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MAX1666SEEE Datasheet(PDF) 10 Page - Maxim Integrated Products |
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MAX1666SEEE Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 16 page Advanced Lithium-Ion Battery-Pack Protector 10 ______________________________________________________________________________________ Detailed Description The MAX1666 battery-pack protectors supervise the charging and discharging processes of Lithium-Ion battery cells. Designed for 2, 3, and 4-cell applications, these devices monitor the voltage across each cell to provide protection against undervoltage, overvoltage, and overcurrent damage. Control pins CGO, TKO, and DSO allow control of external MOSFET gates. This allows fast charging, trickle charging, and discharging processes (see Typical Operating Circuit). The voltage of each cell is measured individually. Also, each cell is measured dif- ferentially between every other cell of the pack. The MAX1666 contains a state machine, a voltage reg- ulator, an oscillator, and other logic functions to selec- tively drive CGO, UVO, TKO, DSO, WRN, and PKF (Figure 1). Modes of Operation Shutdown Mode The MAX1666 goes into shutdown mode when a bat- tery pack is first connected. The quiescent current is less than 1µA. All circuitry is inactive except the com- parator monitoring VSRC and the top-cell voltage. The MAX1666 remains in shutdown mode as long as VSRC is less than the top-cell voltage. When SRC is connect- ed to an external charger and VSRC is 1V above the top-cell voltage, the device goes into standby mode. The MAX1666 returns to shutdown mode under two conditions: the battery is disconnected and then re- connected, or the device detects an undervoltage fault and no charge source. Normal Mode The standby state activates the bias circuitry, overcur- rent comparator, and timer. The standby state lasts 80ms, then the MAX1666 goes into the sample state for 2.5ms. Within the 2.5ms, the MAX1666 checks for overvoltage, undervoltage, and mismatch between cells sequential- ly, and it stores the results in internal latches. The MAX1666 drives the outputs according to the faults (if any) detected by reading the latches (Figure 2) at the end of the sample state. Then the MAX1666 returns to the standby state. Overvoltage Protection The MAX1666 provides overvoltage protection to avoid overcharging of any cell. When any cell is at overvolt- age, CGO and TKO go high, turning off the external MOS- FETs and stopping the charging process ( Typical Operating Circuits). WRN goes low. Overvoltage is set when any cell voltage exceeds the overvoltage thresh- old. Overvoltage threshold is linearly adjustable through an external 1% resistor-divider (Figure 3) from REF. Determine the overvoltage threshold (VOVT) required. VOVT must be between 4V and 4.4V. Set RTOTAL = R1 + R2 = 1M Ω. Calculate R1 and R2 as follows: R2 = [(VOVT - 4V) / (4.4V- 4V)] · RTOTAL R1 = RTOTAL - R2 MODE TIME TYPICAL QUIESCENT CURRENT (µA) CONDITION 80ms 24 Only bias circuitry, overcurrent comparator, and timer are active. Normal 2.5ms 250 All circuitry active. Shutdown — 0.7 All circuitry inactive. Device enters shutdown when it detects an undervolt- age fault and VSRC < VTOP-CELL + 1V (no charge source). Table 1. Operating Modes R1 R3 REF OVA R5 R2 R4 R6 UVA MMA GND MAX1666 Figure 3. Using an External Resistor-Divider to Adjust Overvoltage Threshold STATE Standby Sample — |
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