PM6680 STMicroelectronics, PM6680 Datasheet - Page 27

• Manufacturer Part Number: PM6680
• Description: IC CTRLR DUAL STEP DOWN 32VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6680

• Applications: Controller, Notebook Power System
• Voltage - Input: 6 ~ 28 V
• Number Of Outputs: 2
• Voltage - Output: 0.9 ~ 5.5 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• Output Voltage: 5 V, 0.9 V to 5.5 V, 0.9 V to 3.3 V
• Output Current: 0.33 A
• Input Voltage: 5.5 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 10 C
• 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

PM6680
An internal 100 µA current source is connected to CSENSE pin and determines a voltage
drop on R
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 6
The output current limit depends on the current ripple, as shown in
Figure 34. Current waveforms in current limit conditions
Being fixed the valley threshold, the greater the current ripple is, greater the DC output
current is The valley current limit can be set with resistor R
Equation 7
Where I
Consider the temperature effect and the worst case value in R
The accuracy of the valley current threshold detection depends on the offset of the internal
comparator (∆V
Equation 8
Current
CSENSE
CSENSE
∆
I
Lvalley
I
Lvalley
OFF
= 100 uA, R
. If the voltage across the sensing element is greater than this voltage
=
) and on the accuracy of the current generator(∆V
DC current limit = maximum load
∆
I
CSENSE
I
CSENSE
DSon
+
⎡
⎢
⎣
R
is the drain-source on resistance of the low side switch.
I
R
LOAD
CSENSE
Valley current threshold
CSENSE
Inductor current
(max)
∆
V
=
OFF
×
I
R
=
CSENSE
DSon
I
Lvalley
I
CSENSE
×
I
×
+
Lvalley
100
∆
2
I
L
⎤
⎥
⎦
CSENSE
+
∆
DSon
R
R
Maximum load current
is influenced by the
inductor current ripple
CSENSE
CSENSE
:
Figure 34
calculation.
CSENSE
Device description
+
∆
R
R
):
:
SNS
SNS
Time
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