ltc3207euf-trpbf Linear Technology Corporation, ltc3207euf-trpbf Datasheet - Page 17

• Manufacturer Part Number: ltc3207euf-trpbf
• Description: 600ma Universal Multi-output Led/cam Driver
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Power Effi ciency
To calculate the power effi ciency (
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 cur-
rent sources. Stated mathematically, the power effi ciency
is given by:
The effi ciency of the LTC3207/LTC3207-1 depends upon
the mode in which they are operating. Recall that the
LTC3207/LTC3207-1 operate as pass switches, connect-
ing V
This feature provides the optimum effi ciency available for
a given input voltage and LED forward voltage. When it is
operating as a switch, the effi ciency is approximated by:
since the input current will be very close to the sum of
the LED currents.
At moderate to high output power, the quiescent current
of the LTC3207/LTC3207-1 is negligible and the expres-
sion above is valid.
Once dropout is detected at any the LED pin, the LTC3207/
LTC3207-1 enable the charge pump in 1.5x mode.
η =
η =
BAT
P
P
P
P
LED
LED
to CPO, until dropout is detected at the I
IN
IN
=
V
V
LED
BAT
•
•
I
I
LED
BAT
=
V
V
LED
BAT
η
) of an LED driver chip,
LED
pin.
In 1.5x boost mode, the effi ciency 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
effi ciency would be given by:
Similarly, in 2x boost mode, the effi ciency is similar to
that of a linear regulator with an effective input voltage of
2x the actual input voltage. In an ideal 2x charge pump,
the power effi ciency would be given by:
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3207/
LTC3207-1. If the junction temperature increases above
approximately 150°C the thermal shutdown circuitry will
automatically deactivate the output current sources and
charge pump. To reduce maximum junction temperature,
a good thermal connection to the PC board is recom-
mended. Connecting the Exposed Pad to a ground plane
and maintaining a solid ground plane under the device
will reduce the thermal resistance of the package and PC
board considerably.
η
η
IDEAL
IDEAL
=
=
P
P
P
P
LED
LED
IN
IN
LTC3207/LTC3207-1
=
=
V
V
BAT
BAT
V
V
LED
LED
• . •
• •
1 5
2
•
•
I
LED
I
I
LED
LED
I
LED
=
=
2
V
•
1. . • 5 V
LED
V
B B AT
V
LED
BAT
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