Detailed Description
DC Charging
The MAX8600/MAX8601 are designed to charge a sin-
gle-cell Li+ battery from a DC source voltage between
4.15V and 7V. The precharge current, charge current,
and top-off threshold are programmable with R
SETI
.
USB Charging (MAX8601)
The MAX8601 contains a USB input that allows opera-
tion from either a DC source or a USB port. A USEL input
allows the user to select either a 100mA or 500mA maxi-
mum charging current when using the USB input. If both
V
USB
and V
DC
are valid, the MAX8601 operates from
DC. If V
DC
is invalid (undervoltage/overvoltage), the
MAX8601 operates from USB. When charging at 100mA
from the USB input, the fast-charge timer is inhibited.
EN
Charger-Enable Input
EN is a logic input (active low) that enables the charger.
Drive EN high to disable the charger-control circuitry.
Drive EN low or connect to GND for normal operation.
Soft-Start
To prevent input transients, the rate of change of
charging current is limited. When the charger is turned
on or when the input source is changed, charge current
is ramped from 0 to the set current value in typically
1.2ms. This also means that if charging is taking place
from USB, and the DC input is then powered, charge
current falls to zero and then is reramped to the DC
charge rate. This is done to ensure that the DC source
is not subjected to a severe load current step.
Charge-current ramp up is also limited when transition-
ing from prequal to fast-charge, and when changing
the USB charge current from 100mA to 500mA with
USEL. There is no di/dt limiting, however, if I
SET
is
changed suddenly using a switch at R
SETI
.
Thermal-Limit Control
The MAX8600/MAX8601 feature a thermal limit that
reduces the charge current when the die temperature
exceeds +100°C. As the temperature increases above
+100°C, the IC lowers the charge current by 5%/°C.
CHG
Charge-Indicator Output
CHG is an open-drain output that indicates charger sta-
tus. CHG goes low during charge cycles where V
BAT
is
greater than 3V and I
BAT
is greater than 7.5% of the
maximum charge current set by R
SETI
. When the
MAX8600/MAX8601 are used in conjunction with a
microprocessor (µP), connect a pullup resistor between
CHG and the logic I/O voltage to indicate charge status
to the µP. Alternatively, CHG can sink up to 20mA for
an LED charge indicator.
Fault Indicator (
FLT
)
The MAX8600/MAX8601 contain an open-drain FLT
output to signal the user when a fault occurs. FLT goes
low if the charger is in prequal and the prequal timer
expires, or if the charger is in fast-charge and the fast-
charge time expires. FLT does NOT go low if the THM
thermistor temperature is out of range. Toggle EN or
the input power to reset the FLT indicator.
Power-OK Indicator (
POK
)
The MAX8600/MAX8601 contain an open-drain POK out-
put that goes low when a valid input source is detected
at DC or USB (MAX8601 only). A valid input source is
one whose voltage is between 4.15V and 7V and
exceeds the battery voltage by 320mV. After a valid
input has been established, charging is sustained with
inputs as low as 3.5V as long as the input voltage
remains above the battery voltage by at least 55mV (typ).
POK is high impedance when the charger is disabled.
Applications Information
Figure 2 shows the typical operating circuit for the
MAX8601. The following section describes component
changes for different charging current and timer durations.
MAX8600/MAX8601
Single-/Dual-Input 1-Cell Li+ Chargers with
OVP Protection and Programmable Charge Timer
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