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LT3469

3469f

as short as possible. To prevent electromagnetic interfer-

ence (EMI) problems, proper layout of the high frequency

switching path is essential. The voltage signal of the SW

pin has sharp rise and fall edges. The SW pin should be

surrounded on three sides by metal connected to VCC to

shield +IN and –IN. Minimize the area of all traces con-

nected to the SW pin and always use a ground plane under

the switching regulator to minimize interplane coupling. In

addition, the ground connection for the feedback resistor

R1 should be tied directly to the GND pin and not shared

with any other component, ensuring a clean, noise-free

connection. The ground return of the piezoceramic

microactuator should also have a direct and unshared

connection to the GND pin. The GND connection to R5

should be tied directly to the ground of the source gener-

ating the INPUT signal to avoid error induced by voltage

drops along the GND line. Recommended component

placement is shown in Figure 6.

Thermal Considerations and Power Dissipation

The LT3469 combines large output drive with a small

package. Because of the high supply voltage capability, it

is possible to operate the part under conditions that

exceed the maximum junction temperature. Maximum

junction temperature (TJ) is calculated from the ambient

temperature (TA) and power dissipation (PD) as follows:

TJ = TA + (PD • 250°C/W)

Worst-case power dissipation occurs at maximum output

swing, frequency, capacitance and VCC. For a square wave

input, power dissipation is calculated from the amplifier

quiescent current (IQ), input frequency (f), output swing

(VOUT(P-P)), capacitive load (CL), amplifier supply voltage

(VCC) and switching regulator efficiency (η) as follows:

IfV

()()

OUT(P-P)

Example: LT3469 at TA = 70°C, VCC = 35V, CL = 200nF,

f = 3kHz, VOUT(P-P) = 4V, η = 80%:

kHz

C W

()( )

=° +

() =°

2 5

200

080

214

250

124

.•

•

•/

Do not exceed the maximum junction temperature of

125

°C.

Figure 6. Recommended Component Placement

INPUT

VIN

VIAS TO GROUND PLANE

PIEZ0

ACTUATOR

GND

3469 F06

OPERATIO

Piezo Speaker Driver

–

+IN

GND

VCC

LT3469

VIN

294k

17.4k

0.47

µF

35V

VOUT

1V TO 20V

C1, C2: X5R OR X7R DIELECTRIC

L1: MURATA LQH32CN470

SOUND PRESSURE LEVEL: 87dB AT 750Hz/10VP-P/10cm

WITH A 55nF PIEZO SPEAKER. IVIN WITH VIN = 3.3V:

24mA AT 750Hz/10VP-P WITH A 55nF PIEZO SPEAKER

PIEZO

SPEAKER

8nF < C < 300nF

20k

–

16.9k

113k

µH

–IN

OUT

3469 TA01

VIN

3V TO 6V

INPUT

0V TO 3V

µF

TYPICAL APPLICATIO

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

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