Datasheet

30 pF

3 pF

Conversion Phase - Switch Open

Track Phase - Switch Closed

ADC124S021

www.ti.com

SNAS277F –MARCH 2005–REVISED MARCH 2013

The capacitor C1 in Figure 5 has a typical value of 3 pF, and is mainly the package pin capacitance. Resistor R1

is the on resistance of the multiplexer and track / hold switch, and is typically 500 ohms. Capacitor C2 is the

ADC124S021 sampling capacitor, and is typically 30 pF. The ADC124S021 will deliver best performance when

driven by a low-impedance source to eliminate distortion caused by the charging of the sampling capacitance.

This is especially important when using the ADC124S021 to sample AC signals. Also important when sampling

dynamic signals is a band-pass or low-pass filter to reduce harmonics and noise, improving dynamic

performance.

Figure 50. Equivalent Input Circuit

6.0 DIGITAL INPUTS AND OUTPUTS

The ADC124S021's digital output DOUT is limited by, and cannot exceed, the supply voltage, V

. The digital

input pins are not prone to latch-up and, and although not recommended, SCLK, CS and DIN may be asserted

before V

without any latch-up risk.

7.0 POWER SUPPLY CONSIDERATIONS

The ADC124S021 is fully powered-up whenever CS is low, and fully powered-down whenever CS is high, with

one exception: the ADC124S021 automatically enters power-down mode between the 16th falling edge of a

conversion and the 1st falling edge of the subsequent conversion (see Timing Diagramss).

The ADC124S021 can perform multiple conversions back to back; each conversion requires 16 SCLK cycles.

The ADC124S021 will perform conversions continuously as long as CS is held low.

The user may trade off throughput for power consumption by simply performing fewer conversions per unit time.

Figure 45 in Typical Performance Characteristics shows the typical power consumption of the ADC124S021

versus throughput. To calculate the power consumption, simply multiply the fraction of time spent in the normal

mode by the normal mode power consumption , and add the fraction of time spent in shutdown mode multiplied

by the shutdown mode power dissipation.

7.1 Power Management

When the ADC124S021 is operated continuously in normal mode, the maximum throughput is f

SCLK

/16.

Throughput may be traded for power consumption by running f

SCLK

at its maximum 3.2 MHz and performing

fewer conversions per unit time, putting the ADC124S021 into shutdown mode between conversions. Figure 45

is shown in Typical Performance Characteristics. To calculate the power consumption for a given throughput,

multiply the fraction of time spent in the normal mode by the normal mode power consumption and add the

fraction of time spent in shutdown mode multiplied by the shutdown mode power consumption. Generally, the

user will put the part into normal mode and then put the part back into shutdown mode. Note that Figure 45 is

nearly linear. This is because the power consumption in the shutdown mode is so small that it can be ignored for

all practical purposes.

Product Folder Links: ADC124S021