BQ25798: While switch in backup mode, Load @PMID get restart

Hi Urvi,

Can you provide a scope plot showing V(PMID), V(BAT), I(PMID), V(VBUS) triggering on VBUS removal to show the event?  What are your VBUS trigger point (REG0x10[b6:7] and VINDPM (REG0x05) settings?  Do you have the additional recommended capacitance (2x33uF) on PMID node?

Regards,

Jeff

Hello Jeff,

Thank you for your response.

Here is the scope plots of V(PMID), V(BAT), V(VBUS) triggering on backup mode. 

 Image1: . Channel1-VBUS & Channel2-PMID (While go to Backup mode) (Main Goes to zero) 

Image2: . Channel1-VBUS & Channel2-PMID (While go to Backup mode) (Main Goes to zero)  Zoom in of Image 1

Image3: Channel1-BAT & Channel2-PMID (With Mains)(In normal mode)

Image4: Channel1-BAT & Channel2-PMID (No Mains)(In backup mode)

• VBUS trigger point (REG0x10[b6:7]: At default (80H) (80% * VINDPM)
  
• VINDPM (REG0x05): 2Bh (4300mV)
• We added additional recommended capacitors (2x 33uF Tantalum) at PMID.

Also for your reference here We shared our schematic.

BC25798_V2.pdf

Hi Urvi,

The charger appears to be working normally.  Is the load on PMID restarting because of the slight droop when backup mode turns on?  If you add more capacitance on PMID, does that prevent the restart?

Regards,
Jeff

Yes Jeff,

I have added 1 more 47uf tantalum & 1000uF electrolytic @PMID. 

Regards,

Urvi

Urvi,

Attached are two scope plots. One shows a somewhat zoomed in version of the charger entering backup mode (with watchdog timer disabled and EN_BACKUP=1) and the other is zoomed out version showing the charger entering then exiting backup mode with SDA line.  PMID is light blue.

Test setup is as follows:

VBUS=5V, VOTG=5V, VBAT=7.6V, ICHARGE = 1A, IINDPM=3A, VINDPM=4.7V, BackupModeTrigger=100%, IPMIDload=1A constant current.

The steps are as follows:

I2C write to disable WD timer or to write WD bit periodically

I2C write EN_BACKUP_MODE=1

Remove input power from VAC1

OTG auto starts and ACDRV1 goes low

Reattached input power

I2C write FORCE_ACFET1_ON=1

I2C write EN_OTG=0

after a delay, charge auto restarts and EN_BACKUP auto resets=1

This is simpler than the first revisions of silicon which required more I2C writes for EN_BACKUP to auto reset.

  Regards,

Jeff

Hello Jeff,

Thank you for sharing.

By below settings.

VINDPM=4.7V, BackupModeTrigger=100%

Reset issue has been solved but after some time (Within 10-15 seconds) Load shows low voltage LED indication.

At the same time PMID voltage is constant 5V, still Load get into shutdown mode. 

We have used Khadas VIM3 as load. and in backup mode after some time khadas only glow RED LED. 

According to us, RED LED indicate LOW POWER. 

For your reference, here i shared battery backup code.

/******** Battery Backup*******/	
				 Bat_WriteSingleRegister(0x2E, bat_register.REG2E_ADC_Control | 0x80); //ADC enable bit:7			
				 Bat_WriteSingleRegister(0x18, bat_register.REG18_NTC_Control_1 | 0x01); //TS ignore
				 Bat_WriteSingleRegister(0x0F, bat_register.REG0F_Charger_Control_0 | 0x01);   //EN_BACKUP
         Bat_WriteSingleRegister(0x14, 0x27);   //DISCHATGE CURRENT CONFIG (3A)
         Bat_WriteSingleRegister(0x05, 0x2F);   //VINDPM=4.7V
				 Bat_WriteRegister(0x06, 0x012C);   //IINDPM = 3A
				 Bat_WriteSingleRegister(0x10, 0xC0);   //VBUS BACKUP 100% VINDPM
         
					
/******** re arm back up code added*******/		
				
          Bat_ReadSingleRegister(0x1B,&AC1_PR);
				  AC1_PR1 = AC1_PR  & 0x02;
					if(AC1_PR1 == 0x02)
					{	
						Bat_ReadSingleRegister(0x12,&OTG_1);
						OTG_2 = OTG_1 & 0x40;
						
					if(OTG_2 == 0x40)        //Check DIS_ACDRV=1
					{
						Bat_WriteSingleRegister(0x16, bat_register.REG16_Temperature_Control | 0x01 );  //BKUP_ACFET1_ON =1
						Bat_WriteSingleRegister(0x12, bat_register.REG12_Charger_Control_3 & 0x7F );    //DIS_ACDRV=0
						Bat_WriteSingleRegister(0x13, bat_register.REG13_Charger_Control_4 | 0x40 );    //EN_ACDRV1=1
						Bat_ReadSingleRegister(0x13,&ACDRV1_1);
						ACDRV1_2 = ACDRV1_1 & 0x40;
							if (ACDRV1_2 == 0x40)   //EN_ACDRV1
							{
								
								Bat_WriteSingleRegister(0x12,bat_register.REG12_Charger_Control_3 & 0xBF ); //EN_OTG=0
								HAL_Delay(5000);
								Bat_WriteSingleRegister(0x16, bat_register.REG16_Temperature_Control | 0x01 );  //BKUP_ACFET1_ON =1
							
						    Bat_WriteSingleRegister(0x16, bat_register.REG16_Temperature_Control & 0xFE ); // BKUP_ACFET1_ON=0
				        Bat_WriteSingleRegister(0x0F, bat_register.REG0F_Charger_Control_0 | 0x01); //EN_BACKUP
							}
					}
				}
/******** re arm back up code end*******/