PRELIMINARY
The product can be used with voltage sources from 3 to 30Vdc
Vout = 3.3V, ILOAD = 10A
by using either the remote sense or the voltage trim feature.
The two different circuit schematics are shown in Figures 1 and
2. For either configuration, the source output will increase to
accommodate the headroom setting of the QPO-1 filter to
maintain the load voltage at the required level.
0
VHR=103mV
VHR=134mV
dB
1.
VHR=167mV
VHR=203mV
The user can optimize performance by setting the low current
(100mA) headroom operating point per Table 1 or by using the
formulas in Notes 1 and 2 above the table. The user must be
aware of the sources over-voltage set-point and not create a
headroom voltage that will cause a shutdown condition. For this
reason it is recommended that the QPO-1 be used with power
supplies running at their factory preset voltages or in a trimmed
down configuration.
-
5 0
VHR=256mV
VHR=300mV
-
1
0
0
10Hz
100Hz
1. 0kHz
10kHz
100kHz
1. 0MHz
Frequency
In low voltage applications (<12V), it may be required to use the
CSC capacitor. This creates a soft starting of the source
Figure 5 – Attenuation vs Frequency @ 3.3 volts
preventing the output from tripping the over voltage function
while the QPO-1 output line comes up to the set-point. The CSC
value will be converter dependent but is typically around 5 to
22µF. Remote sensing may also require Qp for start up, use a
logic level low voltage PFET such as IRLML6401 or equivalent.
Vout = 15V, ILOAD = 10A
0
VHR=103mV
VHR=134mV
VHR=167mV
dB
VHR=203mV
The spice simulation Figures 5, 6, and 7 demonstrate the effects
of headroom versus attenuation for 3.3, 15, and 28V respectively.
The attenuation and power dissipation will decrease with
headroom setting so a trade-off can be selected for efficiency
versus attenuation. The transient performance is proportional to
the headroom setting, power source response time and the
capacitance present at the input to the QPO-1. The capacitance
may be within the power supply that is used or supplemented by
external capacitance. Consideration of the source’s sensitivity to
additional output capacitance and stability must be understood
before additional capacitance is added for enhancement of
transient performance.
-
5
0
VHR=256mV
VHR=300mV
-
1
0
0
100Hz
10Hz
1.0kHz
10kHz
100kHz
1. 0MHz
Frequency
Figure 6 – Attenuation vs frequency @ 15 volts
The QPO-1 has two additional features that the user can select to
further optimize performance. The first is a headroom slope
adjustment that reduces the headroom voltage drop with
increasing load current. The second is a peak detector function
that increases the headroom voltage by the peak of the ripple
voltage.
VOUT = 28V, ILOAD = 10A
0
VHR=103mV
VHR=134mV
VHR=167mV
dB
VHR=203mV
Headroom Slope Adjustment
-
5 0
This can be used to allow for more headroom and improved
transient response at lower loads and also to approximate
constant power dissipation over the load range. The slope of this
curve is set by the slope adjust resistor RSA. See below for setting
the RSA value. The headroom in Figures 5, 6, and 7 are at 10A
and have been reduced by 150mV from the low current
headroom setting with the slope function using an RSA value of
8.2kΩ. This feature is useful to improve efficiency when used
with converters that have decreasing ripple with increasing load
current such as is typical with Vicor products.
VHR=256mV
VHR=300mV
-
1
0
0
10Hz
100Hz
1.0kHz
10kHz
100kHz
1. 0MHz
Frequency
Figure 7 – Attenuation vs Frequency @ 28 volts
Vicor Corp. Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
QPO-1 Data Sheet
Page 4 of 8
Set your site on VICOR at www.vicorpower.com
