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3-MODES/ 3W WLED DRIVER WITH 1 OR 2 CELL BATTERY
Description
The PAM2805 is a step-up DC-DC WLED driver with 3 modes cycling
function (100% brightness,25% brightness and 8.5Hz blinking).
The unique 3 modes cycling function can eliminate the needs of extra
functional MCU or IC.
The PAM2805 can deliver up to 750mA output current by setting an
external resistor.
The PAM2805 switches at a 1.0MHz constant frequency, allowing for
the use of small value external inductor and ceramic capacitors.
A low 95mV feedback voltage reduces the power loss in the R
better efficiency. With its internal 2A, 100m device can provide high
efficiency even at heavy load.
The PAM2805 is available in TSOT26 package.
S
for
Features
Diodes Incorporated
Pin Assignments
Applications
White LED Torch (Flashlight)
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Top View
TSOT26
PAM2805
3 Modes Cycling Function:
Power Off
<5S
Bright Dimming Blinking
Reset to Bright Mode if Power Off time More Than 5S
Adjustable Output Current: Up to 750mA
8.5Hz Blinking Mode
Low Start-Up Voltage: 0.9V(typ)
Low SW on Resistance: 100m
Over Temperature Protection
Over Voltage Protection
TSOT26 Package
Pb-Free Package
Power Off
<5S
Power Off
<5S
Typical Applications Circuit
PAM2805
Document number: DSxxxxx Rev. 1 - 0
ILED + 95mV/R
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Pin Description
Pin
Number
1
2
3
4
5 VOUT Output Voltage
6 SW Connected to an internal NMOS switch
Pin
Name
VIN Input Voltage
GND Power Ground
BLK Connect A 1µF CAP for blinking
FB Feedback
Block Diagram
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PAM2805
Function
Absolute Maximum Ratings (@T
These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may
affect device reliability. All voltages are with respect to ground.
Parameter Rating Unit
Supply Voltage 6
Output Voltage 6
Storage Temperature Range -65 to +150
Lead Temperature (Soldering, 5 sec) 300
Recommended Operating Conditions (@T
Parameter Rating Unit
Operation Temperature Range -40 to +85
Junction Temperature Range -40 to +125
PAM2805
Document number: DSxxxxx Rev. 1 - 0
= +25°C, unless otherwise specified.)
A
V
°C
= +25°C, unless otherwise specified.)
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°C
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PAM2805
Thermal Information
Parameter Symbol Package Max Unit
Thermal Resistance (Junction to Case)
Thermal Resistance (Junction to Ambient)
JC
JA
Internal Power Dissipation @ TA = 25°C PD
TSOT26 130
TSOT26 250
°C/W
TSOT26 400 mW
Electrical Characteristics
(@TA = +25°C, L = 2.2µH, CIN = 10µF, C
Parameter Symbol Test Conditions Min Typ Max Units
Input Voltage Range
Feedback Voltage
Start-Up Voltage
Hold Voltage
Oscillator Frequency
Over Temperature Shutdown OTS 150 °C
Over Temperature Hysteresis OTH 30 °C
Maximum Output Current Range
Quiescent Current
Switch On Resistance
Current Limit
Over Voltage Protection (VOUT)
Blinking Frequency
Note: 1. VF ---LED forward voltage
PAM2805
Document number: DSxxxxx Rev. 1 - 0
= 10µF, C
OUT
V
IN
V
FB
VIN: 0V 3V, I
V
START
VIN: 3V 0V, I
V
HOLD
f
OSC
I
VIN = 2.4V
O(MAX)
I
Q
VO = 3.4V
R
DS(ON)
VO = 3.4V
I
LIM
V
OVP
F
C
BLK
= 1µF, V
BLK
= 3.4V unless otherwise specified.)
F
0.9
-0.2
V
F
(Note 1)
V
90 95 100 mV
= 200mA
LED
: 750mA 100mA
LED
0.9 V
0.7 V
0.85 1.0 1.15 MHz
750 mA
= 0mA, VO = 3.4V, Device Switching
I
LED
at 1MHz
1 3 mA
0.1
2 A
4.5 V
BLK
= 1µF
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8.5 10 Hz
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Typical Performance Characteristics
(@TA = +25°C, L = 2.2µF, CIN = 10µF, C
= 10µF, C
OUT
BLK
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PAM2805
= 1µF, unless otherwise specified.)
PAM2805
Document number: DSxxxxx Rev. 1 - 0
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Typical Performance Characteristics (cont.)
(@TA = +25°C, L = 2.2µF, CIN = 10µF, C
= 10µF, C
OUT
= 1µF, unless otherwise specified.)
BLK
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PAM2805
PAM2805
Document number: DSxxxxx Rev. 1 - 0
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PAM2805
Application Information
Inductor Selection
The PAM2805 can use small value inductors due to its switching frequency of 1 MHz. The value of inductor will focus in the range of 2.2µH to
4.7µH for most PAM2805 applications. In typical high current white LED applications, it is recommended to use a 4.7µH inductor. The inductor
should have low DCR (DC resistance) to minimize the I
without saturating.
Capacitor Selection
An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2805. For good input decoupling, Low ESR
(equivalent series resistance) capacitors should be used at the input. At least 2.2µF input capacitor is recommended for most applications.
A minimum output capacitor value of 6.8µF is recommended under normal operating conditions, while a 10µF-22µF capacitor may be required
for higher power LED current. A reasonable value of the output capaci tor depends on the LED current. The ESR of the output capacitor is the
important parameter to determine the output voltage ripple of the converter, so low ESR capacitors should be used at the output to reduce the
output voltage ripple. The small size of ceramic capacitors is an excellent choice for PAM2805 applications. The X5R and X7R types are
preferred because they maintain capacitance over wide voltage and temperature ranges.
Diode Selection
It's indispensable to use a Schottky diode rated at 2A with the PAM2805. Using a Schottky diode with a lower forward voltage drop is better to
improve the power LED efficiency, and its voltage rating should be greater than the output voltage. SS22 is reco mmended Schottky diode for
rectifier.
LED Current Setting
The LED current is set by the single external Rs resistor connected to the FB pin as shown in the typical application circuit on Page 1. The typical
FB reference is internally regulated to 95mV. The LED current is 95mV/R1. It's recommended to use a 1% or better precision resistor for the
better LED current accuracy. The formula for R
Typically, for 1W(330mA) and 3W(750mA) LED light applications, the R
R
/mV95
I
S
atmA
V
INLEDS
3 Modes Cycling
The PAM2805 has three modes: 100% brightness, 25% brightness and blinking (typical 8.5Hz).
The mode change is triggered by power on/off actions and cycles in the following sequence: bright, dimming, blinking and back to bright mode.
The PAM2805 will reset to the bright mode after being power off for more than 5 seconds.
Low Voltage Start-Up and Soft-Start
The PAM2805 has a build-in low voltage startup circuit for the best battery life solution. It can start up at 0.9V VIN typically when the preset LED
current is 200mA.
The soft-start function is made by clamping the output voltage of error amplifier with another voltage source which increases slowly from zero to
near V
dur ing the soft-start period. Therefore, the duty cycle of the PWM will be increased from zero to maximum in this period. The charging
IN
time of the inductor will be limited by the smaller duty so that the inrush current can be reduced to an acceptable value.
Over Voltage Protection
The output voltage of PAM2805 is monitored by Over Voltage Protection circuit. Once V
turned off and SW pin stops switching. Then, the V
Over Current Protection
The inductor current during charging period is detected by a current sensing circuit. When the value is larger than current limiting I
NMOS is turned off so that the inductor will be forced to leave charging stage and enter discharging stage. Therefore, the inductor peak current
will not exceed I
, whose minimum value is 2A.
LIM
PAM2805
Document number: DSxxxxx Rev. 1 - 0
2
R power loss, and it requires a current rating of 2A to handle the peak inductor current
selection is shown as follows:
V3
are 0.288 and 0.127 respectively.
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is clamped to around V
OUT
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OVP
goes over V
OUT
.
, typically 4.5V, the power NMOS is
OVP
, the power
LIM
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PAM2805
Application Information
PCB Layout Guidelines
As for all switching power supplies, the layout and components placement of the PAM2805 is an important step in the design; especially at high
peak currents and high switching frequencies.
The input capacitor and output capacitor should be placed respectively as close as possible to the input pin and output pin of the IC; the inductor
and schottky diode should be placed as close as possible to the switch pin by using wide and short traces for the main current path; the current
sense resistor should be placed as close as possible between the ground pin and feedback pin.
Ordering Information
Part Number Marking Package Type Standard Package
PAM2805AF ECXYW TSOT26 3000 Units/Tape&Reel
Marking Information
Top View
TSOT26
PAM2805
Document number: DSxxxxx Rev. 1 - 0
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Package Outline Dimensions (All dimensions in mm.)
TSOT26
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PAM2805
PAM2805
Document number: DSxxxxx Rev. 1 - 0
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PAM2805
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
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final and determinative format released by Diodes Incorporated.
Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and
any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
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Copyright © 2013, Diodes Incorporated
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IMPORTANT NOTICE
LIFE SUPPORT
PAM2805
Document number: DSxxxxx Rev. 1 - 0
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