltages up to 40V
when using resistors R

RSP

and R

RSN

of 500Ω or greater

as shown in the

Typical Application Circuit

.

Approximately 40mA flows out of each ESD diode dur­ing this condition (20V/500Ω). This current is less than
the 50mA absolute maximum specification for the RSN
and RSP pins.

Skewed Input Offset Voltage

for Production Calibration

Due to low temperature drift of input bias current and
input offset voltage in the MAX9937, the part can be
used to provide powerful application and system bene­fits not normally attainable from other current-sense
amplifiers on the market. For example, input resistors
R

RSP

and R

RSN

can be intentionally mismatched so as
to introduce an external, controlled input offset voltage
into the circuit. Doing so allows microcontroller firmware
to trim out input offset voltages completely by using
production-line calibration during the manufacturing
process or in system operation as long as a zero load­current condition is forced. Only minimal temperature­drift-based errors in the resistor and in the bias currents
then remain.

V

OS-FINAL

= VOS+ IB-x R

RSN

- IB+x R

RSP

while gain = R

OUT/RRSP

.

Since gain can be fixed by choosing R

OUT

and R

RSP

, a
positive offset voltage can be induced by varying the
value of R

RSN

compared to R

RSP

.

For example:

R

OUT

= 10kΩ, R

RSP

= 500Ω fixes gain = 20V/V. Now,

choosing R

RSN

= 2.5kΩ, and knowing ΔIB= ±12% of IB,

the additional VOSbecomes:

ΔVOS(max) = (5.6µA x 2500) ± (0.12 x 5.6µA x 2500) -

(5.6µA x 500) = 11.2mV ± 1.7mV

ΔVOS(min) = (0.8µA x 2500) ± (0.12 x 0.8µA x 2500) -

(0.8µA x 500) = 1.6mV ± 0.24mV

Since the minimum extra VOSintroduced into the part is
greater than the maximum V

OS

of the current-sense
amplifier (= 1mV), the output of the current-sense
amplifier is always greater than zero even at zero sense
voltage, thus allowing the current-sense amplifier to be
calibrated at zero input current.

Operation with VCC= 0V (Shutdown)

The input terminals go into a high-impedance mode
when VCC= 0, as shown by the input bias current in
shutdown 1µA specification. Due to the low 20µA sup­ply current, this then becomes a convenient way to put
the amplifier in shutdown simply by using a digital I/O
port of a microcontroller to power up/down the current­sense amplifier. This can be especially useful in certain
battery-operated applications that need to implement
flexible power-management schemes.

GND

RSNOUT

1 5 RSPVCC

MAX9937

SC70

TOP VIEW

2

34

+

Pin Configuration

Chip Information

PROCESS: BiCMOS

Package Information

For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages

.

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

5 SC70 X5+1

21-0076

MAX9937

Automotive Current-Sense Amplifier

with Reverse-Battery Protection

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________

11

© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

SC70, 5L.EPS

PACKAGE OUTLINE, 5L SC70

21-0076

1

E

1