APPLICATION NOTES

3

INPUT BYPASS CAPACITORS

Unless the regulator is located very close to the main input

filter capacitor, a 1µF to 10µF low ESR tantalum capacitor

should be added to the regulator's input to maximize transient

response and minimize power supply transients. A 0.1µF

ceramic capacitor should also be used for high frequency

bypassing.

FIGURE 1

OUTPUT CAPACITOR SELECTION

For most applications a 10µF low ESR tantalum capacitor,

as close to the regulators output as possible, is all that is

required for the MSK5143 to be stable. When using a 10µF

capacitor on the lower output voltage devices, a minimum

ESR is required of the capacitor. This requirement decreases

from 20mΩ for VOUT ≤ 1.5V to 5mΩ for VOUT ≥ 3.3V. With

an increase in capacitance, the minimum ESR requirement

decreases. At 100µF, the minimum ESR requirement de-

creases to 5mΩ for all versions of the MSK5143. To reduce

ringing and improve transient response, capacitors with

slightly larger ESR in the range of 20mΩ to 50mΩ provides

improved damping. Capacitors with higher ESR can be com-

bined in parallel with low ESR ceramic capacitors for good

high frequency response and settling time. The maximum

ESR value must be less than 3Ω. Care must be taken when

selecting a ceramic type. The X5R and X7R are the best

choice for output stability when considering response due

to applied voltage and temperature.

LOAD REGULATION

In voltage regulator applications where very large load currents

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

connecting the output of the regulator to the load must be

extremely low impedance to avoid affecting the load regulation

specifications.As shown in figure 2, any impedance (Rs) in this

path will form a voltage divider with the load. For best results

the ground pin should be connected directly to the load as

shown in figure 2. The direct connection eliminates the effect

the potential voltage drop in the power ground path can have

on the internal ground sensing, thus improving load regulation.

The MSK5143 ground pin trace must be designed to carry

the ground pin current without significant voltage drops. See

typical performance curves.

FIGURE 2

OVERLOAD PROTECTION

The MSK5143 regulator features both current limit and ther-

mal overload protection. Within the safe operating region,

the regulator will current limit above the 3A amp rating. As

the input to output voltage increases, however, the current

limit decreases to keep the output transistor within its power

dissipation limitation. See the Current Limit Typical Curves for

conditional performance detail. If the device heats enough to

exceed its rated die junction temperature due to excessive

ambient temperature, improper heat sinking etc., the regula-

tor will shutdown until an appropriate junction temperature is

maintained. To bring the regulator out of shutdown, the device

input may need to be cycled to zero and power reapplied to

eliminate the shutdown condition.

REVERSE VOLTAGE PROTECTION

The regulators are protected against reverse input and output

voltages. Reverse input voltages up to 20V will be blocked

from the input while current flow is limited to less than 1mA.

The reverse voltage on the input is also prevented from ap-

pearing on the output and the load. When the input voltage is

pulled down to ground and the output is held up by a second

source, the current flow between them is limited to typically

600µA. See the electrical specifications table.

OUTPUT ADJUST

The output voltage range of the MSK5143 is 1.21V to 20V.

The output voltage is set by the ratio of two external resis-

tors as shown in Figure 1. The device monitors the output

to maintain the voltage at the ADJ pin. The ADJ pin is the

input to the error amplifier. It has a bias current of 3µA which

flows through R2 into the pin. The ADJ pin voltage is 1.21V

referenced to ground. The value of R1 should be less than

4.17K to minimize errors in the output voltage caused by

the ADJ pin bias current. Reference the typical performance

curves for load regulation variation due to the change in the

output voltage.

SHUTDOWN MODE

The SHDN pin is used to put the regulator into its low power

state. The output will be off when the SHDN pin is pulled

low. Quiescent current drops from 1mA to less the 1µA in

shutdown mode. The SHDN pin can be driven by 5V logic or

open-collector logic with a pull-up resistor. The typical SHDN

pin current is 3uA. Connect the SHDN pin to VIN if not used.

If the SHDN pin is not connected, the regulator will go into a

low power shutdown state.

8548-3 Rev. E 12/15