FAQ
AD5165 - FAQ
Can I read back the wiper setting of the digital potentiometers?
Yes if you use the AD5231/5232/5233/5235, AD5263, AD5241/5242, AD5280/5282, AD5245, AD5170/5171/5172/5173, AD5243/5248, AD5246/5247, as well as the AD525X family.
Are ADI's digital potentiometers suitable for use in photodetector amplifiers and will they suffer from leakage currents which could affect the gain of the circuit?
We manufacture this product with a very low leakage analog switch process, which results in low leakage currents. We usually spec a common mode leakage current of 1nA typical.
Can digital potentiometers do log taper adjustment?
Yes, if you use AD5231/5232/5233/5235 or ADN2850. On the other hand, a psuedo log taper adjustment is possible in other linear adjustment pots with this simple configuration. Please see the Linear/Log Taper Article
Are all digital potentiometers limited to |5V|?
No. The AD7376 and AD5290 handle ±15V or single +30V. The AD5260/5262/5280/5282/5263 all handle ±5V or single +12V. The remaining ones are limited to |5V|.
Can a digipot be used to construct a programmable high current source?
A current boosted or Howland current pump can be used as suggested by the AD5231 datasheet.
Are PB-free digital potentiometers available?
Yes, all new DigiPOTs are released as RoHS compliant and therefore lead-free. Most of the earlier parts have new material numbers available to order that are RoHS compliant. Material numbers containing a letter Z following the package code are compliant. Device branding contains the symbol # preceding the date code. Please see product page ordering guide.
After the specified EEMEM data retention timeout period, can the power be turned off and back on so that the part is considered "refreshed"?
No. That will only refresh the RDAC register but not the EEPROM. The data will have to be reloaded again after 15 years in order to put a fresh charge into the EEPROM cell. This can be done by writing the RDAC wiper register data back to the EEPROM before the end of 15 years.
Can I cascade, serialize, or parallel multiple digital potentiometers to get the resistance or resolution I need? My requirement is for a 250 Ω digital potentiometer with approximately 1 Ω/step. I plan to use four 1 kΩ AD8403 in parallel with each set to nominally the same value.
Yes, see the application note AN-582 "Resolution Enhancements of Digital Potentiometers with Multiple Devices."
Can I read back the contents of the two RDAC registers of AD5242 or AD5282 (dual I2C compatible digital potentiometer)?
Yes you can read back the RDAC register content (RDAC value of a specific channel). However, you can only read the RDAC channel that was selected during the previous WRITE mode. If the channel you want to read from is different from the channel previously written to, a dummy WRITE command is necessary to select the desired channel. Please see the datasheet for details.
Are there any evaluation boards for the digital potentiometers?
Yes, we have evaluation boards for most parts. Please see product page ordering guide.
Can I adjust the digital potentiometer for frequencies around 1MHz to 10MHz for adjusting the gain of a video signal?
It depends. Bandwidth is a function of the code and end-to-end resistance RAB. Lower RAB and codes yield higher bandwidth. 10MHz bandwidth or above is possible if you use a 1 kΩ version of AD8400 or AD5273 and limit your codes to a low value range. Please see datasheets for Bode plots.
Can I program two channels of a multi-channel digital potentiometer at the same time?
The AD5251/5252/5253/5254 and AD5232/5233/5235 are able to increment and decrement all the channels simultaneously. In addition, user can write to each EEMEM then issue a RESET command to update all the RDAC settings simultaneously.
Can a digitally controlled variable resistor withstand greater than 20mA?
No.
How is the resistance matching device to device?
Assuming the parts come from the same batch, the resistance matching device-to-device is believed to be ±1% as well.
If I use the digital potentiometer in a "dry" circuit (current through wiper < 1 pA), will it behave as a linear resistor in rheostat mode?
It is linear. RWB is made up by RS + RSW where RS and RSW are step resistors and a switch resistor respectively.
How is the THD performance of digital potentiometer?
This parameter is code and VDD dependant. Typically, it is in the range of 0.005% to 0.1%. Please see datasheet for specific performance. The best THD performance is achieved when the part is operated at its maximum operating voltage.
Is digital potentiometer a real replacement for mechanical potentiometer or are there restrictions regarding voltage potentials?
Strictly speaking, digital potentiometer is not an exact replacement for mechanical potentiometer. The larger one of VA and VB must be smaller than or equal to VDD, and the smaller one of VA and VB must be greater than or equal to VSS, or GND if the part does not have a VSS pin. For example, if the desired VA and VB are +2V and -2V, then VDD must be >= +2V and VSS must be <= -2V. In any case, voltages across terminals W-A, W-B, or A-B of all digital potentiometers (except AD7376, AD5260/2, AD5280/82, AD5290, and AD5263) should be limited to |5V|, the polarity constraint.
How are the wiper values changed on these digital potentiometers?
The wiper positions are controlled via a 3-wire SPI, 2-wire I2C, or up-down digital interface. In addition, the AD5228 is controlled with push buttons.
How do I tell the end-to-end RAB resistance value?
Take AD8400 as an example. The markings AD8400AR1, AD8400AR10, ADR8400AR50, AD8400AR100 (AD8400ARC) stand for 1kΩ, 10kΩ, 50kΩ, and 100kΩ parts respectively. Some parts may have different value designators from these. For example, our very compact packages such as SOT, SC-70, or MSOP are branded with 3-letter codes. Please consult the datasheet prior to ordering.
How many write cycles can the EEMEM go through before it fails?
100,000 cycles.
If I program Ch 1 from zero to full scale, will I expect Ch 2 to be disturbed?
We call this step response crosstalk. It is different from Analog Crosstalk. Again, the datasheet usually publishes such numbers. They are typically in the range of 5-10 nV-s . Please refer to AD5172 datasheet Figure 25.
If I use the digital potentiometer in audio volume control, will I experience zipper noise?
There is a noticeable zipper noise. However, we have developed an external zero-crossing detector that effectively reduces the zipper noise. Please refer to AD5290 datasheet Audio Volume Control section.
I'm unsure about how to use pin 13 write protect (/WP), pin 14 preset (/PR), and pin 16 ready (RDY)?
Please see datasheets.
How good is the resistance matching between Ch1 and Ch2 in the dual digital potentiometer?
The matching is typically 0.1-0.2% and we usually specify ±1% as a maximum.
I would like to know how the digital potentiometer is built. How ideal are the wiper switches?
It is a purely CMOS device. All switches are large CMOS transmission gates operated in the linear region to yield low uniform RDS(on). All resistor elements are poly silicon or thin film resistors.
WPピンとPRピンの使用目的
Q： WPピンとPRピンは具体的にどういったピンですか？仕様書を見てもわかりません。使用する必要があるときプルアップ抵抗で電源につってGNDに落とせばよいのですか。もしそうなら適正な抵抗値はいくらですか。この使用方法は可能ですか？
A： WPピンはEEMEMの内容が不用意に書き換えられないようにプロテクトするピンです。このピンをHにするとコマンドの1, 8およびPRの入力以外の指示を受け付けなくなります。HからLに戻す時は、NOP命令を入れてから戻してください。詳細はAD5231の英語のデータシート14ページの「EEMEM Protection」の項をご覧ください。使用しない場合はプルアップが必要です。抵抗値は2.5µAの入力電流に対して2.4V以上が確保できる値を選んでください。
PR入力がアクティブになると、RDACのスクラッチパッドレジスタの内容をEEMEMの内容でオーバーライド（書き込み）します。EEMEMの内容を電源オン時に設定するにはこの機能を使用します。詳しくはAD5231英語データシート8ページのピンの「Table 4. Pin Function Descriptions」、14ページ、16ページをご覧ください。使用しない時はWPと同じくプルアップが必要です。
使い方としては、電源オンのみでの設定は不可です。パワーオンリセット回路などで電源オン後にPRに信号を入れてやる必要があります。
可変抵抗器として使用できる？
Q： デジタルポテンショメータのAとWの端子を使って、抵抗値を使用したいのですが可能ですか。 通常A-B間をVCC-GNDとしてWで電圧を取出す事は理解しています。
A： デジタルポテンショメータは、可変抵抗器として使用することが可能です。 ただし機械式のポテンショメータと異なり、A,BおよびWの端子に加わる電圧は電源電圧範囲内であることと、電源が入っていない時に各端子に電圧が加わってはいけないという制限があります。
O1, O2, SDOピンの処理方法
Q： ワイパー値をサ－チし適正な抵抗値をEEPROMに書き込みます。電源オフにしても次にオンした時に自動で（コマンドいれずに電源オンのみで）記憶したワイパー値に設定します。 このときO1, O2, SDOピンは使用予定ではないのですがOPENにしていても問題ないですか。
A： O1, O2, SDOを使用しない場合は、オープンでもかまいません。これらは全てオープンドレインの出力です。詳しくはAD5231英語のデータシートの15、16ページをご覧ください。
What is the maximum current I can force into the digital potentiometer?
The maximum current is limited by 3 boundaries at a given resistance setting. They are the terminal voltage range limit, the power dissipation, and the maximum current handling capabilities of the internal switches. Voltage limitation is the dominant factor in most settings. 1 kΩ and 10 kΩ settings yield 5.5mA and 0.55mA maximum respectively for 5V digipots. Maximum power dissipation becomes a factor at low resistance values. At zero scale with a minimum wiper resistance, 20mA is the max allowable pulse current limit imposed by the switches. There are Imax vs. Code graphs shown in the new product datasheets.
What is the resistance tolerance of the digital potentiometers?
It is either a maximum of ±30% or ±20%. Please see datasheets.
If using the pot in the 3-terminal voltage divider mode (without any series resistor), the tolerance is irrelevant because the resistances RWA and RWB are ratiometric. If using the pot in the 2 terminal rheostat mode, you should account for the worst case variation. On the AD525X family and AD5235 digipots resistance tolerance is stored in the EEPROM at factory with an accuracy of 0.1%. Thus users can retrieve the resistance tolerance and calibrate the system accordingly.
What is the ESD rating of digital potentiometers?
All digital potentiometers have ESD protection above 1kV.
デバイスの電源がoffの時に、W（ワイパー）やA、B端子に電圧を印加することは可能ですか？
Q： デバイスの電源がoffの時に、W（ワイパー）やA、B端子に電圧を印加することは可能ですか？（GNDは共通）
A： ストレスにより破壊する危険がありますので、不可です。
計装アンプのゲイン設定端子にデジタル・ポテンショメータは使用可能か？
Q： 計装アンプの利得設定端子（Rg端子）にデジタル・ポテンショメータは使用可能ですか？
A： 電源電圧が+5Vとなっているデジタル・ポテンショメータでは両電源で動作する計装アンプのゲイン抵抗として使用することは出来ません。 ±15V電源で動作可能なデジタル・ポテンショメータをゲイン抵抗として使用可能ですが、抵抗値の誤差が大きいため（±30%）正確なゲイン設定は得られません。
Is there a digital potentiometer controlled by a parallel input?
No, but you may consider using a parallel input DAC instead if you plan to use the digital potentiometer in voltage divider mode.
Is there a particularly low-power digital potentiometer?
Yes. The AD5165 offers ultra-low power consumption.
Is there a power up sequence I should follow?
Yes, it is good practice to power VDD first and VSS second. The order of VA, VB, and VW is not important but they should be powered last. There are ESD protection diodes between the VDD and the A, B, and W terminals. For example, the cathode of one of the diodes connects to VDD and the anode connects to the A terminal. As a result, any voltage occurring at the A terminal before VDD will forward bias the diode and power the VDD. For AD5231/AD5232/AD5233/AD5235 only, the digital signals should also be powered after VDD. Please refer to datasheets for additional information regarding digital signal sequence.
Level Shifting Digital Signals from 0V to +5V to -5V to 0V
Please refer to AD5282 datasheet Figure 9.
Level Shifting Digital Inputs from 3.3V to 5V or Vice Versa
Please refer to AD5247 datasheet Figure 35.
Is there crosstalk between Ch1 and Ch2 of a dual digital potentiometer such that a sine wave applied to Ch1 will occur in Ch2 as well?
It is negligible, and datasheets usually publish such performance and it is typically -70dB. Please refer to AD5172 datasheet Figure 26.
Regarding the spec on R-DNL, I am only concerned with relative adjustments. I'm not concerned with the actual value of the resistor in the digipot but need the digipot to be monotonic.
Yes, the digipot is monotonic.
デジポットの抵抗値の計り方
Q： デジタル・ポテンショメーター（デジポット）の抵抗ラダー抵抗値を、テスターを使用し非通電状態で端子間を実測しようとしましたが測定できませんでした。
A： デジポット・デバイスは、ポテンショメータ（可変抵抗）という意味合いではありますが、実際の内部はラダー抵抗がつながったDA変換器になっています。その点からしますと回路に電源を入れて動作させていないと、内部のトランジスタがオフ状態のままになっていますので、測定はできません。測定したい場合は、測定系を治具として作成し、それに差し込んで規定状態で電気通電し、抵抗を計測するということが一番良いと考えます。
Is there a dependency between the logic level and power consumption?
Yes. If the logical level is lower than the supply VDD, the CMOS gates will not switch completely and the part will consume more power.
What are the common failure modes of digital potentiometers?
- Latch up can occur when the prescribed power-up sequence (VMDD->VMSS->GND->VA ->VB) is not followed.
- A voltage greater than |VMDD - GND| or |VMDD - VMSS| (if dual-supply) applied across terminals A-B, W-B, or W-A can cause failure.
Why are some digital potentiometers' maximum operating temperature only 85°C instead of the standard 125°C?
The digipots that contain EEPROMs usually only work up to 85°C, and this is because EEPROMs are only guaranteed to safely operate below 85°C.
Why Should I replace mechanical potentiometers with digiPOT?
Digital potentiometers have:
What is the tempco of the digital potentiometer?
There are two components that make up the resistance at any given setting. They are the poly silicon resistors (step resistor Rs) and the CMOS switch resistor (Rsw=50 Ω at 5V supply). Together they add up such that RWB = RS + RW, RS = RAB / 2N * D, where D is the decimal code. The tempco of the step resistor, which is published in the datasheet, is typically in the range of a few tens of ppm/°C for thin film or a few hundred ppm/°C for poly. The resistance of the switch, on the other hand, doubles in 100°C. As a result, the overall tempco is nonlinear and it is worse off at low value codes where the switch resistance dominates. Users should refer to the tempco graphs in the datasheets for more detailed information
Will the data in the EEMEM need to be refreshed after 15 yrs when it is operated at 55°C?
Yes. The EEPROM cells will lose charge over the 15 years when operating at 55°C. For other operating temperatures please see the "Retention vs. TJ Junction Temperature" plot in the AD5232 datasheet. Such data applies to all nonvolatile memory digital potentiometers.
What is the maximum frequency that can be applied to the digital potentiometer CLK input?
For SPI and U/D digital interfaced digipots, the maximum clock frequency is in the range of 10MHz to 20MHz. For I2C-compatible digipots, the maximum clock frequency is guaranteed for 400kHz.
What is the noise performance of digital potentiometers?
We usually just specify the thermal noise (Johnson Noise) which is eN = sqrt(4*k*R*T*BW) where k is Boltzman's constant, k=1.38E-23, R is resistance, T is temperature in Kelvin and BW is bandwidth. To reduce noise, one should reduce R in the system and/or the operating BW. Thermal noise is believed to be a major noise component and good for 1st order approximation. The total noise in the system is usually slightly higher.
What should I watch out for when I replace mechanical potentiometers with digital potentiometers?
Voltage and current levels are the two important issues in digiPOT. You must make sure that the voltage and current are below the maximum ratings specified in datasheets
For a digital potentiometer that requires 12-bit word length, how can I control with only 8-bit word length from my micro?
You need to issue a 2 byte word. The first 4 MSB in the first byte are ignored.
Do digital potentiometers handle bipolar and AC operations?
Yes, we have digital potentiometers with dual ±2.5V, ±5V, or ±15V supplies that can handle bipolar or AC operation. You can still achieve AC operation with a single DC supply if you raise the DC offset. Terminals A, B, and W have no polarity constraints with respect to each other.
Do you provide any software to control the digital potentiometers?
We have Visual Basic programs which drive the digital potentiometers via the parallel port of a PC. This software is available with our evaluation board or downloadable from the website.
How do I daisy-chain multiple potentiometers? How does the serial interface work for multiple AD8403's when there are still only two address bits? Are there multiple /CS lines, one for each individual chip?
The address bits are for addressing multi-channels within a device only. For multiple device operation, you will need to daisy-chain them. For example, daisy-chaining two quad-channel AD8403 gives a total of 8 channels. You can program any combination of two channels (in different packages) at the same time with the 1st device's SDO pin tied to the 2nd device's SDI pin with a 10k pull-up resistor. Then, you would send 20 bits into the SDI pin of the 1st device while keeping the /CS of both devices low. The 1st 10 bits go to Device 2 and the 2nd 10-bits go to Device 1. When /CS is pulled high, both channels will be updated.
Digital Feedthrough
Digital Feedthrough is the amount of noise from Clock or Data coupled into the output. It is usually very small in few nV-s range. Please refer to AD5172 datasheet Figure 24.
For dual supply digital potentiometers, if VDD/VSS are +2.5V/-2.5V respectively, can digital inputs be fed from a standard 3.3V CMOS logic component without logic level translation? What are the logic level thresholds when VDD is +2.5V and VSS is -2.5V?
For most of our digipots, you may use a standard 3.3V on the digital inputs. For AD5231/2/3/5, however, the digital input levels cannot be higher than 0.3V above VDD or 0.3V below ground, or +2.8V and -0.3V in this case. Otherwise, the internal protection diodes may be damaged. The logical level thresholds differ from parts to parts and are also supply dependent. For example, for AD5231/2/3/5, at VDD= +2.5V and VSS = -2.5V the logical level high and low are +2.0V and +0.5V, respectively. Please check datasheets for more details.
Does the memory allow the device to return to the last stored value without an update from a micro?
Yes. It is automatically set to the previously stored value every time the device is powered-on.
For a digital potentiometer that requires 6-bit word length, what happens if I have 8-bit word length from my PC?
It will work for SPI parts. Since the data is loaded MSB first, the digital potentiometer will ignore the first two bits and recognize the last six bits.
Can I use the new PB-free DigiPOTs in my traditional solder based PCB assembly process?
All of the PB-free parts are backward compatible with existing Lead (PB) based soldering systems.
For digital potentiometers that do not have nonvolatile memory, what is the state during power up?
Most of our digital potentiometers contain P.O.R. (power on preset) circuitry which presets the wiper-to-terminal resistance to the middle value of the terminal-to-terminal resistance. For example, If RAB = 10 kΩ, then at power-up RWB = RWA = 5 kΩ. For the digital potentiometers that do not have this feature, the wiper-to-terminal resistance can be anything at power-up. Please check the datasheets for more details.
電子ボリュームの各端子は、グランドショート可能でしょうか。
Q： 電子ボリュームのワイパー出力(W1端子)をトランジスタ、またはFETにより直接GNDへ短絡しようと考えています。この端子は、GND等にショートは可能でしょうか。
A： 電子ボリューム素子のワイパー端子（その他の端子も含めて）は電源 / グランド、あるいはそのほかの電源電圧範囲内の低インピーダンスソースに短絡することは可能です。ただしボリューム内部を通過してワイパーに流れる電流に制限があります。この電流は、絶対最大定格に対して十分余裕を持たせてください。信号入力のソースインピーダンスが低く、ワイパー位置がハイ側（信号入力側）に近い場合は、注意が必要です。