TC530 datasheet(14/22 Pages) MICROCHIP

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TC530/TC534

DS21433B-page 14

5.5

Load Value Write Cycle

Following the power-up reset pulse, the LOAD VALUE

(which sets the duration of AZ and INT) must next be

transmitted to the serial port. To accomplish this, the

processor monitors the state of EOC (which is available

as a hardware output or at DOUT). R/W is taken low to

initiate the write cycle only when EOC is low (during the

AZ phase). (Failure to observe EOC low may cause an

offset voltage to be developed across CINT, resulting in

erroneous readings). The 8-bit LOAD VALUE data on

DIN is clockedinbyDCLK. The processor then termi-

nates the write cycle by taking R/W high. (Data is

transferred from the serial input shift register to the time

base counter on the rising edge of R/W and data

conversion is initiated). See Figure 5-2.

5.6

Input Multiplexer (TC534 Only)

A 4-input, differential multiplexer is included in the

TC534. The states of channel address lines A0 and A1

determine which differential VIN pair is routed to the

converter input. A0 is the least significant address bit

(i.e., channel 1 is selected when A0 = 0 and A1 = 0).

The multiplexer is designed to be operated in a differ-

ential mode. For single-ended inputs, the CHx- input for

the channel under selection must be connected to the

ground reference associated with the input signal.

FIGURE 5-2:

TC530/TC534 INITIALIZATION AND LOAD VALUE WRITE CYCLE

5.7

DC/DC Converter

An on-board, TC7660H-type charge pump supplies

negative bias to the converter circuitry, as well as to

external devices. The charge pump develops a nega-

tive output voltage by moving charge from the power

supply to the reservoir capacitor at VSS by way of the

commutating capacitor connected to the CAP+ and

CAP- inputs.

The charge pump clock operates at a typical frequency

of 100kHz. If lower quiescent current is desired, the

charge pump clock can be slowed by connecting an

external capacitor from the OSC pin to VDD. Reference

typical characteristics curves.

EOC

R/W

RESET

DCLK

DIN

1001111

LOAD VALUE

MSB

LSB

INT

DINT

AZ…

Conversion

Phase

Timing

Status

Converter held in AZ

state due to RESET = 1

Write LOAD VALUE to Serial Port

Power-up RESET

Undefined

Converter in Normal Service

R/W brought LOW during AZ

for serial port write cycle

R/W = HIGH strobes

LOAD VALUE into

timebase and starts

conversion

Continuous Conversions

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