The TPIC71004-Q1 is a quad channel squib driver for airbags deployment in automotive applications. Each channel consists of a high side and a low side switch with independent control logic for protection against inadvertent deployment. Both the high and the low side switches have internal current limits, over-temperature protection.
The IC registers are used for four channel configuration, control and status monitoring. To prevent inadvertent deployment, the high and the low side switches will be turned on only if the proper configuration sequence is used and multiple inputs to the deploy controller logic are at the correct level. The registers are programmed using a serial communications interface.
The maximum on time for each channel is limited by programmable Firing Time Out Timer to prevent excessive power dissipation. In addition, a current limit register is used to program the maximum current through the switches during a deployment. The current limitation on the low side switch is larger than the corresponding high side switch. During deployment, the low side switch will be full enhanced and operate with RDS_ON mode and the high side switch will be in current regulation mode.
The implemented diagnostic functions monitor deployment ASIC pin voltages to provide High Side switch test, Low Side switch test, squib resistance measurements, squib leakage measurement to battery, ground and between any squib channels. Furthermore, the squib leakage measurement is provided for both Zx and ZMx pins and does not require the squib load to be present to operate properly. Diagnostic information is communicated through the AMX_OUT pin (for analog signals) and SPI mapped status registers (for status signals latched in digital core).
The high-side and low-side squib drivers have a diagnostic level current limit and a deployment level current limit. The default current limit for high-side and low-side squib drivers is the diagnostic level current limit. The high-side switch deployment current limit for all high-side drivers can be set to either 1.2 A min or 1.75 A min (see Table 1) through SPI mapped registers, device EEPROM settings (see Table 2). The low-side switch deployment current limit is not programmable and is fixed to a level greater than the high-side driver current limit. The ON time duration for each individual squib driver can be programmed through SPI mapped registers.
The deployment sequence requires a specific set of software commands combined with external hardware enable logic lines (TZ0=H, IWD=L) to provide deployment capability. The turn-on sequence of the high-side driver and low-side drivers is software controlled via SPI commands, but the turn-off procedure is automatically provided by the deployment ASIC. After the programmed ON time duration has been achieved, the high-side switch is deactivated first then followed by the low-side driver deactivation by approximately 100µsec.
The RESET_N is an active low input reset signal. This input will be released high by the power supply unit and/or the µC once the external voltage supplies are within the specified limits. The external microcontroller is required to configure and control device through the serial communication interface. Reliable software is critical for the system operation.
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