USB charger IC meets automotive qualifications

September 22, 2014 // By Christoph Hammerschmidt
Charging the batteries of music players or smartphones through a USB interface is commonplace. In cars however, the matter is slightly more complicated, and that's why Elmos Semiconductor has developed its E522.41 chip. The IC supports all USB charging downstream loads according to the Battery Charging Specifications (rev. 1.2). In addition, it emulates all currently known specific USB charging devices.

Depending on the charging current, the bus voltage is increased, which simulates a negative internal resistance of the voltage source, enabling optimum charging process even at very high currents with cable-induced losses.

An I2C interface facilitates system setup and diagnosis in real-time through an external microprocessor. This allows in particular the read-out of USB voltage and application current to enable effective monitoring. The ADR pin can decode three different I2C bus system addresses. For low-cost applications, the E522.41 can also be used with several stand-alone options. To enable device manufacturers designing future individual solutions, an adjustable coding network is available.

The chip is equipped with an internal switching power supply, offering 5V ±3% at the USB port; maximum current is 2.5A. To accommodate for automotive power supplies (batteries) at the input, the chip accepts input voltages between 6 and 32V with short-term peaks up to 42V. The switching frequency can be programmed for four centre frequencies - 250kHz, 500kHz, 1MHz and 2MHz. In master-slave configurations, these frequencies can be synchronised through an internal PLL circuit in the range of ±25%. Light load recognition and spread-spectrum mode help to significantly reduce the EMI behaviour of the circuit.

The focus in developing this chip has on meeting automotive robustness requirements. As a result, the chip meets ISO7637 for input voltage peaks and offers short-circuit protection at the USB output. Additional features are monitoring the USB output for over and undervoltage, monitoring the internal reference voltages and overtemperature protection. Fault conditions and system warnings are signalised through an interrupt output. The E522.41 is entirely qualified according to automotive standard AEC-Q-100. It comes in a 20 pin QFN package with high thermal efficiency and operates at temperatures up to 105°C.

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