Dual, Serial-Input,

Voltage-Output, 12-Bit MDAC

_______________________________________________________________________________________

9

Figure 4. Connections for Microwire

SCLK

DIN

DOUT

CS

LDAC

SK

SO

SI

I/O

I/O

MAX532

MICROWIRE

PORT

5V

1k

THE DOUT-SI CONNECTION IS NOT REQUIRED FOR WRITING TO THE

MAX532, BUT MAY BE USED FOR READ-BACK PURPOSES.

Figure 5. Connections for SPI

DOUT

DIN

SCLK

CS

LDAC

MISO

MOSI

SCK

I/O

I/O

MAX532

SPI

PORT

SS

5V

CPOL = 0,CPHA = 0

1k

THE DOUT-MISO CONNECTION IS NOT REQUIRED FOR WRITING TO THE MAX532,

BUT MAY BE USED FOR READ-BACK PURPOSES.

_______________Detailed Description

Digital Interface

The MAX532 is Microwire and SPI compatible (Figures

4 and 5). Both DACs are programmed by writing three

8-bit words (see Figures 2 and 3, and the

Functional

Diagram). Serial data is clocked into the data registers

MSB first, with DACB information preceding DACA

information. Data is clocked in on the rising edge of

SCLK while

CS is low. With CS high, data can not be

clocked into DIN, and DOUT is high impedance. SCLK

can be driven at rates up to 6.25MHz.

The MAX532 uses either a 3-wire or a 4-wire serial

interface. Three wires may be used (

CS, DIN, SCLK)

by tying

LDAC low. With LDAC low, the DACs are

updated simultaneously when

CS goes high (see

Figure 2 and the

Functional Diagram). The 3-wire inter-

face may be used if the MAX532 is used alone, or if two

or more MAX532s are cascaded (DOUT of one device

tied to DIN of the other) (Figure 6).

The 4-wire interface (

LDAC, CS, DIN, SCLK) is required

if several serial devices are tied to the same data line,

and it is desirable to update them simultaneously

(Figure 7). With the 4-wire interface, the DACs are

updated when

LDAC goes low (see Figure 3 and the

Functional Diagram).

A serial output, DOUT, allows cascading of two or more

MAX532s and allows read-back of the data written to

the device’s 24-bit shift register. The data at DOUT is

delayed 24 clock cycles from the data at DIN (see

Figures 2 and 3, and the

Functional Diagram). DOUT

is an open-drain N-channel MOSFET that requires an

external pull-up resistor (typically 1k

Ω if pulled up to

+5V, and 3k

Ω if pulled up to +12V or +15V). Logic lev-

els are guaranteed with sink currents up to 5mA (see

Electrical Characteristics). Output data changes on the

falling edge of SCLK when

CS is low. If CS is high,

DOUT is three-state (high-impedance).

Daisy-Chaining Devices

Any number of MAX532s can be daisy-chained by con-

necting the DOUT pin of one device (with a pull-up

resistor) to the DIN pin of the following device in the

chain (Figure 6).

spent charging the DOUT capacitance with the external

given in Table 1.