Analog Devices ADSP-21992 EZ-KIT LITE, Системное руководство

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System Architecture
3-6 ADSP-21992 EZ-KIT Lite Evaluation System Manual
Reference Voltage Generation
The ADSP-21992 EZ-KIT Lite board contains an external voltage refer-
ence, the LM4140-1.0 (
U3
), which provides a precise 1.024V output. The
ADSP-21992 EZ-KIT Lite board can be configured to operate from the
internal (ADSP-21992 generated) or the external voltage reference. Two
jumpers control the selection of the internal or external voltage reference.
Jumper
JP3
ties the
SENSE
pin of the ADSP-21992 to the
AVDD
or
GND
lev-
els. Connecting
SENSE
to
AVDD
(
JP3
in position 2-3) selects external voltage
reference operation. In this mode, the ADSP-21992 accepts an input volt-
age reference at the
VREF
pin.
To connect the external voltage reference to the ADSP-21992 on the eval-
uation board, close the
JP4
jumper. This connects the external voltage
reference from the LM4140-1.0 to the
VREF
pin of the ADSP-21992. The
signal, which is buffered using an operational amplifier OP193 (
A11
),
level-shifts the applied analog input signals on the analog inputs connec-
tor,
P4
, (as well as being connected to the
ASHAN
and
BSHAN
inputs to the
sample-and-hold amplifiers).
To operate with the internally derived voltage reference of the
ADSP-21992, tie the
JP3
jumper in position 1-2 to connect the
SENSE
pin
to AGND. Additionally, leave jumper
JP4
open. The ADSP-21992 pro-
vides a 1V reference at the
VREF
pin that is buffered and applied to the
ASHAN
and
BSHAN
inputs. The buffered
VREF
signal is also used in the
level-shifting circuitry.
See “Voltage Reference Selection Jumpers (JP3, JP4)” on page 3-14 for
more information.