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

부품명

상세내역

제조사

MAX9937AXKT
(Rev.:2008)

Automotive Current-Sense Amplifier with Reverse-Battery Protection

Maxim Integrated 

Automotive Current-Sense Amplifier

with Reverse-Battery Protection

VBAT = 4V

TO 28V

RS+

RSENSE

RS-

RRSP

499Ω

CIN*

220nF

RRSN

499Ω

RSP

GND

RSN

VCC

BIAS

BLOCK

LOAD

5V

MICROCONTROLLER

MAX9937

OUT

ADC

GAIN = VOUT = ROUT

VSENSE RRSP

ROUT

10kΩ

COUT*

1nF

*FILTER CAPACITORS ARE OPTIONAL.

Figure 1. Typical Application Circuit with Optional External Filtering

In this case, RRS = RRSP = RRSN, ΔRRS depends on the

tolerance of the RRS resistors used, and ΔIB = input off-

set 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 VOS at

+25°C:

With VOS = ±1.2mV (max), IB = 5.6µA (max), ΔIB =

±12% (max) of 5.6µA (max) = ±0.67µA (max), and RRS

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

VOS-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 dif-

ferential 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 dis-

connected 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 common-

mode voltage and input differential-voltage transients

(see Figure 1).

The capacitor CIN between 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 RRSN and CIN.

fC−IN

=

1

2πRRSN

×

CIN

Similarly, capacitor COUT from OUT to ground helps fil-

ter the output voltage, thus providing not only differen-

tial 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 ROUT and COUT. Note: The MAX9937 is a

current-output device, and has the ability to drive an

infinite amount of load capacitance.

fC−OUT

=

1

2πROUT × COUT

_______________________________________________________________________________________ 9

Share Link: