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MAX34406WETG+ Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX34406WETG+ Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 11 page ����������������������������������������������������������������� Maxim Integrated Products 9 MAX34406 Quad Current-Sense Amplifier with Overcurrent Threshold Comparators Efficiency and Power Dissipation At high current levels, the I2R losses in RSENSE can be significant. Take this into consideration when choosing the resistor value and its power dissipation (wattage) rating. Also, the sense resistor’s value might drift if it is allowed to heat up excessively. The precision VOS of the device allows the use of small sense resistors to reduce power dissipation and reduce hot spots. Kelvin Connections Because of the high currents that flow through RSENSE, take care to eliminate parasitic trace resistance from causing errors in the sense voltage. Either use a four- terminal current-sense resistor or use Kelvin (force and sense) PCB layout techniques. Minimizing Trace Resistance PCB trace resistance from RSENSE to the INx+ inputs contributes to gain error in the current-sense amplifiers. Care should be taken to minimize this resistance (shown as RTRC in Figure 1). Total gain including error caused by trace resistance can be calculated as follows: OUTx TRC R G R1 R = + For example, assume a gain of 100V/V, as in the MAX34406H. From Table 1, R1 = 100I and ROUTx = 10kI. Then every 10mI of PCB trace resistance adds -0.01% gain error. Optional Output Filter Capacitor When designing a system that uses a sample-and-hold stage in the ADC, the sampling capacitor momentarily loads OUTx and causes a drop in the output voltage. If sampling time is very short (less than a microsecond), consider using a ceramic capacitor across OUTx and GND to hold VOUTx constant during sampling. This also decreases the small-signal bandwidth of the current- sense amplifier and reduces noise at OUTx. Input Filters Some applications of current-sense amplifiers need to measure currents accurately even in the presence of both differential and common-mode ripple, as well as a wide variety of input transient conditions. For example, high-frequency ripple at the output of a switching buck or boost regulator results in a common-mode voltage at the device’s inputs. Alternatively, the fast load-current tran- sients, when measuring at the input of a switching buck or boost regulator, can cause high-frequency differential sense voltages to occur at the device’s inputs, although the signal of interest is the average DC value. Such high- frequency differential sense voltages can result in a volt- age offset at the device output. The device allows a method of filtering to help improve performance in the presence of input common-mode voltage and input differential voltage transients. Figure 2 shows a differential input filter. The capacitor CIN between INx+ and INx- along with the resistor RIN between the sense resistor and INx- helps filter against input differential voltages and prevents them from reaching the device. The corner frequency of this filter is determined by the choice of RIN, CIN, and the value of the input resistance at INx- (R1). See Table 1 for R1 values at the different gain options. The value of RIN should be chosen to minimize its effect on the input offset voltage due to the bias current at INx-. Figure 1. Input Trace Resistance Figure 2. Differential Input Filter RSENSE INx+ GND INx- OUTx RTRC MAX34406 LOAD RSENSE CIN INx+ GND INx- OUTx RIN MAX34406 LOAD |
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