TPS56637 is a 6-A synchronous buck converter with D-CAP3™ control. It is pin-to-pin compatible with TPS56837 but doesn't have the large duty function.

According to the previous analysis, the maximum duty which TPS56637 can support is only decided by the frequency and minimum off-time. Thus we can get the maximum duty based on Equation 3. Considering the actual frequency is 550 kHz while the min off-time is 200 ns, we can calculate the maximum Duty is 89%. That means if the output voltage is 5 V, the input voltage would be higher than about 5÷89%=5.62 V.

Figure 4-5 and Figure 4-6 show the line dropout performance in the TPS56837EVM and TPS56637EVM. The EVM test setup is the same as with Table 4-1.

Figure 4-5 6 V input to 4 V input of TPS56637

Figure 4-6 6 V input to 4 V input of TPS56837

From the waveforms, it is obvious that TPS56837 can support 5 V output with a wider input voltage range. TPS56637 would have a output voltage drop after input is less than 5.64 V while it is 5.12 V of TPS56837. After the voltage dropped below 3.7 V, both the device shutdown due to input UVLO.