LTC1661CMS8 データシートの表示（PDF） - Linear Technology

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LTC1661CMS8

Micropower Dual 10-Bit DAC in MSOP

Linear Technology 

LTC1661

OPERATION

Voltage Outputs

Each of the rail-to-rail output amplifiers contained in the

LTC1661 can typically source or sink up to 5mA (VCC = 5V).

The outputs swing to within a few millivolts of either supply

when unloaded and have an equivalent output resistance of

85Ω (typical) when driving a load to the rails. The output

amplifiers are stable driving capacitive loads up to 1000pF.

A small resistor placed in series with the output can be

used to achieve stability for any load capacitance. A 1µF

load can be successfully driven by inserting a 20Ω resis-

tor in series with the VOUT pin. A 2.2µF load needs only a

10Ω resistor, and a 10µF electrolytic capacitor can be used

without any resistor (the equivalent series resistance of the

capacitor itself provides the required small resistance). In

any of these cases, larger values of resistance, capacitance

or both may be substituted for the values given.

Rail-to-Rail Output Considerations

In any rail-to-rail DAC, the output swing is limited to volt-

ages within the supply range.

If the DAC offset is negative, the output for the lowest

codes limits at 0V as shown in Figure 2b.

Similarly, limiting can occur near full scale when the REF

pin is tied to VCC. If VREF = VCC and the DAC full-scale

error (FSE) is positive, the output for the highest codes

limits at VCC as shown in Figure 2c. No full-scale limiting

can occur if VREF is less than VCC – FSE.

Offset and linearity are defined and tested over the region

of the DAC transfer function where no output limiting can

occur.

VREF = VCC

POSITIVE

FSE

OUTPUT

VOLTAGE

OUTPUT

VOLTAGE

VREF = VCC

INPUT CODE

(2c)

OUTPUT

VOLTAGE

0

512

1023

INPUT CODE

(2a)

0V

NEGATIVE

OFFSET

INPUT CODE

(2b)

1661 F02

Figure 2. Effects of Rail-to-Rail Operation On a DAC Transfer Curve. (2a) Overall Transfer Function (2b) Effect of Negative

Offset for Codes Near Zero Scale (2c) Effect of Positive Full-Scale Error for Input Codes Near Full Scale When VREF = VCC

1661fa

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