Nonvolatile Memory, Dual
a
1024-Position Programmable Resistors
ADN2850*
FUNCTIONAL BLOCK DIAGRAM
ADN2850
FEATURES
Dual, 1024-Position Resolution
25 kꢀ, 250 kꢀ Full-Scale Resistance
Low Temperature Coefficient: 35 ppm/ꢁC
ADDR
CS
RDAC1
DECODE
Nonvolatile Memory1 Preset Maintains Wiper Settings
Permanent Memory Write-Protection
Wiper Settings Read Back
REGISTER
CLK
SDI
W1
B1
SERIAL
INTERFACE
RDAC1
SDO
EEMEM1
Actual Tolerance Stored in EEMEM1
Linear Increment/Decrement
PWR ON
PRESET
PR
RDAC2
REGISTER
Log Taper Increment/Decrement
SPI Compatible Serial Interface
3 V to 5 V Single Supply or ꢂ2.5 V Dual Supply
26 Bytes User Nonvolatile Memory for Constant Storage
Current Monitoring Configurable Function
100-Year Typical Data Retention TA = 55ꢁC
WP
EEMEM
CONTROL
W2
B2
RDY
RDAC2
EEMEM2
V
DD
I
V
1
1
V
SS
26 BYTES
USER EEMEM
CURRENT
MONITOR
GND
I
V
2
2
APPLICATIONS
SONET, SDH, ATM, Gigabit Ethernet, DWDM Laser
Diode Driver Optical Supervisory Systems
GENERAL DESCRIPTION
100
The ADN2850 provides dual-channel, digitally controlled program-
mable resistors2 with resolution of 1024 positions. These devices
perform the same electronic adjustment function as a mechanical
rheostat with enhanced resolution, solid-state reliability, and
superior low temperature coefficient performance. The ADN2850’s
versatile programming via a standard serial interface allows
16 modes of operation and adjustment, including scratch pad pro-
gramming, memory storing and retrieving, increment/decrement,
log taper adjustment, wiper setting readback, and extra user
defined EEMEM1.
75
50
25
0
Another key feature of the ADN2850 is that the actual tolerance
is stored in the EEMEM. The actual full-scale resistance can
therefore be known, which is valuable for tolerance matching
and calibration.
0
256
512
768
1023
CODE – Decimal
In the scratch pad programming mode, a specific setting can be
programmed directly to the RDAC2 register, which sets the resis-
tance between terminals W and B. The RDAC register can also
be loaded with a value previously stored in the EEMEM register.
The value in the EEMEM can be changed or protected. When
changes are made to the RDAC register, the value of the new
setting can be saved into the EEMEM. Thereafter, such value will
be transferred automatically to the RDAC register during system
power ON, which is enabled by the internal preset strobe.
EEMEM can also be retrieved through direct programming and
external preset pin control.
Figure 1. RWB(D) vs. Decimal Code
The linear step increment and decrement commands enable the
setting in the RDAC register to be moved UP or DOWN, one step
at a time. For logarithmic changes in wiper setting, a left/right
bit shift command adjusts the level in 6 dB steps.
The ADN2850 is available in the 5 mm ꢀ 5 mm 16-lead frame chip
scale LFCSP and thin 16-lead TSSOP packages. All parts are
guaranteed to operate over the extended industrial temperature
range of –40°C to +85°C.
*Patent pending
NOTES
1The term nonvolatile memory and EEMEM are used interchangeably.
2The term programmable resistor and RDAC are used interchangeably.
REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, norforanyinfringementsofpatentsorotherrightsofthirdpartiesthat
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
www.analog.com
© Analog Devices, Inc., 2002
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