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 0.1Ω to 1Ω.
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.
FIGURE 1
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.
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.
3
Rev. C
1/06
MSK [ M.S. KENNEDY CORPORATION ]
