LM3557

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SNVS338B – NOVEMBER 2004 – REVISED FEBRUARY 2013

Operating Conditions

(1) (2)

−40°C to +125°C

−40°C to +85°C

2.7V to 7.5V

En Pin

(1)

Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical characteristic specifications do not

apply when operating the device outside of its rated operating conditions.

(2)

All voltages are with respect to the potential at the GND pin.

THERMAL CHARACTERISTICS

(1) (2)

over operating free-air temperature range (unless otherwise noted)

Junction-to-Ambient Thermal

55°C/W

Resistance (

(1)

resistance,

dissipation will cause excessive die temperature.

(2)

Junction-to-ambient thermal resistance (

forth in the JEDEC standard JESD51-7. The test board is a 4 layer FR-4 board measuring 102 mm x 76 mm x 1.6 mm with a 2 x 1 array

of thermal vias. The ground plane on the board is 50 mm x 50 mm. Thickness of copper layers are 36 µm/18 µm/18 µm/36 µm (1.5 oz/1

oz/1 oz/1.5 oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1W. In applications where high maximum power

dissipation exists, special care must be paid to thermal dissipation issues. For more information on these topics, please refer to

Application Note 1187: Leadless Leadframe Package (LLP) and the Layout Guidelines section of this datasheet.

Electrical Characteristics

(1) (2)

(

Parameter

Test Conditions

Min

Typ

Max

Units

Input Voltage

2.7

7.5

V

Quiescent Current

0.01

2

µA

0.55

0.8

mA

(Non-Switching)

En

Device Enable Threshold

Device On

0.9

0.3

V

Device Off

0.4

0.8

1.1

A

0.55

0.8

1.02

Power Switch ON Resistance

800

1000

m

Ω

0.5

%/C

OVP

On Threshold

22

26

28.5

V

Off Threshold

21.5

25.5

28

UVP

On Threshold

2.2

V

Off Threshold

2.3

Over-Voltage Protection Pin Bias

4

10

µA

0.8

3

µA

Switching Frequency

0.9

1.25

1.6

MHz

0.459

0.51

0.561

V

0.03

2

µA

Maximum Duty Cycle

85

90

%

(1)

All voltages are with respect to the potential at the GND pin.

(2)

Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the

most likely norm.

(3)

The Power Switch Current Limit is tested in open loop configuration. For closed loop application current limit please see the Current

Limit vs Temperature performance graph.

(4)

The on threshold indicates that the LM3557 is no longer switching or regulating LED current, while the off threshold indicates normal

operation.

(5)

Current flows into the pin.

(6)

Feedback pin voltage is with respect to the voltage at the Sw2 pin.

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