Data Sheet

AD7960

Rev. 0 | Page 17 of 24

Table 8. Voltage Reference Options

EN3

EN2

EN1

EN0

REFIN

Reference Mode Description

X1

0

0

0

X1

Power-down mode. Everything is powered down, including the LVDS interface.

X1

0

0

1

0 V

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.

X1

0

0

1

2.048 V

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.

X1

0

1

0

0 V

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.

X1

0

1

1

0 V

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.

0

1

0

0

X1

Test patterns output on LVDS. The ADC output is not available on the interface.

1

1

0

0

X1

Invalid mode.

X1

1

0

1

0 V

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).

X1

1

0

1

2.048 V

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).

X1

1

1

0

0 V

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).

X1

1

1

1

0 V

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 AD7960 allows buffering of the reference voltage. The

AD7960 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 AD7960 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:













=

0

.

5

096

.

4

log

20

SNR

Wake-Up Time from Power-Down and Snooze Modes

The AD7960 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