lt3652hv Linear Technology Corporation, lt3652hv Datasheet - Page 14

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

LT3652HV
APPLICATIONS INFORMATION
The minimum average diode current rating (I
is calculated with maximum output current (I
maximum operational V
threshold (V
For example, a rectifier diode for a 7.2V, 2A charger with
a 25V maximum input voltage would require:
Battery Float Voltage Programming
The output battery float voltage (V
by connecting a resistor divider from the BAT pin to V
V
Using a resistor divider with an equivalent input resistance
at the V
error. Required resistor values to program desired V
follow the equations:
The charge function operates to achieve the final float
voltage of 3.3V on the V
initiates a new charging cycle when the voltage at the V
pin falls 2.5% below that float voltage.
14
BAT(FLT)
I
I
I
R
R
DIODE(MAX)
DIODE(MAX)
DIODE(MAX)
FB1
FB2
FB
Figure 4. Feedback Resistors from BAT to V
Program Float Voltage
= (V
= (R1 • (2.5 • 10
can be programmed up to 18V.
pin of 250k compensates for input bias current
BAT(FLT)
BAT(PRE)
> I
> 2 • (25 – 0.7[7.2]) / 25), or
> 1.6A
CHG(MAX)
LT3652HV
• 2.5 • 10
, or 0.7 • V
3652 F04
BAT
V
FB
• (V
IN
5
FB
, and output at the precondition
)) / (R1- (2.5 • 10
IN(MAX)
pin. The auto-restart feature
5
R
R
) / 3.3
FB1
FB2
BAT(FLT)
BAT(FLT)
– V
BAT(PRE)
+
):
) is programmed
) / V
5
))
DIODE(MAX)
FB
CHG(MAX)
IN(MAX)
BAT(FLT)
(Ω)
(Ω)
) (A)
FB
FB
),
)
.
For a three-resistor network, R
relation:
Example:
Because the battery voltage is across the V
gramming resistor divider, this divider will draw a small
amount of current from the battery (I
Precision resistors in high values may be hard to ob-
tain, so for some lower V
desirable to use smaller-value feedback resistors with an
additional resistor (R
equivalent resistance. The resulting 3-resistor network,
as shown in Figure 5, can ease component selection
and/or increase output voltage precision, at the expense of
additional current through the feedback divider.
I
R
For V
Setting divider current (I
Solving for R
The divider equivalent resistance is:
RFB
FB2
Figure 5. A Three-Resistor Feedback Network Can
Ease Component Selection
R
R
R
R
R
R
/R
= 3.3 / R
BAT(FLT)
FB2
FB2
FB2
FB1
FB1
FB1
FB1
LT3652HV
/R
||R
= 3.3/10μA
= 330k/11
= 330k
= 30k
= 3.3/(V
FB1
FB2
= 3.6V:
FB1
FB2
3652 F05
= 3.3/(3.6 - 3.3) = 11.
BAT
V
= 27.5k
FB
:
BAT(FLT)
FB3
R
FB3
) to achieve the required 250k
BAT(FLT)
RFB
– 3.3)
R
R
FB1
FB2
) = 10μA yields:
FB1
applications, it may be
+
and R
RFB
) at a rate of:
FB2
BAT(FLT)
follow the
3652hvf
pro-