TC500ACOG datasheet(14/34 Pages) MICROCHIP

14 / 34 page

TC500/A/510/514

DS21428D-page 14

FIGURE 8-1:

Noise Threshold.

8.6

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

absolutely critical that this phase be terminated

immediately so that overshoot is not allowed to occur in

the opposite 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 8-2).

FIGURE 8-2:

Overshoot.

8.7

Using the TC510/TC514

8.7.1

NEGATIVE SUPPLY VOLTAGE

CONVERTER (TC510, TC514)

A capacitive charge pump is employed to invert the

voltage 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 100 kHz 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 2.0 “Typical Performance

Curves”.

8.7.2

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

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

Low VREF

Normal VREF

High VREF

NTH

30V

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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