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QPO-2 Data Sheet Rev. 1.6 Page 9 of 11

Headroom Start-up Clamp Feature

This feature allows for pre-charging the Vref capacitance

to the level just below the steady state headroom voltage.

It reduces the time for the QPOout to reach the desired

regulation voltage and converter output overshoot that

results in the delay through the QPO filter during start-up.

The following formula can be used to calculate the RCP

resistor value to set the clamp at 90% of the final output

value. To set the clamp voltage to different percentages of

the output substitute the 0.90 with the desired factor.

The following is a summary of typical configurations that a

user can select for the QPO-2.

• No slope adjust, no peak detect, fixed headroom,

attenuation vs headroom graph in Figure 7 apply

• No slope adjust, peak detector enabled, headroom will

increase by the peak of the ripple amplitude

• Slope adjust enabled, no peak detect, headroom will

decrease with the increase in load current

• Slope adjust enabled, peak detector enabled,

headroom will vary with ripple amplitude and load

variations

The attributes of these features have been explained in

this datasheet. The optimum use of them requires an

understanding of the characteristics of the power supply

to be filtered.

0.1310

0.0880

0.0655

0.0880

15 places

0.0000

0.1000

0.3000

0.4410

0.3970

0.4850

0.0000

0.1000

0.3000

0.3970

0.4850

0.1500

0.1500

QPO Package Outline

QPO PCB Pad Pattern

(Top View)

4 places

0.492

0.2560

0.2060

Figure 11 - Recommended PCB receptor patterns. (dimensions in

inches)

QPO IN

QPO OUT

0.4410

0.4410

Vias to ground plane

Figure 12 - Recommended PCB copper lands for low thermal resistance.