AN239 - Silicon

AN239 Expanding ADC1 Dyanmic Range

www.DataSheet4U.com AN239 E X PA N D I N G ADC1 D Y N A M I C R A N G E F O R T H E Si8250 1. Introduction The Si8250 data sheet specifies a common mode input range of 0.6 to 1.2 V for ADC1. This range effectively limits the dynamic voltage output range in voltage-controlled converters. For example, the output range for a 3.3 V power supply designed to gen.

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igure 1) is from 0.6 V to the voltage reference which is typically 1.2 V. This simply means that the input voltages to ADC1 from both VSENSE and the REFDAC should stay within the range of 0.6 to 1.2 V referenced to the common ground to achieve good linear response. For input voltages much lower than the common mode specification, ADC1 exhibits non-linear characteristics. Figure 2 shows an example of the ADC1 dc response when the inputs are significantly out of specification. For input voltages above the common mode range the input is effectively “cut off” yielding no change in the ADC output. .