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TELCOM SEMICONDUCTOR, INC.

Analog Input Signal Integration Phase (INT)

The TC5xx integrates the differential voltage between

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-

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

+

–

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

zero and reference deintegrate. If V

–

common, a common-mode voltage exists in the system.

This signal is rejected by the excellent CMR of the converter.

In most applications, V

–

(i.e., power supply common). A common-mode voltage will

exist when V

–

Differential Reference (V

+

–

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

SW

+

RI

SW

–

RI

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)

PRECISION ANALOG FRONT ENDS

TC500

TC500A

TC510

TC514