STEVAL-ISA051V1 STMicroelectronics, STEVAL-ISA051V1 Datasheet - Page 41

• Manufacturer Part Number: STEVAL-ISA051V1
• Description: BOARD EVAL PM6670S DDR2/3
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of STEVAL-ISA051V1

• Design Resources: STEVAL-ISA051V1 Gerber Files STEVAL-ISA051V1 Schematic STEVAL-ISA051V1 Bill of Material
• Main Purpose: Special Purpose DC/DC, DDR Memory Supply
• Outputs And Type: 4, Non-Isolated
• Voltage - Output: 1.5V, 1.8V
• Voltage - Input: 4.5 ~ 28V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: PM6670
• Input Voltage: 4.5 V to 28 V
• Output Voltage: 1.8 V, 1.5 V
• Product: Power Management Modules
• Silicon Manufacturer: ST Micro
• Silicon Core Number: PM6670S
• Kit Application Type: Power Management
• Application Sub Type: DDR2/3 Memory Power Supply Controller
• Kit Contents: Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: PM6670S
• Other names: 497-8411

PM6670S
8.1.1
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 higher efficiency, but the transient response is critical, especially if
V
system stability and jitter-free operations (see output capacitor selection paragraph). The
product of the output capacitor's ESR multiplied by the inductor ripple current must be taken
into 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, ΔI
Given these considerations, the inductance value can be calculated with the following
expression:
Equation 29
where f
ΔI
Once the inductor value is determined, the inductor ripple current is then recalculated:
Equation 30
The next step is the calculation of the maximum r.m.s. inductor current:
Equation 31
The inductor must have an r.m.s. current greater than I
stability.
Then the calculation of the maximum inductor peak current follows:
Equation 32
I
L,PEAK
INmin
L
is the inductor ripple current.
- V
SW
is important in inductor selection in term of its saturation current.
OUT
is the switching frequency, V
is small. Moreover a minimum output ripple voltage is necessary to assure
I
Δ
, L
Doc ID 14432 Rev 4
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
Δ ⋅
,
V
MAX
, occurs at the maximum input voltage.
OUT
,
MAX
I
−
L
⋅
L
)
V
2
OUT
⋅
+
+
V
V
Δ
(
OUT
Δ
IN
I
⋅
, L
I
L,RMS
V
, L
2
MAX
V
12
IN
MAX
OUT
,
MAX
)
in order to assure thermal
2
OUT
Application information
is the output voltage and
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