米6体育平台手机版

ZHCSNZ3B January 2023 – May 2024 TPS62870 , TPS62871 , TPS62872 , TPS62873

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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

8.3.2 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 8-2). PWM operation achieves the lowest output voltage ripple and the best transient performance.

TPS62870 TPS62871 TPS62872 TPS62873 Continuous Conduction Mode (PWM-CCM) Current Waveform

Figure 8-2 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 8-3). In this mode, the device controls the peak inductor current to maintain the selected switching frequency while still being able to regulate the output.

TPS62870 TPS62871 TPS62872 TPS62873 Discontinuous Conduction Mode (PWM-DCM) Current Waveform

Figure 8-3 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 8-4). The switching pulses that occur during PFM-DCM operation are synchronized to the internal clock.

TPS62870 TPS62871 TPS62872 TPS62873 Discontinuous Conduction Mode (PFM-DCM) Current Waveform

Figure 8-4 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 7-5 shows the maximum switching frequency with 3.3V and 5.5V 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 8-5 shows how this threshold typically varies with V_IN and V_OUT for a switching frequency of 2.25MHz.

TPS62870 TPS62871 TPS62872 TPS62873 Output Current PFM-DCM Entry Threshold

Figure 8-5 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 8-1 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 8-1 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