PAM2321

Document number: DSxxxxx Rev. 2 - 1

8 of 11

www.diodes.com

January 2013

© Diodes Incorporated

PAM2321

A Product Line of

Diodes Incorporated

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

+

=

voltage range. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surrounding airflow

and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula:

θ

−

=

JA

A

)

MAX

(

J

D

T

T

P

Setting the Output Voltage

The internal reference is 0.6V (Typical). The output voltage is calculated as below:

The output voltage is given by Table 1.

⎟

⎠

⎞

⎜

⎝

⎛ +

=

2

R

1

R

1

x

6

.

0

Table 1: Resistor selection for output voltage setting.

R1

R2

1.2V

100k

100k

1.5V

150k

100k

1.8V

200k

100k

2.5V

380k

120k

3.3V

540k

120k

Pulse Skipping Mode (PSM) Description

When load current decreases, the peak switch current in Power-PMOS will be lower than skip current threshold and the device will enter into

Pulse Skipping Mode.

In this mode, the device has two states, working state and idle state. First, the device enters into working state control led by internal error

blocks disabled. The output voltage will be reduced by loading or leakage current. When the feedback voltage gets lower than the internal

reference voltage, the convertor will start a working state again.

100% Duty Cycle Operation

As the input voltage approaches the output voltage, the converter turns the P-Channel transistor continuously on. In this mode the output voltage

is equal to the input voltage minus the voltage drop across the P-Channel transistor:

()

R

R

I

V

V

L

DSON

LOAD

IN

OUT

+

−

=

UVLO and Soft-Start

in-rush current during start-up. This prevents possible voltage drops of the input voltage and eliminates the output voltage overshoot.