MIC5216

Micrel

MIC5216

6

January 2000

Applications Information

The MIC5216 is designed for 150mA to 200mA output current

applications where a high current spike (500mA) is needed

for short, startup conditions. Basic application of the device

will be discussed initially followed by a more detailed discus-

sion of higher current applications.

Enable/Shutdown

Forcing EN (enable/shutdown) high (> 2V) enables the regu-

lator. EN is compatible with CMOS logic. If the enable/

shutdown feature is not required, connect EN to IN (supply

input). See Figure 5.

Input Capacitor

A 1

µF capacitor should be placed from IN to GND if there is

more than 10 inches of wire between the input and the ac filter

capacitor or if a battery is used as the input.

Output Capacitor

An output capacitor is required between OUT and GND to

prevent oscillation. 1

µF minimum is recommended. Larger

values improve the regulator’s transient response. The out-

put capacitor value may be increased without limit.

The output capacitor should have an ESR (equivalent series

resistance) of about 5

Ω or less and a resonant frequency

above 1MHz. Ultralow-ESR capacitors could cause oscilla-

tion and/or underdamped transient response. Most tantalum

or aluminum electrolytic capacitors are adequate; film types

will work, but more expensive. Many aluminum electrolytics

have electrolytes that freeze at about –30

°C, so solid tanta-

lums are recommended for operation below –25

°C.

At lower values of output current, less output capacitance is

needed for stability. The capacitor can be reduced to 0.47

µF

for current below 10mA or 0.33

µF for currents below 1mA.

No-Load Stability

The MIC5216 will remain stable and in regulation with no load

(other than the internal voltage divider) unlike many other

voltage regulators. This is especially important in CMOS

RAM keep-alive applications.

Error Flag Ouput

The error flag is an open-collector output and is active (low)

when an undervoltage of approximately 5% below the nomi-

nal output voltage is detected. A pullup resistor from IN to

FLAG is shown in all schematics.

If an error indication is not required, FLAG may be left open

and the pullup resistor may be omitted.

Thermal Considerations

The MIC5216 is designed to provide 200mA of continuous

current in two very small profile packages. Maximum power

dissipation can be calculated based on the output current and

the voltage drop across the part. To determine the maximum

power dissipation of the package, use the thermal resistance,

junction-to-ambient, of the device and the following basic

equation.

P

=

T

– T

D(MAX)

J(MAX)

A

JA

()

θ

T

125

°C, and T

layout dependent; table 1 shows examples of thermal resis-

tance, junction-to-ambient, for the MIC5216.

Package

θθθθθ

θθθθθ

θθθθθ

JC

Minimum Footprint

Copper Clad

MM8™ (MM)

160

°C/W

70

°C/W

30

°C/W

SOT-23-5 (M5)

220

°C/W

170

°C/W

130

°C/W

Table 1. MIC5216 Thermal Resistance

The actual power dissipation of the regulator circuit can be

determined using one simple equation.

P

Substituting P

conditions that are critical to the application will give the

maximum operating conditions for the regulator circuit. For

example, if we are operating the MIC5216-3.3BM5 at room

temperature, with a minimum footprint layout, we can deter-

mine the maximum input voltage for a set output current.

P

=

125 C – 25 C

C/W

D(MAX)

°°

()

°

220

P

455mW

The thermal resistance, junction-to-ambient, for the mini-

mum footprint is 220

°C/W, taken from table 1. The maximum

power dissipation number cannot be exceeded for proper

operation of the device. Using the output voltage of 3.3V, and

an output current of 150mA, we can determine the maximum

input voltage. Ground current, maximum of 3mA for 150mA

of output current, can be taken from the Electrical Character-

istics section of the data sheet.

455mW = (V

V

455mW + 3.3V 150mA

mA + 3mA

IN

()









150

V

6.2V

IN

MAX

=

Therefore, a 3.3V application at 150mA of output current can

accept a maximum input voltage of 6.2V 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 Regu-

lators handbook.

Peak Current Applications

The MIC5216 is designed for applications where high start-

up currents are demanded from space constrained regula-

tors. This device will deliver 500mA start-up current from a

SOT-23-5 or MM8 package, allowing high power from a very

low profile device. The MIC5216 can subsequently provide

output current that is only limited by the thermal characteris-

tics of the device. You can obtain higher continuous currents

from the device with the proper design. This is easily proved

with some thermal calculations.

If we look at a specific example, it may be easier to follow. The

MIC5216 can be used to provide up to 500mA continuous