Hello, everyone!
My customer is considering replacing MCP7940 on BQ32000.
MCP7940 has a special register (address 0x03h):
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Bit 4 is the VBAT bit. This bit is set by hardware when the VCC fails and the VBAT is used to power the Oscillator and the RTCC registers.
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Current version of device is using this feature and control transition between power domains.
BQ32000 has no special register which provide information about switching between power domains (Vback and Vcc). But as I understand we can emulate this feature. In a case when trickle charger isn’t used we can use module registers: TCHE[3:0], TCH2, TCFE:
The main idea:
[datasheet] http://www.ti.com/lit/ds/symlink/bq32000.pdf
p.6:
Some registers are reset to default values when the RTC switches from main power supply to backup power supply. Please see the register definitions to determine what register bits are effected by a backup switchover (effected bits have thier reset value (1/0) shown for 'Cycle', bits that are unchanged by backup are maked 'UC').
If we look at the trickle charger registers description:
It seems that we can initialize some bits by “1” and when RTC switches from main power supply to backup power supply these bits resets to default value.
If trickle charger isn’t used we can detect power domain switching by controlling appropriate bits.
From my side I tell the idea to customer, but when he tries to do the trick using TCFE register the last one didn’t change the value at all.
Below is the experiment descriprion:
1. Power up the device (Vcc is applied);
2. Init TCFE = 1;
3. Power off the device (Vback is applied);
4. Power up the device (Vcc is applied);
5. Reading TCFE bit; // TCFE still “1”, but concerning the data sheet it should be “0”.
How do you think what could be wrong? Is my idea correct or no?
Please help to solve the problem and win the biz.
Thanks in advance!
