The LM73605-Q1/6-Q1 switching action can synchronize to an external clock from 350 kHz to 2.2 MHz. TI recommends connecting the external clock to the SYNC/MODE pin with an appropriate termination resistor. Ground the SYNC/MODE pin if not used.

Figure 8-13 Frequency Synchronization

Recommendations for the external clock include a high level no lower than 2 V, low level no higher than 0.4 V, duty cycle between 10% and 90%, and both positive and negative pulse width no shorter than 80 ns. When the external clock fails at logic high or low, the LM73605-Q1/6-Q1 at the frequency programmed by the R_T resistor after a time-out period. TI recommends connecting a resistor to the RT pin such that the internal oscillator frequency is the same as the external clock frequency. This allows the regulator to continue operating at approximately the same switching frequency if the external clock fails with the same control loop behavior.

The SYNC/MODE pin is also used as an operation mode control input.

• To set the operation in auto mode, connect SYNC/MODE pin to ground, or a logic signal lower than 0.3 V.
• To set the operation in FPWM mode, connect SYNC/MODE pin to a bias voltage or logic signal greater than 0.6 V.
• When the LM73605-Q1/6-Q1 synchronized to an external clock, the operation mode is FPWM.

Table 8-2 summarizes the operation mode and features according to the SYNC/MODE input signal. For more details, see the Section 8.4.3 and Section 8.3.2 sections.