REV. B
a
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ADN2850
*
Nonvolatile Memory, Dual
1024-Position Programmable Resistors
FUNCTIONAL BLOCK DIAGRAM
ADDR
DECODE
ADN2850
RDAC1
SERIAL
INTERFACE
CS
CLK
SDI
SDO
PR
WP
RDY
V
DD
V
SS
GND
RDAC1
REGISTER
EEMEM1
RDAC2
REGISTER
EEMEM2
26 BYTES
USER EEMEM
PWR ON
PRESET
EEMEM
CONTROL
W1
B1
RDAC2
W2
B2
CURRENT
MONITOR
I
1
I
2
V
1
V
2
CODE – Decimal
100
75
0
0 1023256
R
WB
(D) – % of Full-Scale R
WB
512 768
50
25
Figure 1. R
WB
(D) vs. Decimal Code
FEATURES
Dual, 1024-Position Resolution
25 kH9024, 250 kH9024 Full-Scale Resistance
Low Temperature Coefficient: 35 ppm/H11543C
Nonvolatile Memory
1
Preset Maintains Wiper Settings
Permanent Memory Write-Protection
Wiper Settings Read Back
Actual Tolerance Stored in EEMEM
1
Linear Increment/Decrement
Log Taper Increment/Decrement
SPI Compatible Serial Interface
3 V to 5 V Single Supply or H115502.5 V Dual Supply
26 Bytes User Nonvolatile Memory for Constant Storage
Current Monitoring Configurable Function
100-Year Typical Data Retention T
A
= 55H11543C
APPLICATIONS
SONET, SDH, ATM, Gigabit Ethernet, DWDM Laser
Diode Driver Optical Supervisory Systems
GENERAL DESCRIPTION
The ADN2850 provides dual-channel, digitally controlled program-
mable resistors
2
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 EEMEM
1
.
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.
In the scratch pad programming mode, a specific setting can be
programmed directly to the RDAC
2
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.
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 H11003 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
1
The term nonvolatile memory and EEMEM are used interchangeably.
2
The term programmable resistor and RDAC are used interchangeably.