Datasheet

1 4

8 12 1615

A3 A0 D11 D0 A3

B15

B0 B15

SCLK

DOUT

DIN

ADC Phase

(Internal)

AL_PD

(Programmed as

an alarm

Acquisition n+1Conversion n Conversion n+1

Sample n

Sample n + 1

Conversion Result For Sample n

Ch Address

ADS8634

ADS8638

SBAS541A –MAY 2011– REVISED AUGUST 2011

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DEVICE OPERATION

The ADS8634/8 are 12-bit, 4-/8-channel devices. Each frame begins with a CS falling edge. The ADS8634/8

sample the input signal from the selected channel on the CS falling edge and initiate conversion. SCLK is used

for conversion and data are output on the DOUT line while conversion is in process. The 16-bit data word

contains a 4-bit channel address followed by the 12-bit conversion result in MSB-first format. The MSB of the

4-bit channel address is output on the CS falling edge; the remaining address bits are clocked out serially for

three SCLK falling edges. The MSB of the 12-bit conversion result is output on the fourth SCLK falling edge.

Afterwards, the next lower data bits are ouput serially on every subsequen SCLK falling edge. Each data bit can

be read (latched) immediately on the next SCLK falling edge from the SCLK falling edge on which the respective

data bits are output. For example, if the MSB of a 12-bit data word is output on the fourth SCLK falling edge then

the same word can be latched on the fifth SCLK falling edge. Refer to the Hold time, SCLK falling to DOUT valid,

and Delay time, SCLK falling to DOUT parameters in the Timing Requirements section.

The 16-bit word is read on the DIN pin while the data are output on the DOUT pin. DIN data are latched on every

SCLK rising edge, starting with the first clock, as shown in Figure 85.

Figure 85. ADS8634/8 Operation

Device configuration and operation mode are controlled through register settings. It is recommended to write to

the configuration registers after powering on the device. The configuration information is retained until the

devices are powered off or reset. Note that powering down the device with either the AL_PD pin or a register

write does not erase the device configuration.

The ADS8634/8 feature an AL_PD pin that functions as a alarm output/power-down pin. The pin can be

programmed as an alarm output (AL) or it can be programmed as a power-down control pin (PD). When AL_PD

is programmed as an alarm output, it is refreshed on every 16th SCLK rising edge.

Product Folder Link(s): ADS8634 ADS8638