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PM6685TR View Datasheet(PDF) - STMicroelectronics

Part Name
Description
MFG CO.
'PM6685TR' PDF : 52 Pages View PDF
Device description
PM6685
If, due to the load, the frequency is higher than 33kHz, the device works like in skip mode.
No-audible skip mode reduces audio frequency noise that may occur in pulse skip mode at
very light loads, keeping the efficiency higher than in PWM mode.
7.6
Current limit
The current-limit circuit employs a “valley” current-sensing algorithm. During the conduction
time of the low side MOSFET the current flowing through it is sensed. The current-sensing
element is the low side MOSFET on-resistance(Figure 33)
Figure 33. RDSON sensing technique
HS
HGATE
PHASE
Rcsense
CSENSE
LS
RDSon
LGATE
An internal 100µA IL current source (ICSENSE) is connected to CSENSE pin and determines
a voltage drop on RCSENSE. If the voltage across the sensing element is greater than this
voltage drop, the controller doesn’t initiate a new cycle. A new cycle starts only when the
sensed current goes below the current limit.
Since the current limit circuit is a valley current limit, the actual peak current limit is greater
than the current limit threshold by an amount equal to the inductor ripple current. Moreover
the maximum output current is equal to the valley current limit plus half of the inductor ripple
current:
Equation 5
ILOAD (max)
=
ILvalley
+
IL
2
The output current limit depends on the current ripple, as shown in Figure 34 on page 27:
26/52
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