SLVSAT2 – FEBRUARY 2011
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
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
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
Table 1. Potential Deployment Settings for Typical Firing Current
MAXIMUM AVERAGE FIRING VOLTAGE
BETWEEN VZx AND Zx PINS TO
(1) For programming desired dwell (firing) time.
Extended deployment duration activates the over temperature protection circuit and terminates deployment. If
short-to-ground condition occurs during deployment, 35V firing voltage is completely dropped across the
HS_FET: therefore, thermal shut down protection kicks in to protect the device.
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Product Folder Link(s): TPIC71004-Q1
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