Datasheet
LTM8062/LTM8062A
12
8062fd
For more information www.linear.com/LTM8062
Figure 3. Resistive Divider Sets Minimum V
IN
applicaTions inForMaTion
will collapse. A minimum operating supply voltage can
thus be programmed by monitoring the supply through
a resistor divider, such that the desired minimum voltage
corresponds to 2.7V at the V
INREG
pin. The LTM8062/
LTM8062A servo the maximum output charge current to
maintain the voltage on V
INREG
at or above 2.7V.
Programming of the desired minimum voltage is accom
-
plished by connecting a resistor as shown in Figure 3.
R
IN
=
100V
IN
– 270
2.7
k
If the voltage regulation feature is not used, connect the
V
INREG
pin to V
IN
.
physically located far from the battery and the added line
impedance may interfere with the control loop. Case 2:
the battery ESR is very small or very large; the LTM8062/
LTM8062A controller is designed for a wide range, but some
battery packs have an ESR outside of this range. Case3:
there is no battery at all. As the charger is designed to
work with the ESR of the battery, the output may oscillate
if no battery is present.
The optimum ESR is about 100mΩ, but ESR values both
higher and lower will work. Table 2 shows a sample of
parts successfully tested by Linear Technology:
Table 2
PART NUMBER DESCRIPTION MANUFACTURER
16TQC22M 22µF, 16V, POSCAP Sanyo
35SVPD18M 18µF, 35V, OS-CON Sanyo
TPSD226M025R0100 22µF, 25V Tantalum AVX
T495D226K025AS 22µF, 25V, Tantalum Kemet
TPSC686M006R0150 68µF, 6V, Tantalum AVX
TPSB476M006R0250 47µF, 6V, Tantalum AVX
APXE100ARA680ME61G 68µF, 10V Aluminum Nippon Chemicon
APS-150ELL680MHB5S 68µF, 25V Aluminum Nippon Chemicon
If system constraints preclude the use of electrolytic ca-
pacitors, a series R-C network may be used. Use a ceramic
capacitor of at least 22µF and an equivalent resistance of
100mΩ. An example of this is shown in the Typical Ap
-
plications section.
MPPT Temperature Compensation
A typical solar panel is comprised of a number of series-
connected cells, each cell being a forward-biased p-n junc
-
tion. As such, the open-circuit voltage (V
OC
) of a solar cell
has a temperature coefficient that is similar to a common
p-n diode, or about –2mV/°C. The peak power point voltage
(V
MP
) for a crystalline solar panel can be approximated as
a fixed voltage below V
OC
, so the temperature coefficient
for the peak power point is similar to that of V
OC
.
Panel manufacturers typically specify the 25°C values for
V
OC
, V
MP
, and the temperature coefficient for V
OC
, making
determination of the temperature coefficient for V
MP
of a
typical panel straight forward. The LTM8062/LTM8062A
employs a feedback network to program the V
IN
input
regulation voltage. Manipulation of the network makes for
V
IN
V
INREG
8062 F03
LTM8062
INPUT SUPPLY
R
IN
BIAS Pin Considerations
The BIAS pin is used to provide drive power for the in
-
ternal power switching stage and operate other internal
circuitry. For proper operation, it must be powered by at
least 2.8V and no more than the absolute maximum rat
-
ing of 10V. In most applications, connect BIAS to BAT. If
there is no BIAS supply available or the battery voltage is
below 2.8V, the internal switch requires more headroom
from V
IN
for proper operation. Please refer to the Typical
Performance Characteristics curves for minimum start and
running requirements under various battery conditions.
When charging a 2-cell battery using a relatively high
input voltage, the LTM8062/LTM8062A power dissipation
can be reduced by connecting BIAS to a voltage between
2.8V and 3.3V.
Output Capacitance
In many applications, the internal BAT capacitance of the
LTM8062/LTM8062A is sufficient for proper operation.
There are cases, however, where it may be necessary to
add capacitance or otherwise modify the output imped
-
ance of the LTM8062/LTM8062A. Case 1: the µModule is