WM2130 Datasheet, PDF (10/20 Pages) Wolfson Microelectronics plc – 10 - BIT 30MSPS ANALOGUE- TO - DIGITAL CONVERTER

WM2130
Production Data
FULL EXTERNAL REFERENCE MODE (MODE = AGND)
When MODE is connected to AGND, the WM2130 operates in full external reference mode. The
internal reference buffer is powered down and bypassed, so that the ADC core takes the user-
supplied reference voltages at pins REFTS and REFBS (REFTS and REFBS are internally
connected to REFTF and REFBF). The mean of REFTF and REFBF must be equal to AVDD/2. Only
single-ended input is possible in this mode.
REFTF
AIN
REFTS
REFBS
+1
SAMPLE
-1/2 ^AND
HOLD
-1/2
INTERNAL
REFERENCE
BUFFER
ADC
CORE
REFBF
Figure 6 ADC Reference Generation in Full External Mode
The full external mode of operation is useful when the application requires more accurate or lower
drift reference voltages than the WM2130 can provide, or when devices need to share common
reference voltages for best ADC matching. It also offers the possibility of using REFTS and REFBS
as sense lines to drive the REFTF and REFBF lines (Kelvin mode) to eliminate any voltage drops
from remote references within the system (see Figure 7). In Kelvin configurations, take care when
choosing the external op-amps to ensure that they can drive large capacitive loads without
oscillating.
Although the on-chip reference generator is not used by the WM2130 in full external mode, its output
is available on the VREF pin and can be used by other parts of the system. Note that in addition to
the internal connections from REFTS to REFTF and REFBS to REFBF, external wire connections
must also be made as shown in Figure 8 to minimise resistance (except in Kelvin mode).
+FS
AVDD/2
AIN
-FS
REFTS
DC SOURCE =
AVDD/2 + [(+FS) - (-FS)] * GAIN/2
REFBS
DC SOURCE =
AVDD/2 - [(+FS) - (-FS)] * GAIN/2
0.1µF
REFTF
10µF 0.1µF
0.1µF
REFBF
AVDD
REFSENSE
MODE
Figure 7 Full External Reference Mode (Reference Generator Disabled)
WOLFSON MICROELECTRONICS LTD
PD Rev 1.2 April 2001
10