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Switch-Mode Lithium-Ion Battery-Charger

±0.75% Precision Li+ Charger Delivers 4A Without Heating

Product Details

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%.

For a similar device with an SMBus™ microcontroller interface and the ability to charge NiCd and NiMH cells, refer to the MAX1647 and MAX1648. For a low-cost Li+ charger using a linear-regulator control scheme, refer to the MAX846A.

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

Applications/Uses

  • Cell Phones
  • Desktop Cradle Chargers
  • Handheld Instruments (PDAs, Palmtops)
  • Li+ Battery Packs
  • Notebook Computers
Parametric specs for Battery Chargers
Charging VIN (V) (max) 24
Max. ICHG (A) 4
Cell Chemistry Li-Ion
Li-Polymer
# Lithium Ion Cells 1
2
3
4
Protected VIN (V) (max) 24
Charger (V) 18
Oper. Temp. (°C) -40 to +85
Package/Pins SSOP/20
Budgetary
Price (See Notes)
$5.31 @1k
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Simplified Block Diagram

MAX745: Typical Operating Circuit MAX745: Typical Operating Circuit Zoom icon

Technical Docs

Design & Development

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Description

The MAX745 evaluation kit (EV kit) is an assembled and tested PC board that implements a step-down, switching power supply designed for charging lithium-ion (Li- Ion) batteries. The output voltage can be set for one to four cells. The cell voltage can be set between 4.0V and 4.4V, with 0.75% accuracy, using standard 1% resistors. Two LEDs indicate the charging status.

The MAX745 should be used to charge only Li-Ion battery packs. To charge other types of batteries, use the MAX1648 or the MAX712/MAX713. To charge SMBus™ smart-battery packs, use the MAX1645/MAX1647/ MAX1667.

View Details

Features

  • Charges One to Four Li-Ion Cells
  • Low Heat/High Efficiency
  • 300kHz PWM Operation
  • 0.75% Overall Accuracy over Temperature
  • 6V to 24V Input Voltage Range
  • Proven PC Board Layout
  • Fully Assembled and Tested

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Parameters

Parametric specs for Battery Chargers
Charging VIN (V) (max) 24
Max. ICHG (A) 4
Cell Chemistry Li-Ion
Li-Polymer
# Lithium Ion Cells 1
2
3
4
Protected VIN (V) (max) 24
Charger (V) 18
Oper. Temp. (°C) -40 to +85
Package/Pins SSOP/20
Budgetary
Price (See Notes)
$5.31 @1k

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

Applications/Uses

  • Cell Phones
  • Desktop Cradle Chargers
  • Handheld Instruments (PDAs, Palmtops)
  • Li+ Battery Packs
  • Notebook Computers

Description

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%.

For a similar device with an SMBus™ microcontroller interface and the ability to charge NiCd and NiMH cells, refer to the MAX1647 and MAX1648. For a low-cost Li+ charger using a linear-regulator control scheme, refer to the MAX846A.

Simplified Block Diagram

MAX745: Typical Operating Circuit MAX745: Typical Operating Circuit Zoom icon

Technical Docs

Support & Training

Search our knowledge base for answers to your technical questions.

Filtered Search

Our dedicated team of Applications Engineers are also available to answer your technical questions. Visit our support portal