LTC3216 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC3216
Linear Technology
'LTC3216' PDF : 12 Pages View PDF
LTC3216
APPLICATIONS INFORMATION
LED forward voltage. When it is operating as a switch, the
efficiency is approximated by:
PLED
PIN
=
VLED
VIN
• ILED
• IIN
VLED
VIN
(5)
since the input current will be very close to the LED current.
At moderate to high output power, the quiescent current
of the LTC3216 is negligible and the expression above is
valid.
Once dropout is detected at the ILED pin, the LTC3216
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:
IDEAL
PLED
PIN
=
VLED •ILED
VIN • 1.5ILED
VLED
1.5VIN
(6)
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:
IDEAL
PLED
PIN
=
VLED •ILED
VIN • 2 •ILED
VLED
2 • VIN
(7)
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3216.
If the junction temperature increases above approximately
150°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.
3216fc
10
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