To increase the reliability and robustness of the design, TI recommends the following layout guidelines:
- For the VREF pin: decouple this pin to GND with a
good quality ceramic capacitor. A 1μF, X7R, 25V
capacitor is recommended. Keep VREF PCB tracks as
far away as possible from sources of switching
noise.
- For the EA+ pin: this is the noninverting input to the error amplifier. It is a high impedance pin and is susceptible to noise pickup. Keep tracks from this pin as short as possible.
- For theEA– pin: this is the inverting input to the error amplifier. It is a high impedance pin and is susceptible to noise pickup. Keep tracks from this pin as short as possible.
- For theCOMP pin: the error amplifier compensation network is normally connected to this pin. Keep tracks from this pin as short as possible.
- For theSS/EN pin: keep tracks from this pin as short as possible. If the Enable signal is coming from a remote source then avoid running it close to any source of high dv/dt (MOSFET Drain connections for example) and add a simple RC filter at the SS/EN pin.
- For the DELAB, DELCD, DELEF, TMIN, RT, RSUM, DCM, ADELEF and ADEL pins: the components connected to these pins are used to set important operating parameters. Keep these components close to the IC and provide short, low impedance return connections to the GND pin.
- For the CS pin: this connection is arguably the
most important single connection in the entire PSU system. Avoid running the CS
signal traces near to sources of high dv/dt. Provide a simple RC filter as close
to the pin as possible to help filter out leading edge noise spikes which occur
at the beginning of each switching cycle.
- For the SYNC pin: this pin is essentially a
digital I/O port. If it is unused, then it may be
left open circuit or tied to ground through a 1kΩ
resistor. If Synchronisation is used, then route
the incoming Synchronisation signal as far away
from noise sensitive input pins as possible.
- For the OUTA, OUTB, OUTC, OUTD, OUTE and OUTF
pins: these are the gate drive output pins. They have a high dv/dt rate
associated with their rising and falling edges. Keep the tracks from these pins
as far away from noise sensitive input pins as possible. Ensure that the return
currents from these outputs do not cause voltage changes in the analog ground
connections to noise sensitive input pins. Follow the layout recommendation for
analog and power ground planes in Figure 6-18.
- For the VDD pin: this pin must be decoupled to GND using ceramic capacitors as detailed in the Section 7.3 section. Keep this capacitor as close to the VDD and GND pins as possible.
- For the GND pin: this pin provides the ground
reference to the controller. Use a ground plane to minimize the impedance of the
ground connection and to reduce noise pickup.