lt3652hv Linear Technology Corporation, lt3652hv Datasheet - Page 12

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

LT3652HV
APPLICATIONS INFORMATION
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 LT3652HV charger is configurable to charge at aver-
age currents as high as 2A. Maximum charge current is
set by choosing an inductor sense resistor (R
that 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.
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.
12
C
R
IN(BULK)
SENSE
CHG(MAX)
IN
Figure 1. Programming Maximum Charge
Current Using R
), and follows the relation:
= 0.1 / I
= I
LT3652HV
CHG(MAX)
is the maximum average charge current.
BOOST
SENSE
CHG(MAX)
3652 F01
BAT
SW
SENSE
• (V
BAT
/V
IN
) / ΔV
R
SENSE
IN
(μF)
SENSE
) such
V
The LT3652HV operates with a V
however, a start-up voltage requirement exists due to
the nature of the non-synchronous step-down switcher
topology used for the charger. If there is no BOOST supply
available, the internal switch requires (V
to reliably operate. This requirement does not exist if the
BOOST supply is available and (V
When an LT3652HV charger is not switching, the SW pin
is at the same potential as the battery, which can be as
high as V
supply must be at least 3.3V above V
ing begins and the BOOST supply capacitor gets charged
such that (V
longer applies.
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.
IN
/ BOOST Start-Up Requirement
Figure 2. Zener Diode Reduces Refresh
Voltage for BOOST Pin
BAT(FLT)
BOOST
IN(MAX)
LT3652HV
. As such, for reliable start-up, the V
– V
BOOST
SENSE
.
BAT
3652 F02
SW
SW
) > 2V, the V
IN
BOOST
range of 4.95V to 34V,
BAT(FLT)
IN
– V
IN
requirement no
– V
. Once switch-
SW
SW
) > 2V.
) ≥ 3.3V
3652hvf
IN