Bq25504 EVM 5Voutput

If you can precharge the output to above 1.8V, then the IC can raise the voltage to 5V and maintain it for load current <= efficiency * 0.2V * 100mA / 5V where you can get an estimate of efficiency from the datasheet curves. 

But, you will not be able to startup from 0V to 5V with only 0.2V input source.  The input source needs to be at least 0.4V and, from the PIN(CS) spec max of 50 uW, provide at least 50uW / 0.4V = 170uA of current. 

Hi,Mr.Jeff F

Thank you for quick reply.

I understood that you wrote.

In the case of 5V output by 0.4V input source and VBIAS:1.25V,how much value should I set Rok_1 to 3 ?

For example,Rok1:2.2Ω,Rok2:6.6Ω,Rok1:1.2Ω,the result is VBAT_OK_PROG=5V,VBAT_OK_HYST=5.68V,VBAT_OK + hyst =10.68V ,this value is higher than over volatage.

Is there a resolution?

Best Regards.

Taichi

The VBAT_OK_HYST value is 5.86V so the VBAT_OK signal would trip at 5.86V as VSTOR is rising.  There is no need to add VBAT_OK and VBAT_OK_HYST.

Hello Mr.Jeff

Thank you for quick reply.

Let me ask you two additional questions.

First,following content is correct?

・VBAT_0V is a voltage outputted to VSTOR,VBAT.

・VBAT_OK_PROG is a volatage that BAT_OK become HI.

・VBAT_OK_HYST is a volatage that BAT_OK return LOW.

Next,in the case of R0V1:3.6MΩ,ROV2:6.4MΩ,ROK1:2.2MΩ,ROK2:6.6MΩ,ROK3:1.2MΩ,

hom much is VSTOR volatage? 2.4 to 2.8V? 3.3V?

I am looking forward to your reply.

Best regards.

Taichi

The bq25504 main boost charger IC is powered on when VSTOR > 1.8V.  If you attach a depleted storage element to VBAT, the IC uses the cold start circuit is used to raise VSTOR to 1.8V then the main boost charger starts up.  The cold start circuit needs at least 0.4V max and 170uA, assuming no load on VSTOR, to raise the VSTOR voltage to 1.8V. If you attach a partially charged storage element to VBAT, the main boost charger starts immediately. 

Based on the resistors you show, the values are

VSTOR = VBAT = 5.042V

VBAT_OK = 4.840V which is the trip point for VSTOR falling

VBAT_OK_HYST = 5.50V which is trip point when VSTOR is rising

If the bq25504 is not providing those voltages, then it is possible that either the input source cannot provide enough power for the load on VSTOR (including the leakage current of the storage element) or the solder flux from where you changed the resistors on the EVM board has created parasitic resistors that are reducing the effective resistance of those resistors.  The applications section of the bq25505 datasheet examples that more fully.

Correction:

VSTOR = VBAT = 5.21V

VBAT_OK = 5.0V which is the trip point for VSTOR falling

VBAT_OK_HYST = 5.68V which is trip point when VSTOR is rising

 Practically, VBAT_OK_HYST should be set less than VBAT_OV.

Hello.Jeff

Thank you for quick reply.

Still,I don't get first question,so could you tell me following question ?

First,following content is correct?

・VBAT_0V is a voltage outputted to VSTOR,VBAT.

・VBAT_OK_PROG is a volatage that BAT_OK become HI.

・VBAT_OK_HYST is a volatage that BAT_OK return LOW.

Customers invested a  relation between boarded resistors and boarded output volatage with EVM,the result sounds like above.

I am looking forward to your reply.

Best regards.

Taichi.

VBAT_OV is the maximum voltage at VSTOR,VBAT.

・VBAT_OK_PROG is the VSTOR voltage at which VBAT_OK will go low as VSTOR is falling.

・VBAT_OK_HYST is the VSTOR voltage at which VBAT_OK will go high as VSTOR is rising.

Hello Mr.Jeff

Thank you for quick reply.

I udestood that you wrote.

I have two additional questions.

1)VBAT_UV:2.2 to VBAT_0V is written on dataheet_P4 however if  i set a voltage less than 2.2V to VBAT_UV,is there problem?

2)A sentence"it is recommended to add an external PFET between the system load and VSTOR" is written on datasheet_P13 however if normal ,I think that a volatage should supply to load when Battery is stored enough so I think that NFET should be set.My recognition is wrong?

I am looking forward to your reply.

Best regards.

Regarding 1, the minimum VBAT_UV is 2.2V.

Regarding 2, the gate of the NFET would need VSTOR + Vth to turn on where Vth is the threshold voltage of the FET. 

Hello.Mr.Jeff

Thank you for quick reply.

Regarding1,In there any problem when customer set  less than 2.2V to VBAT_UV ?

Customer seem to would like to capacitor(approximately 1.8V) instead of battery.

Best regards.

Taichi

The VSTOR pin needs to be higher than VSTOR_CHGEN (1.6V min to 1.95max) in order for all of the bq25504's main boost charger features to operate.  When below VSTOR_CHGEN, the cold start circuit is the only circuit that turns on.  Setting VBAT_UV no lower than 2.2V gives needed headroom above VSTOR_CHGEN.

Hi,Mr.Jeff

Thank you for quick reply.

I understood that you wrote.

Let me ask you an additional question.

In the case setting RUV1,RUV2 to be VBAT_UV < 2.2V , is there any problem ?

Customer seem to would like to use capacitor charge(instead of battery) down to low voltage as possible.

The capacitor voltage is 1.8V.

I am looking forward to your reply.

Best regards.

Hi,Mr.Jeff

Thank you for reply.

You helped me a great deal.

Best regards.

Taichi.