MAX745EAP+T

The MAX745 provides all functions necessary for charging lithium-ion (Li+) battery packs. It provides a regulated charging current of up to 4A without getting hot, and a regulated voltage with only ±0.75% total error at the battery terminals. It uses low-cost, 1% resistors to set the output voltage, and a low-cost N-channel MOSFET as the power switch. The MAX745 regulates the voltage set point and charging current using two loops that work together to transition smoothly between voltage and current regulation. The per-cell battery voltage regulation limit is set between 4V and 4.4V using standard 1% resistors, and then the number of cells is set from 1 to 4 by pin-strapping. Total output voltage error is less than ±0.75%. The MAX745 is a switch-mode, Li+ battery charger that can achieve 90% efficiency. The charge voltage and current are set independently by external resistor-dividers at SETI and VADJ, and at pin connections at CELL0 and CELL1. VADJ is connected to a resistor-divider to set the charging voltage. The output voltage-adjustment range is ±5%, eliminating the need for 0.1% resistors while still achieving 0.75% set accuracy using 1% resistors. The MAX745 consists of a current-mode, pulse-width modulated (PWM) controller and two transconductance error amplifiers: one for regulating current (GMI) and the other for regulating voltage (GMV). The error amplifiers are controlled through the SETI and VADJ pins. Whether the MAX745 is controlling voltage or current at any time depends on the battery state. If the battery is discharged, the MAX745 output reaches the current regulation limit before the voltage limit, causing the system to regulate current. As the battery charges, the voltage rises to the point where the voltage limit is reached and the charger switches to regulating voltage. The STATUS pin indicates whether the charger is regulating current or voltage.

Applications

• Li+ Battery Packs
• Desktop Cradle Chargers
• Cellular Phones
• Notebook Computers
• Hand-Held Instruments

Key features

• Charges 1 to 4 Li+ Battery Cells ±0.75% Voltage-Regulation Accuracy Using 1% Resistors
• Provides up to 4A without Excessive Heating
• 90% Efficient
• Uses Low-Cost Set Resistors and N-Channel Switch
• Up to 24V Input Up to 18V Maximum Battery Voltage
• 300kHz Pulse-Width Modulated (PWM) Operation
• Low-Noise, Small Components
• Stand-Alone Operation—No Microcontroller Needed