Datasheet

22 Maxim Integrated
Dual-Input Linear Chargers, Smart Power Selector
with Advanced Battery Temperature Monitoring
MAX8934A–MAX8934E
wire-ORed together. The combined output then pulls low
if either USB or DC is valid.
Soft-Start
To prevent input transients that can cause instability in
the USB or AC adapter power source, the rate of change
of input current and charge current is limited. When a
valid DC or USB input is connected, the input current
limit is ramped from zero to the set current-limit value
(as shown in Tables 2a and 2b). If DC is connected with
no USB power present, input current ramps in 1.5ms. If
DC is connected with USB already present, input current
ramps in 50Fs. When USB is connected with no DC pres-
ent, input current also ramps in 50Fs. If USB is connect-
ed with DC already present, the USB input is ignored.
If an adapter is plugged into DC while USB is already
powered, the input current limit reramps from zero back
up to the DC current limit so that the AC adapter does
not see a load step. During this transition, if the input
current limit is below the SYS load current, the battery
supplies the additional current needed to support the
load. Additionally, capacitance can be added to SYS to
support the load during input power transitions. When
the charger is turned on, charge current ramps from
zero to the ISET current value in typically 1.5ms. Charge
current also ramps when transitioning to fast-charge
from prequal and when changing the USB charge cur-
rent from 100mA to 500mA with PEN2. There is no dI/dt
limiting, however, if ISET is changed suddenly using a
switch at R
ISET
.
Battery Charger
The battery charger state diagram is illustrated in Figure
8. With a valid DC or USB input, the battery charger
initiates a charge cycle when the charger is enabled. It
first detects the battery voltage. If the battery voltage is
less than the BATT prequal threshold (3.0V), the charger
enters prequal mode and charges the battery at 10% of
the maximum fast-charge current. This reduced charge
rate ensures that the maximum fast-charge current set-
ting does not damage a deeply discharged battery.
Once the battery voltage rises to 3.0V, the charger tran-
sitions to fast-charge mode and applies the maximum
charge current. As charging continues, the battery volt-
age rises until it approaches the battery regulation volt-
Table 2b. Input Limiter Control Logic (MAX8934D)
FEATURE DC INPUT USB INPUT NOTES
Absolute Maximum Rating 16V 9V —
Input Current Limit
Set by R
PSET
, PEN1, PEN2, and
USUS;
2A (max)
Set by R
PSET
, PEN1,
PEN2, and USUS;
1.5A (max)
PSET sets the same input
current limit for DC and USB
paths.
POWER
SOURCE
DOK UOK PEN1 PEN2 USUS
DC INPUT
CURRENT
LIMIT
USB INPUT
CURRENT
LIMIT
MAXIMUM
CHARGE
CURRENT
AC Adapter
at DC
L X H X X 3000V/R
PSET
USB Input
Off; DC input
has priority
3000V/R
ISET
USB Power
at DC
L X H X X 3000V/R
PSET
3000V/R
ISET
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;
DC Open
H L H H L
No DC input
3000V/R
PSET
3000V/R
ISET
H L H L L 600V/R
PSET
3000V/R
ISET
H L L H L 475mA 475mA
H L L L L 95mA 95mA
H L X X H USB suspend 0
DC and
USB Open
H H X X X
No USB input 0