In case your circuit design has necessities to be tolerant to sure faults and to report their prevalence, you’ll want to check the fault detection and safety options of your design in the course of the take a look at and bring-up course of. To make this testing simpler, take into account constructing fault-injection fixtures and reporting functionality into the prototype printed circuit board.
Overvoltage and undervoltage monitoring
You possibly can construct circuitry into your design to pressure an overvoltage or undervoltage occasion for a voltage supervisor to detect. For an influence provide with a digital interface, you could want solely to reveal the communication pins. For an influence provide with no digital interface, you would wish to reveal the suggestions pin.
A easy approach to modulate the output voltage is to inject present into the suggestions node, thereby artificially miserable the output voltage. It’s a lot simpler to design this circuit into the PCB than including it to the constructed PCB. Determine 1 is an instance of any such circuit design for the TPS628502-Q1 automotive step-down converter from Texas Devices (TI) that gives 1.8 V and as much as 2 A from a 5 V enter. Making use of a pulse-width modulation (PWM) sign at TP80 varies the output voltage between roughly 1.1 V and a couple of.5 V. Designing this circuit such that the output voltage when no present is injected units the output voltage above the designed 1.8 V allows overvoltage fault detection testing.
Determine 1 An output voltage modulation circuit instance.
For extra particulars on choosing part values for this circuit, see the “Analog voltage enter” part of the Analog Design Journal article, “Strategies of Output-Voltage Adjustment for DC/DC Converters.”
This take a look at fixture makes it doable to confirm the overvoltage and undervoltage detection functionality of voltage supervisors corresponding to TI’s TPS389006-Q1. There’s a GUI obtainable for creating circuits with the TPS389006-Q1 that plots the monitored voltages and any detected faults. Determine 2 reveals an undervoltage and subsequent overvoltage occasion created with the circuit in Determine 1. Channel 2 on the supervisor displays the 1.8-V rail. The undervoltage threshold was set to 1.5 V and the overvoltage threshold set to 2.1 V. Modulating the obligation cycle of the PWM sign allowed for synthetic modulation of the output of the TPS528502-Q1, each beneath and above the thresholds.
Determine 2 Undervoltage and overvoltage fault detection within the TPS389006-Q1 GUI.
Along with the fine-grained management that the circuit in Determine 1 permits, it might even be helpful to check the power-supply response to a brief to the availability or floor. Naked headers on the board itself make it straightforward to check momentary or steady shorts. Onboard indicators corresponding to an LED related to the facility provide’s energy good pin present a straightforward indicator of a profitable brief injection and subsequent restoration. Determine 3 illustrates an instance of those take a look at fixtures, as soon as once more utilizing the TPS628502-Q1 as the instance.
Determine 3 Brief to VIN and floor take a look at fixtures with energy good indicator.
The circuitry facilitates injecting the faults. Then the TPS389006-Q1 supervisor GUI signifies a brief to 5V, a restoration, a brief to floor, and a remaining restoration has occurred (Determine 4). The fault register stays set till cleared.
Determine 4 A 1.8-V brief to floor fault detection within the TPS389006-Q1 GUI.
One other widespread fault that you could be wish to detect is wrong sequencing—rails not developing within the right order, rails not developing in any respect, or rails developing with incorrect timing are all examples of incorrect sequencing. Simply as with overvoltage and undervoltage fault injection, there are two strategies to induce sequencing faults: digitally and manually.
Some sequencers, such because the TPS39700-Q1, are run time-configurable. Throughout growth, you should utilize a GUI to configure the sequence order and timing utilizing I2C. Configuring a purposeful mismatch within the sequence outlined within the TPS39700C-Q1 and the anticipated sequence within the supervisor makes it doable to check the fault detection functionality of the system.
If the supervisor just isn’t configurable by software program, then breaking the connection between the sequencer and rails will modify the sequence, which has the additional benefit of permitting you to allow and disable a tool unbiased of the sequence. Determine 5 reveals one technique of system allow management in a 5-V to 1.8-V/2-A TPS628502-Q1 energy provide. If no jumper is put in on J52, the allow pin will pull down. I counsel designing choice headers in such a manner that that enter pins are positioned in a recognized state if no jumper is put in.
Determine 5 Allow pin circuit to allow sequence testing.
Defining an accurate sequence of a 3.3 V to 1.8 V to 1.2 V after which eradicating the J52 jumper ends in a sequencer fault reported by the TPS389006-Q1 supervisor, proven in Determine 6. MON3 displays the 1.8-V rail.
Determine 6 The TPS389006-Q1 sequence fault detection.
It’s necessary to contemplate easy methods to carry out fault testing in any respect phases of the circuit design course of. Incorporating fault injection and indication into the circuit schematic and format may help streamline subsequent testing. I hope these examples encourage you to assist make your individual design verification simpler.
Matt Griessler is a techniques engineer for the Texas Devices Energy Provide Design Providers workforce.