MAX552 datasheet(10/12 Pages) MAXIM

10 / 12 page

ture range, then low-tempco (<300ppm/°C) resistors

should be used.

__________Applications Information

Output Amplifier

For best linearity, terminate OUT and GND at exactly

0V. In most applications, OUT is connected to an

inverting op amp’s summing junction. The amplifier’s

input offset voltage can degrade the DAC’s linearity by

causing OUT to be terminated to a nonzero voltage.

The resulting error is:

Error Voltage = VOS (1 + RFB / RO)

where VOS = is the op amp’s offset and RO is the

DAC’s output resistance, which is code dependent.

The maximum error voltage (Ro = RFB) is 2VOS; the

minimum error voltage (RO= ∞) is VOS. To minimize this

error, use a low-offset amplifier such as the MAX4166

(unipolar output) or the MAX427 (bipolar output).

Otherwise, the amplifier offset must be trimmed to zero.

A good guide rule is that VOS should be no more than

1/10LSB.

The output amplifier’s input bias current (IB) can also

limit performance, since IB x RFB generates an offset

error. Choose an op amp with an IB much less than

(e.g., one-tenth) the DAC’s 1LSB output current (typi-

cally 111nA when VREF = 5V, and 55.5nA when VREF =

2.5V). Offset and linearity can also be impaired if the

output amplifier’s noninverting input is grounded

through a bias-current compensation resistor. This

resistor adds to the offset at this pin and thus should

not be used. For best performance, connect the nonin-

verting input directly to ground.

In static or DC applications, the output amplifier’s char-

acteristics are not critical. In higher speed applications

in which either the reference input is an AC signal or

the DAC output must quickly settle to a new pro-

grammed value, the output op amp’s AC parameters

must be considered.

A compensation capacitor, C1, may be required when

the DAC is used with a high-speed output amplifier.

The purpose of the capacitor is to cancel the pole

formed by the DAC output capacitance, COUT, and the

internal feedback resistor, RFB. Its value depends on

the type of op amp used but typically ranges from 14pF

to 30pF. Too small a value causes output ringing, while

excess capacitance overdamps the output. C1’s size

can be minimized and the output voltage settling time

improved by keeping the circuit-board trace short and

stray capacitance at OUT as low as possible.

Single-Supply Operation

Reference Voltage

The MAX551/MAX552 are true 4-quadrant DACs, mak-

ing them ideal for multiplying applications. The refer-

ence input accepts both AC and DC signals within a

voltage range of ±6V. The R-2R ladder is implemented

with thin-film resistors, enabling the use of unipolar or

bipolar reference voltages with only a single power

supply for the DAC. The voltage at the VREF input sets

the DAC’s full-scale output voltage.

If the reference is too noisy, it should be bypassed to

GND (AGND on the 10-pin µMAX package) with a

0.1µF ceramic capacitor located as close to the REF

pin as possible.

Voltage Mode (MAX551)

The MAX551 can be conveniently used in voltage

mode, single-supply operation with OUT biased at any

voltage between GND and VDD. OUT must not be

allowed to go 0.3V lower than GND or 0.3V higher than

VDD. Otherwise, internal diodes will turn on, causing a

high current flow that could damage the device.

+3V/+5V, 12-Bit, Serial, Multiplying DACs

in 10-Pin µMAX Package

______________________________________________________________________________________

+5V

REF

GND

DIN

OUT

VDD

SCLK

LOAD

REFERENCE

VOLTAGE

VOUT

MAX551

Figure 5. Single-Supply, Voltage Mode Operation

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