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MAX4069 Datasheet(PDF) 10 Page - Maxim Integrated Products |
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MAX4069 Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 18 page Detailed Description The MAX4069–MAX4072 bidirectional, high-side, cur- rent-sense amplifiers are ideal for portable equipment. The wide 1.35V to 24V input common-mode voltage range is independent of the supply voltage, ensuring that the current-sense feedback remains accurate even when connected to a battery pack in deep discharge. The MAX4069/MAX4071/MAX4072 operate from a 2.7V to 24V single supply. Because the MAX4070 has a 2.5V internal reference, it operates from 3.6V to 24V. All devices have a low 100µA supply current that reduces to only 10µA (typ) in shutdown mode. To achieve maxi- mum flexibility, an external current-sense resistor is used along with a gain select pin (GSEL) to choose either 50V/V or 100V/V. Drive GSEL low to select gain of 50V/V or drive GSEL high to choose gain of 100V/V (see Functional Diagram). The MAX4069 has an adjustable reference voltage set by two external resis- tors between REFOUT and ADJ, and GND pins. The MAX4070 contains an internal 2.5V reference. The MAX4071 is similar to the MAX4070 but with a fixed internal reference voltage of 1.5V. The MAX4072 has a reference input pin to allow use of external references. Charging current is represented by an output voltage from the reference voltage to VCC, while discharge cur- rent is given from the reference voltage to GND. The direction of VSENSE is totally arbitrary. The input stage of the MAX4069–MAX4072 is shown in Figure 1. Its unique topology allows for monitoring bidi- rectional currents through the sense resistor (RSENSE). If, for instance, current flows from RS+ to RS-, the MAX4069–MAX4072 match for the voltage drop over the external sense resistor (RSENSE) by increasing the cur- rent through the internal Q1 and RG1. At the same time, the current through Q2 and RG2 decreases, however, internal circuitry not shown in Figure 1 prevents Q2 from turning off completely. Likewise, if current flows from RS- to RS+, the current through Q2 and RG2 increases and the current through Q1 decreases. In this way, the volt- ages at the input terminals 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 MAX4069–MAX4072, the output signal of amplifier A2 is level-shifted towards the reference voltage (VREF), resulting in a voltage at the output pin (OUT) that swings above the VREF voltage for positive-sense voltages and below VREF for negative-sense voltages. Applications Information Bidirectional, Current-Sense Amplifier Systems such as laptop computers and other devices that have internal charge circuitry require a precise bidi- rectional, current-sense amplifier to accurately monitor the battery’s current regardless of polarity. Figure 2 shows the MAX4069–MAX4072 used as a bidirectional current monitor. In Figure 2, the direction of VSENSE is assigned to charge and discharge, assuming charge is greater than discharge. The practical choice of direction is based on dynamic range at OUT, given that the range of REF to VCC is usually greater than from REF to ground. This is useful for implementing either smart bat- tery packs or fuel gauges. High-Current Measurement The MAX4069–MAX4072 can achieve high-current measurements by using low-value sense resistors, which can be paralleled to further increase the current- sense limit. Adjusting VREF (MAX4069) The MAX4069 has an output reference voltage that can be set to a desired voltage by a two-resistor divider between REFOUT, ADJ, and GND. If REFOUT and ADJ are connected together, the minimum output reference voltage is obtained, 1.23V (typ). The maximum voltage for REFOUT is 4V (that requires VCC ≥ 5.1V). The rec- ommended range for the external resistors is: R1 + R2 should be > 20k Ω and < 500kΩ. Bidirectional, High-Side, Current-Sense Amplifiers with Reference 10 ______________________________________________________________________________________ MAX4069–MAX4072 RSENSE RS- RS+ RG2 RG1 A1 A2 Q1 Q2 IOUT OUT Figure 1. Detailed Input Stage Note: RG1 = RG2 = 104k (typ). |
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