MAXIM Battery Charging Solutions

The MAX17085B provides an all-in-one power solution for notebook computers that integrates a multichemistry battery charger, dual fixed-output Quick-PWM™ step-down controllers, and dual always-on linear regulators. This solution can power the system load while charging a multichemistry battery pack. During operation, the EV kit circuit automatically selects the ADAPTER input or the battery as the primary source to power the system load and the step-down converter.

Basic Features:

All-in-one charger with dual main supply buck controller

5V/100mA and 3.3V/50mA LDO regulators

Main power supply

Dual Quick-PWM controller with fast transient response and long on-time

300kHz to 800kHz Switching Frequency

5V and 3.3V fixed SMPS outputs

Low noise ultrasound mode

Automatic retry fault protection

charger

High switching frequency (1.4MHz)

Selectable 2, 3 and 4 cell battery voltages

Automatically select system power

Built-in charge pump to drive n-channel MOSFET adapter select switch

Charging voltage accuracy is ±0.4%

Input current limit accuracy is ±2.5%

Charging current accuracy is ±3%

Monitor output for monitoring

AC adapter current (accuracy ±2%)

Battery discharge current (accuracy ±2%)

AC adapter ready status

Charging current can be set by analog/PWM (100Hz to 500kHz) signal

AC adapter overvoltage and overcurrent protection

Device Block Diagram

Solution Features:

Charger: The high-frequency (approximately 1.4MHz), multi-chemistry battery charger uses a current-mode architecture with constant inductor current ripple, which greatly reduces component size and cost. A low-offset voltage sense amplifier allows the use of a small-value current-sense resistor to sense the charge current and input current limit.

The charger uses an n-channel switching MOSFET. Adjustable charge current, charge voltage, and number of cells allow flexibility in using different types of battery packs, and the charge current can be set via an analog control input or PWM input. A high-precision current-sense amplifier provides fast cycle-by-cycle current-mode control to prevent battery short circuits and quickly respond to system load transients. In addition, the charger provides a high-precision analog output that is proportional to the adapter current.

An internal charge pump controls an n-channel adapter select switch that keeps the charge pump active even when the charger is off. When no adapter is connected, a p-channel MOSFET selects the battery as the input.

Main Power SMPS: Dual Quick-PWM step-down controllers with synchronous rectification provide 5V and 3.3V main power supplies for notebook computers. Low-side MOSFET sensing provides a simple, low-cost, and efficient valley current limit protection. The MAX17085B also provides output undervoltage, output overvoltage, and thermal fault protection.

Each SMPS has an independent enable input and a common open-drain power-good output for flexible power sequencing. Voltage soft-start reduces inrush current, and passive shutdown discharges the output through an internal switch. Fast transient response and long on-time reduce output capacitance requirements. Selectable pulse skipping mode and ultrasonic mode improve efficiency at light loads. Ultrasonic mode maintains the lowest switching frequency at light loads, significantly reducing audible noise.

Dual LDO regulators: The internal 5V/100mA LDO5 has a switching function and can be used to generate the 5V bias required for power-on or as a low-voltage "uninterruptible" power supply. Another 3.3V/50mA LDO3 provides an "uninterruptible" power supply for the system microcontroller.

Reference schematic:

Reference PCB: