EN5339QI
Excess bulk capacitance on the output of the
device can cause an over-current condition at
startup. Since the slew rate varies with the output
voltage setting, the maximum capacitance is a
function of the VOUT setting.
The maximum capacitance on the output power
rail, including the output filter capacitors and all
decoupling and bulk capacitors on the supply rail is
given by:
turns off the converter, allowing the device to cool.
When the junction temperature drops 15°C, the
device will be re-enabled and go through a normal
startup process.
Power OK
The Power OK (POK) feature is an open drain
output signal used to indicate if the output voltage
is within 92% of the set value. Within this range, the
POK output is allowed to be pulled high. Outside
this range, the POK output is maintained low.
During transitions such as power up and power
down, the POK output will not change state until the
transition is complete for enhanced noise immunity.
C
OUT_TOTAL_MAX [µF] = 3.41x103 / VOUT
NOTE: The above number and formula assume a
no load condition at startup.
Over Current/Short Circuit Protection
The POK has 1mA sink capability. When POK is
pulled high, the worst case pin leakage current is
as low as 500nA over temperature. This allows a
large pull up resistor such as 100kΩ to be used for
minimal current consumption in shutdown mode.
The POK output can also be conveniently used as
an enable input of the next stage for power
sequencing of multiple converters.
When an over current condition occurs, VOUT is
pulled low and the device disables switching
internally. This condition is maintained for a period
of 1.2 ms and then a normal soft-start cycle is
initiated. If the over current condition still persists,
this cycle will repeat.
Under Voltage Lockout
An under voltage lockout circuit will hold off
switching during initial power up until the input
voltage reaches sufficient level to ensure proper
operation. If the voltage drops below the UVLO
threshold the lockout circuitry will again disable
switching. Hysteresis is included to prevent
chattering between UVLO high and low states.
Power-Up/Down Sequencing
During power-up, ENABLE should not be asserted
before PVIN, and PVIN should not be asserted
before AVIN. The PVIN should never be powered
when AVIN is off. During power down, the AVIN
should not be powered down before the PVIN.
Tying PVIN and AVIN or all three pins (AVIN, PVIN,
ENABLE) together during power up or power down
meets these requirements.
Enable
The ENABLE pin provides means to shut down the
converter or initiate normal operation. A logic high
on the ENABLE pin will initiate the converter to start
the soft-start cycle and regulate the output voltage
to the desired value. A logic low will allow the
device to discharge the output and go into
shutdown mode for minimal power consumption.
When the output is discharged, an auxiliary NFET
turns on and limits the discharge current to 300 mA
or below. The ENABLE pin should not be left
floating.
Pre-Bias Start-up
The EN5339QI does not support startup into a pre-
biased condition. Be sure the output capacitors are
not charged or the output of the EN5339QI is not
pre-biased when the EN5339QI is first enabled.
Thermal Shutdown
When excessive power is dissipated in the device,
its junction temperature rises. Once the junction
temperature exceeds the thermal shutdown
temperature of 150°C, the thermal shutdown circuit
Enpirion 2012 all rights reserved, E&OE
www.enpirion.com, Page 12
06903
September 12, 2012
Rev: B
ENPIRION [ ENPIRION, INC. ]
