LM3280TLSLASHNOPB datasheet(18/27 Pages) TI

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LM3280

SNOSAU4B – OCTOBER 2006 – REVISED FEBRUARY 2013

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ENBUCK should be set low to turn off the LM3280 during power-up and under voltage conditions when the power

supply is less than the 2.7V minimum operating voltage. The LM3280 is designed for compact portable

applications, such as cellular phones. In such applications, the system controller determines power supply

sequencing and requirements for small package size outweigh the benefit of including UVLO (Under Voltage

Lock-Out) circuitry.

Thermal Overload Protection

The LM3280 has a thermal overload protection function to protect the device from short-term misuse and

overload conditions. When the junction temperature exceeds around 150°C, the device inhibits operation. Both

the PFET and the NFET are turned off in PWM mode, and the Bypass PFET is turned off in Bypass mode. The

LDO is also turned off. When the temperature drops below 125°C, normal operation resumes. Prolonged

operation in thermal overload conditions may damage the device.

APPLICATION INFORMATION

BUCK CONVERTER SETTING THE OUTPUT VOLTAGE

The buck converter features a pin-controlled variable output voltage to eliminate the need for external feedback

resistors. It can be programmed for an output voltage from 0.8V to 3.6V by setting the voltage on the VCON pin,

as in the following formula:

VOUT = 3 x VCON

(1)

When VCON is between 0.267V and 1.20V, the output voltage will follow proportionally by 3 times of VCON.

If VCON is over 1.20V (VOUT = 3.6V), sub-harmonic oscillation may occur because of insufficient slope

compensation.

If VCON voltage is less than 0.267V (VOUT = 0.8V), the output voltage may not be regulated due to the required

on-time being less than the minimum on-time (50ns). The output voltage can go lower than 0.8V providing a

limited VIN range is used. Refer to the Typical Performance Characteristics (Low VCON Voltage vs. Output

Voltage) for details. This curve is for a typical part and there could be part to part variation for output voltages

less than 0.8V over the limited VIN range. In addition, if the VCON is less than approximately 0.15V, the PWM

mode output is turned off, but the internal bias circuits are still active.

INDUCTOR SELECTION

A 2.2

μH inductor with saturation current rating over 940mA is recommended for almost all applications. The

inductor resistance should be less than 0.2

Ω for better efficiency. Table 1 lists suggested inductors and

suppliers.

Table 1. Suggested Inductors and Their Suppliers

Model

Size (WxLxH) [mm]

Vendor

DO3314-222MX

3.3 x 3.3 x 1.4

Coilcraft

LPS3010-222MLC

3.1 x 3.1 x 1.0

Coilcraft

LPS3008-222MLC

3.1 x 3.1 x 0.8

Coilcraft

MIPSA2520D2R2**

2.5 x 2.0 x 1.2

FDK

KSLI252010AG2R2*

2.5 x 2.0 x 1.0

Hitachi-Metal

VLF3010AT-2R2M1R0

2.6 x 2.8 x 1.0

TDK

NR3010T2R2M

3.0 x 3.0 x 1.0

Taiyo-Yuden

NR3012T2R2M

3.0 x 3.0 x 1.2

Taiyo-Yuden

1117AS-2R2M(DE2810C)

2.8 x 3.0 x 1.0

Toko

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