Stand-Alone, Switch-Mode
Li+ Battery Charger with Internal 28V Switch
MAX1758
DCIN
CSS
LEVEL SHIFT
AND
GAIN OF 10
ON
CS
RCS
BATT
CSI
LEVEL SHIFT
AND
GAIN OF 7
ON
GMS
ISETIN
+1
3Rx
Rx
GMI
ISETOUT
+1
3Rx
Rx
REF/2
BDIV
FASTCHG
R2
V/I MODE
OSCILLATOR, SM, TIMERS
THERM CONTROL
TEST CIRCUITRY
FULLCHG
FAULT
TIMER 1
TIMER 2
THM
TO REF
9R
VADJ
+1
R
R
GMV
MIN AND CLAMP
SUMMING
COMPARATOR
BLOCK
ON
PGND
CCV
CCI
CCS
BST
HSD
LEVEL
SHIFT
DRIVER
LX
TO
BATT
ENABLE
5.4V
REGULATOR
INTERNAL
REFERENCE
VL
REF
CSSP
CSSN
REF/2 =
ZERO
CURRENT
TO
BATT
CELL
CNTRL
LOGIC
MAX1758
R
R2 = R(2N -1)
WHERE
N = CELL NUMBER
GND
Figure 3. MAX1758 Functional Diagram
Input Current Regulator
The total input current (from a wall cube or other DC
source) is the sum of system load current plus the bat-
tery-charging current. The input current regulator limits
the source current by reducing charging current when
input current exceeds the set input current limit. System
current will normally fluctuate as portions of the system
are powered up or put to sleep. Without input current
regulation, the input source must be able to supply the
12
maximum system load current plus the maximum
charger input current. By using the input current limiter,
the current capability of the AC wall adapter may be
lowered, reducing system cost.
Input current is measured through an external sense
resistor at CSSP and CSSN. The voltage at ISETIN also
adjusts the input current limit. Full-scale input current is
achieved when ISETIN is connected to REF, setting the
full-scale current-sense regulation voltage to 100mV.
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
