PowTech PT4181 Schematic [ru]

PT4181

White LED Step-Up Converter

GENERAL DESCRIPTION

The PT4181 is a step-up DC/DC converter designed for
driving up to 8 white LEDs in series from a single cell
Lithium Ion battery with constant current. Because it
directly regulates output current, the PT4181 is ideal for
driving light emitting diodes (LEDs) whose light
intensity is proportional to the current passing through
them, not the voltage across their terminals. A single
external resistor sets LED current between 5mA and
20mA, which can then be easily adjusted using either a
DC voltage or a pulse width modulated (PWM) signal.
Its low 104mV feedback voltage reduces power loss
and improves efficiency. The OV pin monitors the
output voltage and turns off the converter if an
over-voltage condition is present due to an open circuit
condition. The PT4181 is available in SOT23-6
packages.

ORDERING INFORMATION

PACKAGE

TEMPERATURE

RANGE

ORDERING PART

NUMBER

FEATURES

z Drives Up to 5 Series White LEDs from 2.5V
z Drives Up to 8 Series White LEDs from 3.6V
z Up to 87% Efficiency
z 1.2MHz Fixed Switching Frequency
z Low 104mV Feedback Voltage
z Open Load Shutdown
z Soft Start/PWM Dimming
z SOT23-6 Packages

APPLICATIONS

z Cell Phones
z Handheld Computers and PDAs
z Digital Cameras
z Small LCD Displays

TRANSPORT

MEDIA

MARKING

SOT23-6 -40 oC to 85 oC PT4181E23F

Tape and Reel

3000 units

4181

TYPICAL APPLICATIONS KEY PERFORMANCE CHART

Efficiency vs n(LED)

90.00%

85.00%

80.00%

75.00%

51015

20 25

Iout (mA) Vin=3.6V

3LED

4LED

5LED

6LED

7LED

8LED

Figure1. Li-Ion Driver for Six White LEDs Figure2. Efficiency vs Number of LEDs

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PT4181_DS Rev EN_2.1

PT4181

PIN ASSIGNMENT

PIN DESCRIPTIONS

SOT

PIN No.

1 SW Power Switch Output. Connect the inductor and the blocking Schottky diode to

2 GND Ground

3 FB Feedback input pin. The reference voltage at this pin is 104mV. Connect the

4 EN Enable pin. A high input at EN enables the device and a low input disables the

5 OV Over Voltage Input. OV measures the output voltage for open circuit protection.

6 IN Input Supply Pin. Must be locally bypassed.

PIN

Names

White LED Step-Up Converter

DESCRIPTION

SW.

cathode of the lowest LED to FB and a current sense resistor between FB and

GND.

devices. When not used, connect EN to the input source for automatic startup.

Connect OV to the output at the top of the LED string.

ABSOLUTE MAXIMUM RATINGS (Note 1)

SYMBOL ITEMS VALUE UNIT

VIN Input Voltage

VSW Voltage at SW Pin

VIO All Other I/O Pins GND-0.3 to VDD+0.3 V

Thermal Resistance，SOT-23-6

P

TR1

Tstg Storage Temperature -55 to 150

Tsolder Package Lead Soldering Temperature 260 , 10s℃

θ
θ

JA

JC

-0.3～6

-0.5～35

220

110

V

V

℃/W

℃

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PT4181_DS Rev EN_2.1

PT4181

White LED Step-Up Converter

RECOMMENDED OPERATING RANGE (Note 2)

SYMBOL ITEMS VALUE UNIT

VIN VIN Supply Voltage 2.5 to +6 V

VSW Output Voltage VIN to 28 V

T

Operating Temperature -40 to +85

OPT

℃

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.

Note 2: Recommended operating Range indicates conditions for which the device is functional, but does not guarantee specific

performance limits.

ELECTRICAL CHARACTERISTICS (Note 3,4,5)

V

SYMBOL ITEMS CONDITIONS Min. Typ. Max. UNIT

Feedback

Operating Current

Chip Enable

Output Switch

Open Circuit Protection

Soft Start

=3V, Topt=25℃ unless specified otherwise.

IN=VEN

VIN Input Voltage 2.5 6 V

VFB FB Pin Voltage 89 104 119 mV

Ibias FB Pin Input Bias Current 0.05 1 µA

Ioff

Isby

Operating Current（Shutdown）

Operating Current（Quiescent）

V

=0V 0.1 1 µA

SW-ON

VFB=0.3V 100 350 µA

Fsw Switching Frequency 1.0 1.25 1.5 MHz

Dmax Maximum Duty Cycle VFB=0V 85 90 %

V

EN Minimum High Level 1.5 V

EN_H

V

EN Maximum Low Level 0.4 V

EN_L

V

EN Hysteresis 90 mV

HYS

EN Input Bias Current V

=0V, 5V 1 µA

SW-ON

RON SW On Resistance (Note 3) 0.5 Ω

I

SW Current Limit 400 mA

LIMIT

I

SW Leakage Current

LEAK

VOV Open Circuit Shutdown

Vsw＝5V

VOV Rising 30 V

0.01 1 µA

Threshold

tss Soft Start Time (Note 3) V

Power On 160 µS

IN

Note 3: Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the recommended operating Range.
Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good
indication of device performance.

Note 4: Typicals are measured at 25˚C and represent the parametric norm.
Note 5:

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PT4181_DS Rev EN_2.1

Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.