MAX745EAP ,Switch-Mode Lithium-Ion Battery-ChargerApplicationsrefer to the MAX1647 and MAX1648. For a low-costlithium-ion charger using a linear-regu ..
MAX745EAP ,Switch-Mode Lithium-Ion Battery-ChargerFeaturesThe MAX745 provides all functions necessary for' Charges 1 to 4 Lithium-Ion Battery Cellsch ..
MAX745EAP+ ,Switch-Mode Lithium-Ion Battery-ChargerApplicationsMAX745C/D 0°C to +70°C Dice*MAX745EAP -40°C to +85°C 20 SSOPLi+ Battery PacksDesktop Cr ..
MAX745EAP+ ,Switch-Mode Lithium-Ion Battery-ChargerFeaturesThe MAX745 provides all functions necessary for ♦ Charges 1 to 4 Li+ Battery Cellscharging ..
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MB6M ,MINIATURE GLASS PASSIVATED SINGLE-PHASE BRIDGE RECTIFIERThermal Characteristics (TA = 25°C unless otherwise noted)Parameter Symbol MB2M MB4M MB6M UnitDevic ..
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MAX745EAP
Switch-Mode Lithium-Ion Battery-Charger
MAX745
Switch-Mode Lithium-Ion
Battery-Charger
General DescriptionThe MAX745 provides all functions necessary for
charging lithium-ion battery packs. It provides a regu-
lated charging current of up to 4A without getting hot,
and a regulated voltage with only ±0.75% total error at
the battery terminals. It uses low-cost, 1% resistors to
set the output voltage, and a low-cost N-channel MOS-
FET as the power switch.
The MAX745 regulates the voltage set point and charg-
ing current using two loops that work together to transi-
tion smoothly between voltage and current regulation.
The per-cell battery voltage regulation limit is set
between 4.0V and 4.4V using standard 1% resistors,
and then the number of cells is set from 1 to 4 by pin-
strapping. Total output voltage error is less than ±0.75%.
For a similar device with an SMBus™ microcontroller
interface and the ability to charge NiCd and NiMH cells,
refer to the MAX1647 and MAX1648. For a low-cost
lithium-ion charger using a linear-regulator control
scheme, refer to the MAX846A.
____________________________FeaturesCharges 1 to 4 Lithium-Ion Battery Cells±0.75% Voltage-Regulation Accuracy
Using 1% ResistorsProvides up to 4A without Excessive Heating90% EfficientUses Low-Cost Set Resistors and
N-Channel SwitchUp to 24V Input Up to 18V Maximum Battery Voltage300kHz PWM Operation: Low-Noise,
Small ComponentsStand-Alone Operation; No Microcontroller
Needed
___________________________________________________Typical Operating Circuit19-1182; Rev 2; 12/98
Ordering Information
Pin Configuration appears on last page.
________________________ApplicationsLithium-Ion Battery Packs
Desktop Cradle Chargers
Cellular Phones
Notebook Computers
Hand-Held Instruments
*Dice are tested at TA= +25°C.
MAX745
Switch-Mode Lithium-Ion
Battery Charger
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VDCIN= 18V, VBATT= 8.4V, TA
= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DCINto GND............................................................-0.3V to 26V
BST, DHI to GND......................................................-0.3V to 30V
BST to LX....................................................................-0.3V to 6V
DHI to LX............................................(LX - 0.3V) to (BST + 0.3V)
LX to GND................................................-0.3V to (DCIN + 0.3V)
VL to GND...................................................................-0.3V to 6V
CELL0, CELL1, IBAT, STATUS, CCI, CCV,
REF, SETI, VADJ, DLO, THM/SHDNto GND..-0.3V to (VL + 0.3V)
BATT, CS to GND.....................................................-0.3V to 20V
PGND to GND..........................................................-0.3V to 0.3V
VL Current...........................................................................50mA
Continuous Power Dissipation (TA= +70°C)
SSOP (derate 8.00mW/°C above +70°C)......................640mW
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature.........................................-60°C to +150°C
Lead Temperature (soldering, 10sec).............................+300°C
MAX745
Switch-Mode Lithium-Ion
Battery Charger
Note 1:When VSETI= 0V, the battery charger turns off.
ELECTRICAL CHARACTERISTICS (continued)(VDCIN= 18V, VBATT= 8.4V, TA
= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.)
ELECTRICAL CHARACTERISTICS(VDCIN= 18V, VBATT= 8.4V,
TA= -40°C to +85°C, unless otherwise noted. Limits over temperature are guaranteed by design.)
MAX745
Switch-Mode Lithium-Ion
Battery Charger
__________________________________________Typical Operating Characteristics
(TA= +25°C, VDCIN= 18V, VBATT= 4.2V, CELL0 = CELL1 = GND, CVL= 4.7mF, CREF= 0.1mF. Circuit of Figure 1, unless
otherwise noted.)
_______________Detailed Description
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
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.
Voltage Control
To set the voltage limit on the battery, tie a resistor-
divider to VADJ from REF. A 0V to VREFchange at
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
MAX745
Switch-Mode Lithium-Ion
Battery Charger
______________________________________________________________Pin Description
MAX745
Switch-Mode Lithium-Ion
Battery Charger
VREF/ 2, the voltage limit is 4.2V. Table 1 defines the
battery cell count.
The battery limit voltage is set by the following:
Solving for VADJ, we get:
Set VADJby choosing a value for R11 (typically 100k),
and determine R3 by:
R3 = [1 - (VADJ/ VREF)] x R11 (Figure 1)
where VREF= 4.2V and cell count is 1, 2, 3, or 4
(Table 1).
The voltage-regulation loop is compensated at the CCV
pin. Typically, a series-resistor-capacitor combination
can be used to form a pole-zero doublet. The pole
introduced rolls off the gain starting at low frequencies.
The zero of the doublet provides sufficient AC gain at
mid-frequencies. The output capacitor (C1) rolls off the
mid-frequency gain to below unity. This guarantees sta-
bility before encountering the zero introduced by the
C1’s equivalent series resistance (ESR). The GMV
amplifier’s output is internally clamped to between one-
fourth and three-fourths of the voltage at REF.
Current Control
The charging current is set by a combination of the cur-
rent-sense resistor value and the SETI pin voltage. The
current-sense amplifier measures the voltage across
the current-sense resistor, between CS and BATT. The
current-sense amplifier’s gain is 6. The voltage on SETI
is buffered and then divided by 4. This voltage is com-
pared to the current-sense amplifier’s output.
Therefore, full-scale current is accomplished by con-
necting SETI to REF. The full-scale charging current
(IFS) is set by the following:
IFS= 185mV / R1 (Figure 1)
Table 1. Cell-Count Programming Table
