1 LM61440-Q1 vs LM62440-Q1 Device Differences

Figure 1-1 highlights the key differences in device pin-out between the LM614xx and LM624xx device set using the LM61440-Q1 and LM62440-Q1 as device examples.

The primary distinctions between the LM614xx and LM624xx are listed below:

• Switching frequency: The LM624xx is internally set to a default switching frequency of 2.1MHz. The LM614xx enables control of the switching frequency through an adjustable RT resistor.
• Mode selection: The LM624xx enables control of the mode operation at light load. Pulling MODE/SYNC high results in FPWM mode setting while pulling MODE/SYNC low results in Auto mode setting. The LM614xx has the mode feature factory set and fixed per device option.
• External synchronization: To synchronize to a desired switching frequency the LM624xx requires a valid switching signal into the “MODE/SYNC” (Pin 6) for synchronization while the LM614xx uses “EN/SYNC” (Pin 7) for synchronization. Note that when using the external synchronization feature of the device spread-spectrum is disabled.
• Output voltage setting: The LM624xx is available in both adjustable and fixed output options. The LM614xx is only available in adjustable output option. For adjustable output options a top and bottom resistor is required while for fixed output options the feedback pin can be tied directly to the output rail for proper regulation.

Table 1-1 and Table 1-2 show the device comparison table of the LM61440-Q1 and LM62440-Q1 example devices and illustrates the difference between a LM614xx and LM624xx. The table provides the orderable device numbers and details the variety of different options the device is factory set to. Figure 1-2 and Figure 1-3 are example application circuits from the data sheet. To create a universal footprint to interchange between the LM614xx and LM624xx device set, several components must be considered.