MIC5216 查看數據表（PDF） - Micrel

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MIC5216

500mA-Peak Output LDO Regulator

Micrel 

Micrel, Inc.

455mW = ⎜⎛ %Duty Cycle ⎟⎞1.66W

⎝ 100 ⎠

0.274 = ⎜⎛ %Duty Cycle ⎟⎞

⎝ 100 ⎠

% Duty Cycle Max = 27.4%

With an output current of 500mA and a three-volt drop

across the MIC5216-xxBMM, the maximum duty cycle is

27.4%.

Applications also call for a set nominal current output

with a greater amount of current needed for short

durations. This is a tricky situation, but it is easily

remedied. Calculate the average power dissipation for

each current section, then add the two numbers giving

the total power dissipation for the regulator. For

example, if the regulator is operating normally at 50mA,

but for 12.5% of the time it operates at 500mA output,

the total power dissipation of the part can be easily

determined. First, calculate the power dissipation of the

device at 50mA. We will use the MIC5216-3.3BM5 with

5V input voltage as our example.

PD × 50mA = (5V – 3.3V) × 50mA + 5V × 650µA

MIC5216

PD × 50mA = 173mW

However, this is continuous power dissipation, the actual

on-time for the device at 50mA is (100%-12.5%) or

87.5% of the time, or 87.5% duty cycle. Therefore, PD

must be multiplied by the duty cycle to obtain the actual

average power dissipation at 50mA.

PD × 50mA = 0.875 × 173mW

PD × 50mA = 151mW

The power dissipation at 500mA must also be

calculated.

PD × 500mA = (5V – 3.3V) 500mA + 5V × 20mA

PD × 500mA = 950mW

This number must be multiplied by the duty cycle at

which it would be operating, 12.5%.

PD × = 0.125mA × 950mW

PD × = 119mW

a. 25°C Ambient

b. 50°C Ambient

c. 85°C Ambient

Figure 1. MIC5216-x.xBM5 (SOT-23-5) on Minimum Recommended Footprint

a. 25°C Ambient

b. 50°C Ambient

c. 85°C Ambient

Figure 2. MIC5216-x.xBM5 (SOT-23-5) on 1-inch2 Copper Cladding

March 2007

10

M9999-032307

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