ZHCSJ24A November 2018 – May 2019 TPS56339
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
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3
Feature Description
- 7.3.1 Advanced Emulated Current Mode Control
- 7.3.2 Enable and Adjusting Undervoltage Lockout
- 7.3.3 Soft Start and Pre-Biased Soft Start
- 7.3.4 Voltage Reference
- 7.3.5 Minimum ON-time, Minimum OFF-time and Frequency Foldback at Dropout Conditions
- 7.3.6 Overcurrent and Undervoltage Protection
- 7.3.7 Thermal Shutdown
- 7.4 Device Functional Modes
- 7.5 Light-Load Operation
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文档支持
- 12机械、封装和可订购信息
8.2.2.4 Output Capacitor Selection
After selecting the inductor, the output capacitor needs to be optimized. The LC filter used as the output filter has double pole at:
At low frequencies, the overall loop gain is set by the output set-point resistor divider network and the internal gain of the device. The low frequency phase is 180°. At the output filter pole frequency, the gain rolls off at a –40 dB per decade rate and the phase drops rapidly. A high frequency zero introduced by internal circuit that reduces the gain roll off to –20 dB per decade and increases the phase to 90° one decade above the zero frequency. The inductor and capacitor for the output filter must be selected so that the double pole of Equation 14 is located below the high frequency zero but close enough that the phase boost provided be the high frequency zero provides adequate phase margin for a stable circuit. To meet this requirement, make sure that the L1·COUT_E value meets the range of L1·COUT_E value recommended in Table 2.
Table 2. Recommended Component Values
| OUTPUT VOLTAGE(1)
(V) |
R6(2)
(kΩ) |
R7
(kΩ) |
L1(3)
(µH) |
COUT(4)
(µF) |
Range of L1·COUT_E(5)
(μH×μF) |
|---|---|---|---|---|---|
| 1.05 | 3.16 | 10.0 | 1.5 | 2×22 | 48 to 188 |
| 1.8 | 12.4 | 10.0 | 2.2 | 2×22 | 64 to 250 |
| 2.5 | 21.5 | 10.0 | 3.3 | 2×22 | 87 to 334 |
| 3.3 | 31.6 | 10.0 | 4.7 | 2×22 | 107 to 404 |
| 5 | 52.3 | 10.0 | 5.6 | 2×22 | 93 to 334 |
| 12 | 140 | 10.0 | 6.8 | 3×22 | 45 to 137 |
The capacitor value and ESR determines the amount of output voltage ripple. TheTPS56339 is intended for use with ceramic or other low ESR capacitors. Use Equation 15 to determine the required RMS current rating for the output capacitor.
For this design two Murata GRM21BR61C226ME44 22-uF, 0805, 16-V output capacitors are used. From the data sheet the estimated DC derating of 51.8% at room temperature with AC voltage of 0.2V. The total output effective capacitance is approximately 22.8 μF. The value of L1·COUT_E is 127.7 μH×μF, which is within the recommended range.