MAX472 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX472

Precision, High-Side Current-Sense Amplifiers

Maxim Integrated 

Precision, High-Side

Current-Sense Amplifiers

require, given the full-scale IOUT determined by

RSENSE, RG1, and RG2. The high compliance of OUT

permits using ROUT values up to 10kΩ with minimal

error. Values above 10kΩ are not usually recommend-

ed. The impedance of OUT’s load (e.g., the input of an

op amp or ADC) must be much greater than ROUT

(e.g., 100 x ROUT) to avoid degrading the measure-

ment accuracy.

High-Current Measurement

The MAX472 can achieve higher current measurements

than the MAX471 can. Low-value sense resistors may

be paralleled to obtain even lower values, or the PC

board trace may be adjusted for any value.

An alternative method is to connect several MAX471s in

parallel and connect the high-impedance current-

source OUT pins together to indicate the total system

current (Figure 3). Pay attention to layout to ensure

equal IR drops in the paralleled connection. This is

necessary to achieve equal current sharing.

Power-Supply Bypassing and Grounding

The MAX471 has been designed as a “high side” (posi-

tive terminal) current monitor to ease the task of

grounding any battery charger, thermistor, etc. that

may be a part of the battery pack. Grounding the

MAX471 requires no special precautions; follow the

same cautionary steps that apply to the system as a

whole. High-current systems can experience large volt-

age drops across a ground plane, and this drop may

add to or subtract from VOUT. For highest current-mea-

surement accuracy, use a single-point “star” ground.

The MAX471/MAX472 require no special bypassing,

and respond quickly to transient changes in line cur-

rent. If the noise at OUT caused by these transients is a

problem, you may want to place a 1µF capacitor at the

OUT pin to ground. You can also place a large capaci-

tor at the RS- terminal (or “load” side of the MAX472) to

decouple the load and, thereby, reduce the current

transients. These capacitors are not required for

MAX471/MAX472 operation or stability, and their use

will not degrade performance.

For the MAX472, the RG1 and RG2 inputs can be fil-

tered by placing a capacitor (e.g., 1µF) between them

to average the sensed current.

MAX471 Layout

The MAX471 must be soldered in place, since sockets

can cause uneven current sharing between the RS+

pins (pins 2 and 3) and the RS- pins (pins 6 and 7),

resulting in typical errors of 0.5%.

In order to dissipate sense-resistor heat from large

sense currents, solder the RS+ pins and the RS- pins to

large copper traces. Keep the part away from other

heat-generating devices. This procedure will ensure

continuous power dissipation rating.

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