lt3652hv Linear Technology Corporation, lt3652hv Datasheet - Page 13

• Manufacturer Part Number: lt3652hv
• Description: Lt3652hv Power Tracking 2a Battery Charger Features
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
In low V
by an external source for start-up, eliminating the V
start-up requirement.
V
An LT3652HV charger output requires bypass capacitance
connected from the BAT pin to ground (C
ceramic capacitor is required for all applications. In systems
where the battery can be disconnected from the charger
output, additional bypass capacitance may be desired for
visual indication for a no-battery condition (see the Status
Pins section).
If it is desired to operate a system load from the LT3652HV
charger output when the battery is disconnected, additional
bypass capacitance is required. In this type of application,
excessive ripple and/or low amplitude oscillations can oc-
cur without additional output bulk capacitance. For these
applications, place a 100μF low ESR non-ceramic capacitor
(chip tantalum or organic semiconductor capacitors such
as Sanyo OS-CONs or POSCAPs) from BAT to ground,
in parallel with the 10μF ceramic bypass capacitor. This
additional bypass capacitance may also be required in
systems where the battery is connected to the charger
with long wires. The voltage rating of C
exceed the battery float voltage.
Inductor Selection
The primary criterion for inductor value selection in an
LT3652HV charger is the ripple current created in that
inductor. Once the inductance value is determined, an
inductor must also have a saturation current equal to or
exceeding the maximum peak current in the inductor. An
inductor value (L), given the desired amount of ripple cur-
rent (ΔI
In the above relation, ΔI
rent, V
BAT
L = (10 R
Output Decoupling
[1 – (V
IN(MAX)
IN
MAX
applications, the BOOST supply can be powered
) can be approximated using the relation:
SENSE
BAT(FLT)
is the maximum operational voltage, and
/ ΔI
/ V
MAX
IN(MAX)
MAX
) • V
is the normalized ripple cur-
)]
BAT(FLT)
(μH)
•
BAT
must meet or
BAT
). A 10μF
IN
Magnetics vendors typically specify inductors with
maximum RMS and saturation current ratings. Select an
inductor that has a saturation current rating at or above (1+
ΔI
Inductors must also meet a maximum volt-second product
requirement. If this specification is not in the data sheet of
an inductor, consult the vendor to make sure the maximum
volt-second product is not being exceeded by your design.
The minimum required volt-second product is:
Rectifier Selection
The rectifier diode from SW to GND, in a LT3652HV 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
V
Ripple current is typically set within a range of 25% to
35% of I
by setting 0.25 < ΔI
F
MAX
V
is the forward voltage of the rectifying Schottky diode.
BAT(FLT)
/2) • I
Figure 3. 14.4V at 1.5A Switched Inductor Values
CHG(MAX)
CHG(MAX)
• (1 – V
14
12
10
24
22
20
18
16
8
6
4
18
MAXIMUM OPERATIONAL V
, so an inductor value can be determined
20
BAT(FLT)
MAX
, and an RMS rating above I
22
< 0.35.
24
/V
IN(MAX)
26
28
IN
VOLTAGE (V)
) (V • μS)
30
LT3652HV
32
3652 F03
34
IN
CHG(MAX)
voltage.
13
3652hvf
.