ZHCSP81B January 2022 – September 2023 LMR38010
PRODUCTION DATA
- 1
- 1 特性
- 2 應(yīng)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 Fixed Frequency Peak Current Mode Control
- 8.3.2 Adjustable Output Voltage
- 8.3.3 Enable
- 8.3.4 Switching Frequency and Synchronization (RT/SYNC)
- 8.3.5 Power-Good Flag Output
- 8.3.6 Minimum On Time, Minimum Off Time, and Frequency Foldback
- 8.3.7 Bootstrap Voltage
- 8.3.8 Overcurrent and Short Circuit Protection
- 8.3.9 Soft Start
- 8.3.10 Thermal Shutdown
- 8.4 Device Functional Modes
- 9 Application and Implementation
- 10Device and Documentation Support
- 11Mechanical, Packaging, and Orderable Information
封裝選項(xiàng)
機(jī)械數(shù)據(jù) (封裝 | 引腳)
- DDA|8
散熱焊盤機(jī)械數(shù)據(jù) (封裝 | 引腳)
- DDA|8
訂購信息
8.3.4 Switching Frequency and Synchronization (RT/SYNC)
The switching frequency of the LMR38010 can be programmed by the resistor RT from the RT/SYNC pin and GND pin. The RT/SYNC pin cannot be left floating or shorted to ground. To determine the timing resistance for a given switching frequency, use Equation 2 or the curve in Figure 8-4. Table 8-1 gives typical RT values for a given fSW.
Figure 8-4 RT Versus Frequency
Curve| fSW (kHz) | RT (k?) |
|---|---|
| 200 | 133 |
| 400 | 64.9 |
| 500 | 52.3 |
| 750 | 34.8 |
| 1000 | 25.5 |
| 1500 | 16.9 |
| 2000 | 12.7 |
| 2200 | 11.5 |
The LMR38010 switching action can also be synchronized to an external clock from 300 kHz to 2.1 MHz. Connect a square wave to the RT/SYNC pin through either circuit network shown in Figure 8-5. The internal oscillator is synchronized by the falling edge of external clock. The recommendations for the external clock include: high level no lower than 2.0 V, low level no higher than 0.6 V, and have a pulse width greater than 50 ns. When using a low impedance signal source, the frequency setting resistor RT is connected in parallel with an AC coupling capacitor, CCOUP, to a termination resistor, RTERM (for example, 50 Ω). The two resistors in series provide the default frequency setting resistance when the signal source is turned off. A 10-pF ceramic capacitor can be used for CCOUP.
Figure 8-5 Synchronizing to an External Clock