MAX4372F datasheet(6/11 Pages) MAXIM

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_______________Detailed Description

The MAX4372 high-side current-sense amplifier fea-

tures a 0 to 28V input common-mode range that is inde-

pendent of supply voltage. This feature allows the

monitoring of current flow out of a battery in deep dis-

charge, and also enables high-side current sensing at

voltages far in excess of the supply voltage (VCC).

Current flows through the sense resistor, generating a

sense voltage (Figure 1). Since A1’s inverting input is

high impedance, the voltage on the negative terminal

equals VIN - VSENSE. A1 forces its positive terminal to

match its negative terminal; therefore, the voltage

across RG1 (VIN - V1-) equals VSENSE. This creates a

current to flow through RG1 equal to VSENSE / RG1. The

transistor and current mirror amplify the current by a

factor of

β. This makes the current flowing out of the

current mirror equal to:

IM =

β VSENSE / RG1

A2’s positive terminal presents high impedance, so this

current flows through RGD, with the following result:

V2+ = RGD

β ·· VSENSE / RG1

R1 and R2 set the closed-loop gain for A2, which ampli-

fies V2+, yielding:

VOUT = RGD ··

β ·· VSENSE / RG1 (1 + R2 / R1)

The gain of the device equals:

VOUT

= RGD ··

β (1 + R2 / R1) / RG1

VSENSE

__________Applications Information

Recommended Component Values

The MAX4372 operates over a wide variety of current

ranges with different sense resistors. Table 1 lists com-

mon resistor values for typical operation of the

MAX4372.

Choosing RSENSE

Given the gain and maximum load current, select RSENSE

such that VOUT does not exceed VCC - 0.25V or 10V. To

measure lower currents more accurately, use a high

value for RSENSE. A higher value develops a higher sense

voltage, which overcomes offset voltage errors of the

internal current amplifier.

In applications monitoring very high current, ensure

RSENSE is able to dissipate its own I

2R losses. If the

resistor’s rated power dissipation is exceeded, its value

may drift or it may fail altogether, causing a differential

voltage across the terminals in excess of the absolute

maximum ratings.

Low-Cost, UCSP/SOT23, Micropower, High-Side

Current-Sense Amplifier with Voltage Output

_______________________________________________________________________________________

MAX4372T/F/H

GND

LOAD

VIN

0 TO 28V

2.7V

28V

RGD

RG2

100k

RS+

RS-

RG1

100k

OUT

V2+

V1+

V1-

V2-

VCC

RSENSE

ILOAD

VSENSE

CURRENT

MIRROR

Pin Description

Ground

Output Voltage. VOUT is proportional to the magnitude of VSENSE

(VRS+ - VRS-).

FUNCTION

SOT23

UCSP

Supply Voltage. Use at least a 0.1µF capacitor to decouple VCC from fast

transients.

Power Connection to the External Sense Resistor

Load-Side Connection to the External Sense Resistor

—

2, 5, 7

No Connection. Not internally connected.

—

Figure 1. Functional Diagram

GND

OUT

NAME

VCC

RS+

RS-

N.C.

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