The Blackbox feature greatly enhances the ability of the system designer to debug power path related issues during design/development and in case of field returns. Along with a snapshot of the parametric data and event information through various status registers, the TPS25990 provides additional information which helps to re-create the sequence of events as they occurred in a certain interval of time. This information is available in both the on-chip volatile memory and the external I2C EEPROM (connected on the EECLK/EEDATA pins) and can be accessed through PMBus®.

During the operation of the device, the Blackbox information is stored inside the Blackbox buffer RAM which is seven (7) bytes deep. At any point of time, issuing the READ_BB_RAM command will retrieve the most recent seven (7) events in a sequence along with the timestamp relative to each other. Each byte of this buffer RAM holds the following information about a single event:

1. A 3-bit event identifier

2. A 5-bit value which indicates the time lapse because the previous event. The lower 4 bits of the timer value represents a snapshot of the free running Blackbox tick timer at the instant of registering the event in the Blackbox RAM. The 5^th bit indicates whether the timer has overflowed at least once since the last event.

The event identifier and relative timer information help the system designer to reconstruct a timeline of events as they occurred, thereby enhancing the debug capabilities as compared to viewing a single snapshot of status registers. The Blackbox tick timer is a free running timer which is reset to zero after every event. The timer update rate can be configured through the BB_CONFIG register. This allows the users to make a tradeoff between fine timing resolution and longer time span as per their debug needs. The BB_TMR_EXP bit in the BB_TIMER register indicates if the Blackbox tick timer has overflowed at least since the last event. This bit indicates whether the event entries in the RAM are relatively recent or old. This bit is latched when the timer overflows and reset to zero along with the free running timer when the next event occurs.

Here are the events which will trigger a write to the Blackbox RAM:

1. VIN_UV_WARN

2. VIN_OV_WARN

3. OC_WARN

4. OT_WARN

5. OC_DET

6. VIN_TRAN

7. IN_OP_WARN

Once the device encounters a global fault or alert event (based on the ALERT_MASK), the Blackbox RAM contents, along with the status registers, peak input voltage, peak input current, peak device temperature, and Blackbox timer values are written to an external EEPROM through the EECLK/EEDATA pins.

The contents of the Blackbox RAM along with some status registers (STATUS_WORD, STATUS_MFR_SPECIFIC, and STATUS_INPUT) and certain parameters (VIN_PEAK, IIN_PEAK, and TEMPERATURE_PEAK) are stored into Page-0 of an external EEPROM when the following conditions are met. At the same time, Blackbox RAM contents and Blackbox tick timer values are locked.

1. An external EEPROM is successfully connected by setting the EXT_EEPROM bit high in the DEVICE_CONFIG register. In addition, it is done by configuring two (2) of the four (4) GPIOs as EECLK and EEDATA appropriately in the GPIO_CONFIG_12 and GPIO_CONFIG_34 registers. Make sure those two (2) selected GPIO pins are physically connected to the EEPROM clock and data pins respectively on the board.

2. Any one of the three BB EEPROM write trigger bits is set in the BB_CONFIG register.

Blackbox EEPROM contents:

1. BB_RAM_0 to BB_RAM_6 [Seven (7) bytes]

2. BB_TIMER [One (1) byte]

3. STATUS_WORD [Two (2) bytes]

4. STATUS_MFR_SPECIFIC [One (1) byte]

5. STATUS_INPUT [One (1) byte]

6. VIN_PEAK [One (1) byte, Eight (8) MSBs from the 10-bit ADC output data]

7. IIN_PEAK [One (1) byte, Eight (8) MSBs from the 10-bit ADC output data]

8. TEMPERATURE_PEAK [One (1) byte, Eight (8) MSBs from the 10-bit ADC output data]

9. CHECKSUM [One (1) byte]