Datasheet

19
Maxim Integrated
Dual-Input Linear Charger, Smart Power Selector
with Advanced Battery Temperature Monitoring
MAX8934G
limiter power loss is (V
DC
– V
SYS
) x I
DC
, where V
SYS
may be as high as 4.35V. The input limiter power loss is
not less than 0.2I x I
DC
2
. Also note that the MAX8934G
turns off when any input exceeds 6.9V (typ).
DC and USB Connections and
Current-Limit Options
Input Current Limit
The input and charger current limits are set as shown
in Table 2. It is often preferable to change the input
current limit as the input power source is changed. The
MAX8934G facilitates this by allowing different input cur-
rent limits for DC and USB as shown in Table 2.
When the input current limit is reached, the first action
taken by the MAX8934G is to reduce the battery charge
current. This allows the regulator to stay in dropout dur-
ing heavy loads, thus reducing power dissipation. If, after
the charge current is reduced to 0mA, the load at SYS
still exceeds the input current limit, SYS voltage begins
to fall. When the SYS voltage drops to BATT, the SYS-
to-BATT switch turns on, using battery power to support
the system load during the load peak. The MAX8934G
features flexible input connections (at the DC and USB
input pins) and current-limit settings (set by PEN1, PEN2,
PSET, and ISET) to accommodate nearly any input
power configuration. However, it is expected that most
systems use one of two external power schemes: sepa-
rate connections for USB and an AC adapter, or a single
connector that accepts either USB or AC adapter output.
Input and charger current limit are controlled by PEN1,
PEN2, R
PSET
, and R
ISET
, as shown in Table 2.
Separate Adapter and USB Connectors
When the AC adapter and USB have separate connec-
tors, the adapter output connects to DC and the USB
source connects to USB. PEN1 is permanently connected
high (to DC or V
L
). The DC current limit is set by R
PSET
,
while the USB current limit is set by PEN2 and USUS.
Single Common Connector
for USB or Adapter
When a single common connector is used for both AC
adapter and USB sources, the DC input is used for
both input sources. The unused USB inputs should be
grounded when an AC adapter is connected at DC,
PEN1 should be pulled high to select the current limit
set by R
PSET
. When a USB source is connected, PEN1
should be low to select 500mA, 100mA, or USB suspend
(further selected by PEN2 and USUS). PEN1 can be
pulled up by the AC adapter power to implement hard-
ware adapter/USB selection.
USB Suspend
Driving USUS high when PEN1 is low turns off the char-
ger and reduces input current to 190FA to accommodate
USB suspend mode. The input limiter is disabled and
SYS is supported by BATT.
Power Monitor Outputs (UOK, DOK)
DOK is an open-drain output that pulls low when the DC
input has valid power. UOK is an open-drain output that
pulls low when the USB input has valid power. A valid
input for DC or USB is between 4.1V and 6.6V. If a single
power-OK output is preferred, DOK and UOK can be
wire-ORed together. The combined output then pulls low
if either USB or DC is valid.
Table 2. Input Limiter Control Logic
*Charge current cannot exceed the input current limit. Actual charge current may be less than the maximum charge current if the
total SYS load exceeds the input current limit.
POWER
SOURCE
DOK UOK
PEN1 PEN2 USUS
DC INPUT
CURRENT LIMIT
USB INPUT
CURRENT LIMIT
MAXIMUM CHARGE
CURRENT*
AC adapter at
DC input
L X H X X 3000V/R
PSET
USB input off;
DC input has
priority
3000V/R
ISET
USB power at
DC input
L X L H L 475mA 475mA
L X L L L 95mA 95mA
L X L X H USB suspend 0
USB power at
USB input; DC
unconnected
H L X H L
No DC input
475mA
3000V/R
ISET
H L X L L 95mA
H L X X H USB suspend 0
DC and USB
unconnected
H H X X X No USB input 0