Loads; Loads On Main Supply; 5.4.2 Power Loads During Sleep - Applied Data Systems Bitsy Plus User Manual

Bitsy Plus User's Manual
5 V Loads
5 V loads come from both onboard and external devices:
External:
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Onboard:
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Loads on Main Supply

The main power supply (DCIN_Pos or VBatt_Pos) is loaded by the 5 V and 3.3 V supplies as
indicated in the diagram of section 5.3.1. Assume 85% efficiency for external loads that cascade
through the 5 V supply. Consider these loads when creating your power budget.

5.4.2 Power Loads During Sleep

When designing systems for minimal power consumption during Sleep mode, make sure to
consider DC losses to external connections. The following are a few of the ways your system may
"leak" when asleep:
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Display
Backlight
Only if powered by 5 V Bitsy Plus power supply
Most PCMCIA cards
USB devices
PS/2 keyboard
Speaker(s)
Assume 80% efficiency
3.3 V Supply
Multiply by 115% to account for 3.3 V power supply efficiency
Supercaps
Use peak inrush current in your budget
PCMCIA and CF cards
Cards in place when the system is asleep can drain power through the Card Detect and
Voltage Sense lines. Assume that all four lines ground the Bitsy Plus PCMCIA pull-ups
(section 6.2.12) while the card is inserted.
Digital I/Os
Review digital I/O connections for potential voltage differences from external
connections when the Bitsy Plus is asleep.
USB
Depending on how USB devices are powered and how the operating system handles
USB, USB devices may draw power during Sleep.
ADS document # 110114-1001A