Maxim DS2711/12K NiMH Charger Kit Board

Board Layout

The DS2711/12K board is designed for flexible configuration of the DS2711 or DS2712 ICs, supporting single-cell, dual-cell series, and dual-cell parallel charging of AA or AAA NiMH cells. It offers selectable on-board regulation of the charge source, on-board regulation with a separate DS2711/12 power supply, or external regulation.

Figure 1: Terminal header and jumper locations on topside of board. This figure illustrates the placement of jumpers (J1-J9) and terminal headers on the board's topside, essential for configuring charging modes and power inputs.

Figure 2: Battery socket locations on bottom side of board. This figure shows the battery socket locations on the board's bottom side, labeled B1, B1B, B2, B2B, B3, and B3B, where AA or AAA NiMH cells are inserted.

LED Flash Selection – Jumper J8

The DS2711/12 is capable of three different LED flash configurations for charge, maintenance, and fault states. Jumper J8 is used to select these modes. The board requires a power cycle after changing jumper settings for the changes to take effect.

Figure 3: LED Flash Mode Selection depicts the three configurations for jumper J8:

• Mode 1: 100% duty cycle during charge, 0% duty cycle during maintenance, 50% duty cycle during fault.
• Mode 2: 80% duty cycle during charge, 100% duty cycle during maintenance, 50% duty cycle during fault.
• Mode 3: 100% duty cycle during charge, 80% duty cycle during maintenance, 50% duty cycle during fault.

Power Input Selection – Jumpers J2, J3, J5, J7, and connection terminal

Figure 4 shows jumper settings and terminal connections for three different modes of regulation. Power cycling is required after changing jumper settings.

Figure 4: Different modes of supplying a charge source.

• Use on-board Regulation: Connect to PWR2 and GND. Requires a supply voltage between 4.0V and 5.5V capable of delivering the required charge current.
• Use on-board Regulation with separate supply for the DS2712: Connect the DS2711/12 supply voltage between PWR1 and GND. Connect the charge source between PWR2 and GND.
• Use externally regulated Charge Source: Connect the DS2711/12 supply voltage between PWR1 and GND. Connect the regulated charge source between PWR3 and GND. Leave PWR2 open. The CSOUT terminal provides a linear feedback voltage for regulating supply current.

Charge Configuration – Jumpers J1, J4, J6, J9, and all battery sockets

The DS2711/12K board supports charging AA or AAA cells in single cell, two cell series, and two cell parallel configurations. Figure 5 illustrates jumper settings and cell socket configurations for each mode. Paired AA and AAA cells should not be populated simultaneously. Power cycling is necessary after changing jumper settings.

Figure 5: Single, Series, and Parallel Charge Configurations

• Single Cell Charging: Set jumpers J1, J4, J6, and J9 as shown in Figure 5. Populate either socket B2 or B2B only.
• Dual Cell Series Charging: Set jumpers J1, J4, J6, and J9 as shown in Figure 5. Populate both sockets B1 and B2, or sockets B1B and B2B. The charge rate is determined by the populated socket (B2 or B2B).
• Dual Cell Parallel Charging: Set jumpers J1, J4, J6, and J9 as shown in Figure 5. Populate cells in any combination of the following: B2 only, B2B only, B3 only, B3B only, B2 and B3, B2 and B3B, B2B and B3, or B2B and B3B.

Charge Rate, Charge Time, and Impedance Test

Charge Rate – Resistors R14 and R15

Resistor R14 sets the charge rate for AA sockets, and the combined resistance of R14+R15 sets the charge rate for AAA sockets. The formulas are:

• DS2711 AA Charge Rate (A) = 0.125 (V) / R14
• DS2711 AAA Charge Rate (A) = 0.125 (V) / (R14 + R15)
• DS2712 AA Charge Rate (A) = 0.113 (V) / R14
• DS2712 AAA Charge Rate (A) = 0.113 (V) / (R14 + R15)

Default values (R14=0.200 Ohms, R15=0.100 Ohms) yield charge rates of 0.625A (AA) and 0.417A (AAA) for DS2711, and 0.565A (AA) and 0.377A (AAA) for DS2712.

Charge Time – Resistor R21

Resistor R21 sets the time limit for fast charge and top-off charge:

• Fast Charge Time (minutes) = 1.5 * R21 / 1000
• Top Off Charge Time (minutes) = ½ Fast Charge Time (minutes)

A default value of R21 = 200K Ohms provides 5 hours fast charge and 2.5 hours top-off charge. Minimum R21 (20K Ohms) gives 30 minutes fast charge; maximum R21 (360K Ohms) gives 9 hours fast charge.

Impedance Test – Resistor R20

Resistor R20 sets the voltage threshold to prohibit charging of non-NiMH cells using the formula:

Impedance threshold (mΩ) = (8000 / R20) * (1 / Charge Rate (A))

A default value of R20 = 68K Ohms sets thresholds at 200mΩ for AA cells and 300mΩ for AAA cells. Max R20 is 250K Ohms, min is 20K Ohms. R20 selection must occur after charge rate is set.

Schematic Description

The schematic diagram details the internal circuitry of the DS2711/12K demo board. It features the DS2711/DS2712 integrated circuit (U1) as the central component. Power is supplied via VDD and GND pins, with additional power inputs VP1 and VP2. The board includes various jumpers (J1-J9) and battery sockets (B1, B1B, B2, B2B, B3, B3B) for configuration and cell insertion. Key external components include resistors (R1-R23), capacitors (C1, C2, C4, C5), diodes (D1-D5), transistors (Q2, Q3), an inductor (L1), and LEDs (LED1, LED2). Specific components like a 4.7V Zener diode (D3), a 47uF capacitor (C1), a 1uF capacitor (C2), a 47uH inductor (L1), and transistors (FCX718) are shown connected to the IC. The schematic also indicates specific resistor values (e.g., R8, R9, R14, R15, R20, R21) that are populated differently for DS2711 versus DS2712, or for different charging parameters. Jumpers are shown to control functions like DMSEL, THM1, THM2, CRATE, CC2, TMR, RSNS, and CSOUT. The diagram illustrates how these components and jumpers are interconnected to manage charging rates, times, impedance detection, and LED status indications.