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Question

What is line regulation? How can I calculate the output voltage change by considering the line regulation?

Answer

LDO Linear RegulatorsHow to use

Line regulation refers to what extent the output voltage varies as the input voltage changes.

The following figure describes a specification example of line regulation.

SymbolParameterTest ConditionsMin.Typ.Max.Unit
ΔVOUT / ΔVINLine RegulationSet VOUT + 0.5 V ≤ VIN ≤ 5.25 V, VIN ≥ 1.4 V 0.020.10%/V
SymbolΔVOUT / ΔVIN
ParameterLine Regulation
Test ConditionsSet VOUT + 0.5 V ≤ VIN ≤ 5.25 V, VIN ≥ 1.4 V
Min. 
Typ.0.02
Max.0.10
Unit%/V

This figure suggests that when the input voltage within the range mentioned in the condition changes by 1 V, the output voltage varies by typically 0.02 % / maximum 0.10%.

With an example of a 1.8 V output LDO regulator whose input voltage varies from 3 V to 4.2 V, the extent of variations of the LDO output voltage by line regulation can be estimated as below:

Input Voltage Variation (ΔVIN) :
4.2 V - 3 V = 1.2 V
Output Voltage Variation (ΔVOUT) :
Based on the line regulation characteristic, ΔVOUT is determined by the following formula:
Typ. 0.02%/V × 1.2 V = 0.024% 1.8 V × 0.024% = 0.432 mV
Max. 0.10%/V × 1.2 V = 0.12% 1.8 V × 0.12% = 2.16 mV

In short, by the input voltage difference between 3 V and 4.2 V, the 1.8 V output changes by typically 0.432 mV / maximum 2.16 mV. The output voltage may be affected both positively and negatively.

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