MAX4073 Просмотр технического описания (PDF) - Maxim Integrated

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MAX4073

Low-Cost, SC70, Voltage-Output, High-Side Current-Sense Amplifier

Maxim Integrated 

MAX4073T/F/H

Low-Cost, SC70, Voltage-Output,

High-Side Current-Sense Amplifier

Pin Description

PIN

SOT23

1, 2

3

4

5

SC70

2

3

4

5

6

1

NAME

GND

VCC

RS+

RS-

OUT

FUNCTION

Ground

Supply Voltage Input. Bypass to GND with a 0.1µF capacitor.

Power-Side Connection to the External Sense Resistor

Load-Side Connection to the External Sense Resistor

Voltage Output. VOUT is proportional to VSENSE. Output impedance is approximately

12kΩ.

Detailed Description

The MAX4073 high-side current-sense amplifier fea-

tures a +2V to +28V input common-mode range that is

independent of supply voltage. This feature allows the

monitoring of current out of a battery as low as +2V and

also enables high-side current sensing at voltages

greater than the supply voltage (VCC).

The MAX4073 operates as follows: current from the

source flows through RSENSE to the load (Figure 1). Since

the internal-sense amplifier’s inverting input has high

impedance, negligible current flows through RG2

(neglecting the input bias current). Therefore, the

sense amplifier’s inverting-input voltage equals

VSOURCE - (ILOAD)(RSENSE). The amplifier’s open-loop

gain forces its noninverting input to the same voltage as

the inverting input. Therefore, the drop across RG1

equals (ILOAD)(RSENSE). Since IRG1 flows through RG1,

IRG1 = (ILOAD)(RSENSE) / RG1. The internal current mirror

multiplies IRG1 by a current gain factor, β, to give

IRGD = β ✕ IRG1. Solving IRGD = β ✕ (ILOAD)(RSENSE)/

RG1. Assuming infinite output impedance, VOUT = (IRGD)

(RGD). Substituting in for IRGD and rearranging, VOUT =

β ✕ (RGD/RG1)(RSENSE ✕ ILOAD). The parts gain equals

β ✕ RGD/RG1. Therefore, VOUT = (GAIN) (RSENSE)

(ILOAD), where GAIN = 20V/V for MAX4073T, GAIN =

50V/V for MAX4073F, and GAIN = 100V/V for MAX4073H.

Set the full-scale output range by selecting RSENSE and

the appropriate gain version of the MAX4073.

Applications Information

Recommended Component Values

The MAX4073 senses a wide variety of currents with

different sense resistor values. Table 1 lists common

resistor values for typical operation of the MAX4073.

Choosing RSENSE

To measure lower currents more accurately, use a

large value for RSENSE. The larger value develops a

VSOURCE

+2V TO +28V

+3V TO +28V

RSENSE

ILOAD

TO LOAD/BATTERY

RS+

RS-

IRG1

VCC

RG1

RG2

A1

MAX4073T/F/H

CURRENT

OUT

VOUT

MIRROR

IRGD

RGD = 12kΩ

GND

Figure 1. Functional Diagram

higher-sense voltage that reduces offset voltage errors

of the internal op amp. Typical sense voltages range

between 10mV and 150mV.

In applications monitoring very high currents, RSENSE

must be able to dissipate the I2R 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 maxi-

mum ratings (±5V).

If ISENSE has a large high-frequency component, mini-

mize the inductance of RSENSE. Wire-wound resistors

have the highest inductance, metal-film resistors are

Maxim Integrated

7

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