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PDF MAX1873 Data sheet ( Hoja de datos )
| Número de pieza | MAX1873 | |
| Descripción | Simple Current-Limited Switch-Mode Li Charger Controller | |
| Fabricantes | Maxim Integrated | |
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19-2099; Rev 0; 7/01
EVALUATION KIT AVAILABLE
Simple Current-Limited Switch-Mode
Li+ Charger Controller
General Description
The low-cost MAX1873R/S/T provides all functions
needed to simply and efficiently charge 2-, 3-, or 4-
series lithium-ion cells at up to 4A or more. It provides a
regulated charging current and voltage with less than
±0.75% total voltage error at the battery terminals. An
external P-channel MOSFET operates in a step-down
DC-DC configuration to efficiently charge batteries in
low-cost designs.
The MAX1873R/S/T regulates the battery voltage and
charging current using two control loops that work
together to transition smoothly between voltage and
current regulation. An additional control loop limits cur-
rent drawn from the input source so that AC adapter
size and cost can be minimized. An analog voltage out-
put proportional to charging current is also supplied so
that an ADC or microcontroller can monitor charging
current.
The MAX1873 may also be used as an efficient current-
limited source to charge NiCd or NiMH batteries in mul-
tichemistry charger designs. The MAX1873R/S/T is
available in a space-saving 16-pin QSOP package. Use
the evaluation kit (MAX1873EVKIT) to help reduce
design time.
Applications
Notebook Computers
Portable Internet Tablets
2-, 3-, or 4-cell Li+ Battery Pack Chargers
6-, 9-, or 10-cell Ni Battery Pack Chargers
Hand-Held Instruments
Portable Desktop Assistants (PDAs)
Desktop Cradle Chargers
PART
MAX1873REEE
MAX1873SEEE
MAX1873TEEE
Selector Guide
SERIES CELLS TO CHARGE
2-Cell Li+ or 5- or 6-cell Ni Battery
3-Cell Li+ or 7- or 9-cell Ni Battery
4-Cell Li+ 10-cell Ni Battery Packs
Pin Configuration appears at end of data sheet.
Features
o Low-Cost and Simple Circuit
o Charges 2-, 3-, or 4-Series Lithium-Ion Cells
o AC Adapter Input-Current-Limit Loop
o Also Charges Ni-Based Batteries
o Analog Output Monitors Charge Current
o ±0.75% Battery-Regulation Voltage
o 5µA Shutdown Battery Current
o Input Voltage Up to 28V
o 200mV Dropout Voltage/100% Duty Cycle
o Adjustable Charging Current
o 300kHz PWM Oscillator Reduces Noise
o Space-Saving 16-Pin QSOP
o MAX1873 Evaluation Kit Available to Speed
Designs
Ordering Information
PART
MAX1873REEE
MAX1873SEEE
MAX1873TEEE
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
16 QSOP
16 QSOP
VIN 9V TO
28V
(9V MIN
FOR 2-
CELLS)
4V OUT PER
200mV ON RCS
Typical Operating Circuit
SYSTEM
LOAD
VH VL
CSSP
MAX1873
DCIN
CSSN
IOUT
ICHG/EN
REF
VADJ
GND
EXT
CSB
BATT
CCI
CCS
CCV
2- TO 4-CELL
Li+
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1 page  
Simple Current-Limited Switch-Mode
Li+ Charger Controller
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDCIN = VCSSP = VCSSN = 18V, VICHG/EN = VREF, VVADJ = VREF/2. MAX1873R: VBATT = VCSB = 8.4V;
MAX1873S: VBATT = VCSB = 12.6V; MAX1873T: VBATT = VCSB = 16.8V; TA = -40°C to +85°C. Typical values are at TA = +25°C,
unless otherwise noted.)
PARAMETER
BATT Undervoltage Threshold
CURRENT SENSE
CSB to BATT Battery Current-Sense
Voltage
CSB to BATT Current-Sense Voltage
when VBATT < 2.5V per Cell
CSSP to CSSN Current-Sense Voltage
CONTROL INPUTS/OUTPUTS
ICHG/EN Input Threshold
ICHG/EN Input Voltage Range for
Charge Current Adjustment
VADJ Input Current
ICHG/EN Input Current
VADJ Input Voltage Range
IOUT Voltage
CONDITIONS
For ICHG/20 trickle
charge
MAX1873R
MAX1873S
MAX1873T
VICHG/EN = VREF
VICHG/EN = VREF/4
6V < VCSSP < 28V
Includes 50mV of hysteresis
VVADJ = VREF/2
VICHG/EN = VREF
Full scale
25% scale
Trickle charge
No charge
current
VCSB - VBATT = 200mV,
0 < IOUT < 500µA
VCSB - VBATT = 50mV,
0 < IOUT < 500µA
VCSB - VBATT = 10mV
VCSB - VBATT = 0,
IIOUT = sinking 20µA
MIN
4.8
7.2
9.6
190
40
5
90
500
700
-100
-100
0
3.6
0.9
75
40
MAX
5.2
7.8
10.4
UNITS
V
210 mV
60 mV
15 mV
110 mV
700
VREF
100
100
VREF
4.4
1.1
325
90
mV
mV
nA
nA
V
V
mV
Note 1: While it may appear possible to set the Battery Regulation Voltage higher than the Battery Overvoltage Cutoff Threshold, this
cannot happen because both parameters are derived from the same reference and track each other.
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________ 5
5 Page 
Simple Current-Limited Switch-Mode
Li+ Charger Controller
Charge-Current Monitor Output
IOUT is an analog voltage output that is proportional to
the actual charge current. With the aid of a microcon-
troller, the IOUT signal can facilitate gas-gauging, indi-
cate percent of charge, or charge-time remaining. The
equation governing this output is:
( )VIOUT = 20 VCSB − VBATT or
( )VOUT = 20 RCSB × ICHG
where VCSB and VBATT are the voltages at the CSB and
BATT pins, and ICHG is the charging current. IOUT can
drive a load capacitance of 5nF.
Design Procedure
Setting the Battery-Regulation Voltage
For Li+ batteries, VADJ sets the per-cell battery-regula-
tion voltage limit. To set the VADJ voltage, use a resis-
tive-divider from REF to GND (Figure 1). For a battery
voltage of 4.2V per cell, use resistors of equal value
(100kΩ each) in the VADJ voltage-divider. To set other
battery-regulation voltages, see the remainder of this
section.
The per-cell battery regulation voltage is a function of
Li+ battery chemistry and construction and is usually
clearly specified by the manufacturer. If this is not
clearly specified, be sure to consult the battery manu-
facturer to determine this voltage before charging any
Li+ battery. Once the per-cell voltage is determined,
the VADJ voltage is calculated by the equation:
[ ]VVADJ = (9.5 VBATTR ) / N − (9VREF )
where VBATTR is the desired battery-regulation voltage
(for the total series-cell stack), N is the number of Li+
battery cells, and VREF is the reference voltage (4.2V).
Set VVADJ by choosing R1. R1 should be selected so
that the total divider resistance (R1+ R2) is near 200kΩ.
R2 can then be calculated as follows:
[ ]( )R2 = VVADJ / VREF − VVADJ × R1
Since the full range of VADJ (from 0 to VREF) results in
a ±5.263% adjustment of the battery-regulation limit
(3.979V to 4.421V), the resistive-divider’s accuracy
need not be as tight as the output-voltage accuracy.
Using 1% resistors for the voltage-divider still provides
±0.75% battery-voltage-regulation accuracy.
Setting the Charging-Current Limit
The charging current ICHG is sensed by the current-
sense resistor RCSB between CSB and BATT, and is
also adjusted by the voltage at ICHG/EN. If ICHG/EN is
connected to REF (the standard connection), the
charge current is given by:
ICHG = 0.2V /RCSB
In some cases, common values for RCSB may not allow
the desired charge-current value. It may also be desir-
able to reduce the 0.2V CSB-to-BATT sense threshold
to reduce power dissipation. In such cases, the
ICHG/EN input may be used to reduce the charge-cur-
rent-sense threshold. In those cases the equation for
charge current becomes:
( )ICHG = 0.2V VICH/EN / VREF /RCSB
Setting the Input-Current Limit
The input-source current limit, IIN, is set by the input-
current sense resistor, RCSS, (Figure 1) connected
between CSSP and CSSN. The equation for the source
current is:
IIN = 0.1V /RCSS
This limit is typically set to the current rating of the input
power source or AC adapter to protect the input source
from overload. Short CSSP and CSSN to DCIN if the
input-source current-limit feature is not used.
Inductor Selection
The inductor value may be selected for more or less
ripple current. The greater the inductance, the lower
the ripple current. However, as the physical size is kept
the same, larger inductance value typically results in
higher inductor series resistance and lower inductor
saturation current. Typically, a good tradeoff is to
choose the inductor such that the ripple current is
approximately 30% to 50% of the DC average charging
current. The ratio of ripple current to DC charging cur-
rent (LIR) can be used to calculate the inductor value:
{ [ ]}L = VBATT VDCIN(MAX) − VBATT /
[ ]VDCIN(MAX) × fSW × ICHG × LIR
where fSW is the switching frequency (nominally
300kHz) and ICHG is the charging current. The peak
inductor current is given by:
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet MAX1873.PDF ] | |
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