V-

V+

Grey area is

ground layer

0.1 µF

bypasses

0.01 µF

bypass

Output

Flag

R2

R1

VIN

DDPAK-7

PDIP-8 and

SOIC-8

Gain Resistor

Gain Resistor

Flag

V+

Bypass

Capacitor

VOUT

V-

VIN

VIN

-

+

GND

OPA551, OPA552

SBOS100B – JULY 1999 – REVISED JANUARY 2016

www.ti.com

10 Layout

10.1 Layout Guidelines

The circuit board must have as much ground plane area as possible. Power supply and output traces must be

sized to handle the required current. Keep input and output terminals separated as much as possible.

10.2 Layout Example

Figure 34. Layout Example (OPA551)

10.3 Power Dissipation

Internal power dissipation of these operational amplifiers can be quite large. Many of the specifications for the

OPA55x are for a specified junction temperature. If the device is not subjected to internal self-heating, the

junction temperature is the same as the ambient. However, in practical applications, the device self-heats and

the junction temperature becomes significantly higher than ambient. After junction temperature has been

established, performance parameters that vary with junction temperature can be determined from the

performance curves. The following calculation can be performed to establish junction temperature as a function

of ambient temperature and the conditions of the application.

Consider the OPA551 in a circuit configuration where the load is 600

Ω and the output voltage is 15 V. The

supplies are at ±30 V and the ambient temperature (TA) is 40°C. The θJA for the 8-pin PDIP package is 100°C/W.

First, the internal heating of the operational amplifier is in Equation 4:

PD(internal) = IQ × VS = 7.2 mA × 60 V = 432 mW

(4)

The output current (IO) can be calculated in Equation 5:

IO = VOUT/RL = 15 V/600 Ω = 25 mA

(5)

The power being dissipated (PD) in the output transistor of the amplifier can be calculated in Equation 6 and

Equation 7:

PD(output stage) = IO× (VS –– VO) = 25 mA × (30 – 15) = 375 mW

(6)

PD(total) = PD(internal) + PD(output stage) = 432 mW + 375 mW = 807 mW

(7)

The resulting junction temperature can be calculated in Equation 8 and Equation 9:

TJ = TA + PD θJA

(8)

TJ = 40°C + 807 mW × 100°C/W = 120.7°C

where

•

TJ = junction temperature (°C)

•

TA = ambient temperature (°C)

•

θJA = junction-to-air thermal resistance (°C/W)

(9)

For the DDPAK/TO-263 package, the

θJA is 65°C/W with no heat sinking, resulting in a junction temperature of

92.5°C.

18

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