Datasheet MAX4080, MAX4081 (Maxim) - 9

MAX4080/MAX4081 76V, High-Side, Current-Sense Amplifiers with Voltage Output
Pin Description PIN NAME FUNCTION MAX4080 MAX4081
1 1 RS+ Power connection to the external-sense resistor. 2 2 VCC Supply Voltage Input. Decouple VCC to GND with at least a 0.1µF capacitor to bypass line transients. 3, 6, 7 3 N.C. No Connection. No internal connection. Leave open or connect to ground. 4 4 GND Ground Voltage Output. For the unidirectional MAX4080, VOUT is proportional to 5 5 OUT VSENSE. For the bidirectional MAX4081, the difference voltage (VOUT - VREF) is proportional to VSENSE and indicates the correct polarity. 8 8 RS- Load connection to the external sense resistor. — 6 REF1B Reference Voltage Input: Connect REF1B to REF1A or to GND (see the External Reference section). Reference Voltage Input: Connect REF1A and REF1B to a fixed reference — 7 REF1A voltage (VREF). VOUT is equal to VREF when VSENSE is zero (see the External Reference section).
Detailed Description Current Monitoring
The MAX4080/MAX4081 unidirectional and bidirectional The MAX4080 operates as follows: current from the high-side, current-sense amplifiers feature a 4.5V to 76V source flows through RSENSE to the load (Figure 2), cre- input common-mode range that is independent of supply ating a sense voltage, VSENSE. Since the internal-sense voltage. This feature allows the monitoring of current out amplifier’s inverting input has high impedance, negligible of a battery as low as 4.5V and also enables high-side cur- current flows through RG2 (neglecting the input bias rent sensing at voltages greater than the supply voltage current). Therefore, the sense amplifier’s inverting input (VCC). The MAX4080/MAX4081 monitors current through voltage equals VSOURCE - (ILOAD)(RSENSE). The ampli- a current-sense resistor and amplifies the voltage across fier’s open-loop gain forces its noninverting input to the the resistor. The MAX4080 senses current unidirectional- same voltage as the inverting input. Therefore, the drop ly, while the MAX4081 senses current bidirectionally. across RG1 equals VSENSE. The internal current mirror The 76V input voltage range of the MAX4080/MAX4081 multiplies IRG1 by a current gain factor, β, to give IA2 = applies independently to both supply voltage (V β × IRG1. Amplifier A2 is used to convert the output CC) and common-mode, input-sense voltage (V current to a voltage and then sent through amplifier RS+). High-side current monitoring does not interfere with the ground A3. Total gain = 5V/V for MAX4080F, 20V/V for the path of the load being measured, making the MAX4080/ MAX4080T, and 60V/V for the MAX4080S. MAX4081 particularly useful in a wide range of high-volt- The MAX4081 input stage differs slightly from the age systems. MAX4080 (Figure 3). Its topology allows for monitoring Battery-powered systems require a precise bidirectional of bidirectional currents through the sense resistor. When current-sense amplifier to accurately monitor the battery’s current flows from RS+ to RS-, the MAX4081 matches the charge and discharge. The MAX4081 charging current voltage drop across the external sense resistor, RSENSE, is represented by an output voltage from V by increasing the current through the Q1 and RG1. In this REF to VCC, while discharge current is given from V way, the voltages at the input terminals of the internal REF to GND. Measurements of OUT with respect to V amplifier A1 are kept constant and an accurate measure- REF yield a posi- tive and negative voltage during charge and discharge, as ment of the sense voltage is achieved. In the following illustrated in Figure 1 for the MAX4081T. amplifier stages of the MAX4081, the output signal of amplifier A2 is level- shifted to the reference voltage (VREF = VREF1A = VREF1B), resulting in a voltage at the output pin (OUT) www.maximintegrated.com Maxim Integrated │ 9