ADS5237 datasheet(22/29 Pages) TI

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DATA OUTPUT FORMAT (MSBI)

OUTPUT LOADING

OUTPUT ENABLE (OE)

SERIAL INTERFACE

OVER-RANGE INDICATOR (OVR)

ADS5237

SBAS420A – AUGUST 2007 – REVISED OCTOBER 2007

range. It changes to high if the applied signal

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

The ADS5237 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 ADS5237 operates with the SOB code

as its default setting. Forcing the MSBI pin high

enables 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 3.

data output lines be kept as low as possible,

preferably below 15pF. Higher capacitive loading

causes larger dynamic currents as the digital outputs

are changing. Such high current surges can feed

Digital outputs of the ADS5237 can be set to

back to the analog portion of the ADS5237 and

high-impedance

(3-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

disables 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 ADS5237 has a serial interface that can be used

Characteristics table to observe the specified 3-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 pulse results

condition

exists.

The

ADS5237

incorporates

in all internal registers resetting to the default value of

function that monitors the input voltage and detects

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

any such out-of-range condition. This operation

registers

may

the

non-default

state

functions for each of the two channels independently.

power-up. This condition may cause the device to

The current state can be read at the over-range

malfunction.

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

when the input voltage is within the defined input

Table 3. 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

D9............D0

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

1111 1111 11

0111 1111 11

+1/2 FS

1100 0000 00

0100 0000 00

Bipolar Zero (IN = IN = CMV)

1000 0000 00

0000 0000 00

–1/2 FS

0100 0000 00

1100 0000 00

–FS (IN = +1V, IN = +2V)

0000 0000 00

1000 0000 00

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