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TC514COI 데이터시트(PDF) 8 Page - TelCom Semiconductor, Inc |
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TC514COI 데이터시트(HTML) 8 Page - TelCom Semiconductor, Inc |
8 / 17 page 3-26 TELCOM SEMICONDUCTOR, INC. Analog Input Signal Integration Phase (INT) The TC5xx integrates the differential voltage between the (V+IN) and (V–IN) inputs. The differential voltage must be within the device's common-mode range VCMR. The input signal polarity is normally checked via soft- ware at the end of this phase: CMPTR = 1 for positive polarity; CMPTR = 0 for negative polarity. Reference Voltage Deintegration Phase (DINT) The previously charged reference capacitor is con- nected with the proper polarity to ramp the integrator output back to zero. An externally-provided, precision timer is used to measure the duration of this phase. The resulting time measurement is proportional to the magnitude of the applied input voltage. Integrator Output Zero Phase (IZ) This phase guarantees the integrator output is at 0V when the Auto Zero phase is entered and that only system offset voltages are compensated. This phase is used at the end of the reference voltage deintegration phase and MUST be used for ALL TC5xx applications having resolutions of 12 bits or more. If this phase is not used, the value of the Auto- Zero capacitor (CAZ) must be about 2 to 3 times the value of the integration capacitor (CINT) to reduce the effects of charge-sharing. The Integrator Output Zero phase should be programmed to operate until the Output of the Compara- tor returns "HIGH". The overall Timing System is shown in Figure 8. ANALOG SECTION Differential Inputs (V + IN, V – IN) The TC5xx operates with differential voltages within the input amplifier common-mode range. The amplifier com- mon-mode range extends from 1.5V below positive supply to 1.5V above negative supply. Within this common-mode voltage range, common-mode rejection is typically 80dB. Full accuracy is maintained, however, when the inputs are no less than 1.5V from either supply. The integrator output also follows the common-mode voltage. The integrator output must not be allowed to satu- rate. A worst-case condition exists, for example, when a large, positive common-mode voltage with a near full-scale negative differential input voltage is applied. The negative input signal drives the integrator positive when most of its swing has been used up by the positive common-mode voltage. For these critical applications, the integrator swing can be reduced. The integrator output can swing within 0.9V of either supply without loss of linearity. Analog Common Analog common is used as VIN return during system- zero and reference deintegrate. If V – IN is different from analog common, a common-mode voltage exists in the system. This signal is rejected by the excellent CMR of the converter. In most applications, V – IN will be set at a fixed known voltage (i.e., power supply common). A common-mode voltage will exist when V – IN is not connected to analog common. Differential Reference (V + REF, V – REF) The reference voltage can be anywhere within 1V of the power supply voltage of the converter. Roll-over error is caused by the reference capacitor losing or gaining charge due to stray capacitance on its nodes. The difference in reference for (+) or (–) input voltages will cause a roll-over error. This error can be minimized by using a large reference capacitor in comparison to the stray capacitance. Phase Control Inputs (A, B) The A, B unlatched logic inputs select the TC5xx oper- ating phase. The A, B inputs are normally driven by a microprocessor I/O port or external logic. Table 1. Internal Analog Gate Status Internal Analog Gate Status Conversion Phase SWI SW + RI SW – RI SWZ SWR SW1 SWIZ Auto-Zero (A = 0, B = 1) Closed Closed Closed Input Signal Integration Closed (A = 1, B = 0) Reference Voltage Closed* Closed Deintegration (A =1, B= 1) Integrator Output Zero Closed Closed Closed (A = 0, B = 0) *Assumes a positive polarity input signal. SW–RI would be closed for a negative input signal. PRECISION ANALOG FRONT ENDS TC500 TC500A TC510 TC514 |
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