LT3580EMS8E-TRPBF(RevC) Ver la hoja de datos (PDF) - Linear Technology

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Fabricante

LT3580EMS8E-TRPBF
(Rev.:RevC)

Boost/Inverting DC/DC Converter with 2A Switch, Soft-Start, and Synchronization

Linear Technology 

LT3580

APPLICATIONS INFORMATION

VIN

VIN

RUVLO1

1.3V –

SHDN

+

RUVLO2

(OPTIONAL)

11.6μA

AT 1.3V

GND

ACTIVE/

LOCKOUT

3580 F07

Figure 7. Configurable UVLO

the regulator from operating at source voltages where

these problems might occur.

The shutdown pin comparator has voltage hysteresis with

typical thresholds of 1.32V (rising) and 1.29V (falling).

Resistor RUVLO2 is optional. RUVLO2 can be included to

reduce the overall UVLO voltage variation caused by varia-

tions in SHDN pin current (see the Electrical Character-

istics). A good choice for RUVLO2 is ≤10k ±1%.

After choosing a value for RUVLO2, RUVLO1 can be deter-

mined from either of the following:

RUVLO1 = 

VIN +
1.32V

1.32V 

 RUVLO2  + 11.6μA

or

RUVLO1

=





VIN

1.29V 

RUVLO2 

1.29V

+ 11.6

μA

where VIN+ and VIN– are the VIN voltages when rising or

falling respectively.

For example, to disable the LT3580 for VIN voltages below

3.5V using the single resistor configuration, choose:

RUVLO1

=





3.5V

1.29V



1.29V





+

11.6μA

=

190.5k

To activate the LT3580 for VIN voltage greater than 4.5V

using the double resistor configuration, choose RUVLO2

= 10k and:

RUVLO1

=





4.5V

1.32V

10k

1.32V





+ 11.6μA

=

22.1k

Internal Undervoltage Lockout

The LT3580 monitors the VIN supply voltage in case VIN

drops below a minimum operating level (typically about

2.3V). When VIN is detected low, the power switch is

deactivated, and while sufficient VIN voltage persists, the

soft-start capacitor is discharged. After VIN is detected

high, the power switch will be reactivated and the soft-

start capacitor will begin charging.

Thermal Considerations

For the LT3580 to deliver its full output power, it is impera-

tive that a good thermal path be provided to dissipate the

heat generated within the package. This is accomplished

by taking advantage of the thermal pad on the underside of

the IC. It is recommended that multiple vias in the printed

circuit board be used to conduct heat away from the IC

and into a copper plane with as much area as possible.

Thermal Lockout

If the die temperature reaches approximately 165°C, the

part will go into thermal lockout, the power switch will be

turned off and the soft-start capacitor will be discharged.

The part will be enabled again when the die temperature

has dropped by ~5°C (nominal).

Thermal Calculations

Power dissipation in the LT3580 chip comes from four

primary sources: switch I2R loss, NPN base drive (AC),

NPN base drive (DC), and additional input current. The

following formulas can be used to approximate the power

losses. These formulas assume continuous mode opera-

3580fc

15

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