ZHCSCY3E October 2014 – October 2018 LM5160 , LM5160A
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 修订历史记录
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1
LM5160 Synchronous Buck (10-V to 60-V Input, 5-V Output, 1.5-A Load)
- 8.2.1.1 Design Requirements
- 8.2.1.2
Detailed Design Procedure
- 8.2.1.2.1 Custom Design With WEBENCH® Tools
- 8.2.1.2.2 Feedback Resistor Divider - RFB1, RFB2
- 8.2.1.2.3 Switching Frequency - RON
- 8.2.1.2.4 Inductor - L
- 8.2.1.2.5 Output Capacitor - COUT
- 8.2.1.2.6 Series Ripple Resistor - RESR
- 8.2.1.2.7 VCC and Bootstrap Capacitors - CVCC, CBST
- 8.2.1.2.8 Input Capacitor - CIN
- 8.2.1.2.9 Soft-Start Capacitor - CSS
- 8.2.1.2.10 EN/UVLO Resistors - RUV1, RUV2
- 8.2.1.3 Application Curves
- 8.2.2 LM5160 Isolated Fly-Buck (18-V to 32-V Input, 12-V, 4.5-W Isolated Output)
- 8.2.3 LM5160A Isolated Fly-Buck (18-V to 32-V Input, 12-V, 4.5-W Isolated Output)
- 8.2.1
LM5160 Synchronous Buck (10-V to 60-V Input, 5-V Output, 1.5-A Load)
- 8.3 Do's and Don'ts
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文档支持
- 12机械、封装和可订购信息
8.1.1 Ripple Configuration
The LM5160 uses an adaptive constant on-time (COT) control scheme in which the PWM on-time is set by a one-shot timer and the off-time is set by the feedback voltage (VFB) falling below the reference voltage. Therefore, for stable operation, the feedback voltage must decrease monotonically in phase with the inductor current during the off-time. Furthermore, this change in feedback voltage (VFB) during the off-time must be large enough to dominate any noise present at the feedback node.
Table 3 presents three different methods for generating appropriate voltage ripple at the feedback node. Type 1 and Type 2 ripple circuits couple the ripple from the output of the converter to the feedback node (FB). The output voltage ripple has two components:
- Capacitive ripple caused by the inductor ripple current charging or discharging the output capacitor.
- Resistive ripple caused by the inductor ripple current flowing through the ESR of the output capacitor and R3.
Table 3. Ripple Configurations
| TYPE 1 | TYPE 2 | TYPE 3 |
|---|---|---|
| Lowest Cost | Reduced Ripple | Minimum Ripple |
 |
 |
 |
|
Equation 6.
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Equation 7.
 |
Equation 8.
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The capacitive ripple is out-of-phase with the inductor current. As a result, the capacitive ripple does not decrease monotonically during the off-time. The resistive ripple is in phase with the inductor current and decreases monotonically during the off-time. The resistive ripple must exceed the capacitive ripple at output (VOUT) for stable operation. If this condition is not satisfied, unstable switching behavior is observed in COT converters with multiple on-time bursts in close succession followed by a long off-time.
Type 3 ripple method uses a ripple injection circuit with RA, CA and the switch-node (SW) voltage to generate a triangular ramp. This ramp is then AC-coupled into the feedback node (FB) using coupling capacitor CB. Because this circuit does not use the output voltage ripple, it is suited for applications where low output voltage ripple is imperative. For more information on each ripple generation method, refer to the AN-1481 Controlling Output Ripple & Achiev ESR Indep Constant On-Time Regulator Designs application note.