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EP-4376299-B1 - A CONTROL CIRCUIT FOR AN OUTPUT DRIVER WITH A SLEW RATE CONTROL CIRCUIT AND AN OUTPUT DRIVER COMPRISING THE SAME

EP4376299B1EP 4376299 B1EP4376299 B1EP 4376299B1EP-4376299-B1

Inventors

  • Asam, Geethanadh
  • PANDYA, KEYUR

Dates

Publication Date
20260506
Application Date
20221125

Claims (11)

  1. A control circuit (30) for an output driver (31) with a slew rate control circuit (32), comprising: - a turn-on facilitating module (410) having a control input and configured to be connected to the output driver and to supply a supplementary voltage to the output driver in response to a control voltage at the control input; and - a sensing module (420) configured to be connected to the turn-on facilitating module (410) and the output driver (31) and to switch off the turn-on facilitating module (410) in response to an input voltage of the output driver (31) sensed by the sensing module (420); wherein the turn-on facilitating module (410) comprises a turn-on path configured to be connected to an input terminal of the output driver (31) and to connect a supply voltage to the input terminal of the output driver (31) in response to the control voltage, and wherein the turn-on path comprises a first switch (MP2) and a second switch (MP1) connected in series, with an enable terminal of the first switch (MP2) coupled to the control voltage, and an enable terminal of the second switch (MP1) coupled to the supply voltage and an output terminal of the sensing module (420), with an output terminal of the second switch (MP1) configured to be connected to the input terminal of the output driver (31), wherein the first switch comprises a first PMOS transistor and the second switch comprises a second PMOS transistor, a source of the first PMOS transistor is coupled to the supply voltage and a drain of the first PMOS transistor is coupled to a source of the second PMOS transistor, characterised in that a drain of the second switch is configured to be connected to the input terminal of the output driver via a limiting resistor (R limit ) comprised in the control circuit and having a first terminal connectable to the input terminal of the output driver (31) and a second terminal coupled to the turn-on facilitating module (410) and the sensing module (420).
  2. The control circuit according to claim 1, wherein a gate of the first PMOS transistor (MP2) is coupled to the control voltage via a first inverter (INV1), a gate of the second PMOS transistor (MP1) is coupled to the supply voltage via a second inverter (INV2) and a feedback resistor (R FB ) connected in series.
  3. The control circuit according to claim 1 or 2, wherein the sensing module (420) comprises a third switch configured to have its input terminal connected to the input terminal of the output driver (31) via the limiting resistor and an output terminal coupled to the supply voltage and the enable terminal of the second switch.
  4. The control circuit according to claim 3, wherein the third switch comprises a first NMOS transistor (MN1), a source of the first NMOS transistor (MN1) is connected to the control voltage via a second NMOS transistor (MN2).
  5. The control circuit according to claim 4, wherein a source of the second NMOS transistor (MN2) is coupled to GND and a gate of the second NMOS transistor (MN2) is coupled to the control voltage.
  6. The control circuit according to claim 3 or 4, wherein the output terminal of the first NMOS transistor (MN1) is coupled to a node between the second inverter (INV2) and the feedback resistor (R FB ).
  7. The control circuit according to claim 3, wherein the second terminal of the limiting resistor (R limit ) is coupled to the source of the second switch (MP1) and the input terminal of the third switch.
  8. The control circuit according to claim 7, wherein the limiting resistor (R limit ) has a resistance in a range of 200 Ohm to 600 Ohm.
  9. An output driver comprising a slew rate control circuit and the control circuit for the slew rate control circuit according to any of the previous claims 1 to 8.
  10. The output driver according to claim 9, comprising an open drain output driver.
  11. The output driver according to claim 9, comprising a push pull driver.

Description

Technical Field The present disclosure generally relates to an output driver, more particularly, to a control circuit for an output driver with a slew rate control circuit as outlined in the preamble of claim 1. Background An output driver is a circuit for driving an output pad to which a predetermined load is connected in order to output a data from a semiconductor device. A push-pull type driver is known as a widely used output driver, and a slew rate control circuit is generally used in connection with the driver for controlling an output slew rate of the driver. The slew rate shows how fast voltage level of an output signal changes. The slew rate is defined as a slope showing a ratio between a voltage level change and a unit time. Applications like Inter-Integrated Circuit, I2C, Electromagnetic Interference, EMI, effected circuits require slow transition output signals to minimize EMI to meet the standard requirements for rise/fall times. For such applications it is necessary to limit rise and fall times of the output in a controlled manner. A conventionally known typical slew rate control circuit controls the output slew rate by injecting a well-defined current into the driver. This current is always a well-controlled current and involves large turn on time. US 2010/176783A1 discloses a switching device drive circuit for receiving a pulse signal, and outputting a drive signal to a control terminal of a switching device including a power converting circuit for a predetermined period corresponding to the pulse signal, and a control circuit for changing a voltage supplied or a current flowing, as a drive signal, to or through the control terminal of the switching device, to a voltage or a current different from a predetermined voltage or a predetermined current; and a control voltage detecting circuit for detecting a voltage of the control terminal of the switching device. US 10790818 B1 discloses a A gate driver circuit includes a first power supply rail providing a first fixed supply voltage; a second power supply rail providing a second fixed supply voltage; a transistor including a gate terminal having a gate voltage; and a gate driver integrated circuit (IC) supplied with the first fixed supply voltage and the second fixed supply voltage, the gate driver IC including an output terminal configured to provide a gate drive voltage at the output terminal in order to drive the transistor between switching states. US 2006/119326 A1 discloses a switching voltage regulator includes a switching transistor connected to conduct a current between a supply voltage and a first node in response to a control signal which cycles the transistor on and off, and a pre-driver circuit which provides the control signal. US 2021/336611 A1 discloses slew-rate controlled drivers. For slew rate control circuit applications requiring small latency while meeting slew rate requirements, it is desired that the turn on time may be shortened. In consideration of the above, it is desirable that the turn on time of an output driver with a slew rate control circuit may be improved, without impacting the slew rate. Summary In a first aspect of the present disclosure, there is presented a control circuit for an output driver with a slew rate control circuit as defined in the characterizing part of claim 1. The control circuit comprises: a turn-on facilitating module having a control input and configured to be connected to the output driver and to supply a supplementary voltage to the output driver in response to a control voltage at the control input; anda sensing module configured to be connected to the turn-on facilitating module and the output driver and to switch off the turn-on facilitating module in response to an input voltage of the output driver sensed by the sensing module. The present disclosure is based on the insight that the turn-on time of an output driver can be reduced or shortened by supplying a supplementary voltage to the output driver by way of a turn-on facilitating module. The supplementary voltage is supplied in addition to a current injected by a slew rate control circuit for turning on the output driver. The supplementary voltage in combination with the current injected by the slew rate control circuit ensures the turning on of the output driver in a short amount of time. The time required to turn on the output driver by for example charging a gate of a transistor functioning as the output driver is not dependent on a bias current used during the subsequent slew rate period. The turn-on facilitating module operates only during a turn-on period of the output driver. Therefore, a sensing module is configured to switch off the turn-on facilitating module by sensing an input voltage of the output driver. Once the input voltage reaches a threshold value, the turn-on facilitating module is switched off, ensuring that the slew rate period remains unimpacted. According to the invention, the turn-on facilitating module c