米6体育平台手机版

ZHCSQ47 March 2022 LP8764-Q1

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RQK|32
- MPQF572A

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9.2.3 Voltage Scaling Precautions

Voltage scaling behavior depends on the set slew rate and output capacitance. Therefore there may be limitations on maximum capacitance with certain slew rate settings. Worst case over- and undershoot also depends on the phase margin of the buck converter. Good phase margin mitigates the over- and undershoot. Reducing the output voltage slew rate reduces the slew rate current thus reducing the worst case over- and undershoot.

Figure 9-7 Power stage

The following equations must be met to ensure the output voltage scaling with regulator switching frequency:

Equation 27.

I_{SR_vout} + I_{load_max} \leq I_{out_max}

Equation 28.

I_{out_min} \leq I_{load_min} - I_{SR_vout}

Where

I_{SR_vout} = {SR}_{Vout} C_{out}

Figure 9-8 Voltage ramp

The worst case overshoot can be calculated with the following equations.

Equation 29.

V_{overshoot} = \frac{t_{Iout_scale_down} I_{SR_vout}}{2 C_{out}}

Where $t_{Iout_scale_down} = \frac{I_{SR_vout}}{{SR}_{Iout_scale_down}}$ and ${SR}_{Iout_scale_down} = \frac{V_{out}}{L_{ind}}$ .

After substitutions

Equation 30.

V_{overshoot} = \frac{{SR}_{Vout}^{2} C_{out} L_{ind}}{2 V_{out}}

Figure 9-9 Overshoot

The worst case undershoot can be calculated with the following equations

Equation 31.

V_{undershoot} = \frac{t_{Iout_scale_up} I_{SR_vout}}{2 C_{out}}

Where $t_{Iout_scale_up} = \frac{I_{SR_vout}}{{SR}_{Iout_scale_up}}$ and ${SR}_{Iout_scale_up} = \frac{V_{in} - V_{out}}{L_{ind}}$ .

After substitutions

Equation 32.

V_{undershoot} = \frac{{SR}_{Vout}^{2} C_{out} L_{ind}}{2 (V_{in} - V_{out})}