ALD1801A/ALD1801B

Advanced Linear Devices

5

ALD1801

APPLICATIONS NOTES:

The ALD1801 is an 8 bit multiplying D/A converter. It has

been designed to operate with standard single or split

power supplies of 5V or

±5V. Functionality extends down

to 3V or

±1.5V power supply, making it ideal for lithium

battery or rechargeable battery operated systems where

power efficiency and performance are important design

parameters.

The ALD1801 features ultra low quiescent bias current

which depends on the operating current in the internal

current steering circuit. A high gain internal operational

amplifier is fully compensated for stable operation without

any need for external capacitor compensation.

The

operational amplifier is placed in a negative feedback loop

to generate the reference current for ratio matched

transistors.

It is trimmed to provide nonlinearity as

specified. In some applications this feature can be used

along with the multiplying nature of the ALD1801 to obtain

9 or 10 bit digital to analog conversion with external

switches.

The ALD1801 is a multiplying D/A converter in which the

output is a current that is a function of an 8 bit digital input

word multiplied by the reference current. The reference

current may be a fixed reference current or a varying input

current. If a fixed reference voltage or a varying low

impedance voltage output source is used, a fixed value

resistor (referred to as RREF) can be used to convert

the voltage into a reference current for most applications.

either connecting a potentiometer in series with a fixed

resistor or by substituting the fixed resistor with a multi-

turn potentiometer. The recommended nominal value of

The ALD1801 can operate from single power supply or

dual supplies up to

±6.6V. Symmetrical supplies are not

required in the case of dual supply operation. However,

V- voltage.

Due to the internal operational amplifier

current determined by: Input reference current

The ALD1801 is fabricated in CMOS technology and

provides direct logic interface to all CMOS logic families

including logic levels of the CD4000 and 74C logic families

operating at logic voltage levels other than 5V. It is

primarily designed to operate in a power supply

environment where interface takes place between digital

logic circuitry and analog circuitry. Both types of circuitry

operate with the same power supplies.

The nonlinearity and monotonicity of the ALD1801 applies

over the full rated operating temperature. The device has

been developed with minimal temperature drift, typically

at

±10ppm/°C. A single array of matched and tracked

resistor networks of nominal 50K

Ω can be used for all the

resistors required for the D/A converter. As an example,

in parallel where output resistors are set at 50K

Ω.

Due to the very low quiescent and reference currents

used, layout of the circuit board to minimize any parasitic

capacitance is important in getting high frequency

operation, as the settling time is due in large part to the

output currents charging and

discharging the node

capacitances at the output. As the internal bias current

levels is adaptive to the reference current, the switching

speed of the device depends on the reference current

selected. Characterization of the settling time has been

performed at full scale current set at 100

µA and device

operation at single 5V supply. Faster operation can be

obtained by using short leads, minimizing output

capacitance, load resistor values, and by adequate bypass

capacitors placed on the board at the supply and reference

nodes.

of the outputs is not used, then it must be connected to

maintain a constant value. Due to internal leakage currents

50

µA to 100µA be used so that 1/2LSB bit current is set at

as high a level as possible. The temperature coefficient