Pam2301, Application information – Diodes PAM2301 User Manual
Page 10
PAM2301
Document number: DSxxxxx Rev. 2 - 7
10 of 13
January 2013
© Diodes Incorporated
PAM2301
A Product Line of
Diodes Incorporated
Application Information
(cont.)
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
)
ON
(
DS
LOAD
IN
OUT
+
×
−
=
where R
DS(ON)
= P-Channel Switch ON Resistance, I = Output Current, R = Inductor DC Resistance.
UVLO AND Soft-Start
The reference and the circuit remain reset until the V
IN
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).
Short Circuit Protection
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.
Thermal Shutdown
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.
PCB Layout Check List
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:
1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide.
2. Does the V
FB
pin connect directly to the feedback resistors? The resistive divider R1/R2 must be connected between the (+) plate of C and
ground.
3. Does the (+) plate of CIN connect to V
IN
as closely as possible? This capacitor provides the AC current to the internal power MOSFETs.
4. Keep the switching node, SW, away from the sensitive VFB node.
5. Keep the (–) plates of C
IN
and C
OUT
as close as possible.
Figure 1. PAM2301 Suggested Layout