Output circuit and microcomputer
AssigneeDenso Corporation
InventorsYoshimitsu Honda, Kouichi Maeda, Yoshinori Yunosawa, Kouji Ichikawa
Life of this patent
Estimating the term…
Abstract
When a control power source voltage becomes lower than an operation guarantee voltage level, the output of a start-up circuit assumes an H-level, a NOR gate produces an output shut-off signal of an L-level, and FETs are turned off. As the control power source voltage further decreases, the output shut-off control circuit loses stability in the operation. In this case, a resistor maintains the FETs in the OFF state due to its pull-down operation. As a result, the output of the output circuit is maintained in a high-impedance state over the whole range of control power source voltages lower than the operation guarantee voltage level.
Claims8
An output circuit which operates with a control power source voltage and produces a logic signal to an external circuit, the output circuit comprising:
- an output transistor configuration for allowing an electric current to flow to and from the external circuit;
- a logic circuit which supplies a drive control signal necessary for producing the logic signal to the control signal input terminal of the output transistor configuration;
- an output shut-off control circuit, provided in a passage for transmitting the drive control signal to the control signal input terminal of the output transistor configuration in the logic circuit, for producing an output shut-off signal for turning off the output transistor configuration instead of producing the drive control signal when the control power source voltage is at least lower than an operation guarantee voltage level at which the logic circuit normally executes the logic operation;
- and
- a resistance element connected between the control signal input terminal of the output transistor configuration and a control signal reference terminal, and having a resistance capable of maintaining the output transistor configuration in an OFF state when the output shut-off control circuit is incapable of producing the output shut-off signal due to a drop in the control power source voltage.
Dependencies are inferred from the claim text.