ZHCSQI6A May   2022  – July 2022

PRODUCTION DATA

1. 特性
2. 应用
3. 说明
4. Revision History
5. 说明（续）
6. Device Options
7. Pin Configuration and Functions
8. Specifications
9. Detailed Description
1. 9.1 Overview
2. 9.2 Functional Block Diagram
3. 9.3 Feature Description
4. 9.4 Device Functional Modes
5. 9.5 Programming
6. 9.6 Register Map
10. 10Application and Implementation
1. 10.1 Application Information
2. 10.2 Typical Application
3. 10.3 Best Design Practices
4. 10.4 Power Supply Recommendations
5. 10.5 Layout
11. 11Device and Documentation Support
1. 11.1 Device Support
2. 11.2 Documentation Support
3. 11.3 接收文档更新通知
4. 11.4 支持资源
6. 11.6 Electrostatic Discharge Caution
7. 11.7 术语表
12. 12Mechanical, Packaging, and Orderable Information

• RXS|16

### 9.3.2 Forced PWM and Power Save Modes

The device can control the inductor current in three different ways to regulate the output:

• Pulse-width modulation with continuous inductor current (PWM-CCM)
• Pulse-width modulation with discontinuous inductor current (PWM-DCM)
• Pulse-frequency modulation with discontinuous inductor current and pulse skipping (PFM-DCM)

During PWM-CCM operation, the device switches at a constant frequency and the inductor current is continuous (see Figure 9-2). PWM operation achieves the lowest output voltage ripple and the best transient performance.

Figure 9-2 Continuous Conduction Mode (PWM-CCM) Current Waveform

During PWM-DCM operation, the device switches at a constant frequency and the inductor current is discontinuous (see Figure 9-3). In this mode, the device controls the peak inductor current to maintain the selected switching frequency while still being able to regulate the output.

Figure 9-3 Discontinuous Conduction Mode (PWM-DCM) Current Waveform

During PFM-DCM operation, the device keeps the peak inductor current constant (at a level corresponding to the minimum on time of the converter) and skips pulses to regulate the output (see Figure 9-4). The switching pulses that occur during PFM-DCM operation are synchronized to the internal clock.

Figure 9-4 Discontinuous Conduction Mode (PFM-DCM) Current Waveform

Use Equation 1 to calculate the output current threshold at which the device enters PFM-DCM.

Equation 1. ${\mathrm{I}}_{\mathrm{O}\mathrm{U}\mathrm{T}\left(\mathrm{P}\mathrm{F}\mathrm{M}\right)}=\frac{\left({\mathrm{V}}_{\mathrm{I}\mathrm{N}}–{\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}\right)}{2\mathrm{L}}{{\mathrm{t}}_{\mathrm{O}\mathrm{N}}}^{2}\left(\frac{{\mathrm{V}}_{\mathrm{I}\mathrm{N}}}{{\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}}\right){\mathrm{f}}_{\mathrm{s}\mathrm{w}}$

Figure 9-5 shows how this threshold typically varies with VIN and VOUT for a switching frequency of 2.25 MHz.

Figure 9-5 Output Current PFM-DCM Entry Threshold
The user can configure the device to use either forced PWM (FPWM) mode or power save mode (PSM):
• In forced PWM mode, the device uses PWM-CCM at all times.
• In power save mode, the device uses PWM-CCM at medium and high loads, PWM-DCM at low loads, and PFM-DCM at very low loads. The transition between the different operating modes is seamless.

Table 9-1 shows the function table of the MODE/SYNC pin and the FPWMEN bit in the CONTROL1 register, which control the operating mode of the device.

Table 9-1 FPWM Mode and Power-Save Mode Selection
MODE/SYNC Pin FPWMEN Bit Operating Mode Remark
Low 0 PSM Do not use in a stacked configuration.
1 FPWM
High X FPWM
Sync Clock X FPWM
Note: If spread-spectrum clocking is enabled, the device automatically operates in FPWM, regardless of the state of FPWMEN bit in the CONTROL1 register (see Section 9.3.9).