Fast detection and discharge for charge pump controller
Circuits and methods that can rapidly detect voltage degradation in a positive charge pump output and discharge control node accumulated charge (CNAC), thereby forcing the positive charge pump into a high-power mode. Embodiments include circuitry configured to provide a load current to a positive charge pump, including a low-dropout regulator (LDO) having a pass device that includes a control input, and a rapid charge transfer circuit coupled to the control input of the pass device and configured to be coupled to a source of a trigger voltage, the rapid charge transfer circuit configured to transfer a charge to or from the control input of the pass device when the trigger voltage falls sufficiently below a specified level so as to rapidly place the pass device in a higher conduction state, and to automatically cease to provide the transfer the charge after a settable amount of time.
1 . An improved circuit configured to provide a load current to a positive charge pump, including:
(a) a low-dropout regulator (LDO) having a pass device that includes a control input; and
(b) a rapid charge transfer circuit coupled to the control input of the pass device and configured to be coupled to a source of a trigger voltage derived from the output of the positive charge pump, the rapid charge transfer circuit configured (1) to electrically connect the control input of the pass device to one of a voltage source or circuit ground so as to enable transfer a charge to or from the control input of the pass device when the trigger voltage falls sufficiently below a specified level so as to rapidly place the pass device in a higher conduction state, and (2) to automatically cease to transfer the charge after a settable amount of time.
2 . The improved circuit of claim 1 , wherein the pass device is a P-type MOSFET and the control input is the gate of the P-type MOSFET.
3 . The improved circuit of claim 1 , wherein the pass device is an N-type MOSFET and the control input is the gate of the N-type MOSFET.
4 . The improved circuit of claim 1 , wherein the rapid charge transfer circuit includes a transient coupling circuit coupled to the source of the trigger voltage.
5 . The improved circuit of claim 4 , wherein the transient coupling circuit includes a high-pass filter.
6 . The improved circuit of claim 1 , wherein the rapid charge transfer circuit includes a high-pass filter having a capacitor coupled between the source of the trigger voltage and a node, and a resistor coupled between the node and a supply voltage.
7 . The improved circuit of claim 6 , wherein the settable amount of time is set by an RC time constant of the high-pass filter.
8 . The improved circuit of claim 1 , wherein the LDO includes a compensation circuit coupled to the control input of the pass device.
9 . An improved circuit configured to provide a load current to a positive charge pump, including:
(1) a low-dropout regulator (LDO) having a PFET pass device that includes a control input; and
(2) a rapid charge transfer circuit coupled to the control input of the pass device and configured to be coupled to a source of a trigger voltage derived from the output of the positive charge pump, the rapid charge transfer circuit configured to transfer a charge to or from the control input of the pass device when the trigger voltage falls sufficiently below a specified level so as to rapidly place the pass device in a higher conduction state, and to automatically cease to transfer the charge after a settable amount of time, wherein the rapid charge transfer circuit includes:
(a) a high-pass filter coupled between the source of the trigger voltage and a supply voltage; and
(b) a P-type MOSFET including a source coupled to the supply voltage, a gate coupled to the high-pass filter, and a drain; and
(c) a current mirror including an input coupled to the drain of the P-type MOSFET and an output coupled to the control input of the pass device.
10 . The improved circuit of claim 9 , wherein the high-pass filter includes a capacitor coupled between the source of the trigger voltage and a node, and a resistor coupled between the node and the supply voltage.
11 . The improved circuit of claim 10 , wherein the gate of the P-type MOSFET is coupled to the node of the high-pass filter.
12 . The improved circuit of claim 9 , further including a clamp circuit coupled to the supply voltage and coupled between the high-pass filter and the gate of the P-type MOSFET.
13 . The improved circuit of claim 9 , wherein the current mirror includes an input FET coupled to the drain of the P-type MOSFET, and an output FET coupled to the control input of the pass device, wherein the gates of the input FET and the output FET are connected.
14 . The improved circuit of claim 13 , wherein the input FET and the output FET are N-type MOSFETs.
15 . An improved circuit configured to provide a load current to a positive charge pump, including:
(1) a low-dropout regulator (LDO) having an NFET pass device that includes a control input; and
(2) a rapid charge transfer circuit coupled to the control input of the pass device and configured to be coupled to a source of a trigger voltage derived from the output of the positive charge pump, the rapid charge transfer circuit configured to transfer a charge to or from the control input of the pass device when the trigger voltage falls sufficiently below a specified level so as to rapidly place the pass device in a higher conduction state, and to automatically cease to transfer the charge after a settable amount of time, wherein the rapid charge transfer circuit includes:
(a) a high-pass filter coupled between the source of the trigger voltage and a supply voltage; and
(b) a P-type MOSFET including a source coupled to the supply voltage, a gate coupled to the high-pass filter, and a drain coupled to the control input of the pass device.
16 . The improved circuit of claim 15 , wherein the high-pass filter includes a capacitor coupled between the source of the trigger voltage and a node, and a resistor coupled between the node and the supply voltage.
17 . The improved circuit of claim 16 , wherein the gate of the P-type MOSFET is coupled to the node of the high-pass filter.
18 . The improved circuit of claim 15 , further including a clamp circuit coupled to the supply voltage and coupled between the high-pass filter and the gate of the P-type MOSFET.