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MAX4080FASA Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX4080FASA Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 14 page 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 cur- rent 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 bat- tery’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 dis- charge, as illustrated in Figure 1 for the MAX4081T. Current Monitoring The MAX4080 operates as follows: current from the source flows through RSENSE to the load (Figure 2), cre- ating 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 ampli- fier’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. The MAX4081 input stage differs slightly from the MAX4080 (Figure 3). Its topology allows for monitoring of bidirectional currents through the sense resistor. When current flows from RS+ to RS-, the MAX4081 matches the voltage drop across the external sense resistor, RSENSE, by increasing the current through the Q1 and RG1. In this way, the voltages at the input ter- minals of the internal amplifier A1 are kept constant and an accurate measurement of the sense voltage is achieved. In the following 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) 76V, High-Side, Current-Sense Amplifiers with Voltage Output _______________________________________________________________________________________ 9 Pin Description PIN MAX4080 MAX4081 NAME FUNCTION 1 1 RS+ Power connection to the external-sense resistor. 22 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 5 5 OUT Voltage Output. For the unidirectional MAX4080, VOUT is proportional to 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). — 7 REF1A Reference Voltage Input: Connect REF1A and REF1B to a fixed reference voltage (VREF). VOUT is equal to VREF when VSENSE is zero (see the External Reference section). |
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