VOUT

EN2

ILED

IIN

2V/DIV

2V/DIV

200 mA/DIV

200 mA/DIV

200 ms/DIV

14

LM2758

SNVS551E – APRIL 2008 – REVISED MAY 2016

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EN1 = VIN = 3.6 V

ILED (flash) = 500 mA

Gain = 1.5×

Figure 15. Indicator to Flash Mode Transition

9 Power Supply Recommendations

The LM2758 is designed to operate from an input voltage supply range from 2.7 V to 5.5 V. This input supply

must be well regulated and capable to supply the required input current. If the input supply is located far from the

device, additional bulk capacitance may be required in addition to the ceramic bypass capacitors.

9.1 Power Dissipation

The power dissipation (PDISSIPATION) and junction temperature (TJ) can be approximated with the equations

below. PIN is the power generated by the 1×/1.5× charge pump, PLED is the power consumed by the LEDs, TA is

the ambient temperature, and RθJA is the junction-to-ambient thermal resistance for the 12-pin DSBGA package.

VIN is the input voltage to the LM2758, VLED is the nominal LED forward voltage, and ILED is the programmed

LED current.

PDISSIPATION = PIN – PLED

(8)

= (Gain × VIN × ILED) − (VLED × ILED)

(9)

TJ = TA + (PDISSIPATION × RJθA)

(10)

The junction temperature rating takes precedence over the ambient temperature rating. The LM2758 may be

operated outside the ambient temperature rating, so long as the junction temperature of the device does not

exceed the maximum operating rating of 125°C. The maximum ambient temperature rating must be derated in

applications where high power dissipation and/or poor thermal resistance causes the junction temperature to

exceed 125°C.