ADA4700-1ARDZ-R7 datasheet(22/28 Pages) AD

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ADA4700-1

Data Sheet

APPLICATIONS INFORMATION

THERMAL MANAGEMENT

Thermal management of high power amplifiers such as the

ADA4700-1 is an essential consideration in system design. Two

conditions affect junction temperature (TJ): power dissipation

(PD) of the device and ambient temperature (TA) surrounding the

package. This relationship is shown in Equation 1.

TJ = PD × θJA + TA

(1)

where θJA is the thermal resistance between the die and the ambient

environment. Power dissipation is the sum of quiescent power of

the device and the power required to drive a load. Power

dissipation for the sourcing current is shown in Equation 2.

PD = ((V+) − (V−)) × ISY + ((V+) − VOUT) × IOUT

(2)

Replace ((V+) − VOUT) in Equation 2 with ((V−) − VOUT) when

sinking current.

The specified thermal resistance of the ADA4700-1 is 45°C/W.

Printed circuit board (PCB) layout and an external heat sink

can improve thermal performance by reducing θJA.

To reduce the thermal resistance between the junction and

ambient environment, the exposed pad of the ADA4700-1 can

be soldered to the V− plane layer of the PCB, which acts as a

heat sink. By using the PCB layout shown in Figure 60, θJA

reduces to 26°C/W.

The ADA4700-1 guards the die from exceeding the absolute

maximum temperature. When the die reaches a junction

temperature greater than 145°C, thermal regulation is triggered,

the supply current is reduced, and the output load current is

limited.

SAFE OPERATING AREA

The safe operating area (SOA) of Figure 59 is the range of voltages,

currents, and temperatures under which an amplifier can safely

operate without failure. It is directly dependent on the ambient

temperature and the thermal resistance. Figure 59 shows the

SOA for the ADA4700-1 at steady state using the PCB shown in

Figure 60. The duration of the 30 mA load driven is 180 seconds.

Different time intervals produce alternate sets of curves. The

guaranteed ambient temperature range of the ADA4700-1 is −40°C

to +85°C. The 125°C shown in Figure 59 is for reference only.

To maintain normal operation, the ADA4700-1 must remain in

the SOA (area under each curve) up to an ambient temperature

of 85°C.

Figure 59. Safe Operating Area with θJA = 26°C/W

Figure 60. Thermal Landing and PCB Material Used to Obtain a θJA of 26°C/W

100

VCC – VOUT (V)

101Ω

V+ = +6V TO +100V

–

V– = –3V

+3V

VOUT

–40°C

+25°C

+85°C

θJA = 26°C/W

+125°C

PAD

COPPER

TOP/BOTTOM: 1.5oz

INTERNAL LAYERS: 1oz

4-LAYER FR4 PCB

WITH INTERNAL

GROUND AND

POWER PLANE.

25.4mm

(1000mil)

9.65mm

(380mil)

12.7mm

(500mil)

6.1mm

(240mil)

9.65mm

(380mil)

LANDING VIAS:

EPOXY FILLED

ARRAY: 3 × 4

DIAMETER: a = 0.3048mm (12mil)

PITCH: b = 0.762mm (30mil)

PADDLE VIAS:

EPOXY FILLED

ARRAY: 10 × 8

DIAMETER: a = 0.3048mm (12mil)

PITCH: c = 1.27mm (50mil)

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