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DS2711 Schematic ( PDF Datasheet ) - Maxim Integrated Products

Teilenummer DS2711
Beschreibung (DS2711 / DS2712) Loose Cell NiMH Chargers
Hersteller Maxim Integrated Products
Logo Maxim Integrated Products Logo 




Gesamt 15 Seiten
DS2711 Datasheet, Funktion
19-5826; Rev 4/11
GENERAL DESCRIPTION
The DS2711 and DS2712 are ideal for in-system or
stand-alone charging of 1 or 2 AA or AAA NiMH
“loose” cells. Temperature, voltage, and charge time
are monitored to provide proper fast-charging control
algorithms for nickel metal hydride (NiMH) batteries.
Battery tests are included to detect defective or
inappropriate cells such as alkaline primary batteries.
The DS2711/DS2712 support series and parallel
topologies, with independent monitoring and control of
each cell. Charging of NiCd chemistry cells is also
supported.
APPLICATIONS
Desktop/Stand-Alone Chargers (AAA/AA)
Digital Still Cameras
Music Players
Games
Toys
FEATURES
Charge 1 or 2 NiMH Cells
Detect and Avoid Charging Alkaline Cells
Precharge Deeply Depleted Cells
Fast Charge NiMH with -V Termination
Sensitivity of 2mV (typ)
Monitor Voltage, Temperature, and Time for
Safety and Secondary Termination
Regulate Charge Current:
Linear Control (DS2711)
Switch-Mode Control (DS2712)
Drive pMOS or pnp-Type Pass Element or
Switch, or an Optocoupler
Compatible with Popular Optocouplers and
Integrated Primary-Side PWM Controllers
Small 16-Pin SO or TSSOP Packages
DS2711/DS2712
Loose-Cell NiMH Chargers
PIN CONFIGURATION
CC1
CC2
LED1
VSS
LED2
CSOUT
VN1
VN0
1
2
3
4
5
6
7
8
16 VP2
15 VP1
14 THM2
13 THM1
12 VDD
11 TMR
10 CTST
9 DMSEL
SO (150 mils)
TSSOP (4.4mm)
PIN DESCRIPTION
PIN NAME
FUNCTION
1 CC1 Cell 1 Charge-Control Output
2 CC2 Cell 2 Charge-Control Output
3 LED1 Cell 1 Status
4
VSS
Ground Reference and Chip-
Supply Return
5 LED2 Cell 2 Status, Mode-Select Input
6 CSOUT Current-Sense Output
7 VN1 Current-Sense + Input
8 VN0 Current-Sense - Input
9 DMSEL Display-Mode Select
10 CTST Cell Test Threshold Set
11 TMR Charge Timer Set
12 VDD Chip-Supply Input (4.0V to 5.5V)
13 THM1 Cell 1 Thermistor Input
14 THM2 Cell 2 Thermistor Input
15
VP1
Cell 1 Positive-Terminal Sense
Input
16
VP2
Cell 2 Positive-Terminal Sense
Input
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DS2711 Datasheet, Funktion
DS2711/DS2712: Loose-Cell NiMH Chargers
DETAILED DESCRIPTION
Charge Algorithm Overview
A charge cycle begins in one of three ways: with the application of power to the DS2711 with cell(s) already
inserted, with the detection of cell insertion after power-up, or when exiting suspend mode with cell(s) inserted. The
charge cycle begins with precharge qualification to prevent fast charging of deeply depleted cells or charging under
extreme temperature conditions. Precharging is performed at a reduced rate until each cell reaches 1V. The
algorithm proceeds to a fast-charge phase, which includes cell tests to avoid accidental charging of alkaline cells or
NiMH cells that are worn-out or damaged. Fast charging continues as long as the cell temperature(s) are less than
50°C (based on THM1, THM2 voltages) and the open-circuit cell voltage(s) are between 1.0V and 1.75V. Fast
charging terminates by the -V (negative delta voltage) method. The top-off charge phase follows to completely
charge the cells. After the top-off charge timer expires, the maintenance charge phase continues indefinitely to
keep the cells at a full state of charge. Maximum voltage, temperature, and charge-time monitoring during all
charge phases act as secondary or safety termination methods to provide additional protection from overcharge.
Each cell is monitored independently, and in parallel mode the charge phase of each cell is independently
controlled.
Series Charge Configuration
The DS2711/DS2712 series configuration supports one or two-slot stand-alone and one or two cell in-system
chargers. The single-cell-series mode charges one cell while the two-cell-series mode charges two series cells.
Since the cells are charged in series, cell sizes should not be mixed in the series configuration. In the application
example in Figure 3, charge current is gated to the battery cells by a PNP transistor under the control of the CC1
pin of the DS2711. Current regulation is performed outside of this example schematic using the current-sense
feedback provided by the DS2711 CSOUT pin. The DS2712 can also be used in this circuit to provide switch-mode
control on the CSOUT pin. RSNS = 0.125sets the charge source current, ICHG, to 1A. In series mode, the
effective charge current is 0.969 x ICHG = 969mA.
Figure 3. Series Configuration with External Current Regulation
ICHG
+5V
IFB
FCX718
10K
100
270
GND
DS2711/12
CC1 VP2
CC2 VP1
LED1
THM2
VSS THM1
LED2
VDD
CSOUT TMR
VN1 CTST
VN0 DMSEL
0.1
75K
10K
x2
103AT-2
x2
100K
RSNS
0.125
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DS2711 pdf, datenblatt
DS2711/DS2712: Loose-Cell NiMH Chargers
Table 2. Charge Mode Selection
LED2 PIN STRAPPING
MODE
Low 1-Cell Series
Open
2-Cell Series
High
Parallel
CC1 and CC2 Outputs
The CC1 and CC2 operate as open-drain outputs that drive active low to connect the charge source to the battery
cell. During charge, the behavior of the CC1 and CC2 outputs depends on the charge-mode configuration. In
parallel mode, CC1 and CC2 are driven low in alternating time slots. The charge source is loaded by just one cell
during any time slot. In the 1-cell and 2-cell series mode, only CC1 is driven. Except for the periodic performance of
impedance and -V tests, series mode charging is continuous during the fast charge phase rather than pulsed in
parallel mode.
Parallel Mode Fast Charge
Referring to Figure 4, CC1 controls the PNP switch that gates current to the cell in slot 1. CC2 controls the PNP
switch that gates current to the cell in slot 2. During fast charge, current is gated to each slot sequentially, with
charge pulses occurring in alternating time frames. The cell in one slot charges while the other relaxes and the
effective fast-charge current is 48.4% of the magnitude set by the charge-source current limit. The parallel
configuration skips a charge pulse every 32 clock cycles to facilitate independent testing of the open- and closed-
circuit cell voltages (VOFF and VON, respectively). Since the charge regime of each cell is independent, one cell may
complete a charge phase before the other. The more fully charged cell of a pair inserted at the same time could
terminate fast charge by -V, then charge in top-off while the less charged cell continues in fast charge. In the case
of an improper or faulty cell (e.g., alkaline) being inserted along with a proper cell (NiMH or NiCd), charging of the
faulty cell would be stopped, while the proper cell is charged to full.
Series Mode Fast Charge
Referring to Figure 3, CC1 controls the PNP switch that gates current to the cell(s). In series mode, 1 or 2 cells can
be charged, depending on whether the 1-cell or 2-cell series mode has been selected. During fast charge, current
is gated to the cell(s) almost continuously, with the effective fast-charge current approximately equal to current limit
of the charge source. The series configuration deactivates CC1 briefly every 32 clock cycles to facilitate
independent testing of VOFF and VON of each cell. The one second deactivation makes the duty factor 0.969 and
therefore the effective current equals approximately 97% of the charge-source current limit. In the 2-cell series
mode, the characteristics of each cell are evaluated individually; however charging stops if either cell is determined
to be improper or faulty.
In the 1-cell charge series mode, CC1 gates the charge current as in the 2-cell series mode. The cell voltage is
monitored between VP1 and VN1, and temperature is monitored with THM1. The VP2 and THM2 pins can be left
disconnected in the 1-cell series mode.
EXAMPLE CAPACITIES AND CHARGE RATES
Parallel Charging Example
A 1700mAH cell is charged using a 1A regulated charge source. During fast charge, the cell is charged at a duty
factor of 0.484 and receives an effective charge current of 0.484A. In terms of C-rate, this is 484mA/1700mAh =
0.285°C (or C/3.5). During precharge and top-off, the duty factor is 0.125 (i.e., 1/8), for an effective average current
of 125mA, corresponding to a C-rate of 125/1700 = 0.073C (or C/13.6). Similarly, in maintenance mode, the duty
factor is 0.0156 (i.e., 1/64) and the C-rate is 15.6/1700 = 0.0092 ( or C/109). The C-rates for charging 3 different
cell capacities using a 500mA and a 1000mA current source are shown in Table 3.
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