米6体育平台手机版

ZHCSQI6C May 2022 – October 2023 TPS62870-Q1 , TPS62871-Q1 , TPS62872-Q1 , TPS62873-Q1

PRODUCTION DATA

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机械数据 (封装 | 引脚)

RXS|16
- MPQF606D

散热焊盘机械数据 (封装 | 引脚)

订购信息

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

For very small output voltages, an absolute minimum on time of approximately 50 ns reduces the switching frequency from the set value. Figure 8-5 shows the maximum switching frequency with 3.3-V and 5.5-V supplies.

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

Equation 1.

I_{O U T (P F M)} = \frac{(V_{I N} - V_{O U T})}{2 L} {t_{O N}}^{2} (\frac{V_{I N}}{V_{O U T}}) f_{s w}

Figure 9-5 shows how this threshold typically varies with V_IN and V_OUT 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.
Low	1	FPWM
High	X	FPWM
Sync Clock	X	FPWM