ZHCSLU1B October 2022 – August 2024 LM64440-Q1 , LM64460-Q1
PRODUCTION DATA
- 1
- 1 特性
- 2 应用
- 3 说明
- 4 Device Comparison Table
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3
Feature Description
- 7.3.1 Input Voltage Range (VIN1, VIN2)
- 7.3.2 Output Voltage Setpoint (FB)
- 7.3.3 Precision Enable and Input Voltage UVLO (EN)
- 7.3.4 MODE/SYNC Operation
- 7.3.5 Clock Locking
- 7.3.6 Power-Good Monitor (PGOOD)
- 7.3.7 Bias Supply Regulator (VCC, BIAS)
- 7.3.8 Bootstrap Voltage and UVLO (CBOOT)
- 7.3.9 Spread Spectrum
- 7.3.10 Soft Start and Recovery From Dropout
- 7.3.11 Overcurrent and Short-Circuit Protection
- 7.3.12 Thermal Shutdown
- 7.3.13 Input Supply Current
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1 Design 1 – Automotive Synchronous 6A Buck Regulator at 2.1MHz
- 8.2.2
Design 2 – Automotive Synchronous 4A Buck Regulator at 2.1MHz
- 8.2.2.1 Design Requirements
- 8.2.2.2
Detailed Design Procedure
- 8.2.2.2.1 Custom Design With WEBENCH® Tools
- 8.2.2.2.2 Setting the Output Voltage
- 8.2.2.2.3 Choosing the Switching Frequency
- 8.2.2.2.4 Inductor Selection
- 8.2.2.2.5 Output Capacitor Selection
- 8.2.2.2.6 Input Capacitor Selection
- 8.2.2.2.7 Bootstrap Capacitor
- 8.2.2.2.8 VCC Capacitor
- 8.2.2.2.9 BIAS Power Connection
- 8.2.2.2.10 Feedforward Network
- 8.2.2.2.11 Input Voltage UVLO
- 8.2.2.3 Application Curves
- 8.3 Power Supply Recommendations
- 8.4 Layout
- 9 Device and Documentation Support
- 10Revision History
- 11Mechanical, Packaging, and Orderable Information
7.3.4.2 Pulse-Dependent MODE/SYNC Control
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.
Figure 7-3 Transition from FPWM Mode to Pulse-Dependent Control
Figure 7-4 Transition from AUTO Mode to Pulse-Dependent
ControlAfter 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.
Figure 7-5 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. 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.
Figure 7-6 Spread Spectrum Disabled in FPWM Mode
Figure 7-7 Spread Spectrum Disabled in AUTO Mode
Figure 7-8 Spread Spectrum Disabled in Transition from
FPWM Mode to AUTO Mode
Figure 7-9 Spread Spectrum Disabled in Transition from
AUTO Mode to FPWM ModeTo 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.
Figure 7-10 Transition from SYNC Mode to AUTO Mode
Figure 7-11 Transition from SYNC Mode to FPWM Mode