Datasheet

LTM8042/LTM8042-1
13
80421fa
Junction Temperature Rise
vs Load, Buck-Boost Mode,
11.2V at 350mA LED String
Junction Temperature Rise
vs Load, Buck-Boost Mode,
15.5V at 350mA LED String
PIN FUNCTIONS
GND (Bank 1): Signal and Power Return. Tie these pads
to a local ground plane below the LTM8042/LTM8042-1
and the circuit components. In most applications, the
bulk of the heat flow out of the LTM8042/LTM8042-1 is
through these pads, so the printed circuit design has a
large impact on the thermal performance of the part. See
the PCB Layout and Thermal Considerations sections for
more details.
V
CC
(Bank 2): Internal Housekeeping Power for the
LTM8042/LTM8042-1. Connect to an external power
source between 3V and 30V. The LTM8042/LTM8042-1
can withstand transients of 40V.
BSTIN/BKLED
–
(Bank 3): Power Input for Boost Operation,
as Well as the Cathode Connection for the LED String in
Buck Mode. If the LTM8042/LTM8042-1 is used in boost
mode, these pins must be locally decoupled.
BSTOUT/BKIN (Bank 4): Output of the Boost Converter,
as Well as the Input for Buck Mode. If the LTM8042/
LTM8042-1 is used in buck mode, these pins must be
locally decoupled.
LED
+
(Bank 5): Connect this to the anode of the LED
string. This can also be connected to the PWM dimming
MOSFET if used.
RUN (Pin F1): Module Enable. Tie to 1.5V or higher to
enable the LTM8042/LTM8042-1 or 0.4V or less to dis-
able device.
SYNC (Pin G1): Frequency Synchronization Pin. Tie an
external clock signal here. The RT resistor should be
chosen to program a switching frequency that is 20%
slower than SYNC pulse frequency. Tie the SYNC pin to
GND if this feature is not used.
RT (Pin H1): Timing Resistor Pin. Used to program the
switching frequency of the LTM8042/LTM8042-1 by con-
necting a resistor from this pin to GND. The Applications
Information section of the data sheet includes a table
to determine the resistance value based on the desired
switching frequency. Minimize capacitance at this pin.
SS (Pin J1): Soft-Start Pin. Place a soft-start capacitor
here. Leave the pin open if not used.
LED CURRENT (mA)
0
0
TEMPERATURE (°C)
20010050
18
16
10
12
14
80421 G77
300250150 350
8
2
4
6
5V
IN
12V
IN
LED CURRENT (mA)
0
0
TEMPERATURE (°C)
20010050
30
25
80421 G78
300250150 350
20
5
10
15
5V
IN
12V
IN
TYPICAL PERFORMANCE CHARACTERISTICS
T
A
= 25°C, unless otherwise noted.
LTM8042-1