ZHCSLO0 数据表 | 德州仪器 TI.com.cn

ZHCSLO0B April 2023 – October 2023 TPS62874-Q1 , TPS62875-Q1 , TPS62876-Q1 , TPS62877-Q1

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RZV|24
- MPQF690A

散热焊盘机械数据 (封装 | 引脚)

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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-CCM)

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.

Figure 8-2 Continuous Conduction Mode (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.

Figure 8-3 Discontinuous Conduction Mode (DCM) 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 in order to regulate the output (see Figure 8-4). The switching pulses that occur during PFM-DCM operation are synchronized to the internal clock

Figure 8-4 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.

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 2.25 MHz

Figure 8-5 Output Current PFM-DCM Entry Threshold for f_SW = 2.25 MHz

You 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. 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