General Description

The MAX4080/MAX4081 are high-side, current-sense amplifiers with an input voltage range that extends from 4.5V to 76V making them ideal for telecom, automotive, backplane, and other systems where high-voltage current monitoring is critical. The MAX4080 is designed for unidirectional current-sense applications and the MAX4081 allows bidirectional current sensing. The MAX4081 single output pin continuously monitors the transition from charge to discharge and avoids the need for a separate polarity output. The MAX4081 requires an external reference to set the zero-current output level (VSENSE = 0V). The charging current is represented by an output voltage from VREF to VCC, while discharge current is given from VREF to GND.

For maximum versatility, the 76V input voltage range applies independently to both supply voltage (VCC) and common-mode input voltage (VRS+). High-side current monitoring does not interfere with the ground path of the load being measured, making the MAX4080/MAX4081 particularly useful in a wide range of high-voltage systems.

The combination of three gain versions (5V/V, 20V/V, 60V/V = F, T, S suffix) and a user-selectable, external sense resistor sets the full-scale current reading and its proportional output voltage. The MAX4080/MAX4081 offer a high level of integration, resulting in a simple, accurate, and compact current-sense solution.

The MAX4080/MAX4081 operate from a 4.5V to 76V single supply and draw only 75µA of supply current. These devices are specified over the automotive operating temperature range (-40°C to +125°C) and are available in a space-saving 8-pin µMAX® or SO package.

 

Applications

Automotive (12V, 24V, or 42V Batteries)

48V Telecom and Backplane Current Measurement

Bidirectional Motor Control

Power-Management Systems

Avalanche Photodiode and PIN-Diode Current Monitoring

General System/Board-Level Current Sensing

Precision High-Voltage Current Sources

 

Benefits and Features

Ideal for High-Voltage Current Monitoring Applications

Wide 4.5V to 76V Input Common-Mode Range

Independent Operating Supply Voltage

High Accuracy and Low Quiescent Current Support Precision Application Requirements

±0.1% Full-Scale Accuracy

Low 100μV Input Offset Voltage

Three Gain Versions Available- 5V/V (MAX4080F/MAX4081F)- 20V/V (MAX4080T/MAX4081T)-60V/V (MAX4080S/MAX4081S)

75μA Supply Current (MAX4080)

Flexible Current Sensing Supports Monitoring of Charge and Discharge of Batteries

Bidirectional (MAX4081) or Unidirectional (MAX4080) ISENSE

Minimizes Required Board Space

8-Pin μMAX Package

 

Detailed Description

The MAX4080/MAX4081 unidirectional and bidirectional high-side, current-sense amplifiers feature a 4.5V to 76V input common-mode range that is independent of supply voltage. This feature allows the monitoring of current out of a battery as low as 4.5V and also enables high-side current sensing at voltages greater than the supply voltage (VCC). The MAX4080/MAX4081 monitors current through a current-sense resistor and amplifies the voltage across the resistor. The MAX4080 senses current unidirectionally, while the MAX4081 senses current bidirectionally.

The 76V input voltage range of the MAX4080/MAX4081 applies independently to both supply voltage (VCC) and common-mode, input-sense voltage (VRS+). High-side current monitoring does not interfere with the ground path of the load being measured, making the MAX4080/MAX4081 particularly useful in a wide range of high-voltage systems.

Battery-powered systems require a precise bidirectional current-sense amplifier to accurately monitor the battery’s charge and discharge. The MAX4081 charging current is represented by an output voltage from VREF to VCC, while discharge current is given from VREF to GND. Measurements of OUT with respect to VREF yield a positive and negative voltage during charge and discharge.

 

Current Monitoring

The MAX4080 operates as follows: current from the source flows through RSENSE to the load, creating a sense voltage, VSENSE. 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 VSENSE. The internal current mirror multiplies IRG1 by a current gain factor, β, to give IA2 =  β × IRG1. Amplifier A2 is used to convert the output  current to a voltage and then sent through amplifier A3. Total gain = 5V/V for MAX4080F, 20V/V for the MAX4080T, and 60V/V for the MAX4080S.