ZADCS0882/0842/0822

8-Bit, 300ksps, ADC Family

Data Sheet

October 12, 2011

© 2011 Zentrum Mikroelektronik Dresden AG — Rev. 2.0

All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without

the prior written consent of the copyright owner. The information furnished in this publication is PRELIMINARY and subject to

changes without notice.

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Output Code Format

ZADCS08x2 family devices do all support unipolar and bipolar operation modes. The digital output code is

straight binary in unipolar mode. It ranges from 0x00 for an input voltage difference of 0V to 0xFF for an input

voltage difference of VREF (Full Scale = FS). The first code transition (0x00  0x01) occurs at a voltage

equivalent to ½ LSB, the last (0xFE  0xFF) at VREF-1.5 LSB. See also Figure 16 for details. In bipolar

mode a two’s complement coding is applied. Code transitions occur again halfway between successive

integer LSB values. The transfer function is shown in Figure 17.

Figure 16: Unipolar Transfer Function

Figure 17: Bipolar Transfer Function

2.5.

Power Dissipation

The ZADCS08x2 family offers three different ways to save operating current between conversions. Two

different software controlled power down modes can be activated to automatically shut-down the device after

completion of a conversion. They differ in the amount of circuitry that is powered down.

Software Power Down

Full Power Down Mode shuts down the entire analog part of the IC, reducing the static IDD of the device to

less than 0.5µA if no external clock is provided at SCLK. Fast Power Down mode is only useful with

ZADCS08x2V devices if the internal voltage reference is used. During Fast Power-Down the bandgap and the

VREFADJ output buffer are kept alive while all other internal analog circuitry is shut down. The benefit of Fast

Power Down mode is a shorter turn on time of the reference compared to Full Power-Down Mode. This is

basically due to the fact that the low pass which is formed at the VREFADJ output by the internal 20kΩ

resistor and the external buffer capacitor of 47nF is not discharged in Fast Power-Down Mode. The settling

time of the low pass at VREFADJ is about 6 ms to reach 8 bit accuracy. The Fast Power Down mode omits

this settling and reduces the turn on time to about 200µs. To wake up the IC out of either software power

down mode, it is sufficient to send a Start Bit while nCS is LOW. Since micro controllers can commonly

transfer full bytes per transaction only, a dummy conversion is usually carried out to wake the device.

In all application cases where an external reference voltage is supplied (basic ZADCS08x2 and ZADCS08x2V

with VREFADJ tied to VDD) there is no turn on time to be considered. The first conversion is already valid.

Fast Power-Down and Full Power-Down Mode do not show any difference in this configuration.

11 … 111

11 … 110

11 … 101

00 … 000

00 … 001

00 … 010

1 2 3

FS

0

Input Voltage (LSB)

FS-3/2 LSB

ZS = V(IN-)

)

1LSB =

256

(ZS)

Output Code

Output Code

ZS = V(IN-)

01 … 111

01 … 110

10 … 000

10 … 001

00 … 000

+FS

1LSB =

256

-FS

Input Voltage (LSB)

+FS-3/2 LSB

00 … 001

00 … 011

11 … 111

11 … 110

ZS

11 … 101