Linear voltage regulator quiescent current is very low?

[treez]

Hello,

The MCP1703 linear voltage regulator |(SOT89 package) claims to consume just 5uA of quiescent current (page 3 of datasheet).....


https://ww1.microchip.com/downloads/en/DeviceDoc/22049f.pdf

..that surely cannot be correct?....its far too low?..........when this regulator is delivering say 20mA of current to the load, is it still only drawing 5uA of quiescent current?

(Vin will be 9.25V, Vout will be 3.3V, Iout will be 20mA)

 

[tpetar]

Quiescent current is current when regulator is on idle.

 

[crutschow]

Nope, it's true. The device's quiescent current to ground is 5µA max. no-load to full-load. The device likely uses MOSFET devices to minimize quiescent current.

 

[Tahmid]

I used to think quiescent current is defined when the device is idle.

In this case, I think quiescent current could refer to the current drawn for the regulator's operation itself (besides the load current).

The datasheet does show such low quiescent currents. Look at the graphs shown in the datasheet.

 

[tpetar]

On page 3 datasheet says :

Input Quiescent Current (Iq) typical 2,0uA and max 5μA at IL=0mA

 

[FvM]

The device's quiescent current to ground is 5µA max. no-load to full-load.

I guess you missed datasheet FIGURE 2-5: Ground Current vs. Load Current. The ground pin current rises to 120 µA at full load. Still very low, but considerably higher than 5 µA. Curiously, there's no full specification of ground current in the datasheet (maximum value in constrast to typical value shown in the diagram).

 

[crutschow]

I guess you missed datasheet FIGURE 2-5: Ground Current vs. Load Current. The ground pin current rises to 120 µA at full load. Still very low, but considerably higher than 5 µA. Curiously, there's no full specification of ground current in the datasheet (maximum value in constrast to typical value shown in the diagram).

Yup, I missed that. Good catch. ;-)

Yes, 120µA is still a low percentage of the full load current so the effect on battery drain would be negligible.

 

[tpetar]

At 120µA load on 9V 650mAh battery, battery can supply power without interruption for 226 days in best way, assuming that battery when fully discharged its around 5V, can still produce 20mA. For this is best to see manufacturer battery datasheet graph.

On that we should add normal usage of device which is around 20mA (from post #1).

 

[crutschow]

At 120µA load on 9V 650mAh battery, battery can supply power without interruption for 226 days in best way, assuming that battery when fully discharged its around 5V, can still produce 20mA. For this is best to see manufacturer battery datasheet graph.

On that we should add normal usage of device which is around 20mA (from post #1).

But the 120µA ground (bias) current is for full output current. For 20mA output current the ground current is about 5µA nominal according to Figure 2-5, which is only 0.025% of the total. Thus the ground current will have negligible effect on battery life. If the regulator was not supplying any current then the minimum battery life in theory would by 650mAh / 5µA = 130k hours or 14.8 years, likely beyond its shelf life.