MAX745 Maxim, MAX745 Datasheet - Page 5

• Manufacturer Part Number: MAX745
• Description: Switch-Mode Lithium-Ion Battery-Charger
• Manufacturer: Maxim

The MAX745 is a switch-mode, lithium-ion battery
charger that can achieve 90% efficiency. The charge
voltage and current are set independently by external
resistor-dividers at SETI and VADJ, and at pin connec-
tions at CELL0 and CELL1. VADJ is connected to a
resistor-divider to set the charging voltage. The output
voltage-adjustment range is ±5%, eliminating the need
for 0.1% resistors while still achieving 0.75% set accu-
racy using 1% resistors.
The MAX745 consists of a current-mode, pulse-width-
modulated (PWM) controller and two transconductance
error amplifiers: one for regulating current (GMI) and
the other for regulating voltage (GMV) (Figure 2). The
error amplifiers are controlled via the SETI and VADJ
pins. Whether the MAX745 is controlling voltage or cur-
rent at any time depends on the battery state. If the bat-
tery is discharged, the MAX745 output reaches the
______________________________________________________________Pin Description
_______________Detailed Description
11, 12
PIN
10
13
14
15
16
17
18
19
20
1
2
3
4
5
6
7
8
9
STATUS
CELL1,
NAME
CELL0
SHDN
PGND
THM/
VADJ
BATT
DCIN
IBAT
GND
CCV
SETI
DLO
REF
BST
CCI
DHI
CS
VL
LX
_______________________________________________________________________________________
Current-Sense Amplifier’s Analog Current-Source Output. See Monitoring Charge Current section for
detailed description.
Charger Input Voltage. Bypass DCIN with a 0.1µF capacitor.
Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL with a 4.7µF capacitor.
Voltage-Regulation-Loop Compensation Point
Current-Regulation-Loop Compensation Point
Thermistor Sense-Voltage Input. THM/SHDN also performs the shutdown function. If pulled low,
the charger turns off.
4.2V Reference Voltage Output. Bypass REF with a 0.1µF or greater capacitor.
Voltage-Adjustment Pin. VADJ is tied to a 1% tolerance external resistor-divider to adjust the voltage set
point by 10%, eliminating the need for precision 0.1% resistors. The input voltage range is 0V to V
SETI is externally tied to the resistor-divider between REF and GND to set the charging current.
Analog Ground
Logic Inputs to Select Cell Count. See Table 1 for cell-count programming.
An open-drain MOSFET sinks current when in current-regulation mode, and is high impedance when in volt-
age-regulation mode. Connect STATUS to VL through a 1k to 100k pull-up resistor. STATUS may also drive
an LED for visual indication of regulation mode (see MAX745 evaluation kit). Leave STATUS floating if not used.
Battery-Voltage-Sense Input and Current-Sense Negative Input
Current-Sense Positive Input
Power Ground
Low-Side Power MOSFET Driver Output
High-Side Power MOSFET Driver Output
Power Connection for the High-Side Power MOSFET Source
Power Input for the High-Side Power MOSFET Driver
Switch-Mode Lithium-Ion
current-regulation limit before the voltage limit, causing
the system to regulate current. As the battery charges,
the voltage rises to the point where the voltage limit is
reached and the charger switches to regulating volt-
age. The STATUS pin indicates whether the charger is
regulating current or voltage.
To set the voltage limit on the battery, tie a resistor-
divider to VADJ from REF. A 0V to V
VADJ sets a ±5% change in the battery limit voltage
around 4.2V. Since the 0 to 4.2V range on VADJ results
in only a 10% change on the voltage limit, the resistor-
divider’s accuracy does not need to be as high as the
output voltage accuracy. Using 1% resistors for the
voltage dividers typically results in no more than 0.1%
degradation in output voltage accuracy. VADJ is inter-
nally buffered so that high-value resistors can be used
to set the output voltage. When the voltage at VADJ is
FUNCTION
Battery Charger
Voltage Control
REF
change at
REF
.
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