ZHCSPF6B february 2022 – may 2023 LMQ66410 , LMQ66420 , LMQ66430
PRODUCTION DATA
- 1
- 1 特性
- 2 應用
- 3 說明
- 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 Enable, Start-Up, and Shutdown
- 8.3.2 Adjustable Switching Frequency (with RT)
- 8.3.3 Power-Good Output Operation
- 8.3.4 Internal LDO, VCC, and VOUT/FB Input
- 8.3.5 Bootstrap Voltage and VBOOT-UVLO (BOOT Terminal)
- 8.3.6 Output Voltage Selection
- 8.3.7 Spread Spectrum
- 8.3.8 Soft Start and Recovery from Dropout
- 8.3.9 Current Limit and Short Circuit
- 8.3.10 Thermal Shutdown
- 8.3.11 Input Supply Current
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Application
- 9.2.1 Synchronous Buck Regulator at 400 kHz
- 9.2.2 Design Requirements
- 9.2.3 Detailed Design Procedure
- 9.2.4 Application Curves
- 9.3 Best Design Practices
- 9.4 Power Supply Recommendations
- 9.5 Layout
- 10Device and Documentation Support
- 11Mechanical, Packaging, and Orderable Information
封裝選項
機械數(shù)據(jù) (封裝 | 引腳)
- RXB|14
散熱焊盤機械數(shù)據(jù) (封裝 | 引腳)
訂購信息
8.3.9 Current Limit and Short Circuit
The device is protected from over current conditions by cycle-by-cycle current limiting on both high-side and low-side MOSFETs. High-side MOSFET over current protection is implemented by the typical peak-current mode control scheme. The HS switch current is sensed when the HS is turned on after a short blanking time. The HS switch current is compared to either the minimum of a fixed current set point or the output of the internal error amplifier loop minus the slope compensation every switching cycle. Because the output of the internal error amplifier loop has a maximum value and slope compensation increases with duty cycle, HS current limit decreases with increased duty factor if duty factor is typically above 35%.
When the LS switch is turned on, the current going through it is also sensed and monitored. Like the high-side device, the low-side device has a turn-off commanded by the internal error amplifier loop. In the case of the low-side device, turn-off is prevented if the current exceeds this value, even if the oscillator normally starts a new switching cycle. Also like the high-side device, there is a limit on how high the turn-off current is allowed to be. This is called the low-side current limit, IVALMAX in Figure 8-10. If the LS current limit is exceeded, the LS MOSFET stays on and the HS switch is not to be turned on. The LS switch is turned off after the LS current falls below this limit and the HS switch is turned on again as long as at least one clock period has passed since the last time the HS device has turned on.
Figure 8-10 Current Limit
WaveformsBecause the current waveform assumes values between IPEAKMAX and IVALMAX, the maximum output current is very close to the average of these two values unless duty factor is very high. After operating in current limit, hysteretic control is used and current does not increase as output voltage approaches zero.
The LMQ664x0 employs hiccup over current protection if there is an extreme overload, and the following conditions are met:
- Output voltage is below approximately 0.4 times the output voltage set point.
- Greater than tSS has passed since soft start has started.
- The part is not operating in dropout, which is defined as having a minimum off time controlled duty cycle.
In hiccup mode, the device shuts itself down and attempts to soft start after tHICCUP. Hiccup mode helps reduce the device power dissipation under severe over current conditions and short circuits. See Figure 8-11.
After the overload is removed, the device recovers as though in soft start; see Figure 8-12.
Figure 8-11 Hiccup Entry
Figure 8-12 Hiccup Exit