LTC3255

9

3255f

APPLICATIONS INFORMATION

The LTC3255 has thermal protection that will shut

down the device if the junction temperature exceeds the

overtemperature threshold (typically 175°C). Thermal

shutdown is included to protect the IC in cases of exces-

sively high ambient temperatures, or in cases of excessive

power dissipation inside the IC. The charge transfer will

reactivate once the junction temperature drops back to

approximately 165°C.

When the thermal protection is active, the junction tem-

perature is beyond the specified operating range. Thermal

protection is intended for momentary overload conditions

outsidenormaloperation.Continuousoperationabovethe

specified maximum operating junction temperature may

impair device reliability.

Programming the Output Voltage (FB Pin)

The LTC3255 output voltage is set by connecting its FB

in Figure 1.

The desired adjustable output voltage is programmed by

=

1.2V

–1

will result in lower operating current.

2:1 Step-Down Charge Pump Operation

happens in two phases. On the first phase, the flying ca-

step-down mode, the input current will be approximately

half of the total output current. The efficiency (

η) and chip

η=

=

1

2

=

2









1:1 Step-Down Charge Pump Operation

1:1 step-down mode is similar to how a linear regulator

most of the internal oscillator period. The charge transfer

is briefly interrupted at the end of the period. When in 1:1

step-down mode the input current will be approximately

equal to the total output current. Thus efficiency (

η) and

η=

=

=

(

FB

3255 F01

GND

LTC3255

1.2V 1 +

Figure 1. Setting the Output Voltage