PAM2863

Document number: DSxxxxx Rev. 1 - 0

8 of 11

www.diodes.com

October 2012

© Diodes Incorporated

PAM2863

A Product Line of

Diodes Incorporated

Application Information

R

1

.

0

I

S

)

NOM

(

OUT

=

application circuit shown on page 1.

Nominal Average Output

Current (mA)

0.05

2000

0.067

1500

0.1

1000

0.13

760

0.15

667

0.3

333

value of sense resistor under these conditions to maintain switch current below the specified maximum value. It is possible to use different

Capacitor Selection

A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and

lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input

supply. A minimum value of 10µF is acceptable if the input source is close to the device, but higher values will improve performance at lower

input voltages, especially when the source impedance is high. The input capacitor should be placed as close as possible to the IC.

For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are recommended. Capacitors with

Y5Vdielectric are not suitable for decoupling in this application and should NOT be used.

Inductor Selection

Recommended inductor values for the PAM2863 are in the range 33µH to 100µH. Higher values of inductance are recommended at higher

supply voltages in order to minimize errors due to switching delays, which in increased ripple and lower efficiency. Higher values of inductance

also result in a smaller change in output current over the supply voltage range. The inductor should be mounted as close to the device as

possilbe with low resistance connections to the LX and VIN pins. The chosen coil should have a saturation current higher than the peak output

current and a continuous current rating above the required mean output current.

The inductor value should be chosen to maintain operating duty cycle and switch ‘on’/’off’ times within the specified limits over the supply voltage

and load current range. The following equations can be used as a guide.

LX Switch ‘On’ time

)

R

R

R

(

I

V

V

I

L

T

LX

L

S

LED

LED

IN

ON

+

+

−

−

Δ

=

Lx Switch ‘Off’ time

)

R

R

(

I

V

V

I

L

T

L

S

LED

D

LED

OFF

+

+

+

Δ

=