Datasheet

LTM8042/LTM8042-1
27
80421fa
APPLICATIONS INFORMATION
The most appropriate way to use the coefficients is when
running a detailed thermal analysis, such as FEA, which
considers all of the thermal resistances simultaneously.
None of them can be individually used to accurately pre-
dict the thermal performance of the product, so it would
be inappropriate to attempt to use any one coefficient to
correlate to the junction temperature versus load graphs
given in the LTM8042/LTM8042-1 data sheet.
A graphical representation of these thermal resistances
is given in Figure 5.
The blue resistances are contained within the µModule
regulator, and the green are outside.
80421 F05
µMODULE DEVICE
JUNCTION-TO-CASE (TOP)
RESISTANCE
JUNCTION-TO-BOARD RESISTANCE
JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)
CASE (TOP)-TO-AMBIENT
RESISTANCE
BOARD-TO-AMBIENT
RESISTANCE
JUNCTION-TO-CASE
(BOTTOM) RESISTANCE
JUNCTION A
t
CASE (BOTTOM)-TO-BOARD
RESISTANCE
The die temperature of the LTM8042/LTM8042-1 must be
lower than the maximum rating of 125°C, so care should
be taken in the layout of the circuit to ensure good heat
sinking of the LTM8042/LTM8042-1. The bulk of the
heat flow out of the LTM8042/LTM8042-1 is through the
bottom of the module and the LGA pads into the printed
circuit board. Consequently, a poor printed circuit board
design can cause excessive heating, resulting in impaired
performance or reliability. Please refer to the PCB Layout
section for printed circuit board design suggestions.
Figure 5
TYPICAL APPLICATIONS
Boost Operation, Driving 6 White LEDs at 1A
80421 TA02
LTM8042
RT GND CTL
V
CC
RUN
BSTIN/BKLED
–
PWM
SYNC
TGEN
SS
V
IN
11.6V TO 19V
LED
+
TG
BSTOUT/BKIN
4.7µF
22.6k
f
SW
= 750kHz
4.7µF
UP TO 20.6V
1A