MIC5305-1.8BML(2004) 查看數據表（PDF） - Micrel

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MIC5305-1.8BML
(Rev.:2004)

150mA µCap Ultra-Low Dropout LDO Regulator

Micrel 

MIC5305

Applications Information

Enable/Shutdown

The MIC5305 comes with an active-high enable pin that

allows the regulator to be disabled. Forcing the enable pin low

disables the regulator and sends it into a “zero” off-mode-

current state. In this state, current consumed by the regulator

goes nearly to zero. Forcing the enable pin high enables the

output voltage. The active-high enable pin uses CMOS

technology and the enable pin cannot be left floating; a

floating enable pin may cause an indeterminate state on the

output.

Input Capacitor

The MIC5305 is a high-performance, high bandwidth device.

Therefore, it requires a well-bypassed input supply for opti-

mal performance. A 1µF capacitor is required from the input

to ground to provide stability. Low-ESR ceramic capacitors

provide optimal performance at a minimum of space. Addi-

tional high frequency capacitors, such as small-valued NPO

dielectric-type capacitors, help filter out high-frequency noise

and are good practice in any RF-based circuit.

Output Capacitor

The MIC5305 requires an output capacitor of 1µF or greater

to maintain stability. The design is optimized for use with low-

ESR ceramic chip capacitors. High ESR capacitors may

cause high frequency oscillation. The output capacitor can be

increased, but performance has been optimized for a 1µF

ceramic output capacitor and does not improve significantly

with larger capacitance.

X7R/X5R dielectric-type ceramic capacitors are recom-

mended because of their temperature performance. X7R-

type capacitors change capacitance by 15% over their oper-

ating temperature range and are the most stable type of

ceramic capacitors. Z5U and Y5V dielectric capacitors change

value by as much as 50% and 60%, respectively, over their

operating temperature ranges. To use a ceramic chip capaci-

tor with Y5V dielectric, the value must be much higher than an

X7R ceramic capacitor to ensure the same minimum capaci-

tance over the equivalent operating temperature range.

Bypass Capacitor

A capacitor can be placed from the noise bypass pin to

ground to reduce output voltage noise. The capacitor by-

passes the internal reference. A 0.1µF capacitor is recom-

mended for applications that require low-noise outputs. The

bypass capacitor can be increased, further reducing noise

and improving PSRR. Turn-on time increases slightly with

respect to bypass capacitance. A unique, quick-start circuit

allows the MIC5305 to drive a large capacitor on the bypass

pin without significantly slowing turn-on time. Refer to the

Typical Characteristics section for performance with different

bypass capacitors.

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No-Load Stability

Unlike many other voltage regulators, the MIC5305 will

remain stable and in regulation with no load. This is especially

import in CMOS RAM keep-alive applications.

Adjustable Regulator Application

Adjustable regulators use the ratio of two resistors to multiply

the reference voltage to produce the desired output voltage.

The MIC5305 can be adjusted from 1.25V to 5.5V by using

two external resistors (Figure 1). The resistors set the output

voltage based on the following equation:

VOUT

=



VREF 1+

R1

R2

VREF = 1.25V

VIN

MIC5305BML

VIN VOUT

1µF

EN ADJ

GND

VOUT

R1

1µF

R2

Figure 1. Adjustable Voltage Application

Thermal Considerations

The MIC5305 is designed to provide 150mA of continuous

current in a very small package. Maximum ambient operating

temperature can be calculated based on the output current

and the voltage drop across the part. Given that the input

voltage is 5.0V, the output voltage is 2.9V and the output

current = 150mA.

The actual power dissipation of the regulator circuit can be

determined using the equation:

PD = (VIN – VOUT) IOUT + VIN IGND

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.

PD = (5.0V – 2.9V) × 150mA

PD = 0.32W

To determine the maximum ambient operating temperature

of the package, use the junction-to-ambient thermal resis-

tance of the device and the following basic equation:

PD(max)

=





TJ(max)

θJA

−

TA





TJ(max) = 125°C, the max. junction temperture of the die

θJA thermal resistance = 93°C/W

August 2004

9

M9999-081704

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