Below is a list of considerations when
using the LM614xx and LM624xx in the universal PCB layout design. Using the
LM61460EVM as the basis for the universal PCB layout, only three additional
components (C10, C13, and R4) are required to enable an easy swap between the
LM614xx and LM624xx (Refer to Figure 2-1 for modified
EVM schematic and Figure 2-2 for 3D EVM
view of additional components).
Additional Components:
- R4 is the MODE_H pull up resistor
for FPWM operation with the LM624xx
- C10 and C13 are the AC coupling
capacitors for external synchronization on the SYNC pin of the LM614xx and
LM624xx
LM614xx Component Selection
Instructions:
- Pin 6 is RT pin on this device.
Populate resistor RT/MODEL_L for desired switching frequency and leave resistor
MODE_H resistor as DNP.
- Pin 7 is EN/SYNC. For external
synchronization, populate (LM614xx)_CSYNC capacitor and leave capacitor
(LM624xx)_CSYNC as DNP. Applying a valid external switching frequency on TP4
will set the device to FPWM Mode.
LM624xx Component Selection
Instructions:
- Pin 6 is MODE/SYNC on this
device.
- For Auto Mode feature, populate
resistor RT/MODE_L and leave resistor MODE_H as DNP.
- For FPWM Mode feature, populate
resistor MODE_H and leave resistor RT/MODE_L as DNP.
- For external synchronization,
populate (LM624xx)_CSYNC capacitor and leave capacitor (LM614xx)_CSYNC as DNP.
Applying a valid external switching frequency on TP4 will set the device to FPWM
Mode.
Figure 2-2 Universal PCB Layout 3D
View
Figure 2-4 Universal PCB Layout Mid
Layer 1
Figure 2-6 Universal PCB Layout
Bottom Layer
Figure 2-3 Universal PCB Layout Top
Layer
Figure 2-5 Universal PCB Layout Mid
Layer 2