VO

Vin

PWM

VDD

VDD

SKIP#

PWM

GND

BST

DRVH

LL

DRVL

HSgate

Vsw

LSgate

VIN

VSW

PGND

A

Gate Drive

Current (IDD)

V

Gate Drive

Voltage (VDD)

V

Input Voltage

(VIN)

V

Averaged Switched

Node Voltage

(VSW_AVG)

A

Output Current

(IOUT)

Averaging

Circuit

Control

FET

Sync

FET

A

Input Current (IIN)

CSD97396Q4M

LO

Boot

Boot_R

CBoot

Cin

Co

SKIP#

CSD97396Q4M

SLPS572 – DECEMBER 2015

www.ti.com

8.3 System Example

8.3.1 Power Loss Curves

MOSFET centric parameters such as RDS(ON) and Qgd are primarily needed by engineers to estimate the loss

generated by the devices. In an effort to simplify the design process for engineers, Texas Instruments has

provided measured power loss performance curves. Figure 4 plots the power loss of the CSD97396Q4M as a

function of load current. This curve is measured by configuring and running the CSD97396Q4M as it would be in

the final application (see Figure 14). The measured power loss is the CSD97396Q4M device power loss which

consists of both input conversion loss and gate drive loss. Equation 1 is used to generate the power loss curve.

Power Loss = (VIN × IIN) + (VDD × IDD) – (VSW_AVG × IOUT)

(1)

The power loss curve in Figure 4 is measured at the maximum recommended junction temperature of

TJ = 125°C under isothermal test conditions.

8.3.2 SOA Curves

The SOA curves in the CSD97396Q4M datasheet give engineers guidance on the temperature boundaries within

an operating system by incorporating the thermal resistance and system power loss. Figure 6 and Figure 7

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 4.0 inches (W) × 3.5 inches (L) × 0.062 inch (T) and 6 copper layers of 1 oz. copper thickness.

8.3.3 Normalized Curves

The normalized curves in the CSD97396Q4M data sheet give engineers 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 14. Power Loss Test Circuit

12

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