TOLL/TOLT Package Series: What Are the Differences?

Both TOLL (Transistor Outline Leadless) and TOLT (Transistor Outline Leaded Topside) packages belong to the TOLx package family, yet they differ significantly in several respects.

Preface

Both TOLL (Transistor Outline Leadless) and TOLT (Transistor Outline Leaded Topside) packages belong to the TOLx package family, yet they differ significantly in several respects.

I. Cooling Methods and Thermal Performance

TOLL package ：

It employs bottom-side heat dissipation.

The thermal path is relatively long: heat conducts from the junction to the case, then through the solder to the PCB, and finally via vias (high-density vias) to the heatsink. The thermal path is relatively long: Junction → Case → Solder → PCB → VIAs → PCB → TIM → Heatsink.

Due to the relatively long heat dissipation path, thermal efficiency may be somewhat compromised.

TOLT package:

It employs top-side heat dissipation.

Shorter thermal path: Heat is conducted directly from the junction to the case, and then through the thermal interface material (TIM) straight to the heatsink. This top‑side cooling approach results in a shorter thermal path: Junction → Case → TIM → Heatsink.

The top‑side heat dissipation approach significantly enhances the device’s thermal performance, reduces thermal management costs, and improves both reliability and overall performance.

Test and analysis indicate that the TOLT package can significantly reduce the thermal resistance between the GaN switch and the heat sink. Compared with the TOLL package, the TOLT package reduces Rth(j‑heatsink) by approximately 30% and enables more than 90% of the generated heat to be dissipated through the heat sink.

II. Board Footprint and Layout

TOLL Package:

Due to the bottom‑side heat dissipation approach, the driver cannot be mounted on the back side of the power devices, resulting in a relatively large footprint.

TOLT package:

Since GaN power devices have no electrical connections beneath them and generate little heat, the driver can be routed on the back side.

It better achieves magnetic-field cancellation in the driver traces, reducing board‑area footprint in high‑density power supplies and thereby enhancing power density.

III. Application Scenarios

TOLL Package:

It has been widely adopted in high-current applications such as data centers, inverter‑based energy storage, and electric vehicles.

TOLT package:

It is primarily intended for applications requiring superior thermal performance, such as electric bicycles, light electric vehicles (LEVs), power tools, and battery management systems.

It is also suitable for high‑power‑density designs, such as high‑performance products like the OptiMOS™ 5 power MOSFET.