MIC5238 查看數據表（PDF） - Micrel

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MIC5238

Ultra-Low Quiescent Current, 150mA µCap LDO Regulator

Micrel 

Micrel, Inc.

Dual Supply Mode Efficiency

By utilizing a bias supply the conversion efficiency can be

greatly enhanced. This can be realized as the higher bias

supply will only consume a few µA’s while the input supply

will require a few mA’s. This equates to higher efficiency

saving valuable power in the system. As an example,

consider an output voltage of 1V with an input supply of

2.5V at a load current of 150mA. The input ground current

under these conditions is 2mA, while the bias current is

only 20µA. If we calculate the conversion efficiency using

the single supply approach, it is as follows:

Input power = VIN × output current + VIN × (VBIAS ground

current + VIN ground current)

Input power = 2.5V × 150mA + 2.5 × (0.0002+0.002) =

380.5mW

Output power = 1V × 0.15 = 150mW

Efficiency = 150/380.5 × 100 = 39.4%

MIC5238

Now, using a lower input supply of 1.5V, and powering the

bias voltage only from the 2.5V input, the efficiency is as

follows:

Input power = VIN × output current + VIN × VIN ground

current + VBIAS x VBIAS ground current

Input power = 1.5 × 150mA + 1.5 × 0.002 + 2.5 × 0.0002 =

225mW

Output power = 1V × 150mA = 150mW

Efficiency = 150/225 × 100 = 66.6 %

Therefore, by using the dual supply MIC5238 LDO the

efficiency is nearly doubled over the single supply version.

This is a valuable asset in portable power management

applications equating to longer battery life and less heat

being generated in the application.

This in turn will allow a smaller footprint design and an

extended operating life.

November 2008

10

M9999-111209

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