PM6680ATR STMicroelectronics, PM6680ATR Datasheet - Page 24

• Manufacturer Part Number: PM6680ATR
• Description: IC CTRLR DUAL STEP DOWN 32VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6680ATR

• Applications: Controller, Embedded Computer System
• Voltage - Input: 6 ~ 36 V
• Number Of Outputs: 2
• Voltage - Output: 0.9 ~ 5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• For Use With: 497-6379 - BOARD EVALUATION FOR PM6680A497-6378 - BOARD EVALUATION FOR PM6680497-6425 - BOARD EVAL BASED ON PM6680A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6896-2; PM6680ATR

Device description
7.6
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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
An internal 100 µA current source 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 DC load is equal to the valley current limit plus half of the inductor
ripple current:
Equation 6
The output current limit depends on the current ripple, as shown in
Figure 34. Current waveforms in current limit conditions
Figure 33. Rsense sensing technique
I
LOAD
HS
LS
(max)
RDS
=
Rcsense
I
on
Lvalley
(Figure
HGATE
CSENSE
PHASE
LGATE
+
∆
33).
2
I
L
Figure
34:
PM6680A