THS5641A

8-BIT, 100 MSPS, CommsDAC

™

DIGITAL-TO-ANALOG CONVERTER

SLAS277 –MARCH 2000

16

POST OFFICE BOX 655303

APPLICATION INFORMATION

reference operation

The THS5641A comprises a bandgap reference and control amplifier for biasing the full-scale output current.

IOUT

I

32

V

EXTIO

R

BIAS

of 1.2 V. This reference is active when terminal EXTLO is connected to AGND. An external decoupling capacitor

can additionally be used for external reference operation. In that case, an external buffer with high impedance

input should be applied in order to limit the bandgap load current to a maximum of 100 nA. The internal reference

hence be omitted. Terminal EXTIO thus serves as either input or output node.

the externally applied reference voltage. The internal control amplifier has a wide input range, supporting the

full-scale output current range of 20 dB. The bandwidth of the internal control amplifier is defined by the internal

1 nF compensation capacitor at pin COMP1 and the external compensation capacitor C1. The relatively weak

internal control amplifier may be overridden by an externally applied amplifier with sufficient drive for the internal

1 nF load, as shown in Figure 25. This provides the user with more flexibility and higher bandwidths, which are

specifically attractive for gain control and multiplying DAC applications. Pin SLEEP should be connected to

AGND or left disconnected when an external control amplifier is used.

AVDD

1.2 V

REF

REF AMP

1 nF

+

–

+

–

AVDD

AGND

EXTLO

EXTIO

BIASJ

AVDD

IOUT1 or IOUT2

External

Control AMP

EXT Reference

Voltage

COMP1

SLEEP

Current Source Array

REXT

Internal

Control AMP

THS4041

Figure 25. Bypassing the Internal Reference and Control Amplifier