APPLICATION NOTES

PIN FUNCTIONS

VIN - This pin provides power to all internal circuitry

including bias, start-up, thermal limit and overcurrent

latch. Input voltage range is 2.9V to 6.5V.

GND - Internally connected to ground, this pin should be

connected externally by the user to the circuit ground.

SHUTDOWN - There are two functions to the SHUT-

DOWN pin. It may be used to disable the output voltage

or to reset a current latch condition. To activate the shut-

down/reset functions the user must apply a voltage

greater than 1.6V to the SHUTDOWN pin. The output

voltage will turn on when the SHUTDOWN pin is pulled

below the threshold voltage. If the SHUTDOWN pin is

not used, it should be connected to ground. It should be

noted that with the shutdown pin tied to ground, a cur-

rent latch condition can only be reset by cycling power

off, then on.

VOUT - This is the output pin for the device.

ADJUST - The ADJUST pin is the inverting input of the

internal error amplifier. The non-inverting input is con-

nected to an internal 1.265V reference. This error ampli-

fier controls the drive to the output transistor to force

the ADJUST pin to 1.265V. An external resistor divider

is connected to the output, ADJUST pin and ground to

set the output voltage.

OUTPUT CAPACITOR SELECTION

Output capacitors are required to maintain regulation

and stability. A 220µF surface mount tantalum capacitor

in parallel with a 1.0µF ceramic capacitor from the out-

put to ground should suffice under most conditions. If

the user finds that tighter voltage regulation is needed

during output transients, more capacitance may be added.

If more capacitance is added to the output, the band-

width may suffer. ESR of the output capacitors should

be maintained at 0.1

Ω to 1Ω.

CURRENT LIMIT AND SOA

The MSK 5921RH current limit function is directly af-

fected by the input and output voltages. Figure 1 illus-

trates the relationship between VIN and ICL for various

output voltages. It is very important for the user to con-

sult the SOA curve when using input voltages which

result in current limit conditions beyond 4.5 Amps. When

using input voltages which result in current limit above

4.5 Amps, the user must maintain output current within

the SOA curve to avoid damage to the device. Note that

5 Amp maximum is due to current carrying capability of

the internal wirebonds.

3

OVERCURRENT LATCH

Overcurrent protection is provided by the MSK5921RH

series through the use of a timed latch off circuit. The

internal latch timeout is triggered by an overcurrent con-

dition. To allow for start up surge currents, the timeout

is approximately 5.5mS at 25°C. If the overcurrent con-

dition remains at the end of the timeout cycle, the regu-

lator will latch off until the latch is reset. The latch con-

dition can be reset by pulling the shutdown pin high or

cycling VIN off then back on. A thermal limit condition

will trigger the latch with no time out delay.

INPUT POWER SUPPLY BYPASSING

To maximize transient response and minimize power

supply transients it is recommended that a 100µF tanta-

lum capacitor is connected between VIN and ground. A

0.1µF ceramic capacitor should also be used for high

frequency bypassing.

FIGURE 1

Rev. C

1/06