AN_PAM2401

PAM2401
Application Note
CONFIDENTIAL INFORMATION
PAM2401 Application Note
AE Department
1. Revision Information
Date
Revision
Description
2014/04
V1.0
Initial release
Comment
DO NOT DISTRIBUTE OR REPRODUCE WITHOUT PERMISSION FROM P.A.M
Pow er Analog Microelectronics, Inc.
Rev. V1.0
April.2014
1
PAM2401
Application Note
CONFIDENTIAL INFORMATION
2. PAM2401 General Description
The PAM2401 is a high efficiency, current mode, fixed frequency, step-up DC/DC converter with
true output disconnect and inrush current limiting. The device includes a 0.10Ù N-channel MOSFET
switch and a 0.15Ù P-channel synchronous rectifier. This product has the ability to simply program
the output voltage from 2.5V to 5.0V.The switching frequency is 1.0MHz, programmable current
limit set by an external resistor from 1.0A to 3.0A with internal soft-start. When loading became light,
the converter will automatically enter into PSM to improve the efficiency. Quiescent current is only
150uA during Pulse Skip Mode operation, maximizing battery life in portable applications. Other
features include :< 1uA shutdown, anti-ringing control, Hiccup mode short protection, over voltage
protection and over temperature protection.
The PAM2401 is available in MSOP-8 and U-DFN3030-12 packages.
3. Key Features
z
Up to 95% Efficiency
z
MSOP-8 and UDFN3030-12 packages
z
True Output Disconnect
z
Guaranteed 1.0V Start-Up
z
Inrush Current Limiting When Power On
z
Internal Soft-Start
z
Output Current up to 1000mA at Vin=3V and
z
Internal Compensation
Vout=5.0V
z
Pulse Sipping Mode at Light Load Operation
z
Fixed Frequency Operation Up to 1MHz
z
Hiccup Mode Short Protection
z
0.9V to 4.75V Input Range
z
Over Voltage Protection
z
2.5V to 5.0V Adjustable Output Voltage
z
Over Temperature Protection
z
Programmable Current Limit
z
<1uA Shutdown Current
z
Power Good Indicator
4.Application
„
Handheld Computers
„
Cordless Phones
„
GPS Receivers
„
Battery Backup Supplies
DO NOT DISTRIBUTE OR REPRODUCE WITHOUT PERMISSION FROM P.A.M
Pow er Analog Microelectronics, Inc.
Rev. V1.0
April.2014
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PAM2401
Application Note
CONFIDENTIAL INFORMATION
5.
EV Board Schematic
‐ OPT 6.
Application Information
Output Voltage Set Equation
The output voltage of the PAM2401 VOUT is set by an external resistor divider from VOUT to
ground as shown in figure 1. The divider tap is connected to the FB pin, and the typical value of
the voltage at the FB pin is 0.6V. The following equation is used to set the VOUT:
VOUT=0.6(1+RFB1/RFB2) For example, if output voltage of 5V is needed, with a chosen RFB2 value
of 110 kΩ, the value of RFB1 can be calculated according to the equation, so a 825kΩ resistor should
be chosen for RFB1.
Vo
RFB1
RFB2
3.3V
680K
150K
3.6V
750K
150K
4.2V
620K
100K
5V
825K
110K
DO NOT DISTRIBUTE OR REPRODUCE WITHOUT PERMISSION FROM P.A.M
Pow er Analog Microelectronics, Inc.
Rev. V1.0
April. 2014
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PAM2401
Application Note
CONFIDENTIAL INFORMATION
Inductor Selection
To select an inductor for use in PAM2401 applications, it is worth noting that the inductor
current saturation rating should be larger than the possible peak inductor current to ensure
proper operation, and should have low DCR(DC resistance). Using an inductor the saturation
current of which is lower than required can cause a dramatic drop in the inductance and can decay
the maximum output current levels severely. For most applications, the value of the inductor
should be in the range of 1.5uH to 4.7uH. Its value is chosen based on the desired ripple current.
Larger value inductors result in lower ripple currents, and smaller value inductors result in higher
ripple currents. A 1.5uH or 2.2uH inductor will be the best choice for most PAM2401 applications. The
following equation can also help give a good approximate value for the inductor.
L=VIN×D/(ΔIL×f)
D: Duty Cycle=1-VIN/VOUT f: Switching Frequency=1.0MHz
∆IL: Ripple Current in the Inductor, i.e.20% to 40% of the maximum inductor current (Ip).
Vo
3.3V
3.6V
4.2V
5V
L
1.5uH
1.5uH
1.5uH
2.2uH
Output and Input Capacitor Selection
Input Capacitor
At least a 10 uF input capacitor is recommended to reduce the input ripple and switching noise for
normal operating conditions, while a 10~22uF capacitor may be required for higher power and
dynamic loads. Larger values and lower ESR (Equivalent Series Resistance) may be needed if the
application require very low input ripple. It follows that ceramic capacitors are a good choice for
applications. Note that the input capacitor should be located as close as possible to the IC.
Output Capacitor
A minimum output capacitor value of 22uF is recommended and may be increase to a larger value.
For output lower than 4.2V application, the minimum value of output capacitor should be 32uF at least.
The ESR of the output capacitor is important because it determines the peak to peak output voltage
ripple by the following equation:
∆VOUT » 2∆IL×RESR
Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are
available in small footprints.
DO NOT DISTRIBUTE OR REPRODUCE WITHOUT PERMISSION FROM P.A.M
Pow er Analog Microelectronics, Inc.
Rev. V1.0
April. 2014
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PAM2401
Application Note
CONFIDENTIAL INFORMATION
7.
PCB Layout Guidance
Careful PCB layout is important for proper operation. Use the following guidelines for good
PCB layout:
(1) Minimize the area of the high current switching loop to avoid excessive switching noise.
(2) Connect high-current input and output components with short and wide connections.
(3) Connect all GND together with short, wide traces or a ground plane. Maximizing the
width of the power ground traces improves efficiency and reduces output-voltage ripple
and noise spikes. If vias are unavoidable, use multiple vias in parallel to reduce
resistance and inductance.
(4) Place the Vin bypass capacitor as close to the device as possible. The input capacitor
should be connected directly to Vin and GND pins with a wide trace.
(5) Place the output voltage setting-divider resistors as close to the FB pin as possible.
The divider's center trace should be kept short. Avoid running the sensing traces near SW trace.
(6) For the good thermal dissipation, PAM2401 has a heat dissipate pad in the bottom side,
it should be soldered to PCB surface. For the copper area can’t be large in the component side, so we
can use multiple vias connect to other side of the PCB.
(7) Refer to the PAM2401 evaluation board for an example of proper board layout.
DO NOT DISTRIBUTE OR REPRODUCE WITHOUT PERMISSION FROM P.A.M
Pow er Analog Microelectronics, Inc.
Rev. V1.0
April. 2014
5
PAM2401
Application Note
CONFIDENTIAL INFORMATION
8.
PCB Layout Example
Top Layer
Bottom Layer
DO NOT DISTRIBUTE OR REPRODUCE WITHOUT PERMISSION FROM P.A.M
Pow er Analog Microelectronics, Inc.
Rev. V1.0
April. 2014
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