LT3652 LINER [Linear Technology], LT3652 Datasheet - Page 12

• Manufacturer Part Number: LT3652
• Description: Power Tracking 2A Battery Charger for Solar Power
• Manufacturer: LINER [Linear Technology]

LT3652
APPLICATIONS INFORMATION
ripple current in the charger, so it must have an adequate
ripple current rating. RMS ripple current (I
where I
(100mV/R
V
The simple worst-case of ½ • I
used for design.
Bulk capacitance is a function of desired input ripple volt-
age (ΔV
Input ripple voltages above 0.1V are not recommended.
10μF is typically adequate for most charger applica-
tions.
Charge Current Programming
The LT3652 charger is configurable to charge at average
currents as high as 2A. Maximum charge current is set by
choosing an inductor sense resistor (R
the desired maximum average current through that sense
resistor creates a 100mV drop, or:
where I
A 2A charger, for example, would use a 0.05Ω sense
resistor.
12
IN
I
I
C
R
CVIN(RMS)
CVIN(RMS)
= 2 • V
IN(BULK)
SENSE
CHG(MAX)
CHG(MAX)
IN
), and follows the relation:
SENSE
= 0.1 / I
BAT
= I
≅ I
, where:
= I
CHG(MAX)
CHG(MAX)
). The above relation has a maximum at
CHG(MAX)
is the maximum average charge current.
is the maximum average charge current
CHG(MAX)
• (V
• (V
/2.
BAT
BAT
/ V
/V
IN
CHG(MAX)
IN
)•([V
) / ΔV
IN
SENSE
IN
/ V
CVIN(RMS)
is commonly
(μF)
BAT
) such that
] – 1)
1/2
) is:
,
BOOST Supply
The BOOST bootstrapped supply rail drives the internal
switch and facilitates saturation of the switch transistor.
Operating range of the BOOST pin is 0V to 8.5V, as refer-
enced to the SW pin. Connect a 1μF or greater capacitor
from the BOOST pin to the SW pin.
The voltage on the decoupling capacitor is refreshed
through a diode, with the anode connected to either the
battery output voltage or an external source, and the
cathode connected to the BOOST pin. Rate the diode
average current greater than 0.1A, and reverse voltage
greater than V
To refresh the decoupling capacitor with a rectifying diode
from the battery with battery float voltages higher than
8.4V, a >100mA Zener diode can be put in series with
the rectifying diode to prevent exceeding the BOOST pin
operating voltage range.
Figure 1. Programming Maximum Charge
Current Using R
LT3652
IN(MAX)
BOOST
SENSE
BAT
3652 F01
SW
SENSE
.
R
SENSE
3652fb