Datasheet

MAX8903A–E/G/H/J/N/Y
2A 1-Cell Li+ DC-DC Chargers
for USB and Adapter Power
18
Maxim Integrated
voltage, the SYS voltage is connected to the battery.
The USB input then supplies the SYS load and charges
the battery with any extra available current, while not
exceeding the maximum-allowed USB current. Load
transients can be absorbed by the battery while mini-
mizing the voltage disturbance on SYS. When battery
charging is completed, or the charger is disabled, SYS
is regulated to V
SYSREG
. If both USB and DC inputs are
valid, power is only taken from the DC input.
USB Suspend
Driving USUS high and DCM low turns off charging as
well as the SYS output and reduces input current to
170µA to accommodate USB suspend mode. See
Table 2 for settings.
Charge Enable ( CEN )
When CEN is low, the charger is on. When CEN is high,
the charger turns off. CEN does not affect the SYS out-
put. In many systems, there is no need for the system
controller (typically a microprocessor) to disable the
charger, because the MAX8903_ smart power selector
circuitry independently manages charging and
adapter/battery power hand-off. In these situations, CEN
may be connected to ground.
Soft-Start
To prevent input transients that can cause instability in
the USB or AC adapter power source, the rate of change
of the input current and charge current is limited. When
an input source is valid, SYS current is ramped from
zero to the set current-limit value in typically 50µs. This
also means that if DC becomes valid after USB, the
SYS current limit is ramped down to zero before switch-
ing from the USB to DC input. At some point, SYS is no
longer able to support the load and may switch over to
BAT. The switchover to BAT occurs when V
SYS
< V
BAT
.
This threshold is a function of the SYS capacitor size
and SYS load. The SYS current limit then ramps from
zero to the set current level and SYS supports the load
again as long as the SYS load current is less than the
set current limit.
POWER SOURCE DOK UOK DCM*** IUSB USUS
DC STEP-DOWN
OUTPUT
CURRENT LIMIT
USB INPUT
CURRENT LIMIT
MAXIMUM
CHARGE
CURRENT**
AC Adapter at DC Input L X H X X 6000V/R
IDC
Lesser of
1200V/R
ISET
and
6000V/R
IDC
L X L L L 100mA
Lesser of
1200V/R
ISET
and
100mA
L X L H L 500mA
Lesser of
1200V/R
ISET
and
500mA
USB Power at DC Input
L X L X H USB suspend
USB input off. DC
input has priority.
0
H L X L L 100mA
Lesser of
1200V/R
ISET
and
100mA
H L X H L 500mA
Lesser of
1200V/R
ISET
and
500mA
USB Power at USB Input,
DC Unconnected
H L X X H USB suspend 0
DC and USB Unconnected H H X X X
No DC input
No USB input 0
Table 2. Input Limiter Control Logic
** Charge current cannot exceed the input current limit. Charge may be less than the maximum charge current if the total SYS load
exceeds the input current limit.
*** There is an internal diode from DCM (anode) to DC (cathode) as shown in Figure 1. If the DCM level needs to be set by a µP, use
a MOSFET for isolation as shown in FIgure 3.
X = Don’t care.