SLVAEP4 October   2023 BQ79600-Q1 , BQ79612-Q1 , BQ79614-Q1 , BQ79616 , BQ79616-Q1 , BQ79652-Q1 , BQ79654-Q1 , BQ79656-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 Receiver Topology and Common Mode Voltages
  6. 3 Signal Integrity Requirements
    1. 3.1 Receiver Timing Requirements
    2. 3.2 Receiver Threshold Requirements
  7. 4 Debug Fault Registers
  8. 5 Isolation Types
    1. 5.1 Transformer Isolation
    2. 5.2 Capacitor Only Isolation
    3. 5.3 Capacitor and Choke Isolation
  9. 6 Mixed Isolation Circuits using bq79600-Q1
  10. 7 Ring Architecture
  11. 8 Noise Immunity and Emissions
  12. 9 Daisy Chain Cable Selection
  13. 10References

3.2 Receiver Threshold Requirements

The thresholds at which the internal digital is able to properly detect a high vs. low transition are shown in Figure 3-1. A good quality waveform will have a differential voltage above 1.8 V (and below -1.8 V on the negative side). It typically resembles a square wave with rounded edges.

The image below shows a poor quality or drooping waveform that still meets the criteria for a valid communication. The first diagram is showing a starting voltage (VSTART) of 1.7 V with an ending voltage (VEND) of 1.2V. The second diagram shows a second scenario where the starting voltage (VSTART) is only 1.6 V with an ending voltage (VEND) of 1.3V. If the starting amplitude is not at least 1.6 V, then the bit will not be detected, regardless of ending amplitude. These types of drooping waveforms most often are seen when there are two adjacent bits of opposite polarity, forming what can be referred to as a double-bit.

Note: The color red indicates the region that the signal may or may not be detected (poor quality waveform zone) whereas orange indicating the area the area near the triggering threshold range. A good quality waveform would remain in the green region above 1.7 V for the duration of the positive pulse width.
GUID-20210122-CA0I-SRJ2-B6BJ-DX7T8CJ4FRSG-low.gif Figure 3-1 Differential Signal Eye Diagram - 1.7 V VSTART
GUID-20210917-SS0I-HDP3-C0PN-1JDVKQMWFZ8W-low.gif Figure 3-2 Differential Signal Eye Diagram - 1.6 V VSTART

Table 3-1 shows the specific timing and voltage requirements for valid daisy-chain communication.

Table 3-1 Timing Chart
Parameter Conditions Min Typ Max
thigh positive pulse width COMP-COMN from +1.2V of rising edge to -1.2V of next falling edge 220 ns 250 ns 280 ns
tlow negative pulse width COMP-COMN from -1.2V of rising edge to +1.2V of next falling edge 220 ns 250 ns 280 ns
trise Rising slew rate COMP-COMN from -1.2V to +1.2V of rising edge 60 ns
tfall Falling slew rate COMP-COMN from +1.2V to -1.2V of falling edge 60 ns
Vstart Starting amplitude If ending amplitude is above 1.3V 1.6 V
Vstart Starting amplitude If ending amplitude is between 1.2V and 1.3V 1.7 V
tblank Blanking time After last bit 4 us
Wake Tone (thigh/tlow) Wake Tone pulse widths COMP-COMN from +1.2V of rising edge to -1.2V of next falling edge during and vice versa for Wake tones 1 us

Figure 3-3 shows the threshold needed for interfacing with the BQ79600 device. The primary difference is the threshold and timing references are based on a 1.8 V threshold.

GUID-20210917-SS0I-S8HD-HDMH-291P6TSRZ4X6-low.gifFigure 3-3 Differential Signal Eye Diagram - BQ79600