Low-current compliance stack using nondeterministically biased Zener strings
AssigneeTexas Instruments Incorporated
InventorRoy Alan Hastings
Life of this patent
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Abstract
Systems and methods are provided for limiting voltage to low-voltage devices employing a high-voltage supply. The systems and methods employ voltage limiting devices to bias cascode devices. The cascode devices are serially connected from a high-voltage supply to a low-voltage node. The voltage limiters are serially connected from the high-voltage supply to ground to bias the cascode devices. Current sources are connected in parallel with the voltage limiters except the one connected to ground. If the current sources are set to deliver substantially equal currents, then the order in which the cascode transistors are biased becomes nondeterministic, but the circuit continues to finction and the overall supply current is thereby minimized.
Claims20
A system for limiting voltage to low-voltage devices employing a high-voltage supply, the system comprising:
- a first cascode device coupled to at least one low-voltage device;
- a first voltage limiter coupled to bias the first cascode device, so that the first cascode device provides a low voltage to the at least one low-voltage device;
- a second cascode device serially coupled between the first cascode device and the high-voltage supply;
- a second voltage limiter serially coupled to the first voltage limiter and coupled to the second cascode device;
- a third voltage limiter serially coupled between the second voltage limiter and the high-voltage supply;
- a first current source coupled in parallel with the second voltage limiter;
- and
- a second current source coupled in parallel with the third voltage limiter, the currents of the first and the second current sources being substantially equal.
A circuit for limiting voltage to low-voltage devices employing a high-voltage supply, the circuit comprising:
- a first cascode transistor coupled to at least one low-voltage device;
- a first Zener clamp consisting of a first plurality of serially connected Zener diodes coupled to a controlling terminal of the first cascode transistor;
- a second cascode transistor coupled between the first cascode transistor and the high-voltage supply;
- a second Zener clamp consisting of a second plurality of serially connected Zener diodes coupled between the controlling terminal of the first cascode transistor and a controlling terminal of the second cascode transistor;
- a third Zener clamp that couples the second Zener clamp to the high-voltage supply;
- a first current source coupled in parallel with the second Zener clamp;
- and
- a second current source coupled in parallel with the third Zener clamp, the currents of the first and the second current sources being substantially equal.
A method for providing a device that limits voltage to low-voltage devices in high-voltage applications, the method comprising:
- determining a number of cascode devices to provide a desired voltage drop between a high-voltage supply and at least one low-voltage device;
- determining a number of Zener clamps to bias the cascode devices;
- determining a minimum current required to bias a Zener clamp;
- and
- determining a number of current sources required to bias the Zener clamps.
Dependencies are inferred from the claim text.