LM25019 datasheet(10/18 Pages) TI

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VIN

UVLO

VIN

RUV1

CIN

RUV2

LM25019

SNVS952 – DECEMBER 2012

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Undervoltage Detector

The LM25019 contains a dual level Undervoltage Lockout (UVLO) circuit. When the UVLO pin voltage is below

0.66V, the controller is in a low current shutdown mode. When the UVLO pin voltage is greater than 0.66V but

less than 1.225V, the controller is in standby mode. In standby mode the VCC bias regulator is active while the

regulator output is disabled. When the VCC pin exceeds the VCC undervoltage threshold and the UVLO pin

voltage is greater than 1.225V, normal operation begins. An external set-point voltage divider from VIN to GND

can be used to set the minimum operating voltage of the regulator.

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

RUV2.

UVLO

VCC

Mode

Description

<0.66V

Shutdown

VCC Regulator Disabled.

Switcher Disabled.

0.66V – 1.225V

Standby

VCC Regulator Enabled

Switcher Disabled.

>1.225V

VCC <4.5V

Standby

VCC Regulator Enabled.

Switcher Disabled.

VCC >4.5V

Operating

VCC enabled.

Switcher enabled.

If the UVLO pin is wired directly to the VIN pin, the regulator will begin operation once the VCC undervoltage is

satisfied.

Figure 14. UVLO Resistor Setting

Thermal Protection

The LM25019 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 LM25019 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,

disabling the buck switch and the VCC regulator. This feature prevents catastrophic failures from accidental

device overheating. When the junction temperature reduces below 145°C (typical hysteresis = 20°C), the VCC

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

100mA

Switching Frequency

400kHz

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