TC500 datasheet(13/28 Pages) MICROCHIP

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DS21428B-page 13

TC500/A/510/514

FIGURE 7-1:

NOISE THRESHOLD

7.6

Integrator Output Zero Phase

The comparator delay and the controller's response

latency may result in overshoot, causing charge

buildup on the integrator at the end of a conversion.

This charge must be removed or performance will

degrade. The Integrator Output Zero phase should be

activated (AB = 00) until CMPTR goes high. It is abso-

lutely critical that this phase be terminated immediately

so that Overshoot is not allowed to occur in the oppo-

site direction. At this point, it can be assured that the

integrator is near zero. Auto Zero should be entered

(AB = 01) and the TC5XX held in this state until the next

cycle is begun (see Figure 7-2).

FIGURE 7-2:

OVERSHOOT

7.7

Using the TC510/TC514

7.7.1

NEGATIVE SUPPLY VOLTAGE

CONVERTER (TC510, TC514)

A capacitive charge pump is employed to invert the volt-

age on VDD for negative bias within the TC510/TC514.

This voltage is also available on the VOUT- pin to provide

negative bias elsewhere in the system. Two external

capacitors are required to perform the conversion.

Timing is generated by an internal state machine driven

from an on-board oscillator. During the first phase,

capacitor CF is switched across the power supply and

charged to VS+. This charge is transferred to capacitor

COUT- during the second phase. The oscillator normally

runs at 100kHz to ensure minimum output ripple. This

frequency can be reduced by placing a capacitor from

OSC to VDD. The relationship between the capacitor

value is shown in Section 9.0.

7.7.2

ANALOG INPUT MULTIPLEXER

(TC514)

The TC514 is equipped with a four input differential

analog multiplexer. Input channels are selected using

select inputs (A1, A0). These are high-true control sig-

nals (i.e., channel 0 is selected when (A1, A0 = 00).

LowREF

Normal VREF

High VREF

NTH

30 µV

NTH

Slope (S) =

NTH = Noise Threshold

VREF

RINT CINT

Integrator

Output

Comparator

Output Comp

Integrate

Phase

De-integrate Phase

Integrator

Zero Phase

Zero

Crossing

Overshoot

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