MAX1757 Maxim, MAX1757 Datasheet - Page 12

• Manufacturer Part Number: MAX1757
• Description: Stand-Alone / Switch-Mode Li Battery Charger with Internal 14V Switch
• Manufacturer: Maxim

Stand-Alone, Switch-Mode
Li+ Battery Charger with Internal 14V Switch
Figure 3. Functional Diagram
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
______________________________________________________________________________________
ISETOUT
ISETIN
CSSP
CSSN
BATT
CELL
VADJ
CS
RCS
N = CELL NUMBER
R2 = R(2N - 1)
WHERE
CNTRL
LOGIC
+1
+1
+1
BATT
TO
LEVEL SHIFT
LEVEL SHIFT
GAIN OF 10
GAIN OF 7
Input Current Regulator
CSS
AND
AND
CSI
ON
ON
3Rx
3Rx
BDIV
Rx
Rx
R2
R
9R
REF/2
BATT
TO
GND
R
GMS
GMV
GMI
MAX1757
R
ENABLE
TO REF
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.
REGULATOR
5.4V
V/I MODE
CURRENT
REF/2 =
ZERO
OSCILLATOR, SM, TIMERS
THERM CONTROL
TEST CIRCUITRY
COMPARATOR
ON
SUMMING
BLOCK
REFERENCE
INTERNAL
LEVEL
SHIFT
DRIVER
FULLCHG
FASTCHG
TIMER 1
TIMER 2
PGND
FAULT
DCIN
CCV
CCS
HSD
THM
BST
REF
CCI
VL
LX