MAX1645EEI Maxim, MAX1645EEI Datasheet - Page 24

• Manufacturer Part Number: MAX1645EEI
• Description: Advanced Chemistry-Independent / Level 2 Battery Chargers with Input Current Limiting
• Manufacturer: Maxim

The MAX1645 includes a timer that terminates charge if
the charger has not received a ChargingVoltage() or
ChargingCurrent() command in 175sec. During charg-
ing, the timer is reset each time a ChargingVoltage() or
ChargingCurrent() command is received; this ensures
that the charging cycle is not terminated.
If timeout occurs, charging will terminate and both
ChargingVoltage() and ChargingCurrent() commands
are required to restart charging. A power-on reset will
also restart charging at 128mA.
The MAX1645 employs a buck regulator with a boot-
strapped NMOS high-side switch and a low-side NMOS
synchronous rectifier.
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Figure 7. ChargingVoltage() Code to Voltage Mapping
24
______________________________________________________________________________________
12.592V
18.432V
16.800V
8.400V
4.192V
1.024V
0
0
V
VDCIN > 20V
REF
0x0400
= 4.096V
DC-to-DC Converter
Charger Timeout
0x106x
ChargingVoltage() D15–D0 DATA
0x20Dx
The control scheme is a constant off-time, variable fre-
quency, cycle-by-cycle current mode. The off-time is
constant for a given BATT voltage; it varies with V
to keep the ripple current constant. During low-dropout
operation, a maximum on-time of 10ms allows the con-
troller to achieve >99% duty cycle with continuous con-
duction. Figure 8 shows the controller functional
diagram.
The low-side driver output DLO swings from 0V to
DLOV. DLOV is usually connected through a filter to
LDO. The high-side driver output DHI is bootstrapped
off LX and swings from V
0x313x
0x41A0
0x4800
LX
to V
BST
. When the low-side
0xFFFF
DC-DC Controller
MOSFET Drivers
BATT