PAM2804

Document number: DS36403 Rev. 3 - 2

6 of 10

www.diodes.com

September 2015

© Diodes Incorporated

PAM2804

Application Information

PWM Dimming

The PAM2804 can be used to dim LED current dimming by driving the EN pin via PWM waveform. The SW pin current is then effectively

switched on and off causing the LED current to turn on and off. The recommended PWM frequency is 500Hz (see Figure on page 5 for details).

Inductor Selection

The basic PAM2804 application circuit is shown in Page 1. External component selection is determined by the load requirement, selecting L first

For most applications, the value of the inductor will fall withi

n the range of 1μH to 4.7μH. Its value is chosen based on the desired ripple current.

current as shown in equation 1. A reasonable starting point for setting ripple current is

  



















V

V

1

V

L

f

1

I

IN

OUT

OUT

L

Equation

(1)

The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation.

Thus, a 1.4A rated inductor should be enough for most applications (1A + 400mA). For better efficiency, choose a low DC-resistance inductor.

Using Ceramic Input Output Capacitors

Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and

low ESR make them ideal for switching regulator applications. Using ceramic capacitors can achieve very low output ripple and small circuit size.

When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best

temperature and voltage characteristics of all the ceramics for a given value and size.

Thermal Consideration

Thermal protection limits power dissipation in the PAM2804. When the junction temperature exceeds +150°C, the OTP (Overtemperature

Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature

drops below +120°C.

For continuous operation, the junction temperature should be maintained below +125°C. The power dissipation is defined as:







I

I

F

t

V

R

V

V

R

V

I

P

IN

Q

O

S

SW

IN

L

)

ON

(

DS

O

IN

H

)

ON

(

DS

O

2

O

D











For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:

V

I

R

I

P

IN

Q

H

)

ON

(

DS

2

O

D



