VDD

ENABLE

PWM

GND

BOOT

DRVH

LL

DRVL

V

DD

PWM

V

IN

V

OUT

Driver IC

CSD87381P

A

V

Averaging

Circuit

V

A

A

V

Averaged Switch

Node Voltage

V

IN

V

SW

P

GND

TG

BG

Gate Drive

CSD87381P

SLPS405B – MARCH 2013 – REVISED MAY 2013

www.ti.com

The CSD87381P NexFET™ power block is an optimized design for synchronous buck applications using 5V gate

drive. The Control FET and Sync FET silicon are parametrically tuned to yield the lowest power loss and highest

system efficiency. As a result, a new rating method is needed which is tailored towards a more systems centric

environment. System level performance curves such as Power Loss, Safe Operating Area, and normalized

graphs allow engineers to predict the product performance in the actual application.

Power Loss Curves

In an effort to simplify the design process for engineers, Texas Instruments has provided measured power loss

performance curves. Figure 1 plots the power loss of the CSD87381P as a function of load current. This curve is

measured by configuring and running the CSD87381P as it would be in the final application (see Figure 27).The

measured power loss is the CSD87381P loss and consists of both input conversion loss and gate drive loss.

Equation 1 is used to generate the power loss curve.

(1)

The power loss curve in Figure 1 is measured at the maximum recommended junction temperatures of 125°C

under isothermal test conditions.

Safe Operating Curves (SOA)

The SOA curves in the CSD87381P data sheet provides guidance on the temperature boundaries within an

operating system by incorporating the thermal resistance and system power loss. Figure 3 to Figure 4 outline the

temperature and airflow conditions required for a given load current. The area under the curve dictates the safe

operating area. All the curves are based on measurements made on a PCB design with dimensions of 4” (W) x

3.5” (L) x 0.062” (T) and 6 copper layers of 1 oz. copper thickness.

Normalized Curves

The normalized curves in the CSD87381P data sheet provides guidance on the Power Loss and SOA

adjustments based on their application specific needs. These curves show how the power loss and SOA

boundaries will adjust for a given set of systems conditions. The primary Y-axis is the normalized change in

power loss and the secondary Y-axis is the change is system temperature required in order to comply with the

SOA curve. The change in power loss is a multiplier for the Power Loss curve and the change in temperature is

subtracted from the SOA curve.

Figure 27. Typical Application

10

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