PAM2301
800mA Step-Down DC-DC Converters
100% Duty Cycle Operation
PCB Layout Check List
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:
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.
VOUT = VIN – ILOAD × (Rdson + RL)
2. Does the VFB pin connect directly to the
feedback resistors? The resistive divider R1/R2
must be connected between the (+) plate of COUT
and ground.
where Rdson = P-channel switch ON resistance,
ILOAD = Output current, RL = Inductor DC
resistance
3. Does the (+) plate of CIN connect to VIN 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.
UVLO and Soft-Start
The reference and the circuit remain reset until
the VIN crosses its UVLO threshold.
5. Keep the (–) plates of CIN and COUT as close
as possible.
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.
Figure 1 :PAM2301 Suggested Layout
Power Analog Microelectronics,Inc
www.poweranalog.com
09/2008 Rev 1.3
11
PAM [ POWER ANALOG MICOELECTRONICS ]
