PAM2301 datasheet(11/13 Pages) PAM

11 / 13 page

Power Analog Microelectronics Inc

www.poweranalog.com

PAM2301

800mA Step-Down DC-DC Converters

09/2008 Rev 1.3

100% Duty Cycle Operation

UVLO and Soft-Start

Short Circuit Protection

Thermal Shutdown

PCB Layout Check List

As the input voltage approaches the output

voltage, the converter turns the P-chan nel

transistor continuously on. In this mode the

output voltage is equal to the input voltage minus

the voltage drop across the P - channel

transistor:

V= V – I

× (R

+ R )

where R

= P-channel switch ON resistance,

= Output current, R

= I nductor D C

resistance

The reference and the circuit remain reset until

the VIN crosses its UVLO threshold.

The PAM2301 has an internal soft-start circuit

that limits the in-rush current during start-up.

This prevents possible voltage drops of the input

voltage and eliminates the output voltage

overshoot. The soft-start acts as a digital circuit

to increase the switch current in several steps to

the P-channel current limit (1500mA).

The switch peak current is limited cycle-by-cycle

to a typical value of 1500mA. In the event of an

output voltage short circuit, the device operates

with a frequency of 400kHz and minimum duty

cycle, therefore the average input current is

typically 200mA.

When the die temperature exceeds 150°C, a

reset occurs and the reset remains until the

temperature decrease to 120°C, at which time

the circuit can be restarted.

When laying out the printed circuit board, the

following checklist should be used to ensure

proper operation of the PAM2301. These items

are also illustrated graphically in Figure 1. Check

the following in your layout:

The power traces, consisting of the GND

trace, the SW trace and the VIN trace should be

kept short, direct and wide.

Does the V

pin connect directly to the

feedback resistors? The resistive divider R1/R2

must be con nected between the (+) plate of C

and ground.

Does the (+) plate of CIN connect to VIN as

closely as possible? This capacitor provides the

AC current to the internal power MOSFETs.

Keep the switching node, SW, away from the

sensitive VFB node.

Keep the (–) plates of C

and C

as close

as possible.

OUT

LOAD

dson

LOAD

OUT

Figure 1 :PAM2301 Suggested Layout

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