On designing a board from scratch Part II
So @RoyEltham says I need to factor in the current draw from the following (information derived from datasheets):
Current List:
EEPROM: 2.5-5.5v
Maximum write current 3 mA at 5.5V
Maximum read current 0.4mA at 5.5V
Standby current 100 nA typical at 5.5V
Propeller Voltage Regulator: ??
2 LEDs: 3.3V @ 40mA
Propeller Chip: 3.3V @ 5mA
Board + Base Components + Crystal: Random 2mA
Loss in the Regulator: For Vin of 5v, max quiescent current is 66mA....
Based on this, the power requirements at max would be around 3.3V @ 116mA
Roy says that the regulator may not need to be the one that parallax uses because the project can take a custom one which may only need 150-200mA max.
So. I looked at another option:
IC LDO REG 3.3V 150mA SOT23-5- LP2985-33DBVR
http://parts.digikey.com/1/parts/609150-ic-ldo-reg-3-3v-150ma-sot23-5-lp2985-33dbvr.html
Datasheet: http://www.ti.com/lit/ds/symlink/lp2985-18.pdf
Temp range: –40°C to 125°C
Size: 3.05 x 3 x 1.45mm
Quiescent current: 0.85mA
Dropout level (when regulation stops, so with a 3.3v you need 3.3v + dropout number as input): 0.28V
Drawing 50mA, the dropout is 0.225v worst case, so you'd need 3.525v input but with a battery you need to size it big enough that when it's dropping voltage as it depletes you stay above that dropout point as long as possible.
Input Range: 2.5v - 16v
And then John chimed in with this one:
http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=LP2950-33&x=20&y=20 Datasheet: http://www.ti.com/lit/ds/symlink/lp2951.pdf Temp range: –40°C to 125°C Size: 5 x 6.2 x 1.75 mm (for the SMT with leads version)
Quiescent Current: 0.075mA Dropout Level: 0.38v Input Range: -3V - 30V
It seems that for this one, quiescent current is significantly better even though dropout level is better in the previous chip...Decisions, decisions!
@atdiy/@tymkrs
