14. Maintain Power Signature
The Si3406 device integrates an MPS circuit which ensures connection with the PSE if the PD application current drops below PSE
threshold level.
There are two modes of MPS operation:
• Automatic mode MPS (consumption-based)
• User mode MPS
Automatic Mode MPS (Consumptions Based):
If
nSLEEP
is low at startup, MPS generation depends on chip current consumption:
• MPS pulses are enabled below a certain level of total PD current consumption to ensure connection with the PSE
• MPS pulses are disabled above a certain level of total PD current consumption not to degrade overall board efficiency
nSLEEP = low
I
IN
Figure 14.1. Automatic MPS Mode, nSLEEP is Low; MPS is Enabled when PD Consumption is Low; MPS is Disabled when PD
Consumption is Higher
User Mode MPS:
If
nSLEEP
is high at startup, MPS generation depends on
nSLEEP.
• if
nSLEEP
is high, MPS disabled (independently of the current consumption)
• if
nSLEEP
is low, MPS enabled (independently of the current consumption)
nSLEEP = high
I
IN
nSLEEP = low
At startup, nSLEEP was high
Figure 14.2. With nSLEEP High, MPS is Disabled (Left); with nSLEEP Low, MPS is Enabled (Right); MPS
Generation is Fully Controlled by the User
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Maintain Power Signature
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