UP9616PDYA datasheet(11/18 Pages) UPI

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Conceptual

uP9616

uP9616-DS-C3202, Feb. 2017

www.upi-semi.com

Application Information

Output Inductor Selection

Output inductor selection is usually based on the

considerations of inductance, rated current value, size

requirements and DC resistance (DCR).

The inductance is chosen based on the desired ripple

current. Large value inductors result in lower ripple currents

and small value inductors result in higher ripple currents.

Higher V

IN or VOUT also increases the ripple current as

shown in the equation below. A reasonable starting point

for setting ripple current is ∆I

L = 900mA (30% of 3000mA).

)

(

OUT

OSC

−

∆

Maximum current ratings of the inductor are generally

specified in two methods: permissible DC current and

saturation current. Permissible DC current is the allowable

DC current that causes 40oC temperature raise. The

saturation current is the allowable current that causes 10%

inductance loss. Make sure that the inductor will not

saturate over the operation conditions including temperature

range, input voltage range, and maximum output current. If

possible, choose an inductor with rated current higher than

5A so that it will not saturate even under current limit

condition.

The size requirements refer to the area and height

requirement for a particular design. For better efficiency,

choose a low DC resistance inductor. DCR is usually

inversely proportional to size.

Different core materials and shapes will change the size,

current and price/current relationship of an inductor. Toroid

or shielded pot cores in ferrite or permalloy materials are

small and don’t radiate much energy, but generally cost

more than powdered iron core inductors with similar electrical

characteristics. The choice of which style inductor to use

often depends on the price vs. size requirements and any

radiated field/EMI requirements.

Input Capacitor Selection

The input capacitor needs to be carefully selected to

maintain sufficiently low ripple at the supply input of the

converter. A low ESR capacitor is highly recommended.

Since large current flows in and out of this capacitor during

switching, its ESR also affects efficiency.

The input capacitance needs to be higher than 22uF. The

best choice is he ceramic type and low ESR electrolytic

types may also be used provided that the RMS ripple

current rating is higher than 50% of the output current. In

the case of the electrolytic types, they can be further away

if a small parallel 1uF ceramic capacitor is placed right

close to the IC. A 100uF elecrolytic capacitor and 1uF

ceramic capacitor are recommended and placed close to

VIN and GND pins, with the shortest traces possible.

Output Capacitor Selection

The ESR of the output capacitor determines the output

ripple voltage and the initial voltage drop following a high

slew rate load transient edge. The output ripple voltage

can be calculated as:

)

ESR

(

OSC

OUT

∆

Where f

OSC =

operating frequency, C

OUT =

output

capacitance and ∆I

C =

∆

L = ripple current in the inductor.

The ceramic capacitor with low ESR value provides the low

output ripple and low size profile.

In the case of electrolytic capacitors, the ripple is dominated

by R

ESR multiplied by the ripple current. Connect a 220uF

electrolytic capacitor at output SENSE+ terminal for good

performance and low output ripple and place output

capacitor5s as close as possible to the device.

In the case of ceramic output capacitors, R

ESR is very small

and does not contribute to the output ripple. Connect a

0.1uF ceramic capacitor at output SENSE- terminal for good

performance and place output capacitors as close as

possible to the device.

PCB Layout Consideration

The PCB layout is an important step to maintain the high

performance of the uP9616. High switching frequencies

and relatively large peak currents make the PCB layout a

very important part of all high frequency switching power

supply design. Both the high current and the fast switching

nodes demand full attention to the PCB layout to save the

robustness of the uP9616 through the PCB layout.

Improper layout might show the symptoms of poor load or

lineregulation, radiate excessive noise at ground or input,

output voltage shifts, stability issues, unsatisfying EMI

behavior or worsened efficiency. Follow the PCB layout

guidelines for optiomal performances of uP9616.

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