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ISL6295CVZ Datasheet(PDF) 7 Page - Intersil Corporation |
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ISL6295CVZ Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 25 page 7 FN9074.2 February 8, 2011 Ictrl programming in a typical application is as follows: VOLTAGE MEASUREMENTS An analog multiplexer and divider network is provided to support measurement of battery pack voltages. The A/D control registers VPctrl and GPADctrl are used to specify the measurement to be made. In typical applications, voltage measurement a pack level is done using the 340mV reference and a 10-bit magnitude resolution. The value of the LSB in a pack voltage measurement using the 340mV reference voltage and 15 bit resolution is given by the formula: VPACK LSB = 10.2V/2 15 = 311.3µV VPctrl programming in a typical application is as follows: The input source fields for the VPctrl, and GPADctrl registers must be programmed to select the pack voltage VP and the general purpose A/D input voltage GPAD in order for these registers to control their intended measurements. The measurable input range for VP is from 2.8V to 7V. The measurable input range for GPAD is from 0V to 6.2V. TEMPERATURE MEASUREMENTS A/D input channels are provided for temperature measurement using either the internal temperature sensor or an external thermistor. Defined within the ITctrl register is settings for the reference utilized and the resolution desired for measurement of temperature using the internal temperature sensor. Due to the voltage output range of the temperature sensor, the 340mV reference must be selected. The temperature measurement given by the internal temperature sensor is derived using the following equation: IT(°C) = (ITres – 22421)/78.95 °C Typically, 10-bit resolution is selected, which results in the following temperature measurement resolution: IT( Δ) = 0.405°C/LSB For temperature measurement using an external sensor, the NTC pin sources a current of 12.5µA. For proper operation, an industry standard 10k Ω at 25°C negative temperature coefficient (NTC) device with a proper resistance range should be connected between the NTC and GND pins. The NTC reference output is only enabled during an external temperature measurement in order to minimize power consumption. Defined within the ETctrl register are settings for the reference utilized and the resolution desired for measurement of temperature using the external temperature sensor. The accuracy of temperature measurement using the external thermistor is directly determined by the characteristic of the NTC device used. It is suggested that temperature measurements be thoroughly characterized to extract the best-fit equation for temperature determination. Internal to the ISL6295, a voltage inverter is provided to translate the NTC voltage to a PTC voltage so that a larger A/D conversion result would correspond to a higher temperature reading. The actual voltage presented to the ADC is as follows: VADC = VREF - VNTC where VREF is the reference voltage selected. For typical NTC devices, the 340mV reference should be used to cover the expected operational temperature range of the battery pack. For a NTC with a 10k Ω resistance at 25°C, the voltage at the NTC pin will be 125mV, which corresponds to an ADC input of (340-125)mV = 215mV. The expected conversion result would be 215/340 * 215 = 20721. OFFSET COMPENSATION The host software can perform offset compensation by using an offset measurement value read from the ISL6295. When the offset calibration is enabled within the OFFSctrl register, the converter input is internally shorted to ground and an A/D conversion is performed at the specified resolution. The offset value is stored in the OFFSres register. ACCUMULATION/TIMING The ISL6295 incorporates four 32-bit accumulators and four 32-bit elapsed time counters. The Discharge Current Accumulator (DCA) and the Charge Current Accumulator (CCA) are intended to record discharge and charge capacity values. The Discharge Time Counter (DTC) and the Charge Time Counter (CTC) are intended to maintain the total discharge time and charge time. Accumulated charge and discharge values can be used to determine state of charge of the battery as well as cycle count information. With information provided by the elapsed time counters, average charge and discharge currents over an extended period of time can be calculated. Each of the four 32-bit accumulator registers is assigned a fixed “source” A/D result register. When the accumulator is BIT(s) NAME VALUE FUNCTION 7 EN 1 ENABLES A/D CONVERSION 6-4 Res 111 Selects 15-bit resolution 3 Ref 0 Selects 170mV Reference 2-0 Sel 000 Selects VSR as ADC input BIT(s) NAME VALUE FUNCTION 7 En 1 Enables A/D conversion 6-4 Res 010 Selects 10-bit resolution 3 Ref 1 Selects 340mV Reference 2-0 Sel 011 Selects Vpack (VP) as ADC input ISL6295 |
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