CHGIN Adaptive Input Current Limit:
The CHGIN input
current is limited to prevent input overload. The input
current limit is controlled by I
2
C. However, if the voltage
at CHGIN collapses because the source is not able to
supply either the current programmed in I
2
C, or the total
current required by the battery charger and system load,
the input current limit will be adaptively reduced.
Thermal Limiting:
In case the die temperature exceeds
the normal limit (T
CHG_LIM
), the MAX20335 attempts to
limit temperature increase by reducing the input current
from CHGIN. In this condition, the system load has prior-
ity over the charger current, so the input current is first
reduced by lowering the charge current. If the junction
temperature continues to rise and reaches the maximum
operating limit (T
CHGIN_SHDN
), no input current is drawn
from CHGIN and the battery powers the entire system
load.
Adaptive Battery Charging:
While the system is powered
from CHGIN, the charger draws power from SYS to charge
the battery. If the total load exceeds the input current limit,
an adaptive charger control loop reduces charge current to
prevent V
SYS
from collapsing.
When the charge current is reduced below 50% due to
I
LIM
or T
DIE
, the timer clock operates at half speed. When
the charge current is reduced below 20% due to I
LIM
or
T
DIE
, the timer clock is paused.
Fast-Charge Current Setting
The MAX20335 uses an external resistor connected from
SET to GND to set the fast-charge current. The pre-charge
and charge-termination currents are programmed as a
percentage of this value through I
2
C registers. The fast-
charge current resistor can be calculated as:
R
SET
= K
SET
x V
SET
/I
FChg
where K
SET
has a typical value of 2000A/A and V
SET
has
a typical value of 1V. The range of acceptable resistors for
R
SET
is 4kΩ to 400kΩ
Thermistor Monitoring with Charger Shutdown
The MAX20335 features three modes for controlling
charger behavior based on battery-pack temperature:
Thermistor Monitoring, JEITA Monitoring 1, and JEITA
Monitoring 2. The divider formed by a pull-up resistor
(RPU) to CAP, optional parallel resistor (RPA) from THM
to ground, and NTC thermistor (RTHM) from THM to
ground, provides a voltage at THM that is proportional to
temperature as a fraction of the CAP voltage. Two sets
of preconfigured default thresholds (0°C/10°C/45°C/60°C
or 0°C/10°C/25°C/45°C as a %CAP) optimized for beta
3380 thermistors are available (see
). The four
default thresholds create five temperature zones, and the
fractional CAP voltage measured at the THM pin is
compared to the thresholds to determine the active
temperature zone during operation.
The behavior in each temperature zone is determined by
the configuration of bits in the I
2
C registers. The active
monitoring mode is selected by ThermEn[1:0] in the
ThrmCfrg register. In all modes, the T2IFchg[2:0] and
T2T3IFchg[2:0], and T3T4IFchg[2:0] fields in the ThrmCfg
registers set the fast charge current in three tempera-
ture zones, T1_T2, T2_T3, and T3_T4. In Thermistor
Monitoring mode, charging is enabled only in T1_T2
and T2_T3 and the battery termination voltage is equal
to V
BATREG
. In both JEITA
Monitoring 1 and JEITA Monitoring 2 the charger is
active in the T1_T2, T2_T3, and T3_T4 zones. However,
JEITA Monitoring 1 sets the battery termination voltage to
V
BATREG
for all zones, while JEITA Monitoring 2 sets the
battery termination voltage to V
BATREG
- 150mV for zones
T1_2 and T3_T4, as shown in
. The behavior of
all three modes is summarized in
MAX20335
PMIC with Ultra-Low I
Q
Voltage Regulators and
Battery Chargers for Small Lithium Ion Systems
www.maximintegrated.com
Maxim Integrated
│
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