JAJSJO5B October 2022 – August 2024 LM64440-Q1 , LM64460-Q1
PRODUCTION DATA
Most systems that require more than a single mode of operation from the LM644x0-Q1 are controlled by digital circuitry such as a microprocessor. These systems can generate dynamic signals easily but have difficulty generating multi-level signals. Pulse-dependent MODE/SYNC control is useful with these systems.
To initiate pulse-dependent MODE/SYNC control, a valid synchronization signal must be applied. Upon completion of the fourth pulse in a valid synchronization pulse train, MODE/SYNC operates in pulse-dependent MODE/SYNC control mode, shown in Figure 7-3 and Figure 7-4. The only way to return to Level-dependent MODE/SYNC control is to restart the LM644x0-Q1.
After Pulse-dependent MODE/SYNC control has been initiated, Table 7-2 shows a summary of the pulse-dependent mode selection settings.
MODE/SYNC | MODE |
---|---|
VMODE/SYNC > VMODE_H | FPWM mode with spread spectrum |
VMODE/SYNC < VMODE_L | AUTO mode with spread spectrum |
Synchronization clock | SYNC mode without spread spectrum |
VMODE/SYNC > VMODE_H and Double Pulse (Figure 7-6) | FPWM mode without spread spectrum |
VMODE/SYNC < VMODE_L and Double Pulse (Figure 7-7) | AUTO mode without spread spectrum |
Figure 7-5 shows the transition between AUTO mode and FPWM mode while in Pulse-dependent MODE/SYNC control. The LM644x0-Q1 transitions to a new mode of operation after tMODE has expired.
Two positive-going pulses can be used to turn off spread spectrum in AUTO and FPWM modes. The two positive pulses must be consistent with the characteristics of a valid sync signal. Figure 7-6 through Figure 7-9 show the only waveforms that result in spread spectrum being turned off. Refer to the Electrical Characteristics for more information about the timing specifications.
To enter SYNC mode, the valid synchronization signal must be present for 2048 cycles.
If the MODE/SYNC voltage becomes constant longer than tMODE, the LM644x0-Q1 enters either AUTO mode or FPWM mode. At this time, spread spectrum is turned on and MODE/SYNC operates in pulse-dependent mode.