MSK5150 데이터 시트보기 (PDF) - Anaren Microwave

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MSK5150

VERY HIGH CURRENT, LOW DROPOUT VOLTAGE REGULATORS

Anaren Microwave 

APPLICATION NOTES

REGULATOR PROTECTION:

The MSK5150 series is fully protected against reversed input

polarity, overcurrent faults, overtemperature conditions (Pd) and

transient voltage spikes of up to 60V. If the regulator is used in dual

supply systems where the load is returned to a negative supply,

the output voltage must be diode clamped to ground.

OUTPUT CAPACITOR:

The output voltage ripple of the MSK5150 series voltage regulators

can be minimized by placing a filter capacitor from the output to

ground. The optimum value for this capacitor may vary from one

application to the next, but a minimum of 20µF is recommended

for optimum performance. This capacitor need not be an expen-

sive low ESR type: aluminum electrolytics are adequate. In fact,

extremely low ESR capacitors may contribute to instability. Tan-

talum capacitors are recommended for systems where fast load

transient response is important. Transient load response can also

be improved by placing a capacitor directly across the load.

LOAD CONNECTIONS:

In voltage regulator applications where very large load currents

are present, the load connection is very important. The path con-

necting the output of the regulator to the load must be extremely

low impedance to avoid affecting the load regulation specifications.

Any impedance in this path will form a voltage divider with the load.

The MSK5150 series requires a minimum of 10mA of load current

to stay in regulation.

ENABLE PIN:

The MSK5150 series of voltage regulators are equipped with a

TTL compatible ENABLE pin. A TTL high level on this pin activates

the internal bias circuit and powers up the device. A TTL low level

on this pin places the controller in shutdown mode and the device

draws approximately 10µA of quiescent current. If the enable

function is not used, simply connect the enable pin to the input.

FLAG OUTPUT PIN:

All of the fixed output voltage versions of the MSK5150 series

are equipped with a flag output pin. Since the flag pin is an open

collector configuration it can be pulled up to any voltage between

3V and 26V. This feature allows direct interfacing to practically any

logic. This active low output has a typical level of 0.22V when the

flag comparator detects an "out of regulation" condition. Flag states

include low input voltage, out of regulation and output current limit.

Extremely high level input voltage transients will also cause the

flag output pin to activate.

HEAT SINK SELECTION:

To select a heat sink for the MSK5150, the following formula for

convective heat flow may be used.

Governing Equation:

Tj = Pd x (Rθjc + Rθcs + Rθsa) + Ta

WHERE:

Tj = Junction Temperature

Pd = Total Power Dissipation

Rθjc = Junction to Case Thermal Resistance

Rθcs = Case to Heat Sink Thermal Resistance

Rθsa = Heat Sink to Ambient Thermal Resistance

Ta = Ambient Temperature

First, the power dissipation must be calculated as follows:

Power Dissipation = (VIN - VOUT) x Iout

Next, the user must select a maximum junction temperature. The

absolute maximum allowable junction temperature is 125°C. The

equation may now be rearranged to solve for the required heat sink

to ambient thermal resistance (Rθsa).

EXAMPLE:

An MSK 5150-3.3 is configured for VIN=+5V and VOUT=+3.3V. Iout

is a continuous 1A DC level. The ambient temperature is +25°C.

The maximum desired junction temperature is 125°C.

Rθjc = 1.5°C/W and Rθcs = 0.15°C/W for most thermal greases

Power Dissipation = (5V - 3.3V) x (1A)

= 1.7 Watts

Solve for Rθsa:

Rθsa = 125°C - 25°C - 1.5°C/W - 0.15°C/W

1.7W

= 57.17°C/W

In this example, a heat sink with a thermal resistance of no more

than 57°C/W must be used to maintain a junction temperature of

no more than 125°C.

MSK5150-00 OUTPUT ADJUSTMENT:

The MSK5150-00 is an adjustable version in the series of high

performance regulators. The diagram below illustrates proper ad-

justment technique for the output voltage. The series resistance of

R1+R2 should be selected to pass the minimum regulator output

current requirement of 10mA.

DEVICE/CASE CONNECTION:

The MSK5150 series are highly thermally conductive devices and

the thermal path from the package heat sink to the internal junctions

is very short. Since the case is electrically isolated from the internal

circuitry, the package can be directly connected to a heat sink.

3

8548-48 Rev. J 1/16

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