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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 (V CC - 1V) s Differential Gain Stage with High Impedance Output (gm Stage) s Quiescent Current (from V ): 2mA CC s Unloaded Gain: 30,000 Typical Switching Regulator 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
s
DESCRIPTIO
The LT(R)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 0.22F, 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.
APPLICATIO S
s s s
Piezo Speakers Piezo Microactuators Varactor Bias
TYPICAL APPLICATIO
47H 5V OR 12V 1F 16V 3 VIN
Piezo Microactuator Driver Response Driving a 33nF Load
VCC FB LT3469 GND 9.09k 7 8 10k 100k 4 1 VOUT 1V TO 33V PIEZO ACTUATOR 5nF < C < 300nF
3469 TA03
5 SW 6 453k 2 16.5k 0.47F 50V
VOUT 10V/DIV IOUT 100mA/DIV
+
INPUT 0V TO 3V
+IN -IN
+ -
OUT
INPUT 5V/DIV 50s/DIV
3469 TA04
-
U
3469f
U
U
1
LT3469
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW OUT 1 FB 2 VIN 3 GND 4 8 -IN 7 +IN 6 VCC 5 SW
VIN Voltage ............................................................. 16V SW Voltage ............................................................. 40V VCC Voltage............................................................. 38V +IN, -IN Voltage ..................................................... 10V FB Voltage ................................................................ 3V Current Into SW Pin ................................................. 1A Operating Temperature Range (Note 2) .. - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LT3469ETS8 TS8 PART MARKING LTACA
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23
TJMAX = 125C, JA = 250C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 2) VIN = 5V, VCC = 35V, unless otherwise noted.
PARAMETER gm Amplifier Input Offset Voltage Input Offset Current Input Bias Current Input Resistance--Differential Mode Input Resistance--Common Mode Common Mode Rejection Ratio Power Supply Rejection Ratio--VIN Power Supply Rejection Ratio--VCC Gain Transconductance Maximum Output Current Maximum Output Voltage, Sourcing Minimum Output Voltage, Sinking Output Resistance Supply Current--VCC Switching Regulator Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage FB Pin Bias Current FB Line Regulation Supply Current--VIN Switching Frequency Maximum Duty Cycle Switch Current Limit (Note 3) Switch VCESAT CONDITIONS VOUT = VCC/2
q q q
ELECTRICAL CHARACTERISTICS
MIN
TYP 3 10 150 1 200 100 120 85 30 20 220 40 34.5 34.9 200 10 100 2
MAX 10 100 500
UNITS mV nA nA M M dB dB dB V/mV V/mV A/mV A/mV mA mA V V mV mV k mA V V V nA %/V mA MHz % mA mV
3469f
VCM = 0V to 10V VIN = 2.5V to 16V VCC = 15V to 35V No Load, VOUT = 2V to 33V RL = 200k, VOUT = 2V to 33V IOUT = 100A
q
VOUT = VCC/2
q
VCC = 35V, IOUT = 10mA VCC = 35V, IOUT = 0mA IOUT = -10mA IOUT = 0mA VCC = 35V, VOUT = 2V to 33V VCC = 35V
70 80 65 15 10 160 140 30 23 34.0 34.5
260 300 55 58
1000 500 2.5 2.5
1.5
q q
16 1.19
2.5V < VIN < 16V
q q q
0.8 88 165
ISW = 100mA
1.23 45 0.03 1.9 1.3 91 220 350
1.265 200 2.6 1.7
500
2
U
W
U
U
WW
W
LT3469
ELECTRICAL CHARACTERISTICS
PARAMETER Switch Leakage Current Diode VF Diode Reverse Leakage Current
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 2) VIN = 5V, VCC = 35V, unless otherwise noted.
CONDITIONS VSW = 5V ID = 100mA VR = 5V MIN TYP 0.01 740 0.1 MAX 1 1100 1 UNITS A mV A
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3469E is guaranteed to meet performance specifications from 0C to 85C. Specifications over the -40C to 85C operating
temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Current limit is guaranteed by design and/or correlation to static test. Slope compensation reduces current limit at higher duty cycles.
TYPICAL PERFOR A CE CHARACTERISTICS
(Switching Regulator)
VIN Quiescent Current
2.4 2.2 2.0 1.6
IQ (mA)
-50C 100C
200
CURRENT LIMIT (mA)
1.8 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 2 4 6
25C
SCHOTTKY CURRENT (mA)
8 VIN (V)
10
12
Schottky Reverse Leakage
25 VR = 5V
SWITCHING FREQUENCY (MHz)
LEAKAGE CURRENT (A)
20
FB VOLTAGE (V)
15
10
5
0 -50
-25
0 25 50 TEMPERATURE (C)
UW
14
3469 G05
Current Limit vs Duty Cycle
250 TA = 25C 250
Schottky Forward Voltage
200 150 25C 100C 100 -50C 50
150
100
50
16
0
0
20
60 40 DUTY CYCLE (%)
80
100
3469 G06
0 200 300 400 500 600 700 800 900 1000 FORWARD VOLTAGE (mV)
3469 G07
Switching Frequency
1.4 1.2
FB Pin Voltage and Bias Current
1.275 50
1.255
1.0 0.8 0.6 0.4
40
FB BIAS CURRENT (nA)
CURRENT 1.235 VOLTAGE 1.215 20 30
1.195
0.2 0 -50
10
75
100
3469 G09
-25
50 25 0 TEMPERATURE (C)
75
100
3469 G10
1.175 -50
-25
0 25 50 TEMPERATURE (C)
75
0 100
3469 G11
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LT3469 TYPICAL PERFOR A CE CHARACTERISTICS
(gm Amplifier)
VCC Quiescent Current
2.5 100C 2.0 -50C
IQ (mA)
OUTPUT CURRENT (mA)
25C 1.5
gm (A/mV)
1.0
0.5
0 15 18 21 27 24 VCC (V) 30 33 36
PI FU CTIO S
OUT (Pin 1): Output of the gm Amplifier. There must be at least 5nF of capacitive load at the output in a gain of 10 configuration. Capacitive loads up to 300nF can be connected to this pin. Piezo actuators below 5nF can be driven if capacitance is placed in parallel to bring the total capacitance to 5nF. FB (Pin 2): Feedback Pin. Reference voltage is 1.23V. Connect feedback resistor divider here. VIN (Pin 3): Input Supply Pin. Must be locally bypassed. GND (Pin 4): Ground Pin. Connect directly to local ground plane. SW (Pin 5): Switch Pin. Connect inductor here. Minimize trace area at this pin to reduce EMI. VCC (Pin 6): Output of Switching Regulator and Supply Rail for gm Amp. There must be 0.22F or more of capacitance here. +IN (Pin 7): Noninverting Terminal of the gm Amplifier. -IN (Pin 8): Inverting Terminal of the gm Amplifier.
BLOCK DIAGRA
+IN 7 -IN 8
+
gm
-
4
UW
3469 G01
Output Current vs Differential Input Voltage
30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30 -50 -40 -30 -20 -10 0 10 20 30 40 50 DIFFERENTIAL INPUT VOLTAGE (mV)
3469 G02
gm vs VCC
250 -50C 25C 200 100C
150
100C -50C 25C
100
50
0
15
20
25 VCC (V)
30
35
3469 G14
W
U
U
U
VIN VCC FB OUT 1 1.23V 2
VIN 3
SW 5 VCC 6
-
A1 SWITCH CONTROLLER Q1
+
4 GND
3469 F01
Figure 1. LT3469 Block Diagram
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LT3469
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/s. 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 2 * A V * COUT
where gm = 200A/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 typi100
SLEW RATE (V/s)
10
BANDWIDTH (kHz)
1
0.1 2 20 CAPACITANCE (nF) 200
3469 F02
Figure 2. Slew Rate vs Capacitance
U
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 values 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 approximately 55, select CBOOST as follows: CBOOST = COUT (R1 / R2 + 1) gm(R1|| R2) where gm = 200A/mV. In a gain of 10 configuration, choosing CBOOST as described 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 regulation. 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 100 WITHOUT PHASE BOOST CAPACITOR 10 2 20 CAPACITANCE (nF) 200
3469 F03
Figure 3. Closed Loop -3dB Bandwidth vs Capacitance in a Gain of 10 Configuration
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LT3469
OPERATIO
INPUT
EFFICIENCY (%)
CBOOST
Figure 4. Boosting the Bandwidth of the gm Amplifier with Capacitance On the Inverting Input
simply an amplified version of the difference between the feedback voltage and the reference voltage of 1.23V. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. The switching regulator provides the boosted supply voltage for the gm amplifier. Inductor Selection A 47H inductor is recommended for most LT3469 applications. Some suitable inductors with small size are listed in Table 1. The efficiency comparison of different inductors is shown in Figure 5.
Table 1. Recommended Inductors
DCR () 1.3 CURRENT RATING (mA) 170
PART NUMBER LQH32CN470
CMD4D11-470
LBC2518T470M
Capacitor Selection The small size of ceramic capacitors makes them ideal for LT3469 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1F input capacitor is sufficient for most LT3469 applications. A 0.22F output capacitor is sufficient for stable
6
U
90
+
gm VOUT
85 80 75 70 65 60 55
VIN = 12V VOUT = 35V
-
R1 R2
3469 F04
50 45 40 0 5
MURATA LQH32CN470 SUMIDA CMD4011-470 TAIYO YUDEN LBC2518T470M 15 20 10 LOAD CURRENT (mA) 25 30
3469 F05
Figure 5. Efficiency Comparison of Different Inductors
transient response, however, more output capacitance can help limit the voltage droop on VCC during transients.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER Taiyo Yuden AVX Murata Kemet PHONE 408-573-4150 843-448-9411 814-237-1431 408-986-0424 URL www.t-yuden.com www.avxcorp.com www.murata.com www.kemet.com
Inrush Current Considerations When Hot Plugging When the supply voltage is applied to VIN, the voltage difference between VIN and VCC generates inrush current flowing from the input through the inductor, the SW pin, and the integrated Schottky diode to charge the output capacitor. Care should be taken not to exceed the LT3469 maximum SW pin current rating of 1A. Worst-case inrush current occurs when the application circuit is hot plugged into a live supply with a large output capacitance. The typical application circuit will maintain a peak SW pin current below 1A when it is hot plugged into a 5V supply. To keep SW pin current below 1A during a hot plug into a 12V supply, 4.7 must be added between the supply and the LT3469 input capacitor. During normal operation, the SW pin current remains significantly less than 1A. Layout Hints As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made
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2.8
180
1.9
150
MANUFACTURER Murata 814-237-1431 www.murata.com Sumida 847-545-6700 www.Sumida.com Taiyo Yuden 408-573-4150 www.t-yuden.com
LT3469
OPERATIO
as short as possible. To prevent electromagnetic interference (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 connected 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 generating 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 * 250C/W) Worst-case power dissipation occurs at maximum output swing, frequency, capacitance and VCC. For a square wave
R2 PIEZ0 ACTUATOR R1
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
U
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 () as follows: Example: LT3469 at TA = 70C, VCC = 35V, CL = 200nF, f = 3kHz, VOUT(P-P) = 4V, = 80%: PD =
(IQ + fVOUT(P-P)CL )(VCC )
PD =
0.80 TJ = 70C + (214mW * 250C / W ) = 124C
(2.5mA + 3kHz * 4V * 200nF )(35V) = 214mW
Do not exceed the maximum junction temperature of 125C.
GND INPUT
R3
R5
R4
C1
C2
L VIN VIAS TO GROUND PLANE
3469 F06
Figure 6. Recommended Component Placement
Piezo Speaker Driver
VIN 3V TO 6V L1 47H C1 1F 3 VIN 5 SW VCC FB LT3469 GND 16.9k 7 8 20k
3469 TA01
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 6 294k 2 17.4k 4 1 VOUT 1V TO 20V PIEZO SPEAKER 8nF < C < 300nF C2 0.47F 35V
+
INPUT 0V TO 3V
+IN -IN
+ -
OUT
-
113k
3469f
7
LT3469
PACKAGE DESCRIPTIO
0.52 MAX
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.09 - 0.20 (NOTE 3) 1.00 MAX DATUM `A' 0.30 - 0.50 REF NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING
0.20 BSC
RELATED PARTS
PART NUMBER LT1611 LT1616 DESCRIPTION 550mA ISW, 1.4MHz, High Efficiency Inverting DC/DC Converter 600mA IOUT, 1.4MHz, High Efficiency Step-Down DC/DC Converter LTC1772B 550kHz, Current Mode Step-Down DC/DC Controller LT1931/LT1931A 1A ISW, 1.2MHz/2.2MHz, High Efficiency Inverting DC/DC Converter LT1940 (Dual) Dual Output 1.4A IOUT, Constant 1.1MHz, High Efficiency Step-Down DC/DC Converter LTC3411 1.25A IOUT, 4MHz Synchronous Step-Down DC/DC Converter LT3464 85mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter with Integrated Schottky and Output Disconnect COMMENTS VIN: 0.9V to 10V, VOUT(MAX): 34V, IQ: 3mA, ISD: <1A, ThinSOT VIN: 3.6V to 25V, VOUT(MIN): 1.25V, IQ: 1.9mA, ISD: <1A, ThinSOT VIN: 2.5V to 9.8V, VOUT(MIN): 0.8V, IQ: 270A, ISD: <8A, ThinSOT VIN: 2.6V to 16V, VOUT(MAX): -34V, IQ: 4.2mA, ISD: <1A, ThinSOT VIN: 3V to 25V, VOUT(MIN): 1.2V, IQ: 2.5mA, ISD: <1A, TSSOP-16E VIN: 2.5V to 5.5V, VOUT(MIN): 0.8V, IQ: 60A, ISD: <1A, MS10, DFN VIN: 2.3V to 10V, VOUT(MAX): 34V, IQ: 25A, ISD: <0.5A, ThinSOT
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
U
TS8 Package 8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.65 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE ID 0.65 BSC 0.80 - 0.90 0.01 - 0.10 0.22 - 0.36 8 PLCS (NOTE 3) 1.95 BSC
TS8 TSOT-23 0802
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
3469f LT/TP 0304 1K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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