PM6680ATR STMicroelectronics, PM6680ATR Datasheet - Page 30

• 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

Design guidelines
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9.1
9.2
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Design guidelines
The design of a switching section starts from two parameters:
●
●
Switching frequency
It's possible to set 3 different working frequency ranges for the two sections with FSEL pin
(
Switching frequency mainly influences two parameters:
●
●
Inductor selection
Once that switching frequency is defined, inductor selection depends on the desired
inductor ripple current and load transient performance.
Low inductance means great ripple current and could generate great output noise. On the
other hand, low inductor values involve fast load transient response.
A good compromise between the transient response time, the efficiency, the cost and the
size is to choose the inductor value in order to maintain the inductor ripple current ∆I
between 20 % and 50 % of the maximum output current I
occurs at the maximum input voltage. With this considerations, the inductor value can be
calculated with the following relationship:
Equation 12
where fsw is the switching frequency, V
∆I
In order to prevent overtemperature working conditions, inductor must be able to provide an
RMS current greater than the maximum RMS inductor current I
Equation 13
Where ∆I
Table 6
L
is the selected inductor ripple current.
Input voltage range: in notebook applications it varies from the minimum battery
voltage, VINmin to the AC adapter voltage, V
Maximum load current: it is the maximum required output current, I
Inductor size: for a given saturation current and RMS current, greater frequency allows
to use lower inductor values, which means smaller size.
Efficiency: switching losses are proportional to frequency. High frequency generally
involves low efficiency.
).
L(max)
is the maximum ripple current:
I
LRMS
=
L
I (
=
LOAD
V
IN
f
IN
sw
is the input voltage, V
(max))
−
×
V
∆
OUT
I
L
2
×
INmax
+
V
(
V
OUT
∆
IN
I
.
L
(max))
12
LOAD(max)
OUT
2
LRMS
. The maximum ∆I
is the output voltage and
:
LOAD(max)
.
PM6680A
L
L