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MCP73855-MF Datasheet(PDF) 11 Page - Microchip Technology |
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MCP73855-MF Datasheet(HTML) 11 Page - Microchip Technology |
11 / 24 page 2004 Microchip Technology Inc. DS21915A-page 11 MCP73853/55 4.0 DEVICE OVERVIEW The MCP7385X devices are highly advanced linear charge management controllers. Refer to the functional block diagram. Figure 4-2 depicts the operational flow algorithm from charge initiation to completion and automatic recharge. 4.1 Charge Qualification and Preconditioning Upon insertion of a battery, or application of an external supply, the MCP7385X devices automatically perform a series of safety checks to qualify the charge. The input source voltage must be above the Undervoltage Lock- out (UVLO) threshold, the enable pin must be above the logic high level, and the cell temperature monitor must be within the upper and lower thresholds (MCP73853 only). The qualification parameters are continuously monitored, with any deviation beyond the limits automat- ically suspending, or terminating, the charge cycle. The input voltage must deviate below the UVLO stop threshold for at least one clock period to be considered valid. Once the qualification parameters have been met, the MCP7385X devices initiate a charge cycle. The charge status output is pulled low throughout the charge cycle (see Tables 5-1 and 5-2 for charge status outputs). If the battery voltage is below the preconditioning thresh- old (VPTH), the MCP7385X devices precondition the battery with a trickle charge. The preconditioning current is set to approximately 10% of the fast charge regulation current. The preconditioning trickle charge safely replenishes deeply depleted cells and minimizes heat dissipation during the initial charge cycle. If the battery voltage has not exceeded the preconditioning threshold before the preconditioning timer has expired, a fault is indicated and the charge cycle is terminated. 4.2 Constant Current Regulation – Fast Charge Preconditioning ends and fast charging begins when the battery voltage exceeds the preconditioning thresh- old. Fast charge regulates to a constant current (IREG), which is set via an external resistor connected to the PROG pin. Fast charge continues until either the battery voltage reaches the regulation voltage (VREG) or the fast charge timer expires; in which case, a fault is indicated and the charge cycle is terminated. 4.3 Constant Voltage Regulation When the battery voltage reaches the regulation volt- age (VREG), constant voltage regulation begins. The MCP7385X devices monitor the battery voltage at the VBAT pin. This input is tied directly to the positive termi- nal of the battery. The MCP7385X devices select the voltage regulation value based on the state of VSET. With VSET tied to VSS, the MCP7385X devices regulate to 4.1V. With VSET tied to VDD, the MCP7385X devices regulate to 4.2V. 4.4 Charge Cycle Completion and Automatic Recharge The MCP7385X devices monitor the charging current during the Constant-voltage Regulation mode. The charge cycle is considered complete when either the charge current has diminished below approximately 7% of the regulation current (IREG), or the elapsed timer has expired. The MCP7385X devices automatically begin a new charge cycle when the battery voltage falls below the recharge threshold (VRTH), assuming all the qualifica- tion parameters are met. 4.5 Thermal Regulation The MCP7385X devices limit the charge current based on the die temperature. Thermal regulation optimizes the charge cycle time while maintaining device reliabil- ity. If thermal regulation is entered, the timer is automat- ically slowed down to ensure that a charge cycle will not terminate prematurely. Figure 4-1 depicts the thermal regulation. FIGURE 4-1: Typical Maximum Charge Current vs. Junction Temperature. 4.6 Thermal Shutdown The MCP7385X devices suspend charge if the die temperature exceeds 155°C. Charging will resume when the die temperature has cooled by approximately 10°C. The thermal shutdown is a secondary safety feature in the event that there is a failure within the thermal regulation circuitry. 0 50 100 150 200 250 300 350 400 450 0 20 40 60 80 100 120 140 Junction Temperature (C) Minimum Maximum |
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