Powering wireless sensor node using solar.

The boost charger core of each is essentially the same, with some of the specs having tighter tolerance on the bq25570 and bq25505.  Also the bq25570 and bq25505 require fewer resistors because the VOC_SAMP pin can be tied to VSTOR or GND for fixed 80% solar panel MPP or 50% GND.  In addition, the threshold for the integrated battery overdischarge prevention FET is fixed internally at 2.0V for these two devices where the bq25504 requires external resistors to set the threshold for this feature.

If you will have a primary, non-rechargeable battery as a back-up, then I suggest bq25505 which has gate driver for an external PFET based MUX to switch the system load between the primary and secondary rechargeable battery.

If you need a second power rail that is lower than the battery, then I suggest the bq25570 which has an integrated buck converter that can provide that rail.

Thanks for your suggestion.

Also is it possible to use bq25570EVM as bq25504EVM board by disabling buck converter,will both be exactly the same.

But is it possible for continuous operation of wireless load with this bq25570EVM board.

If you disable the buck on the bq25570 with its VOUT_EN pin, it will operate the same as the bq25504, except the VBAT_UV threshold is internally fixed at 2.1V.  The bq25504 allows you to set the VBAT_UV threshold, to prevent battery overdischarge, with external resistors.  If your battery has isn't own internal protector, then you do not need this function.

Hi am unable to understand few points regarding BQ25570EVM evaluation board.

These are few doubts I have in powering a wireless node with BQ25570EVM  evaluation board.

1. can you please tell what exactly difference,working of  ok_hyst,  ok_prog and how to set this according to my application in BQ25570EVM evaluation board.
2. vbias is it fixed at 1.21v always?
3. vref for buck output problem:        I want to maintain constant 3v to power wireless transceiver,is it possible to get vout_set=3v with vbias=1.21v.
4.  BQ25570EVM board values (like Vbat_ov pin,ok_hyst, ok_prog  pins) are fixed and cant be changed?
5. I would like to change overvoltage limit of BQ25570-EVM board,Is it possible to connect external resistors ( which makes sum>13M ohms) or is there any other way to change limits of these Vbat_ov pin,ok_hyst, ok_prog  pins.
6. choosing vout_set value if load requires 3v continuous supply.
7. And do I have to connect any other extra components to protect this evaluation board before proceeding to my experiment of connecting wireless transmitter.

Thank you.

1.  OK_HYST is the rising VSTOR voltage at which the VBAT_OK_signal will go high.  OK_PROG is the falling VSTOR voltage at which the VBAT_OK signal will go low.  The intent was for the VBAT_OK to tell your system (and/or the internal buck regulator via the VOUT_EN pin) to turn on and off.  The assumption is that you only want operation when the battery is within the voltage range set by OK_HYST down to OK__PROG.

2.  Yes.

3.  You use the external resistor divider with midpoint connected to the VOUT_SET to set VOUT.  You can use the spreadsheet at this link to help. http://www.ti.com/lit/zip/sluc484

4.  You must change the resistor values on the EVM board in order to get different values.

5.  You change the resistors with midpoint connected to VBAT_OV to change the overvoltage set point.

6.  You can use the spreadsheet at the link above to help size the VOUT resistors.

7.  As long as the open circuit voltage of your harvester connected the IC's VIN_DC pin is less than 5.5, you should not need any protection.  

Also, please read the datasheet Layout section carefully as it warns of solder flux causing parasitic resistors if the boards are not carefully cleaned after soldering.

Thank you very much,But still these are the doubts still remain:

1. Then what is the difference  OK_HYST, bat_UV?
2. Is vbat_ok=1 for battery in the range vbat_uv,vbat_ov (or) ok_prog to ok_hyst?
3. what is the use of two transition points OK_HYST,OK_PROG,these operations can be done by VBAT_UV?
4. what is the output between bat_uv,OK_HYST?
5. how to change resistor values on evaluation board.
6. what is the role of Capacitor of 100uF(already connected on board),If I connect external battery?
7. Role of capacitor CBYP?
8. There is control on V_out of buck converter,then how current I_out is controlled?will excess current damage my load?As in my case I require pulsating output current maximum of 50mA,minimum of 1mA?
9. As my vbias is 1.2v,I can set vout_ref only in between 0,1.2 as we have resistor divider with supply of 1.2v (vbias)?

1.  VBAT_UV provides overdischarge protection and will open the FET between VBAT and VSTOR so that the system connected to VSTOR cannot pull the battery below the VBAT_UV threshold.  The VBAT_OK signal is simply a comparator that signals when the VSTOR=VBAT voltage (where VBAT_UV threshold < OK_PROG threshold) is within the user defined range.

2.  VBAT_OK = hi when the voltage at VSTOR is between OK_HYST and OK_PROG.

3.  & 4.  See 1 and 2 above.

5.  You will need a soldering iron and some solder to replace the resistors.

6.  The IC needs at least 100uF of equivalent capacitance on VBAT to operate.  If you attach a battery with at least that much capacitance, you do not need the 100uF capacitor and can remove it.

7.  CBYP filters out high frequency switching noise that could interfere with some of the internal circuits.

8.  The buck converter will regulate the output voltage to the VOUT_SET point and provide current up to its peak current limit.  If more current is required by the load, the buck converter will simply operate at its peak current limit, turning into a constant current source and the voltage at VOUT will start to drop.

9.  No.  The resistor divider allows you to scale the output voltage from 1.3V to its maximum of VBAT_OV - 0.2V.  Any adjustable output voltage regulating IC uses a resistor divider to divide down the sensed output voltage by the top resistor to the reference voltage, in this case VBIAS=1.21V.

Hi,

1. Is it possible to get constant lower current of Iout=1mA(as my load requires not more than 1mA).
2. Do you mean replacing surface mount resistors from evaluation board with normal resistors to get required specifications of Vov?
3. Can you please send any documentation which details procedure of these changing surface mount resistors, usage of evaluation board for any application?
4. I didnt get your reply to resistor divider question ,As supply voltage to resistor divider is 1.2v,how is it possible to get more than 1.2v?