+5V/+3V, 13-Bit, Serial, Force/Sense DACs

with 10ppm/°C Internal Reference

10

______________________________________________________________________________________

_______________Detailed Description

The MAX5132/MAX5133 13-bit, force/sense DACs are

easily configured with a 3-wire serial interface. They

include a 16-bit data-in/data-out shift register and have a

double-buffered digital input consisting of an input regis-

ter and a DAC register. In addition, these devices

employ precision bandgap references, as well as an out-

put amplifier with accessible feedback and output pins

that can be used for setting the gain externally (Figure 1)

or for forcing and sensing applications. These DACs

are designed with an inverted R-2R ladder network

(Figure 2) that produces a weighted voltage proportion-

al to the digital input code.

Internal Reference

Both devices use an on-board precision bandgap ref-

erence with a low temperature coefficient of only

10ppm/°C (max) to generate an output voltage of +2.5V

(MAX5132) or +1.25V (MAX5133). The REF pin can

source up to 100µA and may become unstable with

capacitive loads exceeding 100pF. REFADJ can be

used for minor adjustments to the reference voltage.

The circuits in Figures 3a and 3b achieve a nominal ref-

erence adjustment range of ±1%. Connect a 33nF

capacitor from REFADJ to AGND to establish low-noise

MAX5132

MAX5133

SR

CONTROL

16-BIT

SHIFT REGISTER

DECODE

CONTROL

INPUT

REGISTER

BANDGAP

REFERENCE

REFERENCE

BUFFER

DAC

REGISTER

DAC

2X

(X1)

DOUT

UPO

OUT

FB

13

4k

1.25V

AGND DGND

DIN SCLK

CS

2.5V (1.25V)

LOGIC

OUTPUT

CLR

PDL

PD

RSTVAL

REFADJ

( ) FOR MAX5133 ONLY.

REF

Figure 1. Simplified Functional Diagram

OUT

FB

SHOWN FOR ALL 1s ON DAC

D0

D10

D11

D12

*INTERNAL REFERENCE: 2.5V (MAX5132),

1.25V (MAX5133); OR EXTERNAL REFERENCE

2R

2R

2R

2R

2R

RR

R

REF*

AGND

Figure 2. Simplified Inverted R-2R DAC Structure