LTC3214EDD Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LTC3214EDD

500mA Camera LED Charge Pump

Linear Technology 

LTC3214

APPLICATIONS INFORMATION

Power Efficiency

To calculate the power efficiency (η) of a white LED

driver chip, the LED power should be compared to the

input power. The difference between these two numbers

represents lost power whether it is in the charge pump

or the current sources. Stated mathematically, the power

efficiency is given by:

η ≡ PLED

PIN

The efficiency of the LTC3214 depends upon the mode in

which it is operating. Recall that the LTC3214 operates

as a pass switch, connecting VIN to CPO, until dropout

is detected at the ILED pin. This feature provides the op-

timum efficiency available for a given input voltage and

LED forward voltage. When it is operating as a switch, the

efficiency is approximated by:

η ≡ PLED = VLED • ILED ≈ VLED

PIN VIN • IIN VIN

since the input current will be very close to the LED

current.

At moderate to high output power, the quiescent current

of the LTC3214 is negligible and the expression above is

valid.

Once dropout is detected at the ILED pin, the LTC3214

enables the charge pump in 1.5x mode.

In 1.5x boost mode, the efficiency is similar to that of a

linear regulator with an effective input voltage of 1.5 times

the actual input voltage. This is because the input current

for a 1.5x charge pump is approximately 1.5 times the

load current. In an ideal 1.5x charge pump, the power

efficiency would be given by:

ηIDEAL

≡

PLED

PIN

=

VLED • ILED

VIN • 1.5ILED

≈

VLED

1.5VIN

Similarly, in 2x boost mode, the efficiency is similar to

that of a linear regulator with an effective input voltage

of 2 times the actual input voltage. In an ideal 2x charge

pump, the power efficiency would be given by:

ηIDEAL

≡

PLED

PIN

=

VLED •ILED

VIN • 2 •ILED

≈

VLED

2VIN

Thermal Management

For higher input voltages and maximum output current,

there can be substantial power dissipation in the LTC3214.

If the junction temperature increases above approximately

165°C, the thermal shutdown circuitry will automatically

deactivate the output. To reduce maximum junction tem-

perature, a good thermal connection to the PC board is

recommended. Connecting the Exposed Pad to a ground

plane and maintaining a solid ground plane under the

device can reduce the thermal resistance of the package

and PC board considerably.

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