Datasheet

AD9481

Rev. 0 | Page 18 of 28

Fixed Reference

The internal reference can be configured for a differential span

of 1 V p-p (see Figure 34). It is recommended to place a 0.1 µF

capacitor as close as possible to the VREF pin; a 10 µF capacitor

is also required (see the PCB layout for guidance). If the internal

reference of the AD9481 is used to drive multiple converters to

improve gain matching, the loading of the reference by the

other converters must be considered. Figure 34 depicts how the

internal reference voltage is affected by loading.

TEMPERATURE (°C)

VREF (V)

1.0085

1.0080

1.0075

1.0060

1.0055

1.0065

1.0070

1.0050

1.0045

1.0040

1.0035

–40 –20 0 20 40 60 80

05045-033

Figure 32. Typical Reference Variation with Temperature

05045-034

0.1µF10µF

VREF

SENSE

Figure 33. Internal Fixed Reference (1 V p-p)

IREF (mA)

% CHANGE IN VREF VOLTAGE

–0.1

–0.2

–0.4

–0.3

–0.5

0 0.5 1.51.0 2.0 2.5 3.0

05045-035

Figure 34. Internal VREF vs. Load Current

Table 8. Reference Configurations

SENSE Voltage Resulting VREF Reference Differential Span

AVDD N/A (external reference input) External 1 × external reference voltage

0.5 V (Self-Biased) 0.5 × (1 + R1/R2) V Programmable 1 × VREF (0.75 V p-p to 1.5 V p-p)

AGND to 0.2 V 1.0 V Internal fixed 1 V p-p