ASIC Mix signal Specification
Automotive application: ASIC's Supply Pin connected to a car battery
ASIC Mix signal Specification
Automotive application: ASIC's Supply Pin connected to a car battery
Maximum Rating
Normal operating conditions
Error handling, Overvoltage and Undervoltage faults
Undervoltage fault (VBAT_uv) , detection hysteresis ( VBAT_uv_hys) and filter time (t_VBAT_uv)
Undervoltage fault
Undervoltage detection filter time
Implementation Note and specification requirement of hysteresis
Undervoltage detection hysteresis
Overvoltage fault (VBAT_ov) , detection hysteresis ( VBAT_ov_hys) and filter time (t_VBAT_ov)
Overvoltage fault
Implementation Note and specification requirement of hysteresis
Overvoltage detection hysteresis
October 4, 2011
Here is one detail of a possible specification of an ASIC Mix signal for automotive applications, that has an analog pin: VBAT, directly connected to a car battery.
An implementation detail related to the specification outlined in the other blog entry: How to implement an ASIC Mix signal for an Automotive application: ASIC's Supply Pin connected to a car battery .
First assumption made here is that ASIC is working together with a microprocessor (MPU) in the system where it is used. MPU (master) and ASIC (slave) are exchanging data using one of common ( or "standard") interfaces of communication ( e.g. automotive ASIC's use a lot Serial Peripheral Interface Bus or SPI ).
In the master/slave configuration MPU can write and read registers in the ASIC using SPI bus.
Possible functionality related to the pin VBAT could include:
- supply of some ASIC's internal functions: such as internal charge pump etc.etc.
- monitoring and reporting Overvoltage and Undervoltage faults on a car battery voltage
Here we will assume that there is already existing another ASIC's analog pin: GND, and all references of voltages in this specification are referenced to it.
Maximum Rating
Maximum rating describes that our ASIC will not get damaged ( but there is no guarantie that would be opertationel either) even if car battery voltage goes to extremes: minimum -0.3 and maximum 40V.
| Pin name | Value= Min, Max |
| VBAT | -0.3V, 40V |
Note: It is very likely that a car battery voltage connected to VBAT with a reverse diode as protection. That is why in VBAT Maximum Rating it is assumed that negative voltage will never get more negative then -0.3V.
Normal operating conditions
| Pin name | Value= Min, Typ, Max |
| VBAT | 6V, 14V, 40V |
Note: During normal operation for the purpose of the ASIC functionality here is specified that the battery will always produce a voltage in the range of 6-40V, and a typical average value of the voltage should be 14V.
Error handling, Overvoltage and Undervoltage faults
The ASIC should monitor and report Overvoltage and Undervoltage faults on the car battery voltage ( or VBAT pin).
In the case of either Overvoltage and Undervoltage faults, a register flag vbat_ouv is set and accessible by MPU( e.g. using SPI register read).
Once set, the register flag vbat_ouv stays 1 until there is MPU read and in the same time the value of the flag is clear by the read.
After the "clear-on-read" of the flag vbat_ouv, evaluation of Overvoltage and Undervoltage faults starts again.
Undervoltage fault (VBAT_uv) , detection hysteresis ( VBAT_uv_hys) and filter time (t_VBAT_uv)
The VBAT Undervoltage fault is detected ( and the register flag vbat_ouv is set ) if VBAT voltage is LESS then VBAT_uv, min=5.0V and max=5.5V ( typical value 5.2V ) , and this event lasts uninterrupted t_VBAT_uv time, between 250 and 350us ( typical value 300us ).| Parameter description | Parameter Symbol | Value: min, typ, max V | Comment |
Undervoltage fault | VBAT_uv | 5.0, 5.2, 5.5 V | Measured on falling edge. |
The time range ( between 250 and 350us, typical value 300us ) of detection/cancelation of VBAT Undervoltage fault is called Undervoltage detection filter time.
| Parameter description | Parameter Symbol | Value: min, typ, max us | Comment |
Undervoltage detection filter time | t_VBAT_uv | 250, 300, 350 us |
Implementation Note and specification requirement of hysteresis
VBAT Undervoltage fault is going to be decided by a comparator.Comparator should satisfy a hysteresis requirement: when VBAT is rising a voltage canceling VBAT Undervoltage fault should be higher of a voltage setting VBAT Undervoltage fault when VBAT is falling.
Difference of the two voltages is called Undervoltage detection hysteresis.
The hysteresis is necessary to avoid that noise on VBAT cause oscillation on comparators output.
| Parameter description | Parameter Symbol | Value: min, typ, max mV | Comment |
Undervoltage detection hysteresis | VBAT_uv_hys | 50, 150, 250 mV |
Overvoltage fault (VBAT_ov) , detection hysteresis ( VBAT_ov_hys) and filter time (t_VBAT_ov)
The VBAT Overvoltage fault is detected ( and the register flag vbat_ouv is set ) if VBAT voltage is MORE then VBAT_ov, min=30.V and max=34V ( typical value 32V ) , and this event lasts uninterrupted Undervoltage detection filter time, t_VBAT_ov= t_VBAT_uv.| Parameter description | Parameter Symbol | Value: min, typ, max V | Comment |
Overvoltage fault | VBAT_ov | 32, 34, 38 V |
Implementation Note and specification requirement of hysteresis
VBAT Overvoltage fault is going to be decided by a comparator.Comparator should satisfy a hysteresis requirement: when VBAT is rising a voltage canceling VBAT Undervoltage fault should be higher of a voltage setting VBAT Undervoltage fault when VBAT is falling.
Difference of the two voltages is called Undervoltage detection hysteresis.
The hysteresis is necessary to avoid that noise on VBAT cause oscillation on comparators output.
| Parameter description | Parameter Symbol | Value: min, typ, max V | Comment |
Overvoltage detection hysteresis | VBAT_ov_hys | 0.5, 1, 2 V |
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