AD ADN2850ACP250 Nonvolatile memory, dual 1024 position programmable resistor Datasheet

a
Nonvolatile Memory, Dual
1024-Position Programmable Resistors
ADN2850*
FEATURES
Dual, 1024-Position Resolution
25 k, 250 k Full-Scale Resistance
Low Temperature Coefficient: 35 ppm/C
Nonvolatile Memory1 Preset Maintains Wiper Settings
Permanent Memory Write-Protection
Wiper Settings Read Back
Actual Tolerance Stored in EEMEM1
Linear Increment/Decrement
Log Taper Increment/Decrement
SPI Compatible Serial Interface
3 V to 5 V Single Supply or 2.5 V Dual Supply
26 Bytes User Nonvolatile Memory for Constant Storage
Current Monitoring Configurable Function
100-Year Typical Data Retention TA = 55C
APPLICATIONS
SONET, SDH, ATM, Gigabit Ethernet, DWDM Laser
Diode Driver Optical Supervisory Systems
FUNCTIONAL BLOCK DIAGRAM
ADN2850
ADDR
DECODE
CS
CLK
RDAC1
REGISTER
W1
SERIAL
INTERFACE
SDI
SDO
RDAC1
EEMEM1
PR
PWR ON
PRESET
WP
EEMEM
CONTROL
RDY
B1
RDAC2
REGISTER
W2
RDAC2
EEMEM2
VDD
VSS
26 BYTES
USER EEMEM
GND
I1
CURRENT
MONITOR
I2
B2
V1
V2
GENERAL DESCRIPTION
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 RDAC2 register, which sets the resistance 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.
*Patent pending
100
RWB(D) – % of Full-Scale RWB
The ADN2850 provides dual-channel, digitally controlled programmable 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 programming, memory storing and retrieving, increment/decrement,
log taper adjustment, wiper setting readback, and extra user
defined EEMEM1.
75
50
25
0
0
256
512
768
1023
CODE – Decimal
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.
NOTES
1
2
The term nonvolatile memory and EEMEM are used interchangeably.
The 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, nor for any infringements of patents or other rights of third parties that
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
www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2002
ADN2850–SPECIFICATIONS
ELECTRICAL CHARACTERISTICS 25 k, 250 k VERSIONS
Parameter
Symbol
Conditions
DC CHARACTERISTICS RHEOSTAT MODE (Specifications apply to all RDACs)
R-DNL
RWB
Resistor Differential Nonlinearity3
Resistor Integral Nonlinearity3
R-INL
RWB
Resistance Temperature Coefficient
RWB/T
VDD = 5 V, IW = 100 µA,
Wiper Resistance
RW
Code = Half-scale
VDD = 3 V, IW = 100 µA,
Code = Half-scale
Channel Resistance Matching
RWB/RWB Ch 1 and 2 RWB, Dx = 3FFH
Nominal Resistor Tolerance
RWB
RESISTOR TERMINALS
Terminal Voltage Range4
Capacitance5 Bx
VW, B
CB
Capacitance5 Wx
CW
Common-Mode Leakage Current6
ICM
DIGITAL INPUTS AND OUTPUTS
Input Logic High
Input Logic Low
Input Logic High
Input Logic Low
Input Logic High
VIH
VIL
VIH
VIL
VIH
Input Logic Low
VIL
Output Logic High (SDO, RDY)
Output Logic Low
Input Current
Input Capacitance5
VOH
VOL
IIL
CIL
POWER SUPPLIES
Single-Supply Power Range
Dual-Supply Power Range
Positive Supply Current
VDD
VDD/VSS
IDD
Positive Supply Current
Programming Mode Current
Read Mode Current7
Negative Supply Current
IDD
IDD(PG)
IDD(XFR)
ISS
Power Dissipation8
Power Supply Sensitivity
PDISS
PSS
CURRENT MONITOR TERMINALS
Current Sink at V19
Current Sink at V2
I1
I2
DYNAMIC CHARACTERISTICS5, 10
Resistor Noise Spectral Density
Analog Crosstalk (CW1/CW2)
eN_WB
CT
(VDD = 3 V to 5.5 V and –40C < TA < +85C,
unless otherwise noted.)1
Min
Max
Unit
+2
+4
LSB
LSB
ppm/°C
100
Ω
–30
+30
Ω
%
%
VSS
VDD
V
–2
–4
35
50
200
0.1
f = 1 MHz, measured to GND,
Code = Half-scale
f = 1 MHz, measured to GND,
Code = Half-scale
VW = VB = VDD/2
With respect to GND, VDD = 5 V
With respect to GND, VDD = 5 V
With respect to GND, VDD = 3 V
With respect to GND, VDD = 3 V
With respect to GND,
VDD = +2.5 V, VSS = –2.5 V
With respect to GND,
VDD = +2.5 V, VSS = –2.5 V
RPULL-UP = 2.2 kΩ to 5 V
IOL = 1.6 mA, VLOGIC = 5 V
VIN = 0 V or VDD
Typ2
11
80
0.01
pF
±2
2.4
0.8
2.1
0.6
2.0
VIH = VDD or VIL = GND,
TA = 25oC
VIH = VDD or VIL = GND
VIH = VDD or VIL = GND
VIH = VDD or VIL = GND
VIH = VDD or VIL = GND,
VDD = +2.5 V, VSS = –2.5 V
VIH = VDD or VIL = GND
∆VDD = 5 V ± 10%
0.5
4.9
0.4
± 2.25
3.0
± 2.25
0.3
–2–
V
V
V
µA
pF
5.5
± 2.75
V
V
4.5
6.0
2
3.5
35
3
9
µA
µA
mA
mA
3.5
18
0.002
6.0
50
0.01
µA
µW
%/%
10
10
mA
mA
0.0001
RWB_FS = 25 kΩ/250 kΩ, f = 1 kHz
VB1 = VB2 = 0 V, Measured VW1 with
VW2 = 100 mV p-p @ f = 100 kHz,
Code 1 = Code 2 = 200H
V
V
V
V
V
5
VSS = 0 V
pF
µA
20/64
nV/√Hz
–65
dB
REV. B
ADN2850
Parameter
Symbol
Conditions
Min
Typ2
Max
Unit
5, 11
INTERFACE TIMING CHARACTERISTICS (apply to all parts)
Clock Cycle Time (tCYC)
t1
CS Setup Time
t2
CLK Shutdown Time to CS Rise
t3
Input Clock Pulsewidth
t 4 , t5
Clock Level High or Low
From Positive CLK Transition
Data Setup Time
t6
From Positive CLK Transition
Data Hold Time
t7
CS to SDO – SPI Line Acquire
t8
CS to SDO – SPI Line Release
t9
t10
RP = 2.2 kΩ, CL < 20 pF
CLK to SDO Propagation Delay12
CS High Pulsewidth13
t12
t13
CS High to CS High13
RDY Rise to CS Fall
t14
CS Rise to RDY Fall Time
t15
Applies to Command 2H, 3H, 9H
Read/Store to Nonvolatile EEMEM14 t16
CS Rise to Clock Edge Setup
t17
Preset Pulsewidth (Asynchronous)
tPRW
Not Shown in Timing Diagram
PR Pulsed Low to Refresh
Preset Response Time to Wiper Setting tPRESP
Wiper Positions
FLASH/EE MEMORY RELIABILITY
Endurance15
Data Retention16
20
10
1
10
5
5
140
ns
ns
tCYC
ns
ns
ns
ns
ns
ns
ns
tCYC
ns
ms
ms
ns
ns
µs
100
K Cycles
Years
40
50
50
10
4
0
0.15
35
10
50
100
0.3
NOTES
1
Parts can be operated at 2.7 V single supply, except from 08C to –408C, where minimum 3 V is needed.
2
Typicals represent average readings at 258C and VDD = 5 V.
3
Resistor position nonlinearity error R-INL is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper positions.
R-DNL measures the relative step change from ideal between successive tap positions. I W ~ 50 µA for VDD = 2.7 V and IW ~ 400 µA for VDD = 5 V.
4
Resistor terminals W and B have no limitations on polarity with respect to each other.
5
Guaranteed by design and not subject to production test.
6
Common-mode leakage current is a measure of the dc leakage from any terminal B and W to a common-mode bias level of V DD/2.
7
Transfer (XFR) mode current is not continuous. Current consumed while EEMEM locations are read and transferred to the RDAC register. See TPC 9.
8
PDISS is calculated from (I DD VDD) + (ISS VSS).
9
Applies to photodiode of optical receiver.
10
All dynamic characteristics use V DD = +2.5 V and V SS = –2.5 V.
11
See timing diagram for location of measured values. All input control voltages are specified with t R = tF = 2.5 ns (10% to 90% of 3 V) and timed from a voltage level of 1.5 V.
Switching characteristics are measured using both V DD = 3 V and 5 V.
12
Propagation delay depends on value of V DD, RPULL_UP, and CL. See Applications section.
13
Valid for commands that do not activate the RDY pin.
14
RDY pin low only for commands 2, 3, 8, 9, 10, and PR hardware pulse: CMD_8 ~ 1 ms; CMD_9, 10 ~ 0.1 ms; CMD_2, 3 ~ 20 ms. Device operation at TA = –40°C
and VDD < 3 V extends the save time to 35 ms.
15
Endurance is qualified to 100,000 cycles as per JEDEC Std. 22 method A117 and measured at –40 °C, +25°C, and +85°C; typical endurance at +25°C is 700,000 cycles.
16
Retention lifetime equivalent at junction temperature (T J ) = 55°C as per JEDEC Std. 22, Method A117. Retention lifetime based on an activation energy of 0.6 V will
derate with junction temperature.
Specifications subject to change without notice.
The ADN2850 contains 16,000 transistors. Die size: 93 mil 103 mil, 10,197 sq mil.
REV. B
–3–
ADN2850
TIMING DIAGRAMS
CS
CPHA = 1
t12
t13
t3
t1
t2
CLK
CPOL = 1
t5
t17
t4
t10
t8
SDO
t11
t9
MSB
*
LSB OUT
t7
t6
SDI
MSB
LSB
t14
t15
t16
RDY
*NOT DEFINED, BUT NORMALLY LSB OF CHARACTER PREVIOUSLY TRANSMITTED.
THE CPOL = 1 MICROCONTROLLER COMMAND ALIGNS THE INCOMING DATA TO THE POSITIVE EDGE OF THE CLOCK.
Figure 2a. CPHA = 1 Timing Diagram
CS
CPHA = 0
t12
t1
t3
t2
t13
t5
CLK
CPOL = 0
t17
t4
t8
t10
t11
SDO
MSB OUT
LSB
t9
*
t7
t6
SDI
LSB
MSB IN
t14
t15
t16
RDY
*NOT DEFINED, BUT NORMALLY MSB OF CHARACTER JUST RECEIVED.
THE CPOL = 0 MICROCONTROLLER COMMAND ALIGNS THE INCOMING DATA TO THE POSITIVE EDGE OF THE CLOCK.
Figure 2b. CPHA = 0 Timing Diagram
–4–
REV. B
ADN2850
Thermal Resistance Junction-to-Ambient θJA,
LFCSP-16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35°C/W
TSSOP-16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C/W
Thermal Resistance Junction-to-Case θJC,
TSSOP-16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28°C/W
Package Power Dissipation = (TJ MAX – TA)/θJA
ABSOLUTE MAXIMUM RATINGS 1
(TA = 25°C, unless otherwise noted.)
VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, +7 V
VSS to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . +0.3 V, –7 V
VDD to VSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 V
VB, VW to GND . . . . . . . . . . . . . . . . VSS – 0.3 V, VDD + 0.3 V
IB, I W
Intermittent2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .± 20 mA
Continuous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 2 mA
Digital Inputs and Output Voltage
to GND . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, VDD + 0.3 V
Operating Temperature Range3 . . . . . . . . . . . –40°C to +85°C
Maximum Junction Temperature (TJ MAX) . . . . . . . . . 150°C
Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature, Soldering4
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220C
NOTES
1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating; functional operation of the device
at these or any other conditions above those listed in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability.
2
Maximum terminal current is bounded by the maximum current handling of the
switches, maximum power dissipation of the package, and maximum applied
voltage across any two of the B and W terminals at a given resistance.
3
Includes programming of nonvolatile memory.
4
Applicable to TSSOP-16 only. For LFCSP-16, please consult factory for details.
ORDERING GUIDE
Model
RWB_FS
(k)
RDNL RINL
(LSB) (LSB)
Temperature Package
Range (°C)
Description
Package
Option
Ordering
Quantity
Top Mark*
ADN2850BCP25
ADN2850BCP25-RL7
25
25
±2
±2
±4
±4
–40 to +85
–40 to +85
CP-16
CP-16
96
1,000
BCP25
BCP25
ADN2850BCP250
ADN2850BCP250-RL7
250
250
±2
±2
±4
±4
–40 to +85
–40 to +85
CP-16
CP-16
96
1,000
BCP250
BCP250
ADN2850BRU25
ADN2850BRU25-RL7
25
25
±2
±2
±4
±4
–40 to +85
–40 to +85
RU-16
RU-16
96
1,000
2850B25
2850B25
LFCSP-16
LFCSP-16
7" Reel
LFCSP-16
LFCSP-16
7" Reel
TSSOP-16
TSSOP-16
7" Reel
*Line 1 contains product number, ADN2850, line 2 Top Mark branding contains differentiating detail by part type, line 3 contains lot number, line 4 contains product
date code YYWW.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the ADN2850 features proprietary ESD protection circuitry, permanent damage may occur on
devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are
recommended to avoid performance degradation or loss of functionality.
REV. B
–5–
WARNING!
ESD SENSITIVE DEVICE
ADN2850
CLK 1
CS
RDY
CLK
SDI
PIN CONFIGURATIONS
16 15 14 13
5
6
7
8
B2
W2
V1 4
CHIP SCALE
PACKAGE
B1
VSS 3
ADN2850BCP
W1
GND 2
15 CS
11 WP
10 VDD
9
14 PR
SDO 3
12 PR
SDO 1
16 RDY
SDI 2
V2
GND 4
ADN2850BRU
13 WP
VSS 5
TOP VIEW
(Not To Scale)
12 VDD
V1 6
11 V2
W1 7
10 W2
B1 8
Pin
No. Mnemonic Description
Pin
No. Mnemonic Description
1
1
CLK
2
SDI
3
SDO
4
5
GND
VSS
6
V1
7
W1
8
9
10
B1
B2
W2
11
V2
12
13
VDD
WP
14
PR
15
CS
16
RDY
2
3
GND
VSS
4
V1
5
W1
6
7
8
B1
B2
W2
9
10
11
12
V2
VDD
WP
PR
13
CS
14
RDY
15
CLK
16
SDI
B2
ADN2850BRU PIN FUNCTION DESCRIPTIONS
ADN2850BCP PIN FUNCTION DESCRIPTIONS
SDO
9
Serial Data Output Pin. Open-Drain output
requires external pull-up resistor. CMD_9 and
CMD_10 activate the SDO output. See
Instruction Operation Truth Table (Table II).
Other commands shift out the previously
loaded SDI bit pattern delayed by 24 clock
pulses. This allows daisy-chain operation of
multiple packages.
Ground Pin, logic ground reference
Negative Supply. Connect to zero volts for
single-supply applications.
Log Output Voltage 1 generated from internal
diode configured transistor
Wiper terminal of RDAC1 ADDR
(RDAC1) = 0H.
B terminal of RDAC1
B terminal of RDAC2
Wiper terminal of RDAC2. ADDR
(RDAC2) = 1H.
Log Output Voltage 2 generated from internal
diode configured transistor
Positive Power Supply Pin
Write Protect Pin. When active low, WP
prevents any changes to the present register
contents, except PR and CMD_1 and CMD_8
will refresh the RDAC register from EEMEM.
Execute a NOP instruction before returning
to WP high.
Hardware Override Preset Pin. Refreshes the
scratch pad register with current contents of
the EEMEM register. Factory default loads
midscale 51210 until EEMEM loaded with
a new value by the user (PR is activated at
the logic high transition).
Serial Register chip select active low.
Serial register operation takes place when
CS returns to logic high.
Ready. Active high open-drain output. Identifies
completion of commands 2, 3, 8, 9, 10, and PR.
Serial Input Register Clock Pin. Shifts in
one bit at a time on positive clock edges.
Serial Data Input Pin. Shifts in one bit at a time
on positive clock CLK edges. MSB loaded first.
–6–
Serial Input Register Clock Pin. Shifts in
one bit at a time on positive clock edges.
Serial Data Input Pin. Shifts in one bit at
a time on positive clock CLK edges.
MSB loaded first.
Serial Data Output Pin. Open-drain out put
requires external pull-up resistor. CMD_9
and CMD_10 activate the SDO output. See
Instruction Operation Truth Table (Table II).
Other commands shift out the previously
loaded SDI bit pattern delayed by 24 clock
pulses. This allows daisy-chain operation of
multiple packages.
Ground Pin, logic ground reference
Negative Supply. Connect to zero volts for
single-supply applications.
Log Output Voltage 1 generated from internal
diode configured transistor
Wiper terminal of RDAC1. ADDR
(RDAC1) = 0H.
B terminal of RDAC1
B terminal of RDAC2
Wiper terminal of RDAC2. ADDR
(RDAC2) = 1H.
Log Output Voltage 2 generated from internal
diode configured transistor
Positive Power Supply Pin
Write Protect Pin. When active low, WP prevents
any changes to the present contents except PR
and CMD_1 and CMD_8 will refresh the
RDAC register from EEMEM. Execute a NOP
instruction before returning to WP high.
Hardware Override Preset Pin. Refreshes the
scratch pad register with current contents of
the EEMEM register. Factory default loads
midscale 51210 until EEMEM loaded with a
new value by the user (PR is activated at the
logic high transition).
Serial Register chip select active low. Serial
register operation takes place when CS returns
to logic high.
Ready. Active high open-drain output. Identifies
completion of commands 2, 3, 8, 9, 10, and PR.
REV. B
ADN2850
Table I. 24-Bit Serial Data-Word
MSB
Instruction Byte 0
RDAC
C3 C2 C1 C0
EEMEM C3 C2 C1 C0
0
A3
Data Byte 1
0
0 A0
A2 A1 A0
Data Byte 0
LSB
X
X
X
X
X
X
D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Command bits are C0 to C3. Address bits are A3–A0. Data bits D0 to D9 are applicable to RDAC wiper register whereas D0 to D15 are applicable to EEMEM
Register. Command instruction codes are defined in Table II.
Table II. Instruction Operation Truth Table 1, 2, 3
Inst
Number
Instruction Byte 0
Data Byte 1
Data Byte 0 Operation
B23 • • • • • • • • • • • • • • • • B16 B15 • • • • • • B8 B7 • • • • • B0
C3 C2 C1 C0 A3 A2 A1 A0 X • • • • D9 D8
D7 • • • • • D0
0
0
0
0
0
X X X X
X••••XX
X • • • • • • X NOP: Do nothing. See Table XI for Programming
example.
1
0
0
0
1
0
0
0
A0
X••••XX
X • • • • • • X Retrieve contents of EEMEM(A0) to RDAC(A0)
Register. This command leaves device in the Read
Program power state. To return part to the idle state,
perform NOP instruction 0. See Table XI.
2
0
0
1
0
0
0
0
A0
X••••XX
X • • • • • • X SAVE WIPER SETTING: Write contents of RDAC(A0)
to EEMEM(A0). See Table X.
34
0
0
1
1
A3 A2 A1 A0
D15 • • • • D8
D7 • • • • • D0 Write contents of Serial Register Data Bytes 0 and
1 (total 16-bit) to EEMEM(ADDR). See Table XIII.
45
0
1
0
0
0
X••••XX
X • • • • • • X Decrement 6 dB: Right shift contents of RDAC(A0)
Register, stops at all “Zeros.”
55
0
1
0
1
X X X X
X••••XX
X • • • • • • X Decrement All 6 dB: Right shift contents of all RDAC
Registers, stops at all “Zeros.”
65
0
1
1
0
0
X••••XX
X • • • • • • X Decrement contents of RDAC(A0) by “One,” stops
at all “Zeros.”
75
0
1
1
1
X X X X
X••••XX
X • • • • • • X Decrement contents of all RDAC Registers by
“One,” stops at all “Zeros.”
8
1
0
0
0
X X X X
X••••XX
X • • • • • • X RESET: Load all RDACs with their corresponding
EEMEM previously saved values.
9
1
0
0
1
A3 A2 A1 A0
X••••XX
X • • • • • • X Transfer contents of EEMEM (ADDR) to Serial
Register Data Bytes 0 and 1, and previously stored
data can be read out from the SDO pin. See Table XIV.
10
1
0
1
0
0
0
0
A0
X••••XX
X • • • • • • X Transfer contents of RDAC (A0) to Serial Register
Data Bytes 0 and 1, and wiper setting can be read
from the SDO pin. See Table XV.
11
1
0
1
1
0
0
0
A0
X • • • • D9 D8
D7 • • • • • D0 Write contents of Serial Register Data Bytes 0 and
1 (total 11-bit) to RDAC(A0). See Table IX.
125
1
1
0
0
0
0
0
A0
X••••XX
X • • • • • • X Increment 6 dB: Left shift contents of RDAC(A0),
stops at all “Ones.” See Table XII.
135
1
1
0
1
X X X X
X••••XX
X • • • • • • X Increment All 6 dB: Left shift contents of all RDAC
Registers, stops at all “Ones.”
145
1
1
1
0
0
X••••XX
X • • • • • • X Increment contents of RDAC(A0) by “One,” stops
at all “Ones.” See Table X.
155
1
1
1
1
X X X X
X••••XX
X • • • • • • X Increment contents of all RDAC Registers by “One,”
stops at all “Ones.”
0
0
0
0
0
0
A0
A0
A0
NOTES
1
The SDO output shifts out the last 24 bits of data clocked into the serial register for daisy-chain operation. Exception: for any instruction following Instruction 9 or 10,
the selected internal register data will be present in data byte 0 and 1. The instructions following 9 and 10 must also be a full 24-bit data-word to completely clock out
the contents of the serial register.
2
The RDAC register is a volatile scratch pad register that is refreshed at power ON from the corresponding nonvolatile EEMEM register.
3
Execution of the above operations takes place when the CS strobe returns to logic high.
4
Instruction 3 writes 2 data bytes (total 16-bit) to EEMEM. But in the cases of addresses 0 and 1, only the last 10 bits are valid for wiper position setting.
5
The increment, decrement, and shift commands ignore the contents of the shift register data bytes 0 and 1.
REV. B
–7–
ADN2850
OPERATIONAL OVERVIEW
The ADN2850 programmable resistor is designed to operate as
a true variable resistor. The resistor wiper position is determined
by the RDAC register contents. The RDAC register acts as a
scratch pad register which allows unlimited changes of resistance
settings. The scratch pad register can be programmed with any
position setting using the standard SPI serial interface by loading
the 24-bit data-word. The format of the data-word is that the first
4 bits are instructions, the following 4 bits are addresses, and the
last 16 bits are data. Once a specific value is set, this value can be
saved into a corresponding EEMEM register. During subsequent
power-ups, the wiper setting will automatically be loaded at that
value. Saving data to the EEMEM takes about 25 ms and consumes approximately 20 mA. During this time the shift register
is locked, preventing any changes from taking place. The RDY pin
indicates the completion of this EEMEM saving process. There
are also 13 two-bytes addresses, of user defined data that can be
stored in EEMEM.
OPERATION DETAIL
There are 16 instructions that facilitate users’ programming
needs. Referring to Table II, the instructions are:
0.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Do Nothing
Restore EEMEM setting to RDAC
Save RDAC setting to EEMEM
Save user data or RDAC setting to EEMEM
Decrement 6 dB
Decrement all 6 dB
Decrement one step
Decrement all one step
Reset all EEMEM settings to RDAC
Read EEMEM to SDO
Read Wiper Setting to SDO
Write data to RDAC
Increment 6 dB
Increment all 6 dB
Increment one step
Increment all one step
Tables VIII to XIV provide a few programming examples by using
some of these instructions.
Scratch Pad and EEMEM Programming
The basic mode of setting the programmable resistor wiper position
(programming the scratch pad register) is done by loading the
serial data input register with the instruction 11, the corresponding
address, and the data. Since the scratch pad register is a standard
logic register, there is no restriction on the number of changes
allowed. When the desired wiper position is determined, the user can
load the serial data input register with the instruction 2, which stores
the setting into the corresponding EEMEM register. The EEMEM
value can be changed at any time or permanently protected by
activating the WP command. Table III provides a programming
example listing the sequence of serial data input (SDI) words and
the corresponding serial data output (SDO) in hexadecimal format.
Table III. Set and Save RDAC with Independent Data
to EEMEM Registers
SDI
SDO
Action
B00100H
XXXXXXH
20xxxxH
B00100H
B10200H
20xxxxH
21xxxxH
B10200H
Loads data 100H into RDAC1 register,
Wiper W1 moves to 1/4 full-scale
position.
Saves copy of RDAC1 register content
into corresponding EEMEM1 register.
Loads 200H data into RDAC2 register,
Wiper W2 moves to 1/2 full-scale
position.
Saves copy of RDAC2 register contents
into corresponding EEMEM2 register.
At system power ON, the scratch pad register is automatically
refreshed with the value previously saved in the corresponding
EEMEM register. The factory preset EEMEM value is midscale.
During operations, the scratch pad register can also be refreshed
with the current contents of the EEMEM registers in three different
ways. First, executing instruction 1 retrieves the corresponding
EEMEM value. Second, executing instruction 8 resets the EEMEM
values of both channels. Finally, pulsing the PR pin also refreshes
both EEMEM settings. Operating the hardware control PR
function, however, requires a complete pulse signal. When PR
goes low, the internal logic sets the wiper at midscale. The
EEMEM value will not be loaded until PR returns to high.
EEMEM Protection
The write-protect (WP) disables any changes of the scratch pad
register contents regardless of the software commands, except
that the EEMEM setting can be refreshed and can overwrite the
WP by using commands 1, 8, and PR pulse. To disable WP, it is
recommended to execute a NOP command before returning
WP to logic high.
Linear Increment and Decrement Commands
The increment and decrement commands (14, 15, 6, 7) are useful
for linear step adjustment applications. These commands simplify
microcontroller software coding by allowing the controller to
just send an increment or decrement command to the device. The
adjustment can be individually or gang controlled. For increment command, executing instruction 14 will automatically move the
wiper to the next resistance segment position. The master increment
instruction 15 will move all resistor wipers up by one position.
Logarithmic Taper Mode Adjustment (6 dB/step)
There are four programming instructions which provide the
logarithmic taper increment and decrement wiper position control by either individual or gang control. 6 dB increment is
activated by instructions 12 and 13 and 6 dB decrement is activated by instructions 4 and 5. For example, starting at zero
scale, executing 11 times the increment instruction 12 will move
the wiper in 6 dB per step from the 0% of the full-scale RWB to
the full-scale RWB. The 6 dB increment instruction doubles the
value of the RDAC register contents each time the command is
executed. When the wiper position is near the maximum setting,
the last 6 dB increment instruction will cause the wiper to go to
the full-scale 1023-code position. Further 6 dB per increment
instruction will no longer change the wiper position beyond its
full-scale, Table IV.
6 dB step increment and decrement are achieved by shifting the bit
internally to the left and right, respectively. The following information explains the nonideal ± 6 dB step adjustment at certain
–8–
REV. B
ADN2850
conditions. Table IV illustrates the operation of the shifting
function on the individual RDAC register data bits. Each line
going down the table represents a successive shift operation. Note
that the left shift 12 and 13 commands were modified such that
if the data in the RDAC register is equal to zero, and the data is
left shifted, the RDAC register is then set to code 1. Similarly, if the
data in the RDAC register is greater than or equal to midscale,
and the data is left shifted, then the data in the RDAC register is
automatically set to full scale. This makes the left shift function
as ideal a logarithmic adjustment as possible.
Using Additional Internal Nonvolatile EEMEM
The ADN2850 contains additional internal user storage registers
(EEMEM) for saving constants and other 16-bit data. Table V
provides an address map of the internal storage registers shown
in the functional block diagram as EEMEM1, EEMEM2, and
and 26 bytes (13 addresses 2 bytes each) of USER EEMEM.
Table V. EEMEM Address Map
The right shift 4 and 5 commands will be ideal only if the LSB is
zero (i.e., ideal logarithmic—no error). If the LSB is a one, then
the right shift function generates a linear half LSB error, which
translates to a number of bits-dependent logarithmic error as
shown in Figure 3. The plot shows the error of the odd numbers
of bits for ADN2850.
Table IV. Detail Left and Right Shift Functions for 6 dB
Step Increment and Decrement
Left Shift
6 dB/step
Left Shift
Right Shift
00 0000 0000
00 0000 0001
00 0000 0010
00 0000 0100
00 0000 1000
00 0001 0000
00 0010 0000
00 0100 0000
00 1000 0000
01 0000 0000
10 0000 0000
11 1111 1111
11 1111 1111
11 1111 1111
01 1111 1111
00 1111 1111
00 0111 1111
00 0011 1111
00 0001 1111
00 0000 1111
00 0000 0111
00 0000 0011
00 0000 0001
00 0000 0000
00 0000 0000
00 0000 0000
EEMEM
Number
Address
EEMEM Content For
1
2
3
4
:
15
16
0000
0001
0010
0011
:
1110
1111
RDAC11, 2
RDAC2
USER13
USER2
:
USER13
% Tolerance4
NOTES
1
RDAC data stored in EEMEM locations are transferred to their corresponding
RDAC REGISTER at power-on, or when instructions 1, 8, and PR are executed.
2
Execution of instruction 1 leaves the device in the read mode power consumption
state. After the last instruction 1 is executed, the user should perform a NOP,
instruction 0 to return the device to the low power idling state.
3
USER <data> are internal nonvolatile EEMEM registers available to store and
retrieve constants and other 16-bit information using instructions 3 and 9 respectively.
4
Read only.
Calculating Actual Full-Scale Resistance
Right Shift
–6 dB/step
The actual tolerance of the rated full-scale resistance RWB1 is
stored in EEMEM register 15 during factory testing. The actual
full-scale resistance can therefore be calculated, which will be
valuable for tolerance matching or calibration. Notice this value
is read only, and the full-scale resistance of RWB2_FS matches
RWB1_FS, of typically 0.1%.
The tolerance in % is stored in the last 16 bits of data in EEMEM
register 15. The format is sign magnitude binary format with the
MSB designates for sign (0 = positive and 1 = negative), the next
7 MSB designate for the integer number, and the 8 LSB designate
for the decimal number. See Table VI.
Actual conformance to a logarithmic curve between the data contents in the RDAC register and the wiper position for each right
shift 4 and 5 command execution contains an error only for odd
numbers of bits. Even numbers of bits are ideal. The graph in
Figure 3 shows plots of Log_Error [i.e., 20 log10 (error/code)]
ADN2850. For example, code 3 Log_Error = 20 log10 (0.5/3)
= –15.56 dB, which is the worst case. The plot of Log_Error is
more significant at the lower codes.
Table VI. Tolerance in % from Rated Full-Scale Resistance
Bit D15 D14 D13 D12 D11 D10 D9 D8
sign
mag sign 26 25 24 23 22 21 20
D7 D6 D5 D4 D3 D2 D1 D0
•
2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8
{
{
{
{
Sign
7 Bits for Integer Number
Decimal
Point
8 Bits for Decimal Number
0
For example, if RWB_FS_RATED = 250 kΩ and the data is 0001
1100 0000 1111, RWB_FS_ACTUAL can be calculated as follows:
MSB:
0 = Positive
Next 7 MSB: 001 1100 = 28
8 LSB:
0000 1111 = 15 2–8 = 0.06
% Tolerance = +28.06%
Thus, RWB_FS_ACTUAL = 320.15 kΩ
dB
–20
–40
–60
–80
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
CODE – From 1 to 1023 by 2.0 103
Figure 3. Plot of Log_Error Conformance for Odd
Numbers of Bits Only (Even Numbers of Bits Are Ideal)
REV. B
–9–
ADN2850
Daisy-Chain Operation
PR
The serial data output pin (SDO) serves two purposes. It can be
used to read out the contents of the wiper settings or EEMEM
values using instructions 10 and 9 respectively. If these instructions are not used, SDO can be used for daisy-chaining multiple
devices in simultaneous operations (see Figure 4). The SDO pin
contains an open-drain N-Ch FET and requires a pull-up resistor if SDO function is used. Users need to tie the SDO pin of
one package to the SDI pin of the next package. Users may need
to increase the clock period because the pull-up resistor and the
capacitive loading at the SDO-SDI interface may induce time
delay to the subsequent devices (see Figure 4). If two ADN2850s
are daisy-chained, a total 48 bits of data is required. The first
24 bits (formatted 4-bit instruction, 4-bit address, and 16-bit
data) go to U2 and the second 24 bits with the same format go
to U1. The CS should be kept low until all 48 bits are clocked into
their respective serial registers. The CS is then pulled high to
complete the operation.
VALID
COMMAND
U1
MOSI
C
SCLK SS
SDI
SDO
RP
2.2k
COMMAND
PROCESSOR
AND ADDRESS
DECODE
COUNTER
5V
RPULLUP
CLK
SERIAL
REGISTER
SDO
CS
GND
SDI
ADN2850
Figure 5. Equivalent Digital Input-Output Logic
VDD
INPUTS
300
LOGIC
PINS
VDD
ADN2850
WP
ADN2850
U2
SDI
SDO
GND
CS
CLK
CS
CLK
Figure 6a. Equivalent ESD Digital Input Protection
VDD
Figure 4. Daisy-Chain Configuration
INPUT
300
DIGITAL INPUT/OUTPUT CONFIGURATION
All digital inputs are ESD protected. Digital inputs are high
impedance and can be driven directly from most digital sources.
Active at logic low, PR and WP should be biased to VDD if they
are not used. There are no internal pull-up resistors present on
any digital input pins. To avoid floating digital pins that may
cause false triggering in a noisy environment, pull-up resistors
should be added to these pins. However, this only applies to the
case where the device will be detached from the driving source
once it is programmed.
The SDO and RDY pins are open-drain digital outputs. Similarly,
pull-up resistors are needed if these functions are used. To optimize
the speed and power trade-off, use 2.2 kΩ pull-up resistors.
The equivalent serial data input and output logic is shown in
Figure 5. The open-drain output SDO is disabled whenever
chip select CS is logic high. ESD protection of the digital inputs
is shown in Figures 6a and 6b.
WP
GND
Figure 6b. Equivalent WP Input Protection
SERIAL DATA INTERFACE
The ADN2850 contains a 4-wire, SPI compatible, digital interface (SDI, SDO, CS, and CLK). The 24-bit serial word must be
loaded with MSB first, and the format of the word is shown in
Table I. The Command Bits (C0 to C3) control the operation of
the programmable resistor according to the instruction shown
in Table II. A0 to A3 are assigned for address bits. A0 is used to
address RDAC1 or RDAC2. Addresses 2 to 14 are accessible by
users. Address 15 is reserved for the factory. Table V provides an
address map of the EEMEM locations. The data bits (D0 to D9) are
the values that are loaded into the RDAC registers at instruction 11. The data bits (D0 to D15) are the values that are loaded
into the EEMEM registers at instruction 3.
The last instruction prior to a period of no programming activity
should be applied with the No Operation (NOP), instruction 0. It
is recommended to do so to ensure minimum power consumption
in the internal logic circuitry
The SPI interface can be used in two slave modes, CPHA = 1,
CPOL = 1 and CPHA = 0, CPOL = 0. CPHA and CPOL refer to
the control bits that dictate SPI timing in these microconverters
and microprocessors: ADuC812/ADuC824, M68HC11,
and MC68HC16R1/916R1.
–10–
REV. B
ADN2850
TERMINAL VOLTAGE OPERATING RANGE
ADN2850
The ADN2850 positive VDD and negative VSS power supply
defines the boundary conditions for proper two-terminal programmable resistance operation. Supply signals present on terminals W
and B that exceed VDD or VSS will be clamped by the internal
forward biased diodes (see Figure 7).
VDD
VSS
C3
10F
+
C1
0.1F
C4
10F
+
C2
0.1F
VDD
VSS
GND
VDD
Figure 8. Power Supply Bypassing
RDAC STRUCTURE
W
B
VSS
Figure 7. Maximum Terminal Voltages Set by VDD and VSS
The ground pin of the ADN2850 device is primarily used as a digital
ground reference that needs to be tied to the PCB’s common
ground. The digital input control signals to the ADN2850 must
be referenced to the device ground pin (GND), and satisfy the
logic level defined in the Specifications table of this data sheet.
An internal level shift circuit ensures that the common-mode
voltage range of the two terminals extends from VSS to VDD
regardless of the digital input level. In addition, there is no
polarity constraint on voltage across terminals W and B. The
magnitude of |VWB| is bounded by VDD – VSS.
The patent-pending RDAC contains a string of equal resistor
segments, with an array of analog switches, that act as the wiper
connection. The number of positions is the resolution of the
device. The ADN2850 has 1024 connection points, allowing it to
provide better than 0.1% setability resolution. Figure 9 shows an
equivalent structure of the connections between the two terminals
that make up one channel of the RDAC. The SWB will always be
ON, while one of the switches SW(0) to SW(2N – 1) will be ON
one at a time depending on the resistance position decoded from
the data bits. Since the switch is not ideal, there is a 50 Ω wiper
resistance, RW. Wiper resistance is a function of supply voltage
and temperature. The lower the supply voltage or the higher the
temperature, the higher the resulting wiper resistance. Users
should be aware of the wiper resistance dynamics if accurate
prediction of the output resistance is needed.
SW(2N–1)
RDAC
WIPER
REGISTER
AND
DECODER
Power-Up Sequence
Since diodes limit the voltage compliance at terminals B and W
(see Figure 7) it is important to power VDD/VSS first before applying any voltage to terminals B and W. Otherwise, the diode will be
forward biased such that VDD/VSS will be powered unintentionally.
For example, applying 5 V across VDD will cause the VDD terminal
to exhibit 4.3 V. Although it is not destructive to the device, it may
affect the rest of the user’s system. As a result, the ideal power-up
sequence is in the following order: GND, VDD, VSS, Digital Inputs,
and VB/W. The order of powering VB, VW, and Digital Inputs is not
important as long as they are powered after VDD/VSS.
Regardless of the power-up sequence and the ramp rates of the
power supplies, once VDD/VSS are powered, the power-on reset
remains effective, which retrieves EEMEM saved values to the
RDAC registers (see TPC 7).
Layout and Power Supply Bypassing
It is a good practice to employ compact, minimum-lead length
layout design. The leads to the input should be as direct as possible with a minimum of conductor length. Ground paths should
have low resistance and low inductance. To minimize the digital
ground bounce, the digital signal ground reference can be joined
remotely to the analog ground terminal of the ADN2850.
Similarly, it is also a good practice to bypass the power supplies
with quality capacitors for optimum stability. Supply leads to the
device should be bypassed with 0.01 µF to 0.1 µF disc or chip
ceramics capacitors. Low ESR 1 µF to 10 µF tantalum or electrolytic capacitors should also be applied at the supplies to minimize
any transient disturbance (see Figure 8).
REV. B
W
RS
SW(2N– 2)
RS
SW(1)
RS
SW(0)
RS = RWB / 2N
DIGITAL
CIRCUITRY
OMITTED FOR
CLARITY
SWB
B
Figure 9. Equivalent RDAC Structure
Table VII. Nominal Individual Segment Resistor Values
Device Resolution
1024-Step
25 kΩ
24.4
250 kΩ
244
CALCULATING THE PROGRAMMABLE RESISTANCE
The nominal full-scale resistance of the RDAC between terminals
W and B, RWB_FS, is available with 25 kΩ and 250 kΩ with 1024
positions (10-bit resolution). The final digits of the part number
determine the nominal resistance value, e.g., 25 kΩ = 25 and
250 kΩ = 250.
The 10-bit data-word in the RDAC latch is decoded to select one
of the 1024 possible settings. The following discussion describes
the calculation of resistance RWB(D) at different codes of a 25 kΩ
part. The wiper’s first connection starts at the B terminal for
data 000H. RWB(0) is 50 Ω because of the wiper resistance and it
is independent of the full-scale resistance. The second connection
is the first tap point where RWB(1) becomes 24.4 Ω + 50 = 74.4 Ω
–11–
ADN2850
for data 001H. The third connection is the next tap point representing RWB(2) = 48.8 + 50 = 98.8 Ω for data 002H and so on. Each
LSB data value increase moves the wiper up the resistor ladder
until the last tap point is reached at RWB(1023) = 25026 Ω. See
Figure 9 for a simplified diagram of the equivalent RDAC circuit.
25
RWB_FS = 25k
RWB (D) – k
20
The general equation that determines the programmed output
resistance between Wx and Bx is:
D
RWB ( D ) =
× RWB _ FS + RW
(1)
1024
where D is the decimal equivalent of the data contained in the
RDAC register, RWB_FS is the full-scale resistance between terminals
W and B, and RW is the wiper resistance.
For example, the following output resistance values will be set for
the following RDAC latch codes with VDD = 5 V (applies to
RWB_FS = 25 kΩ programmable resistors):
15
Table VIII. RWB at Selected Codes (RWB_FS = 25 k)
10
5
0
0
256
512
768
CODE – Decimal
Figure 10. RWB(D) vs. Code
D
(DEC)
RWB(D)
()
Output State
1023
512
1
0
25026
12550
74.4
50
Full-Scale
Mid Scale
1 LSB
Zero-Scale (Wiper contact resistance)
1023
Note that in the zero-scale condition a finite wiper resistance of
50 Ω is present. In this state, care should be taken to limit the
current flow between W and B to no more than 20 mA to avoid
degradation or possible destruction of the internal switches.
Channel-to-channel RWB matching is well within 1% at fullscale. The change in RWB with temperature has a 35 ppm/°C
temperature coefficient.
–12–
REV. B
Typical Performance Characteristics–ADN2850
1.0
36
+25C
–40C
+85C
0.8
34
32
30
0.4
28
OHMS
R-INL ERROR – LSB
0.6
0.2
26
24
0
22
–0.2
20
–0.4
–0.6
18
0
200
400
600
800
16
1000
0
200
400
600
TPC 1. R-INL vs. Code, TA = 40C, 25 C,
85 C Overlay, RAB = 25 kΩ
1000
1200
TPC 4. Wiper On-Resistance vs. Code
4
0.4
0.2
3
IDD @ V DD/V SS = 5V/0V
0
CURRENT – A
R-DNL ERROR – LSB
800
CODE
DIGITAL CODE
–0.2
2
1
ISS @ V DD/V SS = 5V/0V
–0.4
0
IDD @ V DD/V SS = 2.7V/0V
–0.6
ISS @ V DD/V SS = 2.7V/0V
–0.8
0
200
400
600
–1
–40
1000
800
–20
0
TPC 2. R-DNL vs. Code, TA = 40 C, 25 C,
85 C Overlay, RAB = 25 kΩ
40
60
100
80
TPC 5. IDD vs. Temperature, RAB = 25 kΩ
0.25
120
VDD/V SS = 5V/0V
RAR = 25k
VDD /VSS = 5.0V/0V
TA = 25C
100
FULL SCALE
0.20
80
MIDSCALE
60
40
IDD – mA
RHEOSTAT MODE TEMPCO – ppm/ C
20
TEMPERATURE – C
DIGITAL CODE
20
0
0.15
ZERO SCALE
0.10
–20
25k VERSION
0.05
–40
250k VERSION
–60
0
0.0E+00
–80
0
128
256
384
512
640
768
896
1023
4.0E+06
6.0E+06
8.0E+06
1.0E+07
1.2E+07
TPC 6. IDD vs. Clock Frequency, RAB = 25 kΩ
TPC 3. ∆RWB /∆T Rheostat Mode Tempco
REV. B
2.0E+06
FREQUENCY – Hz
CODE – Decimal
–13–
100
IW = IA
TA = 25C
0.5V/DIV
TA = 25C
THEORETICAL – IWB_MAX – mA
NORMALIZED RESISTANCE
ADN2850
RWB(D)
MIDSCALE
EXPECTED
VALUE
50S/DIV
10
1
RWB_FS = 25k
0.1
RWB_FS = 250k
TPC 7. Memory Restore During Power-On Reset
0.01
0
128
256
384
512
640
768
896
1024
CODE – Decimal
5V/DIV
CS
5V/DIV
CLK
5V/DIV
VSDI
TPC 10. IWB_MAX vs. Code
TEST CIRCUITS
Test Circuits 1 to 3 show some of the test conditions used in the
Specifications table.
NC
DUT
A
W
IDD
20mA/DIV
4ms/DIV
IW
B
VMS
TPC 8. IDD vs. Time (Save) Program Mode
NC = NO CONNECT
5V/DIV
CS
5V/DIV
CLK
Test Circuit 1. Resistor Position Nonlinearity
Error (Rheostat Operation; R-INL, R-DNL)
RSW =
DUT
5V/DIV
CODE = 00H
W
SDI
0.1V
ISW
+
B
ISW
IDD
2mA/DIV
_
0.1V
VSS TO V DD
4ms/DIV
SUPPLY CURRENT RETURNS TO MINIMUM POWER
CONSUMPTION IF INSTRUCTION 0 (NOP) IS
EXECUTED IMMEDIATELY AFTER INSTRUCTION 1
(READ EEMEM)
Test Circuit 2. Incremental ON Resistance
NC
TPC 9. IDD vs. Time (Read) Program Mode
VDD
DUT
A
VSS GND
B
ICM
W
VCM
NC
NC = NO CONNECT
Test Circuit 3. Common-Mode Leakage Current
–14–
REV. B
ADN2850
PROGRAMMING EXAMPLES
Table XII. Using Left Shift by One to Increment 6 dB Steps
The following programming examples illustrate the typical sequence
of events for various features of the ADN2850. Users should refer
to Table II for the instructions and data-word format. The instruction numbers, addresses, and data appearing at SDI and SDO pins
are displayed in hexadecimal format in the following examples.
SDI
SDO
Action
C0XXXXH XXXXXXH Moves wiper 1 to double the present
data contained in RDAC1 register.
C1XXXXH C0XXXXH Moves wiper 2 to double the present
data contained in RDAC2 register.
Table IX. Scratch Pad Programming
SDI
SDO
Action
B00100H
XXXXXXH
Loads data 100H into RDAC1 register,
Wiper W1 moves to 1/4 full-scale
position.
Loads data 200H into RDAC2 register,
Wiper 2 moves to 1/2 full-scale position.
B10200H
B00100H
Table XIII. Storing Additional User Data in EEMEM
SDI
SDO
32AAAAH
XXXXXXH Stores data AAAAH into spare EEMEM
location USER1. (Allowable to address
in 13 locations with maximum 16 bits
of data).
32AAAAH Stores data 5555H into spare EEMEM
location USER2. (Allowable to address
in 13 locations with maximum 16 bits
of data).
335555H
Table X. Incrementing RDAC Followed by Storing
the Wiper Setting to EEMEM
SDI
SDO
Action
Action
XXXXXXH Loads data 100H into RDAC1 register,
Wiper W1 moves to 1/4 full-scale position.
E0XXXXH B00100H Increments RDAC1 register by one to 101H.
E0XXXXH E0XXXXH Increments RDAC1 register by one to 102H.
Repeat the increment command –
(E0XXXXH) until desired wiper
position is reached
20XXXXH XXXXXXH Saves RDAC1 data into EEMEM1
Optionally tie WP to GND to protect
EEMEM values
Table XIV. Reading Back Data From Various Memory Locations
Table XI. Restoring EEMEM Values to RDAC Registers
Table XV. Reading Back Wiper Setting
B00100H
EEMEM values for RDACs can be restored by: Power-On,
Strobing PR pin or Programming shown below.
SDI
SDO
Action
10XXXXH XXXXXXH Restores EEMEM1 value to RDAC1
register.
NOP. Recommended step to minimize
00XXXXH 100100H
power consumption.
8XXXXXH 00XXXXH Reset EEMEM1 and EEMEM2
values to RDAC1 and RDAC2 registers
respectively.
REV. B
SDI
SDO
Action
92XXXXH XXXXXXH Prepares data read from USER1
location.
00XXXXH 92AAAAH NOP instruction 0 sends 24-bit word
out of SDO where the last 16 bits
contain the contents of USER1 location.
NOP command ensures device returns
to idle power dissipation state.
SDI
SDO
Action
B00200H
XXXXXXH Sets RDAC1 to midscale.
Doubles RDAC1 from midscale to
C0XXXXH B00200H
full-scale.
A0XXXXH C0XXXXH Prepares reading wiper setting from
RDAC1 register.
Readback full-scale value from RDAC1
XXXXXXH A003FFH
register.
Analog Devices offers a user-friendly ADN2850EVAL evaluation
kit that can be controlled by a personal computer through the printer
port. The driving program is self-contained, so no programming
languages or skills are needed.
–15–
ADN2850
APPLICATIONS
Optical Transmitter Calibration with ADN2841
VCC
Together with the multirate 2.7 Gbps Laser Diode Driver ADN2841,
the ADN2850 forms an optical supervisory system where the dual
programmable resistors are used to set the laser average optical
power and extinction ratio (see Figure 11). The ADN2850 is
particularly ideal for the optical parameter settings because of its
high resolution, compact footprint, and superior temperature
coefficient characteristics.
Incoming Optical Power Monitoring
The ADN2850 comes with a pair of matched diode connected
PNPs, Q1 and Q2, that can be used to configure an incoming optical
power monitoring function. With a reference current source, an
instrumentation amplifier, and a logarithmic amplifier, this feature
can be used to monitor the optical power by knowing the dc
average photodiode current from the following relationships:
I
V1 = VBE1 = VT In C1
(2)
I S1
I
V2 = VBE2 = VT In C 2
(3)
I S2
CS
ADN2841
W1
RDAC1
EEMEM
B1
PSET
IMODP
CONTROL
IBIAS
W2
RDAC2
SDI
ERSET
IDTONE
B2
DINQ
EEMEM
DIN
The ADN2841 is a 2.7 Gbps laser diode driver that uses a unique
control algorithm to manage both the laser average power and
extinction ratio after the laser initial factory calibration. It stabilizes
the laser data transmission by continuously monitoring its optical
power, and correcting the variations caused by temperature and
the laser degradation over time. In the ADN2841, the IMPD monitors
the laser diode current. Through its dual-loop power and extinction
ratio control, calibrated by the ADN2850, the internal driver
controls the bias current IBIAS and consequently the average power.
It also regulates the modulation current IMODP by changing the
modulation current linearly with slope efficiency. Any changes in
the laser threshold current or slope efficiency are therefore compensated. As a result, this optical supervisory system minimizes the
laser characterization efforts and enables designers to apply comparable lasers from multiple sources.
IMPD
ADN2850
CLK
VCC
DIN
DINQ
IDTONE
Figure 11. Optical Supervisory System
Knowing IC1 = a1 IPD, IC2 = a2 IREF, and Q1– Q2 are matched,
therefore a and IS are matched. Combining Equations 2 and 3
theoretically yields:
I

V2 – V1 = VT In  REF 
(4)
I
 PD 
Where IS1 and IS2 are saturation current
V1, V2 are VBE, base-emitted voltages of the diode connector
transistors
VT is the thermal voltage, which is equal to k × T/q.
VT = 26 mV at 25°C
k = Boltzmann’s constant = 1.38E–23 Joules/Kelvin
q = electron charge = 1.6E–19 coulomb
T = temperature in Kelvin
IPD = photodiode current
IREF = reference current
Figure 12 shows such a conceptual circuit.
POST
AMP
LPF
0.75 BIT RATE
TIA
DATA
CDR
CLOCK
10nF
IPD
IREF
RG
VT COMPENSATION
(1 + 100k/R G ) (V 2 – V 1)
AD623
IN AMP
LOG
AVERAGE
POWER
ADN2850
W1
W2
V1
C
PRC
THERMISTOR
V2
VDD
Q1
VSS
B1
B2
Q2
GND
LOG AMP
–5V
Figure 12. Conceptual Incoming Optical Power Monitoring Circuit
–16–
REV. B
ADN2850
The output voltage represents the average incoming optical power.
The output voltage of the log stage does not have to be accurate
from device to device, as the responsivity of the photodiode will
change between devices. An op amp stage is shown after the log
amp stage, which compensates for VT variation over temperature.
B1
Equation 4 is ideal. If the reference current is 1 mA at room
temperature, characterization shows that there is an additional
30 mV offset between V2 and V1. A curve fit approximation yields
V2
— V1
Figure 14. Reduce Resistance by Half with Linear
Adjustment Characteristics
(5)
W1
Such offset is believed to be caused by the transistors self-heating
and the thermal gradient effect. As seen in Figure 13, the error
between an approximation and the actual performance ranges is
less than 0% to –4% from 0.1 mA to 0.1 A.
0.30
R
B1
Figure 15. Resistor Scaling with Pseudo-Log Taper
Adjustment Characteristics
12
IREF = 1mA
TA = 25C
The equivalent resistance at a given setting is approximated as:
9
ERROR
0.20
6
0.15
3
0.10
0
0.05
–3
1.E-06
1.E-05
1.E-04
APPROXIMATING ERROR – %
DEVICE 1
DEVICE 2
DEVICE 3
CURVE FIT
0.25
V2 – V1 – V
W2
B2
Much lower resistance can also be achieved by paralleling a
discrete resistor as shown in Figure 15.
 0.001 
= 0.026 × In 
 + 0.03
 I PD 
0
1.E-07
W1
Req =
D × RWB_FS + 51200
D × RWB _ FS + 51200 + 1024 × R
(6)
In this approach, the adjustment is not linear but pseudologarithmic. Users should be aware of the need for tolerance matching
as well as temperature coefficient matching of the components.
BASIC RDAC SPICE MODEL
RDAC
25k
–6
1.E-03
B
IPD – A
CB = 11pF
Figure 13. Typical V2 – V1 vs. IPD at IREF = 1 mA
and TA = 25°C
CW = 80pF
Resistance Scaling
The ADN2850 offers either 25 kΩ or 250 kΩ full-scale resistance.
Users who need lower resistance and still maintain the numbers
of step adjustment can parallel two or more devices. Figure 14
shows a simple scheme of paralleling both channels of the programmable resistors. In order to adjust half of the resistance
linearly per step, users need to program both devices coherently
with the same settings. Note that since the devices will be programmed one after another, an intermediate state will occur, and
this method may not be suitable for certain applications.
W
Figure 16. RDAC Circuit Simulation Model (RDAC = 25 kΩ)
The internal parasitic capacitances and the external capacitive
loads dominate the ac characteristics of the RADCs. A general
parasitic simulation model is shown in Figure 16.
Listing I provides a macro model net list for the 25 kΩ RDAC:
Listing I. Macro Model Net List for RDAC
.PARAM D = 1024, RDAC = 25E3
*
.SUBCKT RDAC (W, B)
*
RWB W B {D/1024 RDAC 50}
CW W 0 80E-12
CB B 0 11E-12
*
.ENDS RDAC
REV. B
–17–
ADN2850
OUTLINE DIMENSIONS
16-Lead Frame Chip Scale Package [LFCSP]
5 x 5 mm Body
(CP-16 5x5)
Dimensions shown in millimeters
5.0
BSC SQ
PIN 1
INDICATOR
0.60 MAX
PIN 1
INDICATOR
0.60 MAX
13
12
0.80 BSC
4.75
BSC SQ
TOP
VIEW
16
1
BOTTOM
VIEW
0.75
0.60
0.50
9
4
8
3.25
3.10
2.95
2.40 BSC
0.70 MAX
0.65 NOM
12 MAX
5
0.05 MAX
0.01 NOM
0.90 MAX
0.85 NOM
SEATING
PLANE
0.40
0.33
0.28
0.20 REF
COPLANARITY
0.08
COMPLIANT TO JEDEC STANDARDS MO-220VHHB
16-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-16)
Dimensions shown in millimeters
5.10
5.00
4.90
16
9
4.50
4.40
4.30
6.40
BSC
1
8
PIN 1
1.20
MAX
0.15
0.05
0.20
0.09
0.65
BSC
0.30
0.19
COPLANARITY
0.10
SEATING
PLANE
8
0
0.75
0.60
0.45
COMPLIANT TO JEDEC STANDARDS MO-153AB
–18–
REV. B
ADN2850
Revision History
Location
Page
9/02—Data sheet changed from REV. A to REV. B.
Changes to GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Changes to ELECTRICAL CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Changes to Calculating Actual Full-Scale Resistance section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Changes to Table VI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
REV. B
–19–
–20–
PRINTED IN U.S.A.
C02660–0–9/02(B)