Rev 1.0 – July 2005
EN5330
Capacitor Selection
Power Up Sequencing
The EN5330 needs about 20-40uF of input
capacitance. Low-cost, low-ESR ceramic capacitors
can be used as input capacitors for this converter and
it is strongly recommended that they be rated X5R or
X7R. In some applications, lower value capacitors are
needed in parallel with the larger, lossy capacitors in
order to provide high frequency decoupling.
The sequencing of AVIN, PVIN and ENABLE should
meet the following requirements:
1. ENABLE should not be asserted before PVIN.
2. PVIN should not be applied before AVIN.
Note that tying AVIN, PVIN and ENABLE together
and brought up at the same time does meet these
requirements.
The EN5330 has been optimized for use with about
50µF of ceramic output capacitance. It is strongly
recommended that these be low-cost, low-ESR,
ceramic capacitors rated X5R or X7R. (See the
Enpirion application note on ripple comparison for
optimum selection of number and value of these
capacitors based on ripple requirements.) In order to
eliminate high-frequency switching spikes on the
output ripple, usually a low-value, low-ESR ceramic
capacitor is used in parallel with the larger capacitors
right at the load.
POK Operation
The POK signal is an open drain signal from the
converter indicating the output voltage is within the
specified range. The POK signal will be a logic high
when the output voltage is within 90% - 120% of the
programmed output voltage. If the output voltage goes
outside of this range, the POK signal will be a logic
low until the output voltage has returned to within this
range. In the event of an over-voltage condition the
POK signal will go low and will remain in this
condition until the output voltage has dropped to 95%
of the programmed output voltage before returning to
the high state (see also Over Voltage Protection)
Enable Operation
The ENABLE pin provides a means to shut down the
power FET switching or enable normal operation. A
logic low will disable the converter and cause it to
shut down. A logic high will enable the converter into Over-Current Protection
normal operation.
The cycle-by-cycle current limit function is achieved
by sensing the current flowing through the sense P-
MOSFET and a signal generated by a differential
amplifier with a preset over-current threshold. During
a particular cycle, if the over-current threshold is
exceeded, the power P-MOSFET is turned off and the
power N-MOSFET is turned on to protect the P-
Soft-Start Operation
The SS pin in conjunction with a small capacitor
between this pin and AGND provides the soft start
function to limit the in-rush current during start-up.
During start-up of the converter the reference voltage
to the error amplifier is gradually increased to its final MOSFET. If the over-current condition is removed,
level by an internal current source of typically 10uA. the over-current protection circuit will enable the
The whole soft-start procedure is designed to take 1ms PWM operation. If the over-current condition persists,
- 3ms with a 15-30nF soft start capacitor, but can be
programmed by capacitor selection using the
following equation:
the converter will eventually go through a full soft-
start cycle. This circuit is designed to provide high
noise immunity.
Rise Time: TR = Css* 80k
It is possible to raise the over-current set-point by
~50% by connecting a 4.99kΩ resistor between ROCP
and GND.
During the soft-start cycle, when the soft-start
capacitor reaches 0.8V, the output has reached its
programmed regulation range. Note that the soft-start
current source will continue to operate and during
normal operation, the soft-start capacitor will charge
up to a final value of 2.5V.
Over-Voltage Protection
When the output voltage exceeds 120% of the
programmed output voltage, the PWM operation
stops, the lower N-MOSFET is turned on and the
POK signal goes low. When the output voltage drops
below 95% of the programmed output voltage, normal
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