EVAL-AD7961FMCZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7961FMCZ' PDF : 24 Pages View PDF
Data Sheet
AD7961
Table 8. Voltage Reference Options
EN3 EN2 EN1 EN0 REFIN
X1 0
0
0
X1
X1 0
0
1
0V
X1 0
0
1
2.048 V
X1 0
1
0
0V
X1 0
1
1
0V
0
1
0
0
X1
1
1
0
0
X1
X1 1
0
1
0V
X1 1
0
1
2.048 V
X1 1
1
0
0V
X1 1
1
1
0V
Reference Mode Description
Power-down mode. Everything is powered down, including the LVDS interface.
Interface powered up. Reference buffer disabled. An external 5 V reference is applied to the REF pin.
Connect REFIN to 0 V in this mode. The bandwidth of the input sampling network is set to 28 MHz.
Internal reference buffer enabled. An external 2.048 V reference applied to REFIN pin is required. A
buffered 4.096 V reference is available on the REF pin. The bandwidth of the input sampling
network is set to 28 MHz.
Internal reference buffer disabled. Drive the REF pins with a 4.096 V external reference. Connect
REFIN to 0 V in this mode. The bandwidth of the input sampling network is set to 28 MHz.
Snooze mode.2 LVDS powers down. The chip is unresponsive to CNV± start pulses. The wake-up
time is fast (5 μs) when EN3 to EN0 are set to XX01 or XX10. Ensure that the CNV± start pulse is low
when transitioning in and out of this mode.
Test patterns output on LVDS. The ADC output is not available on the interface.
Invalid mode.
Reference buffer disabled. Drive the REF pins with a 5 V external reference. The bandwidth of the
input sampling network is set to narrow (9 MHz).
Internal reference buffer enabled and driving REF pin to 4.096 V. The bandwidth of the input
sampling network is set to narrow (9 MHz).
Reference buffer disabled. Drive the REF pins with a 4.096 V external reference. The bandwidth of
the input sampling network is set to narrow (9 MHz).
Snooze mode.2 LVDS powers down. The chip is unresponsive to CNV± start pulses. The wake-up
time is fast (5 μs) when EN3 to EN0 are set to XX01 or XX10.
1 X = don’t care.
2 The snooze mode is not useful when the internal reference buffer is used because the fast wake-up is not possible due to the settling of the internal reference buffer.
VOLTAGE REFERENCE OPTIONS
The AD7961 allows buffering of the reference voltage. The
AD7961 conversions are referred to a 5 V or 4.096 V reference
voltage. There are three options for using an external reference:
Externally buffered reference source of 5 V applied to the
REF pin.
Externally buffered reference source of 4.096 V applied to
the REF pin.
External reference of 2.048 V applied to the REFIN pin
(high impedance input). The on-chip buffer gains this by 2
and drives the REF pin with 4.096 V.
The recommended external references for the AD7961 are the
ADR4520/ADR4540/ADR4550 and ADR440/ADR444/ADR445.
The various options for creating this reference are controlled by
the EN1 and EN0 pins (see Table 8). The −3 dB input bandwidth
is controlled by EN2. EN2 = 0 sets a −3 dB input bandwidth of
28 MHz, and EN2 = 1 sets a −3 dB input bandwidth of 9 MHz.
Use this lower bandwidth (9 MHz) only when the sample rate is
2 MSPS or lower. EN3 = 1 enables the VCM reference output,
and EN3 = 0 disables the VCM reference output voltage. The
best SNR and dynamic range performance is achieved by using
the larger 5 V external voltage reference option. The improvement
achieved is approximately 1.7 dB and is calculated using the
following equation:
SNR 20 log 5.0
4.096
Wake-Up Time from Power-Down and Snooze Modes
The AD7961 powers down when EN3 to EN0 = X000 and operates
in snooze mode when EN3 to EN0 = XX11 using the correct
reference choice as shown in Table 8. Typical wake-up times for
the selected reference settings from power-down and snooze
mode are shown in Table 9 and Table 10. Each wake-up time
represents the duration from the EN3 to EN0 logic transition to
when the ADC is ready for a CNV± rising edge. For example,
the user must wait 1.4 ms from power-down before applying
CNV± pulses to receive data conversion results when using
REFIN = 0 V.
Table 9. Wake-Up Time from Power-Down Mode, EN3 to
EN0 = X000
To Active Mode
Wake-Up Time
EN3 to EN0 = XX01, REFIN = 0 V
1.4 ms
EN3 to EN0 = XX01, REFIN = 2.048 V 8 ms
EN3 to EN0 = XX10, REFIN = 0 V
1.4 ms
Table 10. Wake-Up Time from Snooze Mode, EN3 to EN0 =
XX11
To Active Mode
Wake-Up Time
EN3 to EN0 = XX01, REFIN = 0 V
5 μs
EN3 to EN0 = XX01, REFIN = 2.048 V 8 ms
EN3 to EN0 = XX10, REFIN = 0 V
5 μs
Rev. B | Page 17 of 24
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