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AS1504, AS1505

Data Sheet

DAC Outputs

DAC Outputs

The 8 DAC outputs (OUT1:OUT8) present a constant output resistance of approximately 5k

Ω independent of code set-

Note:

During shutdown the OUTx outputs are open-circuited.

Serial Interface

The AS1504/AS1505 are controlled via a standard three-wire serial input. The three input pins are CLK, CSN and SDI.

The positive-edge sensitive CLK input requires a clean transition to avoid clocking spurious data into the serial input

register (standard logic families are perfectly adequate). If mechanical switches are used for device evaluation, they

should be de-bounced by a flip-flop or other suitable means.

Figure 11 on page 8 shows details of the internal digital circuitry. When CSN is pulled low, the clock can load data into

the serial register on each positive clock edge (see Table 7).

The data setup and data hold times in Table 3 on page 3 determine the valid data time requirements. The last 11 bits of

the data word entered into the serial register are held when CSN goes high. When CSN goes high it gates the address

decoder which enables one of the eight positive-edge triggered DAC registers (see Figure 16).

Figure 16. Equivalent Control Logic

The target DAC register is loaded with the last eight bits of the serial data word completing one DAC update. To

change all eight output settings, eight separate 11-bit data words must be clocked in to the device.

Note:

All digital inputs (CSN, SDI, RSN, SHDNN, and CLK) are protected with the series input resistor and parallel

zener diode ESD circuit illustrated in Figure 17.

Figure 17. Equivalent ESD Protection Circuit

Note:

the device is operated from a 3V supply.

Table 7. Function of Pins CSN and CLK

CSN

CLK

Register Activity

1

X

No effect.

0

Positive Edge Shifts serial register one bit loading the next bit in from the SDI pin.

Positive Edge

X

Data is transferred from the serial register to the decoded DAC register (see Figure

16).

Address

Decode

DAC1

Serial

Register

DAC2

DAC8

SDI

CLK

CSN

AS1504/

AS1505

Logic

50

Ω