+

UVLO

VIN

2

3

LM25018

LM25018

SNVS953 – DECEMBER 2012

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UVLO hysteresis is accomplished with an internal 20

μA current source that is switched on or off into the

impedance of the set-point divider. When the UVLO threshold is exceeded, the current source is activated to

quickly raise the voltage at the UVLO pin. The hysteresis is equal to the value of this current times the resistance

UVLO

Mode

Description

<0.66V

Shutdown

Switcher Disabled.

0.66V – 1.225V

Standby

Switcher Disabled.

>1.225V

Standby

Switcher Disabled.

Operating

Switcher Enabled.

satisfied.

Figure 14. UVLO Resistor Setting

Thermal Protection

The LM25018 should be operated so the junction temperature does not exceed 150°C during normal operation.

An internal Thermal Shutdown circuit is provided to protect the LM25018 in the event of a higher than normal

junction temperature. When activated, typically at 165°C, the controller is forced into a low power reset state,

regulator is enabled, and normal operation is resumed.

Application Information

SELECTION OF EXTERNAL COMPONENTS

Selection of external components is illustrated through a design example. The design example specifications are

as follows:

Buck Converter Design Specifications

Input Voltage Range

12.5V to 48V

Output Voltage

10V

Maximum Load Current

325mA

Switching Frequency

400kHz

values of 6.98k

Ω and 1.00kΩ are chosen. Other values could be used as long as the 7:1 ratio is maintained.

Frequency Selection:

At the minimum input voltage, the maximum switching frequency of LM25018 is restricted by the forced minimum

10

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