Texas Instruments BQ25504 Battery Management Evaluation Board, Ultra Low Power Boost Converter IC | Energy Harvester BQ2 BQ25504EVM-674 Datenbogen
Produktcode
BQ25504EVM-674
Vphase
Vstor
Vbat
Vp/s#1
Test Summary
Figure 2. Startup with no Battery and 10k Load
3.3.2
Power-up with Battery less than UV (less than a diode drop below UV)
1. Same setup, as 3.3.1, except move the probe on V
BAT
to V
IN
and apply a charge element set to 1.9VDC
between BAT and GND. Arm scope to trigger on V
P/S #1
.
2. Set PS#1 to 1VDC and hot plug to input with 20
Ω
series resistor, see
The start up is similar to the case without the battery but after the initial ~40ms period the STOR charges
to 2.8V or ~0.9V above the battery and is charging the element via the BAT FET body diode. The next
sampling cycle for UV detects that the VSTOR is greater than UV (2.2V) and then turns on the BAT FET.
Since the battery is at 1.9V, VSTOR is pulled down to ~1.9V and the next UV sampling turns off the BAT
FET. The cycling continues until the battery gets charged to the UV threshold and then finally the BAT
FET stays on. A less complicated design would turn off the system load once the battery drops near the
UV threshold to avoid this cycling.
to 2.8V or ~0.9V above the battery and is charging the element via the BAT FET body diode. The next
sampling cycle for UV detects that the VSTOR is greater than UV (2.2V) and then turns on the BAT FET.
Since the battery is at 1.9V, VSTOR is pulled down to ~1.9V and the next UV sampling turns off the BAT
FET. The cycling continues until the battery gets charged to the UV threshold and then finally the BAT
FET stays on. A less complicated design would turn off the system load once the battery drops near the
UV threshold to avoid this cycling.
If the storage element is lower than the maximum voltage (OV) then the element can theoretically take all
of the available input power. As the harvesting source is loaded, its output voltage drops until reaching the
MPPT threshold, which is currently programmed to 78% of the OC voltage and then the boost converter
regulates the input voltage at this level by controlling the power transferred to the load. Note how Vin
regulates to 78% of P/S#1 when the battery is lower than the OV voltage. Vary the input voltage slightly
and wait for the 16 second update cycle to see how the MPPT is updated.
of the available input power. As the harvesting source is loaded, its output voltage drops until reaching the
MPPT threshold, which is currently programmed to 78% of the OC voltage and then the boost converter
regulates the input voltage at this level by controlling the power transferred to the load. Note how Vin
regulates to 78% of P/S#1 when the battery is lower than the OV voltage. Vary the input voltage slightly
and wait for the 16 second update cycle to see how the MPPT is updated.
For a battery that is more than a diode drop below 1.8V, the charger may get stuck in cold startup which is
less efficient and would take longer to recover. Once the STOR voltage gets above 1.8V and more than
32ms after power is applied, the low power cold start circuit is disabled and the main boost converter
takes over.
less efficient and would take longer to recover. Once the STOR voltage gets above 1.8V and more than
32ms after power is applied, the low power cold start circuit is disabled and the main boost converter
takes over.
6
bq25504 EVM
–
Ultra Low Power Boost Converter with Battery Management for
SLUU654A
–
October 2011
–
Revised October 2011
Energy Harvester Applications
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2011, Texas Instruments Incorporated