Texas Instruments bq76920EVM, Руководство пользователя, Страница: 26 / 46

DC Power Supply
+ -
Boot
switch
MCU
evaluation
board
Pull-ups if
required
Remove gauge shunts,
Wire to MCU board
Cell simulator switches
on for
power supply
bq76920 Circuit Module Use
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26 SLVU924D – March 2014 – Revised November 2018
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bq76920 Evaluation Module User's Guide
Figure 20. Host Connection Concept
6.6 Gauge Circuits
The EVM contains a gauge circuit consisting of U2 and an SMBus interface connector, J14. This bq78350
IC and circuit can be used to control the AFE if configured and connected at the J12 header. By default
the AFE on the EVM is a 2.5-V output device, only connect the gauge circuitry to a 2.5-V output AFE IC.
Shunts may be placed on the /KEY and /PRES headers to simulate control of these signals. An alternate
SMBus address may be selected using the SMBus header. Refer to the bq78350-R1 TRM for details and
configuration selections for these device features.
Basic operation of the gauge is shown in Section 2.2.2 , for more details on operation see the bq78350-R1
TRM.
6.7 Unused Components
The EVM contains a number of component patterns which may be useful for evaluation.
Test points are not typically populated. The patterns may be used as probe points or wires or test points
could be soldered to provide probing, if desired.
Normally the power filter R14 and C13 keeps the supply voltage for the AFE in a safe operating range. For
situations with large transients, D3 provides a clamp for the supply voltage to the AFE, if needed. The
pattern is large and it is easy to fit other component sizes. Be aware that if the system transients are large
enough that a clamp is needed at D3, the cell inputs should also be inspected for excessive voltages and
an improved filter or clamp be added there, if needed.
The ALERT line switches high and low in normal operation as status bits are asserted and cleared. A
large load is not desired since it consumes power. If it is useful to slow the transition, the pattern C10 is
available. C10 should not be large in order to avoid current and slowing the edge to where the bq76920
would see the ALERT high as an input and set the OVRD_ALERT condition.
When the charge FET turns on with a large charger voltage present, a large voltage could be impressed
on the gate of the charge FET. With the voltages typically used on the bq76920EVM, this should not be
high enough to damage the charge FET. If special circumstances require, the D5 pattern is available for a
clamp diode.