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MAX4378FAUD Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX4378FAUD Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 9 page Single/Dual/Quad, High-Side Current-Sense Amplifiers with Internal Gain _______________________________________________________________________________________ 7 Detailed Description The MAX4376/MAX4377/MAX4378 high-side current- sense amplifiers feature a 0 to +28V input common-mode range that is independent of supply voltage. This feature allows the monitoring of current out of a battery in deep discharge and also enables high-side current sensing at voltages greater than the supply voltage (VCC). The MAX4376/MAX4377/MAX4378 operate 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 multi- plies IRG1 by a current gain factor, β, to give IRGD = β x IRG1. Solving IRGD = β x (ILOAD)(RSENSE)/RG1. Therefore: VOUT = β x (RGD/RG1)(RSENSE x ILOAD) x amp gain where amp gain is 2, 5, or 10. The part’s gain equals ( β x RGD / RG1) x amp gain. Therefore: VOUT = (GAIN)(RSENSE)(ILOAD) where GAIN = 20 for MAX437_T. GAIN = 50 for MAX437_F. GAIN = 100 for MAX437_H. Set the full-scale output range by selecting RSENSE and the appropriate gain version of the MAX4376/ MAX4377/MAX4378. Applications Information Recommended Component Values The MAX4376/MAX4377/MAX4378 sense a wide variety of currents with different sense resistor values. Table 1 lists common resistor values for typical operation of the MAX4376/MAX4377/MAX4378. Choosing RSENSE To measure lower currents more accurately, use a high value for RSENSE. The high value develops a higher sense voltage that reduces offset voltage errors of the internal op amp. 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. 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 somewhat better, and low-inductance metal-film resis- tors are best suited for these applications. Bidirectional Current-Sense Amplifier Systems such as laptop computers and other devices that have internal charge circuitry require a precise bidirectional current-sense amplifier to monitor accu- rately the battery’s current regardless of polarity. Figure 2 shows the MAX4377 used as a bidirectional current Pin Description PIN MAX4376 MAX4376 MAX4377 MAX4378 SOT23-5 SO-8 µMAX-8/ SO-8 SO-14/ TSSOP-14 NAME FUNCTION 1 4 1, 7 1, 7, 8, 14 OUT, OUT_ Output Voltage. VOUT_ is proportional to the magnitude of the sense voltage (VRS+ - VRS-). VOUT_ is approximately zero when VRS - > VRS - + (no phase reversal). 2 3 4 11 GND Ground 3184 VCC Supply Voltage 4 8 3, 5 3, 5, 10, 12 RS+, RS_+ Power connection to the external sense resistor 5 6 2, 6 2, 6, 9, 13 RS-, RS_- Load-side connection to the external sense resistor — 2, 5, 7 —— N.C. No Connection. Not internally connected. |
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