MAX8662 Datasheet, PDF (23/36 Pages) Maxim Integrated Products – Power-Management ICs for Single-Cell, Li+ Battery-Operated Devices

Power-Management ICs for
Single-Cell, Li+ Battery-Operated Devices
• Thermal Limiting: The input limiter includes a ther-
mal-limiting circuit that reduces the current drawn
from DC when the IC junction temperature increases
beyond +100°C in an attempt to prevent further
heating. The current limit is be reduced by 5%/°C for
temperatures above +100°C, dropping to 0mA at
+120°C. Due to the adaptive nature of the charging
circuitry, the charger current reduces to 0mA before
the system load is affected by thermal limiting.
• Adaptive Battery Charging: While the system is
powered from DC, the charger can also draw
power from SYS to charge the battery. If the charg-
er load plus system load exceeds the current capa-
bility of the input source, an adaptive charger
control loop reduces charge current to prevent the
SYS voltage from collapsing. Maintaining a higher
SYS voltage improves efficiency and reduces
power dissipation in the input limiter by running the
switching regulators at lower current.
Figure 3 shows the SYS voltage and its relationship to
DC and BAT under three conditions:
a) Charger is off and SYS is driven from DC.
b) Charger is on and adaptive charger control is limiting
charge current.
c) The load at SYS is greater than the available input current.
The adaptive battery-charger circuit reduces charging
current when the SYS voltage drops 550mV below DC.
For example, if DC is at 5V, the charge current reduces
to prevent SYS from dropping below 4.45V. When DC is
greater than 5.55V, the adaptive charging circuitry
reduces charging current when SYS drops 300mV
below the 5.3V SYS regulation point (5.0V). Finally, the
circuit prevents itself from pulling SYS down to within
100mV of BAT.
DC
INPUT: 500mA USB
CHARGER: RISET = 4Ω (750mA)
SYS
5.3V
(CHARGER OFF)
SYS
5.0V
(CHARGER ON)
I(SYS) x 150mAΩ
550mV
BAT
SYS
(SYS OVERLOAD)
BAT CHARGE
CURRENT
(CHARGE ON)
4.0V
3.9V
475mA
100mV
100mV
I(SYS) x 30mΩ
0mA
Figure 3. SYS Voltage and Charge Current vs. DC and BAT Voltage
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