DCM4623xD2H31E0y7z
Thermal Design
Based on the safe thermal operating area shown in page 5, the full
rated power of the DCM4623xD2H31E0y7z can be processed
provided that the top, bottom, and leads are all held below 90°C.
These curves highlight the benefits of dual sided thermal
management, but also demonstrate the flexibility of the Vicor ChiP
platform for customers who are limited to cooling only the top or the
bottom surface.
Thermal Resistance Top
INT-TOP°C / W
MAX INTERNAL TEMP
θ
Thermal Resistance Bottom
INT-BOTTOM°C / W
Thermal Resistance Leads
θ
θINT-LEADS°C / W
+
–
+
–
T
CASE_BOTTOM(°C)
TLEADS(°C)
TCASE_TOP(°C)
Power Dissipation (W)
The OTP sensor is located on the top side of the internal PCB
structure. Therefore in order to ensure effective over-temperature
fault protection, the case bottom temperature must be constrained
by the thermal solution such that it does not exceed the temperature
of the case top.
Figure 18 — One side cooling and leads thermal model
Figure 18 shows a scenario where there is no bottom side cooling.
In this case, the heat flow path to the bottom is left open and the
equations now simplify to:
The ChiP package provides a high degree of flexibility in that it
presents three pathways to remove heat from internal power
dissipating components. Heat may be removed from the top surface,
the bottom surface and the leads. The extent to which these three
surfaces are cooled is a key component for determining the
maximum power that is available from a ChiP, as can be seen from
Figure 17.
TINT – PD1 • θINT-TOP = TCASE_TOP
TINT – PD3 • θINT-LEADS = TLEADS
PDTOTAL = PD1 + PD3
Since the ChiP has a maximum internal temperature rating, it is
necessary to estimate this internal temperature based on a real
thermal solution. Given that there are three pathways to remove heat
from the ChiP, it is helpful to simplify the thermal solution into a
roughly equivalent circuit where power dissipation is modeled as a
current source, isothermal surface temperatures are represented as
voltage sources and the thermal resistances are represented as
resistors. Figure 17 shows the "thermal circuit" for a 4623 ChiP DCM,
in an application where both case top and case bottom, and leads are
cooled. In this case, the DCM power dissipation is PDTOTAL and the
Thermal Resistance Top
INT-TOP°C / W
MAX INTERNAL TEMP
θ
Thermal Resistance Bottom
INT-BOTTOM°C / W
Thermal Resistance Leads
θ
θINT-LEADS°C / W
+
–
T
CASE_BOTTOM(°C)
TLEADS(°C)
TCASE_TOP(°C)
Power Dissipation (W)
three surface temperatures are represented as TCASE_TOP, TCASE_BOTTOM
and TLEADS. This thermal system can now be very easily analyzed
with simple resistors, voltage sources, and a current source.
,
Figure 19 — One side cooling thermal model
Figure 19 shows a scenario where there is no bottom side and leads
cooling. In this case, the heat flow path to the bottom is left open and
the equations now simplify to:
This analysis provides an estimate of heat flow through the various
pathways as well as internal temperature.
TINT – PD1 • θINT-TOP = TCASE_TOP
Thermal Resistance Top
INT-TOP°C / W
MAX INTERNAL TEMP
PDTOTAL = PD1
θ
Thermal Resistance Bottom
INT-BOTTOM°C / W
Thermal Resistance Leads
θ
θINT-LEADS°C / W
+
–
+
–
+
–
T
CASE_BOTTOM(°C)
TLEADS(°C)
TCASE_TOP(°C)
Power Dissipation (W)
Figure 17 — Double side cooling and leads thermal model
Alternatively, equations can be written around this circuit and
analyzed algebraically:
TINT – PD1 • θINT-TOP = TCASE_TOP
TINT – PD2 • θINT-BOTTOM = TCASE_BOTTOM
TINT – PD3 • θINT-LEADS = TLEADS
PDTOTAL = PD1+ PD2+ PD3
Where TINT represents the internal temperature and PD1, PD2, and
PD3 represent the heat flow through the top side, bottom side, and
leads respectively.
Figure 20 — Thermal Specified Operating Area: Max Power
Dissipation vs. Case Temp for current
limited operation
DCM™ DC-DC Converter
Rev 1.0
Page 19 of 23
08/2017
VICOR [ VICOR CORPORATION ]
