AD5231 datasheet(18/24 Pages) AD

Part #	AD5231

Description	Nonvolatile Memory, 1024-Position Digital Potentiometers

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REV. 0

AD5231

–18–

FLASH/EEMEM RELIABILITY

The Flash/EE Memory array on the AD5231 is fully qualified for two

key Flash/EE memory characteristics, namely Flash/EE Memory

Cycling Endurance and Flash/EE Memory Data Retention.

Endurance quantifies the ability of the Flash/EE memory to be

cycled through many Program, Read, and Erase cycles. In real

terms, a single endurance cycle is composed of four independent,

sequential events. These events are defined as:

• Initial Page Erase Sequence

• Read/Verify Sequence

• Byte Program Sequence

• Second Read/Verify Sequence

During reliability qualification Flash/EE memory is cycled from

000H to 3FFH until a first fail is recorded signifying the endurance

limit of the on-chip Flash/EE memory.

As indicated in the specification pages of this data sheet, the AD5231

Flash/EE Memory Endurance qualification has been carried out in

accordance with JEDEC Specification A117 over the industrial

temperature range of –40

°C to +85°C. The results allow the

specification of a minimum endurance figure over supply and

temperature of 100,000 cycles, with an endurance figure of

700,000 cycles being typical of operation at 25

°C.

Retention quantifies the ability of the Flash/EE memory to retain

its programmed data over time. Again, the AD5231 has been

qualified in accordance with the formal JEDEC Retention Lifetime

Specification (A117) at a specific junction temperature (TJ = 55

°C).

As part of this qualification procedure, the Flash/EE memory is

cycled to its specified endurance limit described above, before data

retention is characterized. This means that the Flash/EE memory

is guaranteed to retain its data for its full specified retention lifetime

every time the Flash/EE memory is reprogrammed. It should also

be noted that retention lifetime, based on an activation energy of

0.6 eV, will derate with TJ as shown in Figure 20. For example, the

data is retained for 100 years at 55

°C operation, but reduces to

15 years at 85

°C operation. Beyond such limit, the part must be

reprogrammed so that the data can be restored.

TJ JUNCTION TEMPERATURE – C

300

250

0

40

200

150

100

50

60

70

80

90

100

110

ADI TYPICAL

PERFORMANCE

AT

TJ = 55 C

Figure 20. Flash/EE Memory Data Retention

APPLICATIONS

Bipolar Operation From Dual Supplies

The AD5231 can be operated from dual supplies

±2.5 V, which

enables control of ground referenced ac signals or bipolar operation.

AC signal, as high as VDD/VSS, can be applied directly across

terminals A-B with output taking from terminal W. (See Figure

21 for a typical circuit connection.)

2.5V p-p

AD5231

VSS

GND

SDI

CLK

SS

SCLK

MOSI

GND

VDD

C

1.25V p-p

VDD

+2.5V

–2.5V

CS

D = MIDSCALE

A

W

B

Figure 21. Bipolar Operation from Dual Supplies

High Voltage Operation

The Digital Potentiometer can be placed directly in the feedback or

input path of an op amp for gain control, provided that the voltage

across terminals A-B, W-A, or W-B does not exceed |5 V|. When

high voltage gain is needed, users should set a fixed gain in an op

amp operated at +15 V, and let the digital potentiometer control

the adjustable input. Figure 22 shows a simple implementation.

R2R

5V

AD5231

A

W

B

15V

V+

V–

VO

0 TO 15V

A1

–

+

Figure 22. 15 V Voltage Span Control

Bipolar Programmable Gain Amplifier

There are several ways to achieve bipolar gain. Figure 23 shows one

versatile implementation. Digital potentiometer U1 sets the

adjustment range, the wiper voltage VW2 can therefore be

programmed between Vi and –KVi at a given U2 setting. For linear

adjustment, configure A2 as a noninverting amplifier and the trans-

fer function becomes:

V

R

D

KK

O

i

=+







 ×× +

()









1

2

1

1024

1

2

–

(4)

where:

K is the ratio of RWB/RWA which is set by U1.

D = Decimal Equivalent of the Input Code

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