STEVAL-ISA052V1 STMicroelectronics, STEVAL-ISA052V1 Datasheet - Page 40

• Manufacturer Part Number: STEVAL-ISA052V1
• Description: KIT EVAL PM6675S HE CTLR 2A REG
• Manufacturer: STMicroelectronics

Specifications of STEVAL-ISA052V1

• Main Purpose: DC/DC, Step Down with LDO
• Outputs And Type: 2, Non-Isolated
• Voltage - Output: 1.5V, 0.6 ~ 3.3V
• Current - Output: 10A, 2A
• Voltage - Input: 4.5 ~ 28 V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: PM6675
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-8426

Application information
8.1.1
40/53
Inductor selection
Once the switching frequency has been defined, the inductance value depends on the
desired inductor ripple current. Low inductance value means great ripple current that brings
poor efficiency and great output noise. On the other hand a great current ripple is desirable
for fast transient response when a load step is applied.
High inductance brings to good efficiency but the transient response is critical, especially if
V
system stability and jitter-free operations (see
page 42
must be taken in consideration. A good trade-off between the transient response time, the
efficiency, the cost and the size is choosing the inductance value in order to maintain the
inductor ripple current between 20 % and 50 % (usually 40 %) of the maximum output
current.
The maximum inductor ripple current, ∆I
Given these considerations, the inductance value can be calculated using the following
expression:
Equation 30
where f
∆I
Once the inductor value is determined, the inductor ripple current is then recalculated:
Equation 31
The next step is the calculation of the maximum r.m.s. inductor current:
Equation 32
The inductor must have an r.m.s. current greater than I
stability.
Then the calculation of the maximum inductor peak current follows:
Equation 33
I
L,PEAK
INmin
L
is the inductor ripple current.
- V
SW
is important when choosing the inductor, in term of its saturation current.
). The product of the output capacitor ESR multiplied by the inductor ripple current
OUT
is the switching frequency, V
is little. Moreover a minimum output ripple voltage is necessary to assure
I
∆
, L
RMS
I
, L
I
MAX
, L
PEAK
L
=
=
=
I (
IN
V
V
=
LOAD
L,MAX
fsw
IN
IN
I
is the input voltage, V
LOAD
,
MAX
−
fsw
∆ ⋅
,
V
MAX
OUT
,
MAX
Section 8.1.3: Output capacitor selection on
, occurs at the maximum input voltage.
I
−
L
⋅
L
)
V
2
OUT
⋅
+
+
V
V
∆
(
OUT
∆
IN
I
⋅
, L
I
L,RMS
V
2
, L
MAX
V
12
IN
MAX
OUT
,
MAX
)
in order to assure thermal
2
OUT
is the output voltage and
PM6675S