Datasheet

LT3650-8.2/LT3650-8.4
13
36508284fd
Rectifier Selection
The rectifier diode in an LT3650 battery charger provides a
current path for the inductor current when the main power
switch is disabled. The rectifier is selected based upon
forward voltage, reverse voltage, and maximum current.
A Schottky diode is required, as low forward voltage yields
the lowest power loss and highest efficiency. The rectifier
diode must be rated to withstand reverse voltages greater
than the maximum V
IN
voltage.
The minimum average diode current rating (I
DIODE(MAX)
) is
calculated with maximum output current (I
MAX
), maximum
operational V
IN
, and output at the precondition threshold
(V
BAT(PRE)
):
I
DIODE(MAX)
>
I
MAX
•(V
IN(MAX)
− V
BAT(PRE)
)
V
IN(MAX)
(A)
For example, a rectifier diode for an 8.2V, 1.5A charger
with a 20V maximum input voltage would require:
I
DIODE(MAX)
>
1.5 •(20
−
5.65)
20
,or
I
DIODE(MAX)
> 1.1A
CLP: System Current Limit
The LT3650 contains a PowerPath
TM
control feature to
support multiple load systems. The charger adjusts out-
put current in response to a system load if overall input
supply current exceeds the programmed maximum value.
Maximum input supply current is set by choosing a sense
resistor (R
CLP
) such that the desired maximum current
through that sense resistor creates a 50mV drop, or:
R
CLP
=
0.05
I
MAX(IN)
where I
MAX(IN)
is the maximum input current. A 1.5A sys-
tem limit, for example, would use a 33mΩ sense resistor.
The LT3650 integrates the CLP signal internally, so aver-
age current limiting is performed in most cases without
the need for external filter elements.
applicaTions inForMaTion
Figure 4. R
CLP
Sets the Input Supply Current Limit
365082 F04
CLP
SYSTEM LOAD
INPUT SUPPLY
V
IN
R
CLP
LT3650
365082 F05
0.5A
1.0A
1.5A
LT3650 INPUT
CURRENT (I
VIN
)
SYSTEM LOAD
CURRENT
Figure 5. CLP Limit: Charger Current vs
System Load Current with 1.5A Limit