LTM4607 datasheet(13/32 Pages) LINER

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LTM8042/LTM8042-1

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.

VCC (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)

200

100

80421 G77

300

250

150

350

5VIN

12VIN

LED CURRENT (mA)

200

100

80421 G78

300

250

150

350

5VIN

12VIN

TYPICAL PERFORMANCE CHARACTERISTICS T

A = 25°C, unless otherwise noted.

LTM8042-1

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