www.SiliconStandard.com

4 of 5

SS7646

8/21/2004 Rev.2.01

FUNCTIONAL DESCRIPTION

OVERVIEW

The SS7646 is a 12-bit switched-capacitor SAR

Analog-to-Digital converter (ADC). The converter is

fabricated using a 0.6µm CMOS process and packaged

in the very small 16-pin SSOP package.

The typical operation of the SS7646 is shown in Figure

12. The SS7646 operates on a single supply

ranging from +2.2V to +5.5V. The SS7646

features an internal 2.5V reference and an external

clock. The reference voltage directly sets the input

range of the converter. The internal 2.5V reference can

be tu r n e d O N or O F F in d e p e n de n t l y of

the ADC.

The SS7646 contains six channel inputs, a serial

interface and low on-resistance switches for the touch

screen (see Block Diagram). The input to the

converter is selected via the six-channel multiplexer

as shown in Figure 5.

SERIAL INTERFACE

The typical operation of the SS7646 serial interface

(/CS, DCLK, DIN and DOUT) is shown in Figure 2.

The SS7646 communicates with microprocessors

or digital signal processors via a synchronous serial

interface. One complete conversion can be

accomplished with three serial communications for a

total 24 clock cycles on the DCLK input.

Operation of 24-Clocks

The operation is initiated by a falling signal on Chip

Select (/CS) input. After /CS falls, the SS7646 looks

for a start bit on the DIN input. The first eight clock

cycles are used to provide the control byte. At the end

of the operation the /CS pin should be brought high.

Bringing /CS high after the conversion also minimizes

supply current if DCLK is left running.

Bit 7 Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Start

A2

A1

A0 Mode1Mode0 PD1

PD0

Table I. Control Bits in the Control Byte

BIT

NAME

DESCRIPTION

7

Start

Start Bit.

6, 5, 4

A2, A1, A0

Input Channel Select Bits.

3, 2

Mode1,

Mode0

12-Bit / 8-Bit Resolution and

Int. Reference Configuration

Bits

1, 0

PD1, PD0

Power Down Control Bits

Table II. Description of the Control Bits

/CS

DCLK

X/Y SWITCH

DIN

BUSY

DOUT

18

1

18

START

A2

A1

A0

MODE0

MODE1

PD1 PD0

ON

Conversion

Acquire

Tri-State

Tri-State

Tri-State

Tri-State

11

(MSB)

(LSB)

0

8

1

Figure 2. Serial Interface of SS7646