LM76005 datasheet(37/51 Pages) TI2

37 / 51 page

• RθJA = junction-to-ambient thermal resistance of the device in °C/W

• TA = ambient temperature in °C.

The maximum operating junction temperature of the LM76005 is 125°C. RθJA is highly related to PCB size and

layout, as well as environmental factors such as heat sinking and air flow. Figure 10-2 shows measured results

of RθJA with different copper area on a 2-layer board and a 4-layer board.

1W @0 fpm - 2layer

1W @0 fpm - 4layer

2W @0 fpm - 2layer

2W @0 fpm - 4layer

Copper Area

30mm × 30mm

40mm × 40mm

50mm × 50mm

70mm ×70mm

Figure 10-2. Measured RθJA versus PCB Copper Area on a 2-Layer Board and a 4-Layer Board

10.1.4 Feedback Resistors

To reduce noise sensitivity of the output voltage feedback path, it is important to place the resistor divider and

CFF close to the FB pin, rather than close to the load. The FB pin is the input to the error amplifier, so it is a high

impedance node and very sensitive to noise. Placing the resistor divider and CFF closer to the FB pin reduces

the trace length of FB signal and reduces noise coupling. The output node is a low impedance node, so the trace

from VOUT to the resistor divider can be long if short path is not available.

If voltage accuracy at the load is important, make sure voltage sense is made at the load. Doing so corrects for

voltage drops along the traces and provide the best output accuracy. The voltage sense trace from the load to

the feedback resistor divider must be routed away from the SW node path, the inductor, and VIN path to avoid

contaminating the feedback signal with switch noise, while also minimizing the trace length. This is most

important when high value resistors are used to set the output voltage. TI recommends routing the voltage sense

trace on a different layer than the inductor, SW node, and VIN path, such that there is a ground plane in between

the feedback trace and inductor / SW node / VIN polygon. This provides further shielding for the voltage

feedback path from switching noises.

www.ti.com

LM76005

SNVSBK5A – FEBRUARY 2020 – REVISED JULY 2020

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LM76005 Datasheet(PDF) 37 Page - Texas Instruments