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參數(shù)資料
| 型號(hào)： | QPO-2LZ-01 |
| 廠商： | Vicor Corporation |
| 文件頁(yè)數(shù)： | 9/11頁(yè) |
| 文件大?。?/td> | 0K |
| 描述： | IC INTERFACE FILTER |
| 標(biāo)準(zhǔn)包裝： | 20 |
| 系列： | Picor®, QUIETPOWER® |
| 其它名稱： | 1102-1094-5 |
Picor Corporation www.picorpower.com
QPO-2 Data Sheet Rev. 1.6 Page 7 of 11
The line inductance from the output of the QPO-2 to the
load should be minimized. This inductance will cause
voltage spikes and ringing proportional to the inductance
and the rate of change in the transient load current. This
effect is outside the control of the QPO-2 and may require
low ESR capacitance placed at the switching load when
long lines exists between the QPO-2 output and reference
ground and load. The rate of load change should be less
than 1 Amp per microsecond to minimize excessive
voltage ringing during the di/dt. The line inductance
between the power supply output and QPO input should
also follow low inductance layout practices.
The user must be aware of the converter’s 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-2 be used with power supplies running at
the factory pre-set voltages or in a trimmed down
configuration.
SC/Trim Adjustment
The RSC resistor is tied between QPOOUT and SC SET pin
and controls the correction current used to trim the
converter to compensate for the headroom voltage.
The value for the SC SET resistor is calculated by the
following equation:
where; RSC is SC SET resistor value,
RIN is the input resistance of the SC or TRIM
input of the converter (4)
VOUT is the desired QPO output voltage,
VRPT is the pre-trimmed reference of the
SC or TRIM.
This feature can be used in conjunction with an initially
trimmed down supply.
Note 4: When applicable consider the equivalent impedance of
the SC/Trim pin after a trimmed down adjustment has been made
to the supply. Use the power supply manufacturer’s trim down
procedure by connecting a resistor from the SC/Trim pin to
ground.
The active loop performance of the QPO-2 has been
optimized to provide adequate phase margin over a worse
case load impedance range. Loading the QPO-2 directly
with low ESR ceramic capacitance however will
significantly reduce the phase margin and is not
recommended. The effects of the typical distributed
inductance of the load path will mitigate the reduction in
phase margin when low ESR ceramic capacitors are
dispersed about the load path. Tantalum and Electrolytic
capacitors are higher ESR components and are not a
concern for phase margin.
When using the QPO as shown in Figure 4 the CSC
capacitor creates a soft starting of the headroom
correction current being sourced into the SC/Trim input of
the converter, preventing the output from tripping the
over voltage function while the QPO-2 output reaches
regulation. The QPO-2 ramp up time is typically 5 to 10
milliseconds. The CSC value will be supply dependent but
is typically around 1 to 10 F.
The RSL resistor provides a means to isolate the SC/Trim pin
of the converter from CSC as well as limit the correction
current to a level below what will cause an OVP trip
condition during start up. The compliance of the SC
output current source is QPOIN plus 10 volts so the RSL
formula below can be used to limit the worst-case
correction current below the maximum trim up
specification of the converter being used. Note the
correction current set by RSC must always be lower than
the ISCMAX current after the start-up settling time interval
for proper headroom correction.
Headroom Slope Adjustment
This feature can be used to allow more headroom at
lighter loads inceasing the delta voltage available to
improve transient load capability, while approximating
constant power dissipation of the QPO-2 over the full load
range. The slope of this curve is set by the slope adjust
resistor RSA. Figure 9 shows the relationship of headroom
resistance versus power dissipation for a load current of 10
Amps. The same data is plotted in Figure 10 with the slope
adjust feature reducing the headroom by 150 mV over the
load range of 1 to 10 A, for a typical range of RHR values
with a 3.3 volt output. The headroom setting RHR value
was selected at the minimum load condition while
enabling the slope function using an RSA value of 8.2 k.
This feature is useful in improving the QPO-2 efficiency
RSC =
R IN * VOUT
VRPT
RSL =
QPOIN + 10 V
ISCMAX
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