Datasheet

LTM8061
12
8061fa
For more information www.linear.com/LTM8601
applicaTions inForMaTion
V
IN
Input Supply
The LTM8061 is biased directly from the charger input
supply through the V
IN
pin. This pin carries large switched
currents, so a high quality, low ESR decoupling capacitor
is recommended to minimize voltage glitches on V
IN
. A
4.7µF capacitor is typically adequate for most charger
applications.
Reverse Protection Diode
The LTM8061 integrates a high voltage power Schottky
diode to provide input reverse voltage protection. The
anode of this diode is connected to V
INA
, and the cath-
ode is connected to V
INC/CLP
. There is a small amount of
capacitance at each end; please see the Block Diagram.
BIAS Pin Considerations
The BIAS pin is used to provide drive power for the internal
power switching stage and operate other internal circuitry.
For proper operation, it must be powered by at least 2.9V
and no more than the absolute maximum rating of 10V.
In most applications, connect BIAS to BAT.
When charging a 2-cell battery using a relatively high input
voltage, the LTM8061 power dissipation can be reduced
by connecting BIAS to a 3.3V source.
BAT Decoupling Capacitance
In many applications, the internal BAT capacitance of the
LTM8061 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 LTM8061.
Case 1: the µModule charger 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 LTM8061 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.
V
IN
V
INC
/CLP
8061 F03
LTM8061
INPUT SUPPLY
SYSTEM LOAD
R
CLP
Figure 3. R
CLP
Sets the Input Supply Current Limit
The optimum ESR is about 100mΩ, but ESR values both
higher and lower will work. Table 1 shows a sample of
parts verified by Linear Technology:
Table 1. Recommended BAT Capacitors
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.
CLP: Input Current Limit
The LTM8061 contains a PowerPath™ control feature to
support multiple load systems. The charger adjusts charge
current in response to a system load if input supply current
exceeds the programmed maximum value. Maximum input
supply current is set by connecting a sense resistor (R
CLP
)
as shown in Figure 3. The LTM8061 begins to limit the
charge current when the voltage across the sense resistor
is 50mV. The maximum input current is defined by:
R
CLP
= 0.05/(Max Input Current)