ADS5231IPAG datasheet(21/32 Pages) TI2

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DATA OUTPUT FORMAT (MSBI)

OUTPUT LOADING

OUTPUT ENABLE (OE)

SERIAL INTERFACE

OVER-RANGE INDICATOR (OVR)

ADS5231

SBAS295A – JULY 2004 – REVISED JANUARY 2007

range. It will change to high if the applied signal

exceeds the full-scale range. It should be noted that

The ADS5231 makes two data output formats

each of the OVR outputs is updated along with the

available: the Straight Offset Binary code (SOB) or

data output corresponding to the particular sampled

the Binary Two's Complement code (BTC). The

analog input voltage. Therefore, the OVR state is

selection of the output coding is controlled by the

subject to the same pipeline delay as the digital data

MSBI (pin 41). Because the MSBI pin has an internal

(six clock cycles).

pull-down, the ADS5231 will operate with the SOB

code as its default setting. Forcing the MSBI pin high

will enable BTC coding. The two code structures are

identical, with the exception that the MSB is inverted

It is recommended that the capacitive loading on the

for BTC format; as shown in Table 1.

data output lines be kept as low as possible,

preferably below 15pF. Higher capacitive loading will

cause larger dynamic currents as the digital outputs

are changing. Such high current surges can feed

Digital outputs of the ADS5231 can be set to

back to the analog portion of the ADS5231 and

high-impedance (tri-state), exercising the output

adversely affect device performance. If necessary,

enable pins, OEA (pin 42), and OEB (pin 6). Internal

external buffers or latches close to the converter

pull-downs configure the output in enable mode for

output pins may be used to minimize the capacitive

normal operation. Applying a logic high voltage will

disable the outputs. Note that the OE-function is not

designed to be operated dynamically (that is, as a

fast multiplexer) because it may lead to corrupt

conversion

results.

Refer

the

Electrical

The ADS5231 has a serial interface that can be used

Characteristics table to observe the specified tri-state

to program internal registers. The serial interface is

enable and disable times.

disabled if SEL is connected to 0.

When the serial interface is to be enabled, SEL

serves the function of a RESET signal. After the

If the analog input voltage exceeds the full-scale

supplies have stabilized, it is necessary to give the

range set by the reference voltages, an over-range

device a low-going pulse on SEL. This results in all

condition

exists.

The

ADS5231

incorporates

internal registers resetting to their default value of 0

function that monitors the input voltage and detects

(inactive). Without a reset, it is possible that registers

any such out-of-range condition. This operation

may be in their non-default state on power-up. This

functions for each of the two channels independently.

condition may cause the device to malfunction.

The current state can be read at the over-range

indicator pins (pins 9 and 39). This output is low

when the input voltage is within the defined input

Table 1. Coding Table for Differential Input Configuration and 2VPP Full-Scale Input Range

STRAIGHT OFFSET BINARY (SOB; MSBI = 0)

BINARY TWO'S COMPLEMENT (BTC; MSBI = 1)

DIFFERENTIAL INPUT

D11............D0

+FS (IN = +2V, IN = +1V)

1111 1111 1111

0111 1111 1111

+1/2 FS

1100 0000 0000

0100 0000 0000

Bipolar Zero (IN = IN = CMV)

1000 0000 0000

0000 0000 0000

–1/2 FS

0100 0000 0000

1100 0000 0000

–FS (IN = +1V, IN = +2V)

0000 0000 0000

1000 0000 0000

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