LTM8062EVPBF datasheet(11/20 Pages) LINER

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LTM8062

8062f

APPLICATIONS INFORMATION

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 VIN 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 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 is sufficient for proper operation. There are cases,

however, where it may be necessary to add capacitance or

otherwise modify the output impedance of the LTM8062.

Case 1: the μModule is 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 controller is designed for a wide

range, but some battery packs have an ESR outside of this

range. Case 3: 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-con-

nected cells, each cell being a forward-biased p-n junction.

As such, the open-circuit voltage (VOC) 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

(VMP) for a crystalline solar panel can be approximated as

a fixed voltage below VOC, so the temperature coefficient

for the peak power point is similar to that of VOC.

Panel manufacturers typically specify the 25°C values for

VOC, VMP, and the temperature coefficient for VOC, making

determination of the temperature coefficient for VMP of

a typical panel straight forward. The LTM8062 employs

a feedback network to program the VIN input regulation

voltage. Manipulation of the network makes for efficient

implementation of various temperature compensation

schemes for a maximum peak power tracking (MPPT)

application. As the temperature characteristic for a typical

solar panel VMP voltage is highly linear, a simple solution

for tracking that characteristic can be implemented using a

Linear Technology LM234 3-terminal temperature sensor.

This creates an easily programmable, linear temperature

dependent characteristic.

In the circuit shown in Figure 4,

RIN1 = –RSET •(TC • 4405), and

RIN2 =

RIN1

VMP(25°C)+RIN1 •(0.0674 / RSET)

VINREG − 1

where TC = temperature coefficient (in V/°C), and

VMP(25°C) = maximum power voltage at 25°C.

Figure 4. MPPT Temperature Compensation Network

VINREG

8062 F04

LTM8062

LINEAR

TECHNOLOGY

LM234

RIN1

RIN2

VIN

V+

V–

RSET

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