NQ04009VMA15NRS Datasheet, PDF (18/20 Pages) SynQor Worldwide Headquarters – 16Amp, wide ouput range, Non-Isolated DC/DC Converter

Technical Specification
Non-Isolated
SIP Converter
3.0 - 5.5Vin 16A
provide damping of the distribution network with their inherent
ESR, which is low, but higher than ceramics. Additional output
capacitance in the range of 300-500µF is beneficial for reduc-
ing the deviation in response to a fast load transient.
Input Over-Voltage Prevention: The power system
designer must take precautions to prevent damaging the NiQor
converters by input overvoltage. This is another reason to be
careful about damping the input filter so that no ringing occurs
from an underdamped filter. The voltage must be prevented
from exceeding the absolute maximum voltage indicated in the
Electrical Specifications section of the data sheet under all con-
ditions of turn-on, turn-off and load transients and fault condi-
tions. The power source should have an over voltage shutdown
threshold as close as reasonably possible to the operating
point.
Additional protection can come from additional input capaci-
tance, perhaps on the order of 1,000µF, but contingent on the
source inductance value. A large source inductance would
require more capacitance to keep the input voltage below the
absolute maximum, if the load current were interrupted sud-
denly. This can be caused by either a shutdown of the NiQor
from a fault or from the load itself, for example when a card is
hot-swapped out, suddenly dropping the load to zero. This is
further justification for keeping the source inductance low, as
mentioned above. When the power source is configured with
remote sensing, the series resistance of the filter inductor and
any other conductors or devices between the source and the
sense point will result in a voltage drop which, in the event of
a load current interruption, would add to the NiQor input volt-
age.
A TVS device could also be used to clamp the voltage level dur-
ing these conditions, but the relatively narrow range between
operating voltage and the absolute maximum voltage restrict
the use of these devices to lower source current levels that will
not drive the transient voltage suppressor above the voltage
limit when all the source current is flowing into the clamp. A
TVS would be a good supplemental control, in addition to care-
ful selection of inductance and capacitance values.
Equivalent Model for Input Ripple: A simple but reason-
ably accurate model of input ripple is to treat the NiQor input
as a pulsed AC current source at 300 kHz.in parallel with a
very low ESR capacitor, see Figure B. The peak-to-peak current
of the source model is equal to the NiQor load current, repre-
senting the peak current in the NiQor's smoothing choke. The
capacitor represents the 40µF input ceramic capacitance of the
NiQor converter, with a nearly negligible ESR of less than 1
mΩ. A further refinement can be made by setting the duty cycle
of the pulsed source to the output voltage divided by the input
voltage.
The only error in this simplified model is that it ignores the
inductive current in the choke, usually less than 20% of the load
current, and it ignores the resistive losses inside the NiQor con-
verter, which would alter the duty cycle very slightly.
The model is a good guide for calculating the effects of exter-
nal input capacitors and other filter elements on ripple voltage
and ripple current stress on capacitors.
40µF _INPUT
I_p-p
<1mΩ
I _p-p = I _Load
Figure B: Equivalent model for input ripple
High Capacitance Loads with Backdrive: When using
two or more NiQor converters with high capacitance loads
(greater than 1,000µF), special consideration must be given to
the following condition. If a back-drive source is feeding volt-
age back to a NiQor output, perhaps through some ASIC or
other load device, and the back-driving source is greater than
60% of the input voltage to the NiQor that has not been
enabled yet, an overcurrent condition may exist on startup. This
condition could prevent a proper startup when the second
NiQor is enabled. The condition is caused by the second
NiQor having to ramp the voltage to a high duty cycle with a
high capacitance load, which can trip the overcurrent shut-
down, preventing a startup. The following remedies for this sit-
uation can be applied:
1) Limit output capacitance on higher voltage outputs to
1,000µF. OR,
2) Prevent back-drive conditions that raise the off-state output
voltage to more than 60% of the input voltage.
Thermal Considerations: For vertical mount applications
at elevated temperatures that call for forced air cooling (see
thermal derating curves - measured using 6 layer 2oz copper
board), the preferred airflow direction is from pin 11 to pin 1,
as indicated in the thermal images provided. If airflow is in the
opposite direction (pin 1 to pin 11) the power devices will run
hotter by about 5 ^OC (corresponding to an additional 1 ampere
of load derating at conditions where derating occurs).
Product # NQ04T33VMA16
Phone [phone]
Doc.# 005-2NV4T3E Rev. B
7/6/04
Page 18