STEVAL-ISA052V2 STMicroelectronics, STEVAL-ISA052V2 Datasheet - Page 34

• Manufacturer Part Number: STEVAL-ISA052V2
• Description: BOARD EVAL BASED ON PM6675A
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of STEVAL-ISA052V2

• Design Resources: STEVAL-ISA052V2 Gerber Files STEVAL-ISA052V2 Schematic STEVAL-ISA052V2 Bill of Material
• Main Purpose: DC/DC, Step Down with LDO
• Outputs And Type: 2, Non-Isolated
• Voltage - Output: 1.5V, 0.6 ~ 3.3V
• Voltage - Input: 4.5 ~ 36 V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: PM6675AS
• Input Voltage: 4.5 V to 36 V
• Output Voltage: 1.5 V
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Supplier Unconfirmed
• For Use With/related Products: PM6675AS
• Other names: 497-8413

Application information
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Application information
The purpose of this chapter is to show the design procedure of the switching section.
The design starts from three main specifications:
●
●
●
It’s also possible that specific designs should involve other specifications.
The following paragraphs will guide the user into a step-by-step design.
External components selection
The PM6675AS employes a pseudo-fixed frequency, Constant On-Time (COT) controller as
the core of the switching section. The switching frequency can be set by connecting an
external divider to the VOSC pin. The voltage seen at this pin must be greater than 0.8 V
and lower than 2 V in order to take advantage of the internal block linearity.
Nearly constant switching frequency is achieved by the system loop in steady-state
operating conditions by varying the On-Time duration, avoiding thus the need for a clock
generator. The On-Time one shot duration is directly proportional to the output voltage,
sensed at VSNS pin, and inversely proportional to the input voltage, sensed at the VOSC
pin, as follows:
Equation 25
where K
(40 ns typ.).
The duty-cycle of the buck converter is, in steady-state conditions, given by
Equation 26
The switching frequency is thus calculated as
Equation 27
The input voltage range, provided by the battery or the AC adapter. The two extreme
values (V
The maximum load current, indicated with I
The maximum allowed output voltage ripple V
OSC
is a constant value (130 ns typ.) and τ is the internal propagation delay
INmax
and V
f
SW
INmin
=
) are important for the design.
T
D
ON
T
=
ON
K
=
OSC
D =
K
V
V
OSC
OUT
⋅
IN
V
V
V
V
OUT
OSC
SNS
IN
V
V
LOAD,MAX
OSC
SNS
RIPPLE,MAX
=
+
α
α
τ
OSC
OUT
.
⋅
K
.
OSC
1
PM6675AS