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  • +Documents
  • 1/f noise of the ADM7150/ADM7151 be reduced?
  • ADIsimPE Powering Dual Supplies Precision ADCs
  • ADIsimPE support
  • ADIsimPower Design Tools Download
  • ADIsimPower user guide 832
  • ADIsimPower user guide 842
  • Adjustable vs. fixed voltage option
  • ADM1030: Lowest pull resistor
  • ADM1030: Lowest pull up resistor
  • ADM1031: Unused D+ and D+ pins
  • ADM1060 Power Sequencer support for USB interface
  • ADM1062: ADC readback mode
  • ADM1062: Data storage on EEPROM
  • ADM1066 AUX Signals in the State Machine
  • ADM1066: application questions
  • ADM1068: internal Reference maximum current
  • ADM1085: transistor count
  • ADM1166 - CRC, configuration, EEPROM and RAM at startup query
  • ADM1166 Sequencing differential voltage query  (SR#: 1239446)
  • ADM1171: Current limit device
  • ADM1175_Vbus spec
  • ADM1232: Spikes on VCC
  • ADM1816: Voltage on reset line does not go to zero until the supply is approx 1V
  • ADM2483_ESD AB impedance
  • ADM2483_PV pin function
  • ADM2484 revA board
  • ADM2484E voltage specification
  • ADM2485 VDD2 voltage
  • ADM2587 layout to pass EMI/EMC tests
  • ADM2587E isolation ratings
  • ADM2587E max allowable voltages on RS485 pins
  • ADM2587E power consumption
  • ADM2587E Power consumption (1)
  • ADM2682E start up currents
  • ADM2682E/ADM2687E Creepage and Clearance
  • ADM2682E/ADM2687E Isolation Voltage
  • ADM2682E/ADM2687E providing additional current to external devices
  • ADM2682E/ADM2687E Recommended Application Notes
  • ADM2687E: Minimum and Maximum Viso specifications
  • ADM2687E: Power consumption while dissabled
  • ADM3053 max current on Visoout
  • ADM3053 Round Trip Propogation Delay
  • ADM3053 stitching capacitance
  • ADM3053/3053/3054 Isolated CAN Transceiver
  • ADM305x differences
  • ADM3075EARZ: What's its impedance when no supply is applied?
  • ADM3202 alternatve with swapped CMOS/RS-232 pins?
  • ADM3251 heat generation
  • ADM3251E - Prevent - minimize EMI isses
  • ADM3251E: Gerber file EVAL-ADM3251EEBZ
  • ADM3251_application high working temperature
  • ADM3252: Detecting the cable connection
  • ADM3491: Is resistor Rt needed between Y and Z (transmitter side) or only on the receiver side?
  • ADM4073T: Settling Time
  • ADM483E: Operation in fail safe mode
  • ADM485 - how does the fail-safe feature mentioned in the datasheet work
  • ADM6320CX and WDI query/comments(SR#: 1200246)
  • ADM696: Datasheet reset assertion guarantee
  • ADM706: IBIS model
  • ADM706: what happens if WDI Pin is left open or "High Impedance"
  • ADM706: What is the difference between difference ADM706PARZ and ADM706RARZ?
  • ADM709RAR_theta JA & theta JC
  • ADM7154, ADM7155: Are there any other design considerations for low noise?
  • ADM7154, ADM7155: Is the soft start time programmable?
  • ADM7154, ADM7155: What is the recommended headroom voltage?
  • ADM869L: absolute maximum ratings
  • ADP-I2C-USB _USB to I2C Interface Connector
  • ADP1046 Daughter Board compatible with existing one for ADP1043
  • ADP1048 - is is possible to use the ADP1048 with higher input frequencies?
  • ADP1048: Which control mode is used: continous current or  discontinuous current?
  • ADP1051: EEPROM programming procedure
  • ADP125 and ESR values
  • ADP130: Does the datasheet undervoltage lockout spec apply to Vin or Vbias?
  • ADP160-IGND Max
  • ADP1607 reverse current protection with EN high/low
  • ADP1607 to supply ADAU1761
  • ADP1621 and ADP2300/01: positive to negative conversion
  • ADP1829 Dual buck controller with a high side N channel FET
  • ADP197:
  • ADP198  What happens when Vout > Vin ?
  • ADP2108 layout considerations (high frequency switching regulator layout considerations)
  • ADP2118: fixed Output FB Pin
  • ADP2384, ADP2386 - Benefits of hiccup mode during over current/short circuit
  • ADP2384, ADP2386 - Deglitch time when PGOOD reversing
  • ADP2384, ADP2386 - Fastest soft start time
  • ADP2384, ADP2386 - Leaving RT pin open
  • ADP2384, ADP2386 - PGOOD feature
  • ADP2384, ADP2386 - PGOOD pin open
  • ADP2384, ADP2386 - Programming soft start time
  • ADP2384, ADP2386 - Setting the switching frequency
  • ADP2384, ADP2386 - SS pin unconnected
  • ADP2384, ADP2386 - Treatment of GND-EP (pin 25) and SW-EP (pin 26)
  • ADP2384, ADP2386 - Use of EN threshold to set input voltage UVLO
  • ADP2386, ADP2384 - Support of pre-charge start up
  • ADP2441 External Diode between SW and PGND
  • ADP2441 Floating Pins
  • ADP2441 Minimum ON Time
  • ADP2441 Peak Current Limit
  • ADP2441 Precharge Startup
  • ADP2441 VCC Pin
  • ADP2441: Factors to Improve Efficiency
  • ADP2441ACPZ-R7 Power Dissipation
  • ADP2504  Issues with supplied current and current limiting
  • ADP3040 - information available?
  • ADP3302: Input protection
  • ADP3330: max reverse voltage
  • ADP3330: Reverse current
  • ADP3338: Thermal and overcurrent protections
  • ADP5046 shuts down
  • ADP5050 considerations for simulations under Simplis
  • ADP5050 Pin20 as address pin
  • ADP5061 reading via I2C
  • ADP5090_91: Need to cut the load of ADP5090 if temperature is under 0�C and above 40�C for Li-Ion Battery Charging
  • ADP5585 interrupt (/INT pin) not asserting
  • ADP5588_work under 3.3V
  • ADP7112: Materials declaration is missing from ADP7112 web page
  • ADR01 reference's output long-term drift calculation
  • ADR125: Output Capacitance
  • ADR127: Turn-on time when using a 0.1uF in parallel with a 10uF at its output?
  • ADR3450
  • ADR365 supplied with DCDC converter
  • ADR366: External Capacitors
  • ADR381 output capacitor ESR
  • any isolated RS-422 driver with no bit errors during EFT test?
  • Are any external components required?
  • Are there any layout considerations when designing in the ADP5052?
  • Are these devices automotive replacements for the ADM6316/18/19/20/21/22 parts?
  • Boost converter recommendation
  • CAN FD version of ADM3053
  • Can I configure ADM3491 in half duplex mode of operation
  • Can the 4 bucks run at different frequency?
  • Can the ADP1047/8 be used as a three-phase PFC controller?
  • Can the ADP1051 be used to control a buck fed push pull (or full bridge) power stage?
  • Can the CS1 pin of the ADP1043A, ADP1046A, ADP1050, ADP1051, ADP1055 be floating?
  • Can the voltage VS- pin (VS3- for ADP1046A) of ADP1050/51/55 operate at a voltage higher than 0.3V?
  • Can you supply PVIN1, PVIN2, PVIN3, PVIN4 and PVIN5 independently?
  • Can you use an inductor not specified in the datasheet?
  • Customer programmable fuses on ADP5053?
  • DAC power up default state of ADM1066
  • Difference between ADM2682E and ADM2687E
  • Does the output noise of the ADM7154/ADM7155 scale with the output voltage?
  • Drivers for Linux, No-OS microcontrollers and FPGA
  • Emissions by ADM2582E at 1.5GHz .. 1.1GHz
  • Explanation on ADM3483 Driver Output/Receiver Input Voltage
  • FAQ: Can I use the square wave at 50% duty cycle to sync with the ADP1047/48?
  • FAQ: How can I program Analog Devices' Digital Power products?
  • FAQ: How close to drop out voltage can one operate an LDO in order to squeeze the last ounce out of my circuits efficiency?
  • FAQ: How is voltage noise of an LDO measured?
  • FAQ: Layout of Switching Power Supply
  • FAQ: Layout recommendations for uPMU/PMU
  • FAQ: Photosensitive?
  • FAQ: Powering op-amps (or ADCs) with Dual Supplies
  • FAQ: Switching Regulators vs LDOs
  • FAQ: Tips for building the ADIsimPower  boards
  • FAQ: Tips for soldering a LFCSP (QFN) package for a prototype
  • FAQ: Tips for taking efficiency data
  • FAQ: Vin range on an Adjustable Output LDO.
  • FAQ: Where to find package information for ADI parts
  • Green idle power saving
  • Half-bridge dc/dc controller
  • Hand soldering a 12 pin LFCSP
  • Hand soldering the dual belly pad ADP2384
  • How are the datasheets split out for these products?
  • How can I disable one channel when I don't' use it?
  • How close to drop out voltage can one operate an LDO in order to squeeze the last ounce out of my circuits efficiency?
  • How close to drop out voltage can one operate an LDO in order to squeeze the last ounce out of my circuits efficiency? (1)
  • How Do I Generate Negative Supplies?
  • How does the windowed watchdog operate at power up or after a reset event?
  • How is the output noise spectral density of a low noise LDO measured?
  • How is the output noise spectral density of an ultra-low noise LDO measured?
  • How is the RMS output noise of a low noise LDO measured?
  • How is the RMS output noise of an ultra-low noise LDO measured?
  • How much current can the ADN8831 supply to a TEC?
  • How should I connect ADM2483's Power Valid Pin (PVP) when not using it?
  • How to handle the sequence in ADP5052?
  • How to use the ADIsimPower design tools with ADIsimPE integration
  • Ib +- of Op
  • Inquiry on MAX Junction Temp Ratings.
  • Interface box for ADM1062 Sequencer
  • Is it possible to disable the watchdog functionality if not required?
  • Is it possible to order a version with factory programmed output voltages?
  • Is there any guideline for EEPROM programming and factory calibration for ADP1050 and ADP1051?
  • Isolated DC-DC Power Supply 20W, 36-72V Input , 5V output
  • Key difference between the ADM268xE and ADM258xE
  • level of automotive qualification do these parts have?
  • LT3439 Power Dissipation Calculation
  • LT8705 alternative
  • Measuring Signals in a Switching Power Supply
  • Minimum Load Current Operation - Zero load Operation
  • Paralleling LDOs to Create More Output Current
  • Power by Linear Support Community INTRO
  • Power Management solution for Altera Arria 10 FPGA
  • Powering Analog circuit through SMPS.
  • Product Analog Devices USB-SMBUS-CABLEZ.
  • PWM Setup ZVS app note
  • Ref design recommendation
  • selecting an external FET?
  • soldering temperature and soldering time
  • Thermal Information
  • Thermal Information of ADR01TUJZ-EP-R7
  • Typical markets/applications for this device
  • USB-SDP-CABLEZ software installer link is broken on User Guide.
  • Use ADM1062's ADC from inputs VX1-5, VP1-4, VH & Temp sensor without averaging?
  • Voltage Regulator for 16-bit ADC AD7626
  • VPx input impedance of ADM1069
  • What are "Standard models" listed in the datasheets?
  • What is ADIsimPower?
  • what is the best digital controller for  isolated boost mode current fed converter?
  • What is the difference between MTBF and MTTF?
  • What type of passive filters can be added to the output of a linear regulator without causing instability?
  • What's the ADP3634's internal driver's resistance, Rdson?
  • What's the big differentiation for ADP5052 in the market?
  • Where can I find a programming procedure to implement EEPROM programming of  ADP1051?
  • Where can I find the ADP1870 EVB Gerber Files?
  • Where can I find the Package/Leadframe material information for ADR225HFZ (8 ld Ceramic Flatpack)?
  • Why would a customer require a windowed watchdog part over a normal watchdog?

Minimum Load Current Operation - Zero load Operation

As an application engineer working with customers in the design of linear regulators and switching regulators I have been asked multiple times if a specific device needs to have a minimum load.

I have worked with LDOs and Switchers for the last 20 years and I have only seen a few devices that were NOT designed to operate at no load.

In most cases it is not an issue of stability but an issue of leakage current through the pass element. Most devices are stable at no load, so why do people ask repeatedly about this issue?  It's possible that in the past some power devices were designed to operate with a minimum load to guarantee stability, but recent devices are most likely all designed to operate with no load.

How to tell?

If the device had an issue operating at no load the datasheet would surely have a line a note or comment about it.

As an example the ADP1740, a very low voltage high current LDO (2A), falls into this category. Mostly because at high temperature above 85degC the leakage current from the integrated large power switch may be in the order of 100uA and may reach 500uA at 125degC (worse case). If there is true no load, that leakage current could charge the output cap higher until the VDS of the switch is low enough to reduce that leakage current to a negligible level. Effectively this creates a potential rise in output voltage at no load.

This is what you would see in the datasheet. It says 500uA min load. In this case if the user wants to use the device at high temperature a dummy load may be advisable. This load would be fairly low compared to the 2A current rating of the device.

This is an issue more prevalent with high current low voltage (<1.5V) type of devices and I have not seen it in other higher voltage lower current regulators. But it's always good to double check the fine prints in the datasheet.

I believe though that there are still other sources of confusion about this topic as customers ask repeatedly even (or especially) if the datasheet does not specify a min load.

Here are some of the examples of concern explained:

- The datasheets do not specifically talk about minimum load (because there is no limitation) but often the datasheet contain typical operating graphs that show a certain range of operation. Most of these graphs are logarithmic and show multiple decades of load ranges, but of course a log scale cannot go to zero. Here is an example from the ADM7160 datasheet that shows the load range from 10uA to 200mA. This does not mean that 10uA is the min load, it's just the point where the datasheet editor decided to start taking data.

- In other tests listed in the datasheet there are graphs measured at multiple load currents (example Iq vs Vin) and most of the times there is no graph at zero current, Why is that? Just an oversight, again not because the device is not stable at zero load current.

- Another source of concern in datasheets is the fact that parameters such as PSRR, Line Regulation, Load Regulation or Noise may be listed over a certain load current range.

Here is an example of a Load Regulation specification from the ADM7160 datasheet, it states that load reg is specified from 100uA to 200mA

It does not mean that the LDO cannot operate at say 10uA or zero load, this is just the range of currents the test is performed at during production.

- In the case of switching regulators, users are often worried about the operation at light load when a device has what's called a PSM mode (Power Saving mode) that reduces the operating frequency, skips pulses, bursts pulses or a combination of all of these. PSM mode is not an unstable operating condition, it is a mode specifically designed to reduce power consumption and therefore increase efficiency at light loads. The typical disadvantage is a noticeable increase in output ripple that some users may believe it's instability. The device is not unstable in this operating mode and it can easily operate with no load at all.

Here is an example of a picture from the ADP2370 datasheet that shows the increased ripple due to PSM operation when the load changes from 800mA to 1mA back to 800mA. The increase in ripple is due to the PSM mode, the device is stable. Also the fact that the test was done at 1mA does not indicate that 1mA is the min load for this condition.

This other graph shows the ripple voltage changing with load current. In this case the graph goes all the way to zero. Indicating both the fact the load can be zero and the fact that the noise at no load may not be any worse than the noise at 1mA or 10mA.

Hopefully this FAQ is able to appease some of the concerns that customers have when asking about no load operation. Again I have never seen in the last many years a device that was not stable at no load.

Let me know if you have had other sources of concerns about no load operation and I will try to respond to it.

Best Regards,

LucaV

  • ldo stability
  • no_load
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Anonymous
  • hyao
    hyao
    •  Analog Employees 
    over 5 years ago


    Hi Jim,

    It is not clear to me from the one line ASCII schematic. Would you send your full schematic to my email address? hong.yao@analog.com

    Thanks,

    Hong

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  • jimacb
    jimacb over 5 years ago in reply to hyao

    Of course...  I thought of the body diode a little later.  Silly me.  How about if I protect ADP with a diode from the sometimes lower source to the input of the ADP.  That way the body diode would only have to source the quiescent current of the ADP.  See ASCII schematic below.  Thanks, Hong!

    12.1V -|>|---[VIN  {ADP2442}  SW]-----12.6V

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  • hyao
    hyao
    •  Analog Employees 
    over 5 years ago in reply to jimacb

    Hi Jim,

    Basically the answer should be no because of the bode diode of the high side switch.

    Regards,

    Hong

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  • jimacb
    jimacb over 5 years ago in reply to LucaV

    I want to run an ADP2442 as a redundant supply which only steps in if a battery fails.  My idea is to set the regulated voltage below the minimum allowed battery voltage.  It's possible that during normal operation (ADP2442 inactive) that the input voltage to the ADP2442 may be more, less, or equal to the battery.  I think according to what you're saying, I'm OK.  To be clear, can I have the output voltage slightly higher than the input voltage?

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  • LucaV
    LucaV
    •  Analog Employees 
    over 6 years ago

    I have an update to this posting as the questions keep coming ...

    Recently a customer asked about a strange behavior at light load for one of his LDOs. The output voltage is going out of regulation and drifting higher than the target regulation point.

    It turns out on his board he had a leakage path where current was sourced to the output of the LDO from another device. LDOs are designed to source current to the load and not sink current from the load. In his case this leakage current (of a few uA) was higher than the load current putting the LDO in a situation where that current needed to be absorbed by the LDO (sink) and of course that cannot happen.

    LDOs cannot sink current unless that is specifically stated in the datasheet.

    Some references, like the ADR44x, fall into the LDO category and are designed to source and sink current, so if you need a device to absorb leakage current you may want to look into that capability in the datasheet or look at a reference device.

    This may fall into the category of "no load issues with LDOs" but it's because there is a "negative" load and not a true zero or light load.

    LucaV

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