Help understanding voltage regulator specification - Page 1
Forum section: electronics / beginners

author: RoadRunner
author_rank: Frequent Contributor
timestamp: August 06, 2024, 10:37:49 pm
content: Hello,I am trying to build a circuit with LT3042 Voltage regulator, Regulator has Load regulation specification for Iload = 1mA to 200mA with Vin =2V and Vout =1.3V , Specification say Load regulation (delta Vos) = Max 0.5mVDoes this mean, With Vin=2V Vout = 1.3V, Load can change from 1mA to 200mA and Ouput voltage will not change more than 0.5mV?I hope someone can spend there time to share there knowledge.I have test this circuit in exact same condition with load from 10mA to 200mA and output voltage change is around 1.9mV.Thank you in advance for your time and help.

author: TimFox
author_rank: Super Contributor
timestamp: August 06, 2024, 10:50:12 pm
content: That spec requires that the input voltage is constant while the output current is varied.One tricky bit about a rectifier driving a regulator is that as the current drawn from the filter (somewhat higher than the regulator output current) increases, the peak-to-peak ripple increases, mostly at the bottom of the waveform, which requires a ‘scope to see what is happening.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: August 06, 2024, 11:18:50 pm
content: Quote from: TimFox on August 06, 2024, 10:50:12 pmI am supplying 2V from a bench supply. I have made sure that input voltage to regulator remains constant 2.000VBut still I see around 1.9mV drop in regulator output voltage with full 200mA load compared to 10mA load.Thank you for your time

author: thm_w
author_rank: Super Contributor
timestamp: August 06, 2024, 11:27:05 pm
content: "Does this mean, With Vin=2V Vout = 1.3V, Load can change from 1mA to 200mA and Ouput voltage will not change more than 0.5mV? "Thats what it looks like. Dropout max is 0.35V at 200mA so you should be within that.- Does your schematic match the Typical Application schematic or better?- Are you measuring directly across pins 8 and 10 to measure the output voltage?edit: You'll add a bit from offset vs. temperature as well (page 5).

author: TimFox
author_rank: Super Contributor
timestamp: August 07, 2024, 12:38:28 am
content: Also consider the connections between the IC output pin and your voltmeter.2 mV drop for 200 mA current is only 10 m\$\Omega\$ of series resistance.

author: PGPG
author_rank: Frequent Contributor
timestamp: August 07, 2024, 12:42:06 am
content: Quote from: RoadRunner on August 06, 2024, 10:37:49 pmFor me not.For me the 0.5mV limit is for Vos (difference between Vout and Vset) and not for Vout.ΔVout = ΔVset + ΔVos.You can probably directly measure Vos to see if its changes are less than 0.5mV (these two points are not too high impedance, I think).Vset depends on Iset that according to specification can change ±2% for Iload 1..200mA (load change certainly changes IC temperature and this way changes Iset).The other source of Vout changes can be voltage drop generated by Iload between reference resistor GND connection and output (where you measure Vout) GND connection if these both are not the same point.The output current change can also indirectly change reference resistor temperature and this way its resistance.

author: AnalogTodd
author_rank: Regular Contributor
timestamp: August 07, 2024, 01:01:33 pm
content: You need to reviewwhereyou are making your measurements. Are you taking the output of the regulator out to a test point where you connect both the load and your voltmeter? That can easily get you the 10mOhm needed to give that level of load regulation.No connection, trace, or wire is zero resistance. The LT3042 is going to regulate its output voltage based on where the GND pin is, the SET pin is, and where OUTS is connected. The part is tested, measured, and specifiedat the pinsof the package. Any parasitic resistance you add in when building it up in an application will throw off your results.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: August 07, 2024, 05:53:05 pm
content: Quote from: TimFox on August 07, 2024, 12:38:28 amQuote from: AnalogTodd on August 07, 2024, 01:01:33 pmThis exactly appears to be the issue. Dummy load was connected with crocodile clips and I was probing a little away on PCB trace PCB traces itself was causing drop of around 1.3mV.Once I measure on package pin every thing is well within specification.I am thankful for TimFox for being as clever as fox, and also AnalogTodd.Regards

author: AnalogTodd
author_rank: Regular Contributor
timestamp: August 08, 2024, 12:46:53 pm
content: Glad to help.