Data Sheet

LT7200S

analog.com

Rev 0

25 of 35

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Other “hidden” losses such as transition loss, copper trace, and internal load resistances can account for

additional efficiency degradations in the overall power system. It is very important to include these “system” level

losses in the system design. Transition loss arises from the brief amount of time the top power MOSFET spends in

the saturated region during switch node transitions. The LT7200S internal power devices switch quickly enough

that these losses are not significant compared to other sources. Other losses including diode conduction losses

during dead-time and inductor core losses, which generally account for less than 2% total additional loss.

Thermal Conditions

In some applications where the LT7200S is operated at a combination of high ambient temperature, high switching

frequency, high VIN, and high output load, the required power dissipation might push the part to exceed its maximum

junction temperature.

To avoid the LT7200S from exceeding the maximum junction temperature, maximum current rating is derated

depending on the operating conditions. The temperature rise of the part varies depending on the thickness of copper

on the PCB board, the number of layers of the board, and the shape of copper trace. In general, a thick continuous

piece of copper on the top layer of the PCB for SW and GND pins greatly improves the thermal performance of the

part.

Figure 37 shows case temperature rise curve of the LT7200S on a standard 6-layer, 2oz copper per layer PCB board

(LT7200S standard demo board). VOUT is set to 1.2V in all curves.

Figure 37. Case Temperature Rise

Silent Switcher Architecture

The LT7200S has integrated capacitors that allow it to operate at high switching frequencies efficiently. The internal

VIN bypass capacitors allow the SW edges to transition extremely fast, effectively reducing transition loss. The

capacitors also greatly reduce SW overshoot during top FET turn-on, which improves the robustness of the device

over time.

Board Layout Considerations

When laying out the printed circuit board, use the following checklist to ensure proper operation of the LT7200S (see

Figure 38). Check the following in the layout:

1. Do the capacitors CIN connect to the PVIN and GND as close as possible? These capacitors provide the AC current to

the internal power MOSFETs and their drivers.