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AS1543/44

Data Sheet - D e t a i l e d D e s c r i p t i o n

8 Detailed Description

The AS1543/44 is a fast, 8/4-channel, 12-bit, single-supply, A/D converter, which can be operated from a 2.7 to 5.25V

supply. The AS1543/44 is capable of throughput rates of up to 1Msps when provided with a 20MHz clock. The

AS1543/44 features on-chip track/hold, A/D converter, sequencer and a serial interface in a TQFN(4x4)-20 package.

The AS1543/44 has 8/4 single-ended or 4/2 fully-differential input channels with a channel sequencer, allowing the

selection of the sequence of channels the ADC can cycle through on (each consecutive CSN falling edge). The serial

clock input accesses data from the AS1543/44, controls the transfer of data written to the ADC, and provides the clock

source for the successive-approximation A/D converter.

to 5.25V supply.

The AS1543/44 provides flexible power management options (see bits PM1, PM0 (page 14) of the control register) for

the best power performance for a given throughput rate.

Converter Operation

The AS1543/44 is a 12-bit successive approximation analog-to-digital converter based around a capacitive DAC. The

Figure 21 and Figure 22 show simplified diagrams of the ADC operation. The ADC circuitry is made up of control logic,

SAR, and a capacitive DAC, which are used to redistribute fixed amounts of charge with the capacitive DAC to bring

the comparator back into a balanced condition. Figure 21 shows the ADC during its acquisition phase. Sample switch

Figure 21. Data Acquisition

When a conversion is started (see Figure 22), sample switch and input switch opens causing the comparator to

become unbalanced. The control logic and the capacitive DAC are used to redistribute fixed amounts of charge from

the sampling capacitor to bring the comparator back into a balanced condition. When the comparator is re-balanced,

the conversion is complete. Control logic generates the ADC output code.

See page 16 for the ADC transfer functions.

+

–

+

Comparator

11pF

13pF

–

CH0

CH1

CH2

CH3

CH4

CH5

CH7

AGND

REFIN

AIN+

11pF

+

13pF

–

Sample

Switch

Analog Input

Multiplexer

AIN-

Input

Switch

Input

Switch

AGND

S&H and capacitive DAC

Control

Logic