Diodes PAM2803 User Manual

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Description

The PAM2803 is a set-up DC-DC converter that delivers a regulated
output current. The device switches at a 1.0MHz constant frequency,
allowing for the use of small value external inductor and ceramic
capacitors.

The PAM2803 is targeted to be used for driving loads up to 1A from a
two-cell alkaline battery. The LED current can be programmed by the
external current sense resistor, R
pin (FB) and ground. A low 95mV feedback voltage reduces the
power loss in the Rs for better efficiency. With its internal 2A, 100m
NMOS switch, the device can provide high efficiency even at heavy
load. During the shutdown mode, the feedback resistor R
load are completely disconnected and the current consumption is
reduced to less than 1µA.

The PAM2803 is available in the 6-lead TSOT26 package.

, connected between the feedback

S

and the

S

Features

 LED Power Efficiency: up to 90%
 Current Accuracy: 5%(V
 Low Start-Up Voltage: 0.9V (I
 Low Hold Voltage: 0.75 (I
 1MHz Switching Frequency
 Uses Small, Low Profile External Components
 Low R
 Over Temperature Protection
 Low Profile TSOT26 Package
 Pb-Free Package

: 100m (typ)

DS(ON)

= 3.6V to 1.8V @VF = 3.7V)

IN

= 270mA)

LED

= 200mA)

LED

Typical Applications Circuit

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3W HIGH POWER WHITE LED DRIVER

Pin Assignments

Top View

TSOT26

Applications

 White LED Torch (Flashlight)
 White LED Camera Flash
 DSC(Digital Still Camera)Flash
 Cellular Camera Phone Flash
 PDA Camera Flash
 Camcorder Torch(Flashlight) Lamp

PAM2803

= 750mA, RS = 0.127Ω

I

LED

PAM2803

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Pin Description

Pin

Number

1
2
3
4

5 VOUT Output
6 VIN Input

Pin

Name

SW Switch

GND Ground

FB Feedback

SHDN Shut Down

Block Diagram

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PAM2803

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

Input Pin Voltage -0.3 to +6
SW Pin Voltage -0.3 to +6
SHDN, FB Pin Voltage -0.3 to +6
Operating Temperature Range -40 to +85
Storage Temperature Range -65 to +125
Lead Temperature (Soldering, 5 sec) 300

Recommended Operating Conditions (@T

Parameter Rating Unit

Junction Temperature -40 to +125
Ambient Temperature -40 to +85

PAM2803

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= +25°C, unless otherwise specified.)

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V

°C

= +25°C, unless otherwise specified.)

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PAM2803

Thermal Information

Parameter Symbol Package Max Unit

Thermal Resistance (Junction to Case)
Thermal Resistance (Junction to Ambient)
Internal Power Dissipation



JC



JA

P

D

TSOT26 130
TSOT26 250

°C/W

TSOT26 400 mW

Electrical Characteristics

(@TA = +25°C, VIN = 2.4V, I

Parameter Symbol Test Conditions Min Typ Max Units

Input Voltage Range

Feedback Voltage

Start-Up Voltage
Hold Voltage
Oscillator Frequency
SHDN Input High
SHDN Input Low
Over Temperature Shutdown OTS 150 °C

Over Temperature Hysteresis OTH 15 °C
Maximum Output Current Range

Quiescent Current
Shutdown Current

Switch On Resistance
Current Limit
Efficiency 

Note: 1. VF – LED forward voltage.

PAM2803

Document number: DSxxxxx Rev. 1 - 1

= 750mA, V

LED

= VIN, L = 2.2µH, CIN = 10µF, CO = 10µF, unless otherwise specified.)

SHDN

V

IN

V

FB

V

VIN: 0V – 3V, I

START

VIN: 3V – 0V, I

V

HOLD

F

OSC

VIN = 1.8V

V

SH

V

VIN = 1.8V

SL

I

O(MAX)

I

Q

I

SD

VO = 3.4V

R

DS(ON)

VO = 3.4V

I

LIM

0.9

-0.2

V

F

(Note 1)

V

90 95 100 mV

= 370mA

LED

: 750mA – 200mA

LED

0.9 V

0.75 V

0.85 1.0 1.15 MHz

1.0 V

0.4 V

750 mA

= 0mA, VO = 3.4V,

I

LED

Device Switching @ 1MHz

1 3 mA

Shutdown Mode 1 µA

0.1 

2 A

= 750mA

I

LED

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Typical Performance Characteristics (@T

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PAM2803

= +25°C, L = 2.2µF, CIN = 10µF, CO = 10µF, unless otherwise specified.)

A

PAM2803

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Typical Performance Characteristics (cont.) @T

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PAM2803

= +25°C, L = 2.2µF, CIN = 10µF, CO = 10µF, unless otherwise specified.)

A

PAM2803

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PAM2803

Application Information

Inductor Selection

The PAM2803 can use small value inductors due to its switching frequency of 1MHz. The value of inductor will focus in the range of 2.2µH to

4.7µH for most PAM2803 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 PAM 2803. 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-22µ F 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 PAM2803 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 PAM2803. 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. In application, the ON Semi conductor
MBRA210LT3G is recommended.

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/R
better LED current accuracy. The formula and table 1 for R

Table 1. R

Standard Value (Ω)



R

Resistor Value Selection

S

0.18 528

0.15 633

0.12 792

0.10 950

/mV95

I

LEDS

(mA)

I

LED

PCB Layout Guidelines

As for all switching power supplies, the layout and components placement of the PAM2803 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.

PAM2803

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2

R power loss, and it requires a current rating of 2A to handle the peak inducto r current

. It's recommended to use a 1% or better precision resistor for the

S

selection are shown as follows:

S

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Ordering Information

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PAM2803

Part Number Marking Package Type Standard Package

PAM2803AAF095

Refer to Marking

Information Below

TSOT26 3000 Units/Tape&Reel

Marking Information

Top View

TSOT26

PAM2803

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Package Outline Dimensions (All dimensions in mm.)

TSOT26

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PAM2803

PAM2803

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PAM2803

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IMPORTANT NOTICE

LIFE SUPPORT

PAM2803

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