Achieving nano I_Q in voltage supervisors

In standby mode, automotive OEMs have a 100µA budget for all of the electronics sitting on the supply voltage rail, which could include supply supervisors, load switches, protection transient voltage suppression diodes and DC/DC converters. Nano-I_Q levels in voltage supervisors can help automotive OEMs meet this system-level standby-mode I_Q budget. While the standby I_Q is lowered, the voltage supervisor device cannot relax its standby fault response time. Functional safety requirements specify the device’s fault response, characterized by the fault-tolerant time interval from detection to reporting a failure, to scale from the 100µs range to the sub-10µs range.

Conventional supply voltage supervisor solutions with a 1.5% threshold detection accuracy have used a configurable potential divider with discrete resistors on the printed circuit board (PCB). To reduce system I_Q, the values of these discrete resistors need to be scaled up to several tens of megaohms. Since PCB designers do not typically add high-impedance sense-resistor ladders to their boards given area constraints, the resistor ladders are integrated onto the die of the TPS37-Q1 window supervisor. Low I_Q becomes possible on the reference path by duty-cycling the voltage reference and storing the reference on a capacitor, and by constructing the internal sense-resistor ladder as a nonlinear resistor ladder reconfigured between a constant-resistance region into a constant-current region to create a very high-impedance sense ladder at higher voltages.

Wide-V_IN window supervisors such as the TPS37-Q1 need to handle voltage swings between external high-voltage input and internal subregulated voltages. Dynamic circuits detect both rise and fall transitions to boost the performance of the level shifters between the external high voltage and internal regulated domains into a temporary turbo mode to improve system response times while still supporting low I_Q.