Controlled transient responses in four-switch buck boost power stages
Four-switch buck boost power stages with reduced overshoot conditions at an output node are presented. Based on a detected condition for a decrease in a quantity of the active load elements, the method includes enabling an active discharge circuit coupled to an output node of a power stage before the quantity of the active load elements is decreased. Based on a detected condition for an increase in the quantity of the active load elements, the method includes activating the load elements and applying a restricted gain to the voltage conversion circuit.
1 . A method, comprising:
obtaining a request for a change in a quantity of active load elements at an output node supplied by a voltage conversion circuit;
based on the request indicating a decrease in the quantity of the active load elements, enabling an active discharge circuit coupled to the output node before the quantity of the active load elements is decreased; and
based on the request indicating an increase in the quantity of the active load elements, activating the load elements, applying a linear gain increase to the voltage conversion circuit for a first amount of time, and applying a constant gain to the voltage conversion circuit for a second amount of time.
2 . The method of claim 1 , wherein enabling the active discharge circuit comprises disabling switching elements of the voltage conversion circuit and activating a discharge transistor coupled to the output node that reduces charge stored at the output node.
3 . The method of claim 2 , further comprising, responsive to the active discharge circuit reaching a discharge setpoint voltage at the output node, decreasing the quantity of the active load elements and deactivating the discharge transistor.
4 . The method of claim 3 , further comprising:
retrieving an indication of the discharge setpoint voltage from a programmable register.
5 . The method of claim 2 , wherein enabling the active discharge circuit further comprises placing the switching elements of the voltage conversion circuit into high impedance states.
6 . The method of claim 1 , further comprising, after applying the constant gain for the second amount of time, returning the voltage conversion circuit to a load regulation operation for the output node.
7 . The method of claim 1 , further comprising:
retrieving indications of the first amount of time, the second amount of time, and the linear gain increase from a programmable register.
8 . The method of claim 1 , further comprising:
based on the request indicating the decrease in the quantity of the active load elements, causing the voltage conversion circuit to supply a reduced voltage at the output node; and
based on the request indicating the increase in the quantity of the active load elements, causing the voltage conversion circuit to supply an increased voltage at the output node.
9 . An apparatus, comprising:
a power controller configurable to obtain a request for a change in a quantity of active load elements at an output node supplied by a voltage conversion circuit; and
a transient control circuit configurable to:
based on the request indicating a decrease in the quantity of the active load elements, enable an active discharge circuit coupled to the output node before the quantity of the active load elements is decreased; and
based on the request indicating an increase in the quantity of the active load elements, activate the load elements, apply a linear gain increase for a first amount of time, and apply a constant gain for a second amount of time.
10 . The apparatus of claim 9 , wherein to enable the active discharge circuit, the transient control circuit is configurable to disable switching elements of the voltage conversion circuit and activate a discharge transistor coupled to the output node that reduces charge stored at the output node.
11 . The apparatus of claim 10 , wherein the transient control circuit is configurable to disable the active discharge circuit responsive to reaching a discharge setpoint voltage at the output node.
12 . The apparatus of claim 11 , further comprising:
a programmable register configurable to store an indication of the discharge setpoint voltage.
13 . The apparatus of claim 9 , wherein the transient control circuit is configurable to:
apply the linear gain increase by at least indicating to the power controller to apply the linear gain increase to the voltage conversion circuit for the first amount of time; and
apply the constant gain by at least indicating to the power controller to apply the constant gain to the voltage conversion circuit for the second amount of time.
14 . The apparatus of claim 9 , wherein after applying the constant gain for the second amount of time, the power controller is configurable to return the voltage conversion circuit to a load regulation operation for the output node.
15 . The apparatus of claim 9 , further comprising:
programmable registers configurable to store indications of the first amount of time, the second amount of time, and the linear gain increase.
16 . The apparatus of claim 9 , wherein the power controller is configurable to cause the voltage conversion circuit to supply a reduced voltage at the output node based on the request indicating the decrease in the quantity of the active load elements; and
wherein the power controller is configurable to cause the voltage conversion circuit to supply an increased voltage at the output node based on the request indicating the increase in the quantity of the active load elements.
17 . The apparatus of claim 9 , wherein the quantity of the active load elements comprise a set of light-emitting diodes (LEDs) coupled in series at the output node; and
wherein the power controller is configurable to decrease the quantity of the active load elements by at least establishing a low resistance path across a portion of the set.
18 . A system, comprising:
a power controller configurable to provide control signals for a voltage conversion unit providing power to an output node; and
an active discharge circuit coupled to the output node and comprising a selectable discharge connection to ground;
wherein the power controller is configurable to:
enable the active discharge circuit prior to a decrease in a quantity of activated load elements at the output node; and
increase the quantity of the activated load elements at the output node;
apply a linear gain increase to the voltage conversion unit for a first amount of time; and
apply a constant gain to the voltage conversion unit for a second amount of time.
19 . The system of claim 18 , wherein the power controller is configurable to:
disable the voltage conversion unit when enabling the active discharge circuit;
enable the voltage conversion unit when disabling the active discharge circuit responsive to reaching a discharge setpoint voltage at the output node;
apply the linear gain increase for the first amount of time;
apply the constant gain for the second amount of time; and
return to a load regulation operation for the output node after the second amount of time.
20 . The system of claim 18 , wherein the power controller is configurable to disable the active discharge circuit responsive to reaching a discharge setpoint voltage at the output node.