Datasheet

LT3469
7
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 V
CC
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 (T
J
) is calculated from the ambient
temperature (T
A
) and power dissipation (P
D
) as follows:
T
J
= T
A
+ (P
D
• 250°C/W)
Worst-case power dissipation occurs at maximum output
swing, frequency, capacitance and V
CC
. For a square wave
input, power dissipation is calculated from the amplifier
quiescent current (I
Q
), input frequency (f), output swing
(V
OUT(P-P)
), capacitive load (C
L
), amplifier supply voltage
(V
CC
) and switching regulator efficiency (η) as follows:
P
IfV CV
D
QLCC
=
+
()
()
OUT(P-P)
η
Example: LT3469 at T
A
= 70°C, V
CC
= 35V, C
L
= 200nF,
f = 3kHz, V
OUT(P-P)
= 4V, η = 80%:
P
mA kHz V nF V
mW
T C mW C W C
D
J
=
+
()()
=
=°+ °
()
=°
2 5 3 4 200 35
080
214
70 214 250 124
.••
.
•/
Do not exceed the maximum junction temperature of
125°C.
Figure 6. Recommended Component Placement
R4
INPUT
R5
R1
R3
R2
C1 C2
V
IN
VIAS TO GROUND PLANE
PIEZ0
ACTUATOR
GND
L
3469 F06
OPERATIO
U
Piezo Speaker Driver
+
–
+IN
35
6
2
4
1
8
7
GND
FB
V
CC
SW
LT3469
V
IN
294k
17.4k
C2
0.47µF
35V
V
OUT
1V TO 20V
C1, C2: X5R OR X7R DIELECTRIC
L1: MURATA LQH32CN470
SOUND PRESSURE LEVEL: 87dB AT 750Hz/10V
P-P
/10cm
WITH A 55nF PIEZO SPEAKER. I
VIN
WITH V
IN
= 3.3V:
24mA AT 750Hz/10V
P-P
WITH A 55nF PIEZO SPEAKER
PIEZO
SPEAKER
8nF < C
< 300nF
20k
+
–
16.9k
113k
L1
47µH
–IN
OUT
3469 TA01
V
IN
3V TO 6V
INPUT
0V TO 3V
C1
1µF
U
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.