@abatardi That’s good info. I think we’re getting close.
I’m getting 850 mA without touching the Data Wires. I’m powering the Boron w/ the USB Connector, since that’s how I’ll connect a Solar Panel in the field.
But connecting the Data wires and Restarting had no impact on my measurements, when using the USB connector for power.
I cut the USB cable that’s included with the Boron, and used the Black and Red Wires to power the Boron on it’s USB connector from a PSU.
HOWEVER, if I land my power on the V(USB) and Ground Pins, instead of using the USB connector; I get similar results as yours:
450 mA when D+/D- USB wires NOT connected
1030 mA when D+/D- USB wires ARE connected
So it matters where we land our Power Source.
[Back to my results from today using the USB connector]
I’m able to maintain 850mA charging using the following PMIC Settings and a PSU in Constant Voltage Mode on the USB Connector, charging a 10,000 mAh Li-po @ 3.90 resting voltage, Boron LTE 0.9.0 Manual Mode w/ Modem OFF drawing 7 mA, D+/D- USB wires not connected :
pmic.setInputVoltageLimit(4200); //
pmic.setInputCurrentLimit(2000) ; // 2000 mA
pmic.setChargeVoltage(4208); // Set Li-Po charge termination voltage to 4.21V, CAUTION! not for everyone
pmic.setChargeCurrent(0,0,1,1,1,0); // 1408 mA [0+0+512mA+256mA+128mA+0] + 512 Offset
pmic.enableDPDM();
pmic.enableBuck();
The PMIC will start to reduce the charging current if/when the VUSB drops to 4.35V (using pmic.setInputVoltageLimit(4200)). That’s not the supply voltage, but the measured operating voltage at the VUSB pin. I’m supplying power at the USB Connector.
V(PSU) V(USB) I(charging) Notes
5.20V 4.35V 830 mA This is where DPM kicks in and reduces charging current
5.40V 4.50V 850 mA 850mA appears to be the max for this particular setup
6.25V 5.30V 850 mA Increasing Supply Voltage doesn't increase charging current beyond 850 MA
My assumption is that in the first line of the results, V(USB) = 4.35 is related to the setting pmic.setInputVoltageLimit(4200). I guess there is a small voltage reduction from V(USB) to the PMIC, because the Current gets reduced when V(USB) drops to slightly higher (~0.15V) than the setInputVoltageLimit setting.
I don’t know why 850 mA is the actual limit when everything “appears” to be good for 1408 mA.
I changed back to pmic.setInputVoltageLimit(5080); which should be the best available setting for a 6 Volt Solar Panel, and the charging current is still 850 mA 
I slowly reduced the Supply Voltage until the PMIC started to reduce the Charging Current.
The V(USB) was 5.20V when this happened, reinforcing the above results.
The Dynamic Power Management of the PMIC kicks-in when V(USB) falls to about 0.10 to 0.15 V above the set-point of pmic.setInputVoltageLimit(x)
I believe to rate any particular 6V Solar panel for a Boron, we’d check the current produced by the Panel at 5.20V, since that’s the highest “actual” Input Voltage that the firmware allows the PMIC to attempt to maintain in DPM when recharging via Solar. This rating would be limited to 4.4 watts maximum for the Boron LTE, per my results if connecting the solar Panel via the USB connector. The Boron LTE is still a good fit for a 6-watt panel if needed.
// This can provide (up-to) 850 mA of Charging Current on my test rig, using the USB connector:
pmic.setInputVoltageLimit(5080); // 6V Solar Panel, actual condition is ~ 5.20V for DPM
pmic.setInputCurrentLimit(2000) ; // 2000 mA, higher than req'd
pmic.setChargeVoltage(4208); // Set Li-Po charge termination voltage to 4.21V, CAUTION: You MUST Monitor TEMP!
pmic.setChargeCurrent(0,0,1,1,1,0); // 1408 mA [0+0+512mA+256mA+128mA+0] + 512 Offset
pmic.enableDPDM(); // This may be a default, and not req'd
/* Notes: When using pmic.setInputVoltageLimit(5080), the Boron LTE may no longer Boot when only powered from a USB port on some Computers.
You will need to attach the Li-Po when re-flashing, etc, since some USB ports have trouble maintaining the Voltage when using this setting.
It appears the charging current can be increased to 1000 mA if you don't use the USB connector, using V(USB) and GND Pins instead.
But you must tie the USB data lines (use a dummy usb connection) together for the PMIC to allow higher than 500 mA in this case.
*/
Li-Po Charging Results for Boron LTE, when the source has sufficient Voltage & Current Capability:
- 850 mA using a USB Cable/Connector for recharging, Red and Black wires Only
- 450 mA using V(USB) and GND Pins for Recharging
- 1000 mA using V(USB) and GND Pins for Recharging, using a dummy USB that connects the Data Lines together (Green and White).