STEVAL-ISA052V1 STMicroelectronics, STEVAL-ISA052V1 Datasheet - Page 38

• 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
8.1
38/53
Application information
The purpose of this chapter is showing 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 PM6675S uses 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 0.8V and lower
than 2 V in order to ensure system 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 under 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 external supply. 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
f
SW
and V
=
T
D
ON
INmin
T
=
ON
K
=
OSC
) are important for the design.
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
PM6675S