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PDF LT3469 Data sheet ( Hoja de datos )
| Número de pieza | LT3469 | |
| Descripción | Piezo Microactuator Driver with Boost Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT3469
Piezo Microactuator Driver
with Boost Regulator
FEATURES
Amplifier
s Current Limit: ±40mA Typical
s Input Common Mode Range: 0V to 10V
s Output Voltage Range: 1V to (VCC – 1V)
s Differential Gain Stage with High Impedance Output
(gm Stage)
s Quiescent Current (from VCC): 2mA
s Unloaded Gain: 30,000 Typical
Switching Regulator
s Generates VCC Up to 35V
s Wide Operating Supply Range: 2.5V to 16V
s High Switching Frequency: 1.3MHz
s Internal Schottky Diode
s Tiny External Components
s Current Mode Switcher with Internal Compensation
s Low Profile (1mm) SOT-23 Package
U
APPLICATIO S
s Piezo Speakers
s Piezo Microactuators
s Varactor Bias
DESCRIPTIO
The LT®3469 is a transconductance (gm) amplifier that can
drive outputs up to 33V from a 5V or 12V supply. An
internal switching regulator generates a boosted supply
voltage for the gm amplifier. The amplifier can drive
capacitive loads in the range of 5nF to 300nF. Slew rate is
limited only by the maximum output current. The 35V
output voltage capability of the switching regulator, along
with the high supply voltage of the amplifier, combine to
allow the wide output voltage range needed to drive a
piezoceramic microactuator.
The LT3469 switching regulator switches at 1.3MHz,
allowing the use of tiny external components. The output
capacitor can be as small as 0.22µF, saving space and cost
versus alternative solutions.
The LT3469 is available in a low profile ThinSOTTM package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
Piezo Microactuator Driver
5V OR 12V
47µH
35
1µF
16V
VIN
SW
VCC 6
9.09k
+
INPUT
0V TO 3V
– 10k
7
+IN
8
–IN
LT3469
+
–
2
FB
4
GND
1
OUT
100k
453k
16.5k
0.47µF
50V
VOUT
1V TO 33V
PIEZO
ACTUATOR
5nF < C < 300nF
3469 TA03
IOUT
100mA/DIV
Response Driving a 33nF Load
VOUT
10V/DIV
INPUT
5V/DIV
50µs/DIV
3469 TA04
3469f
1
1 page  
U
OPERATIO
gm Amplifier
The LT3469 is a wide output voltage range gm amplifier
designed to drive capacitive loads. Input common mode
range extends from 10V to ground. The output current is
proportional to the voltage difference across the input
terminals. When the output voltage has settled, the input
terminals will be at the same voltage; supply current of the
amplifier will be low and power dissipation will be low. If
presented with an input differential, however, the output
current can increase significantly, up to the maximum
output current (typically 40mA). The output voltage slew
rate is determined by the maximum output current and the
output capacitance, and can be quite high. With a 10nF
load, the output slew rate will typically be 4V/µs. The
capacitive load compensates the gm amplifier and must be
present for stable operation. The gain capacitance product
of the amplifier must be at least 50nF. For example, if the
amplifier is operated in a gain of 10 configuration, a
minimum capacitance of 5nF is necessary. In a gain of 20
configuration, a minimum of 2.5nF is necessary. Closed
loop –3dB bandwidth is set by the output capacitance.
Typical closed loop bandwidth is approximately:
gm
2π • AV • COUT
where gm = 200µA/mV
For example, an amplifier in a gain of 10 configuration with
10nF of output capacitance will have a closed loop –3dB
bandwidth of approximately 300kHz. Figure 3 shows typi-
100
LT3469
cal bandwidth of a gain of 10 configuration per output
capacitance.
In applications where negative phase contributions below
crossover frequency must be minimized, a phase boost
capacitor can be added, as shown in Figure 4. Larger val-
ues of CBOOST will further reduce the closed-loop negative
phase contribution, however, the amplifier phase margin
will be reduced. For an amplifier phase margin of approxi-
mately 55°, select CBOOST as follows:
CBOOST
=
COUT(R1/ R2 +
gm(R1|| R2)
1)
where gm = 200µA/mV.
In a gain of 10 configuration, choosing CBOOST as de-
scribed will lead to nearly zero closed-loop negative phase
contribution at 3kHz for values of COUT from 10nF to
200nF. The phase boost capacitor should not be used if
COUT is less than twice the minimum for stable operation.
The gain capacitance product should therefore be higher
than 100nF if a phase boost capacitor is used.
Switching Regulator
The LT3469 uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. Operation can be best understood by referring to the
Block Diagram in Figure 1. The switch controller sets the
peak current in Q1 proportional to its input. The input to the
switch controller is set by the error amplifier, A1, and is
1000
WITH PHASE
BOOST CAPACITOR
10
100
WITHOUT PHASE
BOOST CAPACITOR
1
0.1
2
20
CAPACITANCE (nF)
200
3469 F02
Figure 2. Slew Rate vs Capacitance
10
2
20
CAPACITANCE (nF)
200
3469 F03
Figure 3. Closed Loop –3dB Bandwidth
vs Capacitance in a Gain of 10 Configuration
3469f
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT3469.PDF ] | |
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