MP26075 – HIGH EFFICIENCY CRADLE CHARGER
MP26075 Rev. 1.01 www.MonolithicPower.com 9
5/23/2011 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
condition, the on-chip timer will terminate the
charger to prevent charging the dead battery for
excessive long time and the fault condition will be
flagged by floating LED-R and LED-G pins.
Charge Termination
The charge current will gradually decrease in CV
mode as the battery approaches full. The battery
full threshold is internally programmed to be 10%
of the I
CHG. When the charge current reaches this
threshold, the charger IC will be automatically
turned off.
Automatic Recharge
Upon V
BATT
drops to 8% of V
BATT
, the charger will
automatically restart the charge cycle until the
10% I
CHG
condition is met again. When the input
adapter is unplugged or the charger is disabled
and/or terminated, the leakage current from the
battery to MP26075 is less than 2μA.
Programming of Charge Current
The charge current (I
CHG
) is set by a resistor
(R
CHG
) connecting from the ISET pin to GND. The
relationship of the charge current and the
programming resistance is established by the
following formula.
1400(A)
(k)R
1.23V
I
CHG
CHG
Timer Operation
The TMR pin is used to set the internal oscillator
frequency, T=900000*CTMR (sec). The on-chip
timer will start count down after initial power-up
or every time being enabled. This timer will limit
the max pre-charge time to 512 internal cycles
and max trickle-charge time to 16384 internal
oscillating cycles. If the charger stays in pre-
charge mode for longer than 512 cycles or in
trickle mode for longer than 16384 cycles, it will
be terminated and a fault will be set by floating
LED-R and LED-G pins. After fault reporting, the
charger can be re-initiated only by recycling the
power supply. If the charger successfully goes
through trickle charge within the allowed time
limit, it will start CC charge and then CV charge.
If the total charge time exceeds 262144 cycles
and the battery full has not been qualified, the
charger will be terminated and a fault will also be
set by floating LED-R and LED-G pins. This
function prevents charging a dead battery for
prolonged duration. The timer function can be
disabled by shorting TMR pin to ground.
Table1— Timer of Each Times
Item Calculation formula
1mA charge timer
Tx512
Trickle charge timer
Tx16384
Total charge timer
Tx262144
Negative Thermal Coefficient (NTC)
Thermistor
The MP26075 has a built-in NTC resistance
window comparator, which allows MP26075 to
sense the battery temperature via the thermistor
packed internally in the battery pack to ensure a
safe operating environment of the battery. A
resistor with appropriate value should be
connected from VIN to NTC pin and the
thermistor is connected from NTC pin to GND.
The voltage on NTC pin depends on the ratio of
the resistor divider. When the voltage of pin NTC
falls out of the NTC window range, MP26075 will
stop the charge. The charger will restart if the
temperature goes back into the NTC window
range.
Thermal Protection
The MP26075 has proprietary thermal protection
to prevent the IC from overheating. When in
thermal protection mode, the average charge
current will be reduced to prevent the IC from
overheating. Operating in thermal protection
mode will slow down the charge process.
Lowering the input voltage and enhancing
thermal dissipation to the environment can
effectively prevent the IC from going into thermal
protection mode.
Status Indication
MP26075 has two open-drain status outputs:
LED-R and LED_G. Both LED-R and LED-G are
used to indicate the status of the charge cycle.
Table 2 describes the status of the charge cycle
based on the LED-R and LED_G outputs. The
LED-R and LED_G pins pull high when any fault
happens.
