The FAN5234 PWM controller provides high efficiency and adjustable output from 0.9V to 5.5V power required for I/Os, chipsets, memory banks, or peripherals in high-performance laptops, PDAs, and Internet appliances. Synchronized trim and hysteretic operation contributes to high efficiency loads over a wide range at light loads. Hysteresis mode of operation can be disabled if all load levels are required for PWM mode. Efficiency is further improved by using the RDS(ON) of the MOSFET as the current sensing element. Feedforward ramp modulation, average current mode control and internal feedback compensation provide fast load transient response. The FAN5234 displays these outputs and generates a PGOOD (power good) signal when the soft-start ends, the output is at ±10% of its set point. Built-in overvoltage protection prevents the output voltage from going above the 120 % set point. Normal operation is automatic recovery when stopped under overvoltage conditions. The undervoltage protection latch chip turns off when the soft output is lower than 75% of its set value after the start-up process is complete. An adjustable overcurrent function monitors the output current by sensing the voltage drop across the lower MOSFET.

Function Description

The FAN5234 is a PWM controller for low voltage power supply applications in laptops, desktops and sub-notebooks. The output voltage of the controller can be set externally in the range of 0.9V to a 5.5V resistor divider. Synchronous buck converters can operate from an unstable DC power source (such as a laptop battery) with voltages from 2V to 24V , or from a regulated rail system. In either case, the IC is biased by a +5V source. The PWM modulator employs average current-mode control and feedforward of the input voltage for simple feedback loop compensation and modification regulations. The controller includes integrated feedback loop compensation, which greatly reduces the number of external components. Depending on the load level, the converter can operate in either fixed frequency PWM mode or hysteresis mode. Switching from PWM to hysteretic mode improves the converter's efficiency at light loads and extends battery runtime. Entering hysteretic mode, the comparison is synchronized to the master clock to allow for seamless transitions between modes of operation and reduced channel-to-channel interaction. Operation in hysteresis mode can suppress undesired operation if the frequency conversion is used independently of the FPWM pin.

Layout Considerations

Switching converters, even in normal operation, generate short pulses of current that can cause large oscillations and EMI source constraints if the layout is not respected. There are two sets of key components in the DC-DC converter. Switching power supply components process at high rates and large amounts of energy are noisy generators. Responsible for the bias and feedback functions of this low power component, which is sensitive to noise. A multilayer printed circuit board is recommended. Provide a dedicated solid layer ground plane. Dedicate another solid layer to the power layer, and break this plane down to a smaller island with a common voltage rating. Note that all nodes are experiencing high dV/dt voltage swings; such as SW, HDRV and LDRV. All peripheral circuits tend to couple signals from these nodes through stray capacitances. Do not oversize the copper traces connected to these nodes. Do not connect these traces to traces adjacent to the feedback element. We do not recommend the use of high-density interconnect systems, or microvias, on these signals. The use of blind or buried vias should be limited to low current signals. Utilizing normal thermal vents is at the designer's discretion.