MIC5256-3.1YM5 データシートの表示（PDF） - Micrel

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MIC5256-3.1YM5

150mA µCap LDO with Error Flag

Micrel 

Micrel, Inc.

TJ(max) is the maximum junction temperature of the die,

125°C, and TA is the ambient operating temperature. θJA

is layout dependent; Table 1 shows examples of

junction-to-ambient thermal resistance for the MIC5256.

Package

SOT23-5

(M5 or D5)

θJA Recommended

Minimum Footprint

235°C/W

θJA 1” Square

Copper Clad

185°C/W

θJC

145°C/W

Table 1. SOT-23-5 Thermal Resistance

The actual power dissipation of the regulator circuit can

be determined using the equation:

PD = (VIN – VOUT) IOUT + VIN IGND

Substituting PD(max) for PD and solving for the operating

conditions that are critical to the application will give the

maximum operating conditions for the regulator circuit.

For example, when operating the MIC5256-3.0BM5 at

50°C with a minimum footprint layout, the maximum

input voltage for a set output current can be determined

as follows:

PD(max)

=

⎜⎛ 125°C − 50°C ⎟⎞

⎝ 235°C/W ⎠

PD(max) = 315mW

The junction-to-ambient thermal resistance for the

minimum footprint is 235°C/W, from Table 1. The

maximum power dissipation must not be exceeded for

proper operation. Using the output voltage of 3.0V and

an output current of 150mA, the maximum input voltage

MIC5256

can be determined. Because this device is CMOS and

the ground current is typically 100µA over the load

range, the power dissipation contributed by the ground

current is < 1% and can be ignored for this calculation.

315mW = (VIN – 3.0V) 150mA

315mW = VIN·•150mA – 450mW

810mW = VIN·•150mA

VIN(max) = 5.4V

Therefore, a 3.0V application at 150mA of output current

can accept a maximum input voltage of 5.4V in a SOT-

23-5 package. For a full discussion of heat sinking and

thermal effects on voltage regulators, refer to the

“Regulator Thermals” section of Micrel’s Designing with

Low-Dropout Voltage Regulators handbook.

Fixed Regulator Applications

Figure 1. Low-Noise Fixed Voltage Application

Figure 1 shows a standard low-noise configuration with a

47kΩ pull-up resistor from the error flag to the input

voltage and a pull-down capacitor to ground for the

purpose of fault indication. EN (Pin 3) is connected to IN

(Pin 1) for an application where enable/shutdown is not

required. COUT = 1.0µF minimum.

August 2010

11

M9999-080510

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