ZHCSLD0B May 2020 – June 2021 LM62435-Q1
PRODUCTION DATA
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 Device Comparison Table
- 6 Pin Configuration and Functions
- 7 Specifications
-
8 Detailed Description
- 8.1 Overview
- 8.2 Functional Block Diagram
- 8.3
Feature Description
- 8.3.1 EN Uses for Enable and VIN UVLO
- 8.3.2 MODE/SYNC Pin Operation
- 8.3.3 PGOOD Output Operation
- 8.3.4 Internal LDO, VCC UVLO, and BIAS Input
- 8.3.5 Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
- 8.3.6 Adjustable SW Node Slew Rate
- 8.3.7 Spread Spectrum
- 8.3.8 Soft Start and Recovery From Dropout
- 8.3.9 Output Voltage Setting
- 8.3.10 Overcurrent and Short Circuit Protection
- 8.3.11 Thermal Shutdown
- 8.3.12 Input Supply Current
- 8.4 Device Functional Modes
- 9 Application and Implementation
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.2.2 Pulse-Dependent MODE/SYNC Pin Control
Most systems that require more than a single mode of operation from the LM62345-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 pin control is useful with these systems.
To initiate Pulse-Dependent MODE/SYNC pin control, a valid sync signal must be applied. Upon completion of the fourth pulse in a valid synchronization pulse train, the SYNC mode pin operates in Pulse-Dependent MODE/SYNC control mode, shown in Figure 8-3 and Figure 8-4. The only way to return to Level-Dependent MODE/SYNC control is to restart the LM62345-Q1.
Figure 8-3 Transition from FPWM Mode to
Pulse-Dependent Control
Figure 8-4 Transition from Auto Mode to
Pulse-Dependent ControlOnce Pulse Dependent MODE/SYNC control has been initiated, Table 8-2 shows a summary of the pulse dependent mode selection settings.
| MODE/SYNC INPUT | MODE |
|---|---|
| > VMODE_H | FPWM with Spread Spectrum |
| < VMODE_L | Auto Mode with Spread Spectrum |
| Synchronization Clock | SYNC Mode without Spread Spectrum |
| > VMODE_H AND Double Pulse (Figure 8-6) | FPWM without Spread Spectrum |
| < VMODE_L AND Double Pulse (Figure 8-7) | Auto Mode without Spread Spectrum |
Figure 8-5 shows the transition between AUTO Mode and FPWM Mode while in Pulse-Dependent MODE/SYNC control. The LMQ6240-Q1 transitions to a new mode of operation after the time, tMODE.
Figure 8-5 Transition from Auto Mode and
FPWM ModeTwo 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. The following four diagrams, Figure 8-6 through Figure 8-9, show the only waveforms that result in spread spectrum being turned off. Refer to Section 7.5 for more information about the timing specifications.
Figure 8-6 Spread Spectrum Disabled in
FPWM Mode
Figure 8-7 Spread Spectrum Disabled in
Auto Mode
Figure 8-8 Spread Spectrum Disabled in
Transition from FPWM Mode to Auto Mode
Figure 8-9 Spread Spectrum Disabled in
Transition from Auto Mode to FPWM ModeTo enter the SYNC Mode, the valid synchronization signal must be present for 2048 cycles.
If MODE/SYNC voltage becomes constant longer than tMODE, the LM62345-Q1 enters either Auto mode or FPWM mode. At this time, spread spectrum is turned on and MODE/SYNC operates in Pulse-Dependent mode.
Figure 8-10 Transition from SYNC Mode to
Auto Mode
Figure 8-11 Transition from SYNC Mode to
FPWM Mode