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PRELIMINARY
Vicor Corp. Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
QPO-1 Data Sheet
Page 5 of 8
The slope adjust feature can be set to zero providing relative
constant headroom versus load using an RSA of 100k. The user
can optimize performance based on the expected variation in load
current and the desired power dissipation range. The formula
below should be used to calculate the RSA value for the desired
headroom versus current slope. If the peak detector is enabled,
the peak of the ripple will be added back to the headroom at a
given load condition.
RSA = ((I*0.05)/V) *2500
Example: For a 5A maximum load and a 150mV
reduction in headroom.
RSA =((5A*0.05/0.15V)*2500 = 4.167k
Peak Detector Function
This feature dynamically adds to the headroom voltage to
accommodate converter ripple variation. This feature can be
enabled by connecting the PEAKIN pin to the QPOIN pin and
disabled by putting a small RC filter at the PEAKIN pin as shown
in Figure 8.
The active loop performance has been optimized for 45 degrees
of phase margin over the expected load range. CCO shown in Figs
1 and 2 must be a low ESR ceramic capacitor. Loading the
QPO-1 directly with low ESR ceramic capacitance will affect the
phase margin and is not recommended. The distributed load
capacitance and inductance of the load path will vary depending
on the application. The effects of a distributed load impedance
on phase margin when very low ESR load capacitance is present
will typically be mitigated by the distributed inductance of the
load path. The transient load response in Figure 4 was measured
with approximately 10nH of distributed inductance between
QPO-1 output and the load board which had a 15F low ESR
ceramic capacitor across the static load resistance.
The following is a summary of the optional configurations that a
user can select for the QPO-1.
No slope adjust, no peak detect:
fixed headroom over ripple amplitude and current.
Same as above, but with peak detect enabled:
peak of ripple amplitude is added to the headroom voltage
optimizing headroom with varying ripple amplitude.
No peak detection with slope adjust:
to improve transient load range and efficiency trading off
attenuation at high current.
Using both peak detection and slope adjust:
to accommodate ripple amplitude variation with increased
transient capability and efficiency.
Module
+ OUT
QPOIN
PEAKIN
1k
0.1
F
Figure 8 – Peak detector Disable Circuit
QPO-1 Attenuation vs. Power
Iload=10A
1% Rhr std. values for VOUT=3.3V 15V 28V
Rss=100k (delta Vhr = 0mV from 0.1 to 10A)
3.3V
15V
28V
69.8k 324k 602k
47.5k 215k 402k
39.2k 178k 332k
30.1k 137k 255k
24.9k 113k 210k
21k 95.3k 178k
-60
-50
-40
-30
-20
-10
0
1234
Watts
dB
500kHz
50Hz
Figure 9 – Power vs Attenuation without slope
QPO-1 Attenuation vs. Power
Iload=10A
1% Rhr std. values for VOUT=3.3V 15V 28V
Rss=7.1k (delta Vhr =150mV from 0.1 to 10A)
14.3k 64.9k 121k
16.5k 75k 140k
18.2k 82.5k 154k
21k 95.3k 178k
22.6k 102k 191k
24.9k 113k 210k
3.3V 15V 28V
27.4k 124k 232k
-60
-50
-40
-30
-20
-10
0
12
34
Watt
dB
500kHz
50Hz
Figure 10 – Power vs Attenuation with slope adjust