ICM7561/7541/7521

Rev. A6

ICmic reserves the right to change specifications without prior notice

7

Power-Down Mode

The DACs have three Software-Selectable Power-Down

Output Impedances (1 K Ohm, 100 K Ohm and Hi-Z) as

additional safety feature for applications that drive

transducers or valves. The power down (or wake up

command) can be done by loading the control word with

1111 (C3 to C0). In power down mode, the selection of the

output impedance of the DAC is controlled by the last two

bits (D0 and D1 for the ICM7561, or A0 and A1 for the

ICM7541/7521). See Table 1 and Table 2 for details of

operation of this function.

Power-On Reset

There is a power-on reset on board that will clear the

contents of all the latches to all 0s on power-up and the

DAC voltage output will go to ground.

APPLICATIONS INFORMATION

Power Supply Bypassing and Layout Considerations

As in any precision circuit, careful consideration has to be

given to layout of the supply and ground. The return path

from the GND to the supply ground should be short with

low impedance. Using a ground plane would be ideal. The

supply should have some bypassing on it. A 10

F

tantalum capacitor in parallel with a 0.1 F ceramic with a

low ESR can be used. Ideally these would be placed as

close as possible to the device. Avoid crossing digital and

analog signals, specially the reference, or running them

close to each other.

Output Swing Limitations

However, offset and gain error limit this ability. Figure 4

illustrates how a negative offset error will affect the output.

The output will limit close to ground since this is single

supply part, resulting in a dead-band area. As a larger

input is loaded into the DAC the output will eventually rise

above ground. This is why the linearity is specified for a

starting code greater than zero.

Figure 5 illustrates how a gain error or positive offset error

error or positive offset will cause the output to be limited to

the positive supply voltage resulting in a dead-band of

codes close to full-scale.

DEADBAND

NEGATIVE

OFFSET

Figure 4. Effect of Negative Offset

DEADBAND

POSITIVE

OFFSET

OFFSET AND

GAIN ERROR

Figure 5. Effect of Gain Error and Positive Offset