LTC1960CUHF-TRPBF View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1960CUHF-TRPBF' PDF : 28 Pages View PDF
LTC1960
APPLICATIONS INFORMATION
Watchdog Timer
Charging will begin when either CHARGE_BAT1 or
CHARGE_BAT2 bits are set in the charger register (ad-
dress: 111). Charging will stop if the charger register is
not updated prior to the expiration of the watchdog timer.
Simply repeating the same data transmission to the charger
register at a rate higher than once per second will ensure
that charging will continue uninterrupted.
Extending System to More Than Two Batteries
The LTC1960 can be extended to manage systems with more
than three sources of power. Contact Linear Technology
Applications Engineering for more information.
Charging Depleted Batteries
Some batteries contain internal protection switches that
disconnect a load if the battery voltage falls below what
is considered a reasonable minimum. In this case, the
charger may not start because the voltage at the battery
terminal is less than 5V. The low current mode of the IDAC
must be used in this case to condition the battery. In low
current mode, there is no minimum voltage requirement
(but dual charging is not allowed). Usually, the battery will
detect that it is being charged and then close its protec-
tion switch, which will allow the IDAC to switch to normal
mode. Smart batteries require that charging current not
exceed 100mA until valid charging voltage and charging
current parameters are transmitted via the SMBus. The
low current IDAC mode is ideal for this purpose.
Starting Charge with Dissimilar Batteries in Dual
Charge Mode
When charging batteries of different charger termination
voltages, the charger should be started using the follow-
ing procedure:
Step 1. Select only the lowest termination voltage bat-
tery for charging, and set the charger to its charging
parameters.
Step 2. When the battery current is flowing into that bat-
tery, change to dual charging mode (without stopping the
charger) and set the appropriate charging parameters for
this dual charger condition.
20
If this procedure is not followed, and BAT2 is significantly
higher voltage than BAT1, the charger could refuse to
charge either battery.
Charge Termination Issues
Batteries with constant-current charging and voltage-based
charger termination might experience problems with re-
ductions of charger current caused by adapter limiting. It
is recommended that input limiting feature be defeated in
such cases. Consult the battery manufacturer for informa-
tion on how your battery terminates charging.
Setting Output Current Limit
The full-scale output current setting of the IDAC will produce
VMAX = 102.3mV between CSP and CSN. To set the full-
scale current of the DAC simply divide VMAX by RSNS.
This is expressed by the following equation:
RSNS = 0.1023/IMAX
Table 1. Recommended RSNS Resistor Values
IMAX (A)
RSNS (Ω) 1%
1.023
0.100
2.046
0.050
4.092
0.025
8.184
0.012
RSNS (W)
0.25
0.25
0.5
1
Use resistors with low ESL.
Inductor Selection
Higher operating frequencies allow the use of smaller
inductor and capacitor values. A higher frequency gener-
ally results in lower efficiency because of MOSFET gate
charge losses. In addition, the effect of inductor value
on ripple current and low current operation must also be
considered. The inductor ripple current ∆IL decreases with
higher frequency and increases with higher VIN.
∆IL
=
1
(f)(L)
VOUT
1−
VOUT
VIN
Accepting larger values of ∆IL allows the use of low
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is ∆IL = 0.4(IMAX). In no case should
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