ZN426E8 View Datasheet(PDF) - Zarlink Semiconductor Inc

Part Name

Description

Manufacturer

ZN426E8

8-BIT D-A CONVERTER

Zarlink Semiconductor Inc 

The converter is of the voltage switching type and uses

an R-2R resistor ladder network as shown in Fig.3.

Each 2R element is connected either to 0V or VREF by

transistor switches specially designed for low offset voltage

(typically 1mV).

ZN426

Binary weighted voltages are produced at the output of

the R-2R ladder, the value depending on the digital number

applied to the bit inputs.

APPLICATIONS

Fig.3 The R-2R ladder network

8-bit D-A Converter

The ZN426 gives an analog voltage output directly from

pin 4 therefore the usual current to voltage converting

amplifier is not required. The output voltage drift, due to the

temperature coefficient of the analog output resistance RO,

will be less than 0.004% per °C (or 1LSB/100°C) if RL is

chosen to be ≥ 650kΩ.

In order to remove the offset voltage and to calibrate the

converter a buffer amplifier is necessary. Fig.4 shows a

typical scheme using the internal reference voltage. To

minimise temperature drift in this and similar applications the

source resistance to the inverting input of the operational

amplifier should be approximately 6kΩ. The calibration

procedure is as follows:

i. Set all bits to OFF (low) and adjust R2 until

VOUT = 0.000V.

ii. Set all bits to ON (high) and adjust R1 until

VOUT = Normal full-scale reading - 1LSB

iii. Repeat i. and ii.

e.g. Set F.S.R. to + 3.840V - 1LSB

=3.825V

(1LSB

=

3.84

256

=15.0mV)

Fig.4 8-bit D-A converter

3

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