MAX9937AXKT(2008) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX9937AXKT
(Rev.:2008)

Automotive Current-Sense Amplifier with Reverse-Battery Protection

Maxim Integrated 

Automotive Current-Sense Amplifier

with Reverse-Battery Protection

At frequencies below the output corner frequency, the

MAX9937 itself provides excellent 100dB (DC) com-

mon-mode rejection. At higher frequencies, as the

CMRR of the MAX9937 degrades, the output filter

formed by ROUT and COUT helps boost the common-

mode rejection of the circuit.

Input Common-Mode Voltages

> 28V and < 0V

Short-duration overvoltages on the battery line are iso-

lated from the RSP and RSN pins of the MAX9937 by

the use of input resistors RRSP and RRSN. The input

ESD clamp structure is designed so that the device can

withstand short-duration (< 1s) overvoltages up to 40V

when using resistors RRSP and RRSN of 500Ω or greater

as shown in the Typical Application Circuit.

Approximately 40mA flows out of each ESD diode dur-

ing 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 bene-

fits not normally attainable from other current-sense

amplifiers on the market. For example, input resistors

RRSP and RRSN 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 load-

current condition is forced. Only minimal temperature-

drift-based errors in the resistor and in the bias currents

then remain.

VOS-FINAL = VOS + IB- x RRSN - IB+ x RRSP

while gain = ROUT/RRSP.

Since gain can be fixed by choosing ROUT and RRSP, a

positive offset voltage can be induced by varying the

value of RRSN compared to RRSP.

For example:

ROUT = 10kΩ, RRSP = 500Ω fixes gain = 20V/V. Now,

choosing RRSN = 2.5kΩ, and knowing ΔIB= ±12% of IB,

the additional VOS becomes:

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 VOS introduced into the part is

greater than the maximum VOS 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 sup-

ply 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 current-

sense amplifier. This can be especially useful in certain

battery-operated applications that need to implement

flexible power-management schemes.

Pin Configuration

TOP VIEW

+

VCC 1

5 RSP

MAX9937

GND 2

OUT 3

4 RSN

SC70

PROCESS: BiCMOS

Chip Information

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

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