16-Bit DACs with 16-Channel

Sample-and-Hold Outputs

10

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The resistive voltage-divider formed by the output resis-

Ground Sense

The MAX5621/MAX5622/MAX5623 include a ground-

sense input (GS), which allows the output voltages to

be referenced to a remote ground. The voltage at GS is

added to the output voltage with unity gain. Note that

the resulting output voltage must be within the valid

output voltage range set by the power supplies.

Output Clamp

The MAX5621/MAX5622/MAX5623 clamp the output

between two externally applied voltages. Internal

diodes at each channel restrict the output voltage to:

The clamping diodes allow the MAX5621/MAX5622/

MAX5623 to drive devices with restricted input ranges.

The diodes also allow the outputs to be clamped during

power-up or fault conditions. To disable output clamping,

voltages beyond the maximum output voltage range.

Serial Interface

The MAX5621/MAX5622/MAX5623 are controlled by an

SPI/QSPI/MICROWIRE-compatible 3-wire interface.

Serial data is clocked into the 24-bit shift register in an

MSB-first format, with the 16-bit DAC data preceding

the 4-bit SRAM address, required zero bit, 2-bit control,

and a fill 0 (Figure 4). The input word is framed by CS.

The first rising edge of SCLK after CS goes low clocks

in the MSB of the input word.

When each serial word is complete, the value is stored

in the SRAM at the address indicated and the control

bits are saved. Note that data can be corrupted if CS is

not held low for an integer multiple of 24 bits.

All of the digital inputs include Schmitt-trigger buffers to

accept slow-transition interfaces. Their switching thresh-

old is compatible with TTL and most CMOS logic levels.

Serial Input Data Format and

Control Codes

The 24-bit serial input format, shown in Figure 4, compris-

es 16 data bits (D15–D0), 4 address bits (A3–A0), 1

required zero bit after the address bits, 2 control bits (C1,

C0), and a fill zero. The address code selects the output

channel as shown in Table 2. The control code configures

the device as follows:

1) If C1 = 1, immediate update mode is selected.

If C1 = 0, burst mode is selected.

2) If C0 = 0, the internal sequencer clock is selected. If

C0 = 1, the external sequencer clock is selected.

This must be repeated with each data word to main-

tain external input.

The operating modes can also be selected externally

through CLKSEL and IMMED. In the case where the

control bit in the serial word and the external signal

conflict, the signal that is a logic 1 is dominant.

VV

V

V

V

CH

OUT

CL

+

−

07

07

..

_

Scaling Factor

R

RR

V

V

scaling factor

L

LO

OUT

CHOLD

=

+

=×

_

DATA

ADDRESS

CONTROL

D15 D14 D13 D12 D11 D10 D09 D08 D07 D06 D05 D04 D03 D02 D01

D0

A3

A2

A1

A0

0

C1

C0

0

MSB

LSB

Figure 4. Input Word Sequence

A3

A2

A1

A0

OUTPUT

0

0

0

0

OUT0 selected

0

0

0

1

OUT1 selected

0

0

1

0

OUT2 selected

0

0

1

1

OUT3 selected

0

1

0

0

OUT4 selected

0

1

0

1

OUT5 selected

0

1

1

0

OUT6 selected

0

1

1

1

OUT7 selected

1

0

0

0

OUT8 selected

1

0

0

1

OUT9 selected

1

0

1

0

OUT10 selected

1

0

1

1

OUT11 selected

1

1

0

0

OUT12 selected

1

1

0

1

OUT13 selected

1

1

1

0

OUT14 selected

1

1

1

1

OUT15 selected

Table 2. Channel/Output Selection