Rainbow Electronics MAX1555 - Manual (Page 6)

MAX1551/MAX1555
Precharge Current
The MAX1551/MAX1555 feature a precharge current to
protect deeply discharged cells. If V
BAT is less than 3V,
the device enters precharge mode where charging cur-
rent is limited to 40mA.
Package Thermal Limiting
On-chip thermal limiting in the MAX1551/MAX1555 sim-
plifies PC board layout and allows charging rates to be
optimized without the limits imposed by worst-case bat-
tery and input voltages. The device reduces the power
dissipation at BAT to prevent overheating. This allows
the board design to be optimized for compact size and
typical thermal conditions. When the MAX1551/
MAX1555 thermal limits are reached, the chargers do
not shut down, but progressively reduce charging cur-
rent by 17mA/
°C above a die temperature of +110°C.
Solder the MAX1551/MAX1555s’ GND to a large
ground plane to help dissipate power and keep the die
temperature below the thermal limit. The USB charge
current of 100mA is unlikely to induce thermal limiting.
Bypass Capacitors
Use ceramic bypass capacitors at DC, USB, and BAT.
Mount these capacitors within 1cm of their respective
pins. X7R and X5R dielectrics are recommended.
Chip Information
TRANSISTOR COUNT: 541
PROCESS: BiCMOS
SOT23 Dual-Input USB/AC Adapter 1-Cell Li+
Battery Chargers
6 _______________________________________________________________________________________
MAX1551
(MAX1555)
DC
USB
BAT AC ADAPTER
3.7V TO 7V
USB
3.7V TO 6V
TO SYSTEM
LOAD
Li+
GND
TO LOGIC RAIL
CHARGE
CONTROL
POK
(CHG)
LOGIC
CONTROL
C1
1 µF
C2
1 µF
C3
1
µF
R1
100k
Ω
INDICATES
THAT POWER
IS PRESENT
(EITHER DC
OR USB)
Typical Application Circuit