Datasheet

ADC108S052
SNAS337G –SEPTEMBER 2005–REVISED MARCH 2013 www.ti.com
SERIAL INTERFACE
An operational timing diagram and a serial interface timing diagram for the ADC108S052 are shown in The
Timing Diagrams section. CS, chip select, initiates conversions and frames the serial data transfers. SCLK (serial
clock) controls both the conversion process and the timing of serial data. DOUT is the serial data output pin,
where a conversion result is sent as a serial data stream, MSB first. Data to be written to the ADC108S052's
Control Register is placed on DIN, the serial data input pin. New data is written to DIN with each conversion.
A serial frame is initiated on the falling edge of CS and ends on the rising edge of CS. Each frame must contain
an integer multiple of 16 rising SCLK edges. The ADC's DOUT pin is in a high impedance state when CS is high
and is active when CS is low. Thus, CS acts as an output enable. Similarly, SCLK is internally gated off when CS
is brought high.
During the first 3 cycles of SCLK, the ADC is in the track mode, acquiring the input voltage. For the next 13
SCLK cycles the conversion is accomplished and the data is clocked out. SCLK falling edges 1 through 4 clock
out leading zeros, falling edges 5 through 14 clock out the conversion result, MSB first, and falling edges 15 and
16 clock out trailing zeros. If there is more than one conversion in a frame (continuous conversion mode), the
ADC will re-enter the track mode on the falling edge of SCLK after the N*16th rising edge of SCLK and re-enter
the hold/convert mode on the N*16+4th falling edge of SCLK. "N" is an integer value.
The ADC108S052 enters track mode under three different conditions. In Figure 2, CS goes low with SCLK high
and the ADC enters track mode on the first falling edge of SCLK. In the second condition, CS goes low with
SCLK low. Under this condition, the ADC automatically enters track mode and the falling edge of CS is seen as
the first falling edge of SCLK. In the third condition, CS and SCLK go low simultaneously and the ADC enters
track mode. While there is no timing restriction with respect to the rising edges of CS and SCLK, see Figure 4 for
setup and hold time requirements for the falling edge of CS with respect to the rising edge of SCLK.
While a conversion is in progress, the address of the next input for conversion is clocked into a control register
through the DIN pin on the first 8 rising edges of SCLK after the fall of CS. See Table 1, Table 2, and Table 3.
There is no need to incorporate a power-up delay or dummy conversion as the ADC108S052 is able to acquire
the input signal to full resolution in the first conversion immediately following power-up. The first conversion result
after power-up will be that of IN0.
Table 1. Control Register Bits
Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
DONTC DONTC ADD2 ADD1 ADD0 DONTC DONTC DONTC
Table 2. Control Register Bit Descriptions
Bit #: Symbol: Description
7, 6, 2, 1, 0 DONTC Don't care. The values of these bits do not affect the device.
5 ADD2 These three bits determine which input channel will be sampled and converted at the next
conversion cycle. The mapping between codes and channels is shown in Table 3.
4 ADD1
3 ADD0
Table 3. Input Channel Selection
ADD2 ADD1 ADD0 Input Channel
0 0 0 IN0 (Default)
0 0 1 IN1
0 1 0 IN2
0 1 1 IN3
1 0 0 IN4
1 0 1 IN5
1 1 0 IN6
1 1 1 IN7
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