PAM2805 Datasheet. Www.s Manuals.com. Diodes

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A Product Line of
Diodes Incorporated

PAM2805
3-MODES/ 3W WLED DRIVER WITH 1 OR 2 CELL BATTERY

Description

Pin Assignments

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 RS for
better efficiency. With its internal 2A, 100mΩ device can provide high
efficiency even at heavy load.
The PAM2805 is available in SOT23-6 package.

Applications
•

White LED Torch (Flashlight)

Features
•

3 Modes Cycling Function:
Power Off
<5S

Bright

Power Off
<5S

Dimming

Blinking

Power Off
<5S

•

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: 100mΩ

•

Over Temperature Protection

•

Over Voltage Protection

•

SOT23-6 Package

•

Pb-Free Package

Typical Applications Circuit

ILED + 95mV/RS

PAM2805
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Pin Description
Pin
Number

Pin
Name

1
2
3
4

VIN

5
6

Function
Input Voltage

GND

Power Ground

BLK

Connect A 1µF CAP for blinking

FB
VOUT
SW

Feedback
Output Voltage
Connected to an internal NMOS switch

Block Diagram

Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.)
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
Supply Voltage
Output Voltage
Storage Temperature Range
Lead Temperature (Soldering, 5 sec)

Rating
6
6
-65 to +150
300

Unit
V
°C

Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Parameter

Rating

Operation Temperature Range

-40 to +85

Junction Temperature Range

-40 to +125

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Unit
°C

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PAM2805

Thermal Information
Parameter

Symbol

Package

Max

Thermal Resistance (Junction to Case)

θJC

SOT23-6

130

Thermal Resistance (Junction to Ambient)

θJA

SOT23-6

250

Internal Power Dissipation @ TA = 25°C

PD

SOT23-6

400

Unit
°C/W
mW

Electrical Characteristics
(@TA = +25°C, L = 2.2µH, CIN = 10µF, COUT = 10µF, CBLK = 1µF, VF = 3.4V unless otherwise specified.)

Parameter

Symbol

Test Conditions

Min

Input Voltage Range

VIN

0.9

Feedback Voltage

VFB

90

Typ

95

Max

Units

VF -0.2
(Note 1)

V

100

mV

Start-Up Voltage

VSTART

VIN: 0V →3V, ILED = 200mA

0.9

V

Hold Voltage

VHOLD

VIN: 3V → 0V, ILED: 750mA → 100mA

0.7

V

Oscillator Frequency
Over Temperature Shutdown
Over Temperature Hysteresis
Maximum Output Current Range
Quiescent Current
Switch On Resistance
Current Limit

IO(MAX)
IQ

VO = 3.4V
VO = 3.4V

Blinking Frequency

FBLK

1.15

mA
1

3

0.1

mA
Ω

2

A
4.5
8.5

CBLK = 1µF

MHz
°C
°C

750

VIN = 2.4V
ILED = 0mA, VO = 3.4V, Device Switching
at 1MHz

ILIM
VOVP

1.0
150
30

RDS(ON)

Over Voltage Protection (VOUT)

Note:

0.85

fOSC
OTS
OTH

V
10

Hz

1. VF ---LED forward voltage

PAM2805
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PAM2805

Typical Performance Characteristics
(@TA = +25°C, L = 2.2µF, CIN = 10µF, COUT = 10µF, CBLK = 1µF, unless otherwise specified.)

PAM2805
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PAM2805

Typical Performance Characteristics (cont.)
(@TA = +25°C, L = 2.2µF, CIN = 10µF, COUT = 10µF, CBLK = 1µF, unless otherwise specified.)

PAM2805
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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
2

should have low DCR (DC resistance) to minimize the I R power loss, and it requires a current rating of 2A to handle the peak inductor current
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 recommended 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 RS selection is shown as follows:

RS (Ω ) = 95mV / ILED (mA )at VIN = 3 V
Typically, for 1W(330mA) and 3W(750mA) LED light applications, the RS are 0.288Ω and 0.127Ω respectively.

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 VIN 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
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 VOUT goes over VOVP, typically 4.5V, the power NMOS is
turned off and SW pin stops switching. Then, the VOUT is clamped to around VOVP.

Over Current Protection
The inductor current during charging period is detected by a current sensing circuit. When the value is larger than current limiting ILIM, the power
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 ILIM, whose minimum value is 2A.

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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
PAM2805AF

Marking
ECXYW

Package Type
SOT23-6

Standard Package
3000 Units/Tape&Reel

Marking Information

PAM2805
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PAM2805

Package Outline Dimensions (All dimensions in mm.)
SOT23-6

PAM2805
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PAM2805

IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT,
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).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume
all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated
website, harmless against all damages.
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channel.
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This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the
final and determinative format released by Diodes Incorporated.
LIFE SUPPORT
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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representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or
systems.
Copyright © 2012, Diodes Incorporated
www.diodes.com

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