LT3652HV
19
3652hvfb
For more information www.linear.com/LT3652HV
When the internal timer is used for termination, bad battery
detection is engaged. There is no provision for bad battery
detection if C/10 termination is used. A bad battery fault
is triggered when the voltage on V
FB
remains below the
precondition threshold for greater than 1/8 of a full timer
cycle (1/8 EOC). A bad battery fault is also triggered if a
normally charging battery re-enters precondition mode
after 1/8 EOC.
When a bad battery fault is triggered, the charging cycle
is suspended, so the CHRG status pin becomes high-
impedance. The FAULT pin is pulled low to signal a fault
detection.
Cycling the charger’s power or SHDN function initiates
a new charging cycle, but a LT3652HV charger does not
require a reset. Once a bad battery fault is detected, a new
timer charging cycle initiates when the V
FB
pin exceeds the
precondition threshold voltage. During a bad battery fault,
0.5mA is sourced from the charger, so removing the failed
battery allows the charger output voltage to rise and initi
-
ate a charge cycle reset. As such, removing a bad battery
resets the LT3652HV, so a new charge cycle is started by
connecting another battery to the charger output.
Battery Temperature Monitor and Fault
The LT3652HV can accommodate battery temperature
monitoring by using an NTC (negative temperature co-effi
-
cient) thermistor close to the battery pack. The temperature
monitoring function is enabled by connecting a 10kΩ,
B = 3380 NTC thermistor from the NTC pin to ground. If the
NTC function is not desired, leave the pin unconnected.
The NTC pin sources 50µA, and monitors the voltage
dropped across the 10kΩ thermistor. When the voltage
on this pin is above 1.36V (0°C) or below 0.29V (40°C),
the battery temperature is out of range, and the LT3652HV
triggers an NTC fault. The NTC fault condition remains until
the voltage on the NTC pin corresponds to a temperature
within the 0°C to 40°C range. Both hot and cold thresholds
incorporate hysteresis that correspond to 5°C.
APPLICATIONS INFORMATION
If higher operational charging temperatures are desired,
the temperature range can be expanded by adding series
resistance to the 10k NTC resistor. Adding a 0.91k resistor
will increase the effective hot temperature to 45°C.
During an NTC fault, charging is halted and both status
pins are pulled low. If timer termination is enabled, the
timer count is suspended and held until the fault condi
-
tion is relieved.
Thermal Foldback
The LT3652HV contains a thermal foldback protection
feature that reduces maximum charger output current if
the IC junction temperature approaches 125°C. In most
cases, on-chip temperatures servo such that any exces
-
sive temperature conditions are relieved with only slight
reductions in maximum charger current.
In some cases, the thermal foldback protection feature
can reduce charger currents below the C/10 threshold.
In applications that use C/10 termination (TIMER = 0V),
the LT3652HV will suspend charging and enter standby
mode until the excessive temperature condition is relieved.
Layout Considerations
The LT3652HV switch node has rise and fall times that are
typically less than 10nS to maximize conversion efficiency.
The switch node (Pin SW) trace should be kept as short
as possible to minimize high frequency noise. The input
capacitor (C
IN
) should be placed close to the IC to minimize
this switching noise. Short, wide traces on these nodes
also help to avoid voltage stress from inductive ringing.
The BOOST decoupling capacitor should also be in close
proximity to the IC to minimize inductive ringing. The
SENSE and BAT traces should be routed together, and
these and the V
FB
trace should be kept as short as pos-
sible. Shielding these signals from switching noise with
a ground plane is recommended.
