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LT3460 1.3MHz Step-Up DC/DC Converter in SC70 and ThinSOT
FEATURES
s s s s s s s s s
DESCRIPTIO
1.3MHz Switching Frequency High Output Voltage: Up to 36V 300mA Integrated Switch 12V at 70mA from 5V Input 5V at 60mA from 3.3V Input Wide Input Range: 2.5V to 16V Uses Small Surface Mount Components Low Shutdown Current: <1A Low Profile (1mm) SC70 and SOT-23 (ThinSOTTM) Packages
The LT(R)3460 is a general purpose step-up DC/DC converter. The LT3460 switches at 1.3MHz, allowing the use of tiny, low cost and low height capacitors and inductors. The constant frequency results in low, predictable output noise that is easy to filter. The high voltage switch in the LT3460 is rated at 38V, making the device ideal for boost converters up to 36V. The LT3460 can generate 12V at up to 70mA from a 5V supply. The LT3460 is available in SC70 and SOT-23 packages.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation
APPLICATIO S
s s s s s s s
Digital Cameras CCD Bias Supply XDSL Power Supply TFT-LCD Bias Supply Local 5V or 12V Supply Medical Diagnostic Equipment Battery Backup
TYPICAL APPLICATIO
90 85
EFFICIENCY (%)
80 75 70 65 60
5V to 12V, 70mA Step-Up DC/DC Converter
VIN 5V 4.7F VIN LT3460 OFF ON SHDN GND FB 15k 1F 22H VOUT 12V 70mA SW 130k 22pF
0
3460 F01
VSW 5V/DIV IL 100mA/DIV
U
Efficiency
20 40 60 LOAD CURRENT (mA) 80
3460 F01a
U
U
Switching Waveforms
0.2s/DIV
3460 F01b
3460f
1
LT3460
ABSOLUTE AXI U RATI GS
Input Voltage (VIN) .................................................. 16V SW Voltage .............................................................. 38V FB Voltage ................................................................. 5V SHDN Voltage .......................................................... 16V
PACKAGE/ORDER I FOR ATIO
TOP VIEW SW 1 GND 2 FB 3 4 SHDN 5 VIN
ORDER PART NUMBER
TOP VIEW
LT3460ES5
S5 PACKAGE 5-LEAD PLASTIC TSOT-23
TJMAX = 125C, JA = 256C/W IN FREE AIR JA = 120C ON BOARD OVER GROUND PLANE
S5 PART MARKING LTB1
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, VIN = 3V, VSHDN = 3V, unless otherwise noted.
PARAMETER Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
Feedback Line Regulation FB Pin Bias Current Supply Current
2.5V < VIN < 16V
q
SHDN = 0V Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current SHDN Voltage High SHDN Voltage Low SHDN Pin Bias Current Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. ISW = 250mA VSW = 5V 1.5 1.0 85 300
2
U
U
W
WW
U
W
(Note 1)
Operating Ambient Temperature Range (Note 2) .................. - 40C to 85C Maximum Junction Temperature .......................... 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER
SW 1 GND 2 FB 3 6 VIN 5 GND 4 SHDN
LT3460ESC6
SC6 PACKAGE 6-LEAD PLASTIC SC70
TJMAX = 125C, JA = 400C/W IN FREE AIR JA = 270C/W ON BOARD OVER GROUND PLANE
SC6 PART MARKING LAAF
MIN 2.5
TYP
MAX 16
UNITS V V V V %/V nA mA A MHz % mA mV A V V A
1.235 1.225 5
1.255 0.015 25 2.0 0.1 1.3 90 420 320 0.01
1.275 1.280 80 3.0 0.5 1.7 600 450 1 0.4
40
Note 2: The LT3460E is guaranteed to meet specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
3460f
LT3460 TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
2.5 -50C
SWITCHING FREQUENCY (MHz)
2.0
25C 100C
SHDN PIN BIAS CURRENT (A)
IQ (mA)
1.5
1.0
0.5
0 0 5 VIN (V)
3460 G01
10
Feedback Bias Current
30
FEEDBACK BIAS CURRENT (nA)
1.260
25
1.255
20 15 10
1.245
VFB (V)
5 0 -50
1.240 -50
Switch Saturation Voltage (VCESAT)
400 350 300 IC = 250mA
CURRENT LIMIT (mA)
VCESAT (mV)
250 200 150 100 50 0 -50
UW
15
Switching Frequency
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -50 400 350 300 250 200 150 100 50 -25 50 25 0 TEMPERATURE (C) 75 100
3460 G02
SHDN Pin Bias Current
SHDN = 16V
SHDN = 3V -25 50 25 0 TEMPERATURE (C) 75 100
3460 G03
0 -50
Feedback Voltage
1.250
-25
50 25 0 TEMPERATURE (C)
75
100
3460 G04
-25
50 25 0 TEMPERATURE (C)
75
100
3460 G05
Current Limit vs Duty Cycle
450 400 350 300 250 200 150 100 50 0
IC = 200mA
IC = 100mA
-25
50 25 0 TEMPERATURE (C)
75
100
3460 G06
0
0.2
0.6 0.4 DUTY CYCLE
0.8
1.0
3460 G07
3460f
3
LT3460
PI FU CTIO S
SW (Pin 1/Pin 1): Switch Pin. Connect inductor/diode here. Minimize trace at this pin to reduce EMI. GND (Pin 2/Pins 2 and 5): Ground Pin. Tie directly to local ground plane. FB (Pin 3/Pin 3): Feedback Pin. Reference voltage is 1.255V. Connect resistor divider tap here. Minimize trace area at FB. Set VOUT according to VOUT = 1.255V (1 + R1/R2).
BLOCK DIAGRA
VIN (PIN 6 SC70 PACKAGE) 5 VOUT R1 (EXTERNAL) FB R2 (EXTERNAL)
1.255V REFERENCE
SHUTDOWN
RS (EXTERNAL)
4 SHDN CS (EXTERNAL)
RS, CS OPTIONAL SOFT-START COMPONENTS
OPERATIO
The LT3460 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. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the SR
4
W
U
U
U
U
(ThinSOT/SC70 Packages)
SHDN (Pin 4/Pin 4): Shutdown Pin. Tie to 1.5V or higher to enable device; 0.4V or less to disable device. Also functions as soft-start. Use RC filter (47k, 47nF typ) as shown in Figure 1. VIN (Pin 5/Pin 6): Input Supply Pin. Must be locally bypassed.
+
A1
COMPARATOR
1 DRIVER
SW
-
RC CC A2 R S Q
-
3 FB
Q1
+
+
0.1
-
RAMP GENERATOR
1.3MHz OSCILLATOR
2
GND (PINS 2 AND 5 SC70 PACKAGE)
3460 BD
Figure 1. Block Diagram
latch is reset turning off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 1.255V. 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.
3460f
LT3460
OPERATIO
Feedback Loop Compensation The LT3460 has an internal feedback compensation network as shown in Figure 1 (RC and CC). However, because the small signal characteristics of a boost converter change with operation conditions, the internal compensation network cannot satisfy all applications. A properly designed external feed forward capacitor from VOUT to FB (CF in Figure 2) will correct the loop compensation for most applications.
VIN 5V C1 4.7F OFF ON 4 L1 22H 5 VIN LT3460 SHDN GND 2 C1: TAIYO YUDEN X5R JMK212BJ475KG C2: TAIYO YUDEN X5R EMK316BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT FB 3 R1 15k C2 1F 1 SW D1 VOUT 12V 70mA
GAIN (dB)
Figure 2. 5V to 12V Step-Up Converter
The LT3460 uses peak current mode control. The current feedback makes the inductor very similar to a current source in the medium frequency range. The power stage transfer function in the medium frequency range can be approximated as: GP(s ) = K1 , s * C2
where C2 is the output capacitance, and K1 is a constant based on the operating point of the converter. In continuous current mode, K1 increases as the duty cycle decreases. The internal compensation network RC, CC can be approximated as follows in medium frequency range:
GC(s ) = K2 *
The zero
s * RC * CC + 1 s * CC
fZ =
1 2 * * RC * CC
U
is about 70kHz. The feedback loop gain T(s) = K3 * GP(s) * GC(s). If it crosses over 0dB far before fZ, the phase margin will be small. Figure 3 is the Bode plot of the feedback loop gain measured from the converter shown in Figure 2 without the feedforward capacitor CF. The result agrees with the previous discussion: Phase margin of about 20 is insufficient.
60 50 40 30 20 10 0 -10 -20 -30 -40
3460 F02
90 GAIN 45 0 -45
R2 130k
CF 22pF
PHASE (DEG)
-90 PHASE -135 -180 -225 -270 -315 1 10 100 FREQUENCY (kHz) -360 1000
3460 F03
Figure 3
In order to improve the phase margin, a feed-forward capacitor CF in Figure 2 can be used. Without the feed-forward capacitor, the transfer function from VOUT to FB is:
FB R1 = VOUT R1 + R2
With the feed-forward capacitor CF, the transfer function becomes: FB R1 s * R2 * CF + 1 * = VOUT R1 + R2 s * R1 * R2 * C + 1 F R1 + R2 The feed-forward capacitor CF generates a zero and a pole. The zero always appears before the pole. The frequency distance between the zero and the pole is determined only by the ratio between VOUT and FB. To give maximum phase
3460f
5
LT3460
OPERATIO
margin, CF should be chosen so that the midpoint frequency between the zero and the pole is at the cross over frequency. With CF = 20pF, the feedback loop Bode plot is reshaped as shown in Figure 4. The phase margin is about 60.
60 50 40 30 GAIN 90 45 0 -45
GAIN (dB)
20 10 0 -10 -20 -30 -40 1 10 100 FREQUENCY (kHz) PHASE
VOUT
+
C2 R2 SHUTDOWN
GND
6
U
The feed-forward capacitor increases the gain at high frequency. The feedback loop therefore needs to have enough attenuation at the switching frequency to reject the switching noise. Additional internal compensation components have taken this into consideration. For most of the applications of LT3460, the output capacitor ESR zero is at very high frequency and can be ignored. If a low frequency ESR zero exists, for example, when a high-ESR Tantalum capacitor is used at the output, the phase margin may be enough even without a feed-forward capacitor. In these cases, the feed-forward capacitor should not be added because it may cause the feedback loop to not have enough attenuation at the switching frequency. Layout Hints The high speed operation of the LT3460 demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 5 shows the recommended component placement.
PHASE (DEG)
-90 -135 -180 -225 -270 -315 -360 1000
3460 F04
Figure 4.
D1
L1
C1
D1 VIN VOUT
L1
C1
+
+
VIN
+
C2 R2 SHUTDOWN
R1
CF
GND
R1
CF
(SOT-23 PACKAGE)
(SC70 PACKAGE)
3460 F05
Figure 5. Suggested Layout
3460f
LT3460
TYPICAL APPLICATIO S
5V to 12V Step-Up Converter
VIN 5V C1 4.7F SHDN 4 L1 22H 5 VIN LT3460 SHDN GND 2 C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT FB 3 15k C2 1F 1 SW 130k 22pF
90
D1
EFFICIENCY (%)
VOUT 100mV/DIV
58mA ILOAD 34mA 100s/DIV
5V to 12V with Soft-Start Circuit
VIN 5V C1 4.7F CONTROL SIGNAL VIN 47k SHDN 47nF GND LT3460 FB 15k SW 130k 22pF C2 1F 16V
VO 5V/DIV CONTROL SIGNAL 2V/DIV
3460 TA02
L1 22H
D1
C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT
U
Efficiency
VOUT 12V 70mA
85 80 75 70 65
3460 TA01
60
0
20 40 60 LOAD CURRENT (mA)
80
3460 TA01a
Load Step Response
3460 TA01b
Input Current and Output Voltage
VOUT 12V 70mA
IIN 100mA/DIV
500s/DIV
3460 TA02b
3460f
7
LT3460
TYPICAL APPLICATIO S
3.3V to 12V Step-Up Converter
VIN 3.3V C1 4.7F L1 22H 85 D1 VOUT 12V 40mA 130k 22pF C2 1F 16V 15k EFFICIENCY (%) 80 75 70 65 60 C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT
3460 TA03
VIN LT3460 SHDN GND
SW
FB
Li-Ion to 5V Step-Up Converter
VIN 2.7V TO 4.2V L1 10H
D1
+ C1
4.7F
VIN LT3460 SHDN GND
SW
39.2k
50pF C2 4.7F 6.3V
EFFICIENCY (%)
FB 13k
C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R JMK212BJ475 D1: PHILIPS PMEG2010 L1: MURATA LQH32CN-100 OR EQUIVALENT
8
U
Efficiency
55 0 20 30 10 LOAD CURRENT (mA) 40
3460 TA03a
Efficiency
90
VOUT 5V
88 86 84 82 80 78 76 74 VIN = 3V VIN = 2.7V
VIN = 4.2V
VIN = 3.6V
3460 TA07
72 70 0 50 200 150 100 LOAD CURRENT (mA) 250
3460 TA07a
3460f
LT3460
TYPICAL APPLICATIO S
12V to 36V Step-Up Converter
VIN 12V C1 1F 16V L1 47H D1 VOUT 36V 4mA 278k 22pF C2 0.22F 50V 10k ILOAD C1: TAIYO YUDEN X5R EMK212BJ105 C2: TAIYO YUDEN X7R UMK212BJ224 D1, D2: CENTRAL SEMICONDUCTOR CMOD4448 L1: TAIYO YUDEN LB2012
3460 TA04
D2 VIN LT3460 SHDN GND FB SW VOUT 100mV/DIV
5V to 36V Step-Up Converter
VIN 5V C1 1F 6.3V L1 47H D1 VOUT 36V 4mA 278k 22pF C2 0.22F 50V 10k ILOAD C1: TAIYO YUDEN X5R JMK107BJ105 C2: TAIYO YUDEN X7R UMK212BJ224 D1, D2: CENTRAL SEMICONDUCTOR CMOD4448 L1: TAIYO YUDEN LB2012
3460 TA05
D2 VIN LT3460 SHDN GND FB SW VOUT 100mV/DIV
U
Load Step Response
4mA 2mA 100s/DIV
3460 TA04a
Load Step Response
4mA 2mA 100s/DIV
3460 TA05a
3460f
9
LT3460
PACKAGE DESCRIPTIO
0.62 MAX
0.95 REF
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.20 BSC 1.00 MAX DATUM `A'
0.30 - 0.50 REF 0.09 - 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 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
10
U
S5 Package 5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE 0.30 - 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 - 0.90 0.01 - 0.10 1.90 BSC
S5 TSOT-23 0302
3460f
LT3460
PACKAGE DESCRIPTIO U
SC6 Package 6-Lead Plastic SC70
(Reference LTC DWG # 05-08-1638)
0.47 MAX 0.65 REF 1.80 - 2.20 (NOTE 4) 1.16 REF 0.96 MIN 1.80 - 2.40 1.15 - 1.35 (NOTE 4) INDEX AREA (NOTE 6) PIN 1 0.65 BSC 0.15 - 0.30 6 PLCS (NOTE 3) 0.80 - 1.00 0.00 - 0.10 REF 1.00 MAX 0.10 - 0.18 (NOTE 3)
SC6 SC70 0802
3.26 MAX 2.1 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.10 - 0.40
0.10 - 0.30 NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. DETAILS OF THE PIN 1 INDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE INDEX AREA 7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70
3460f
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.
11
LT3460
TYPICAL APPLICATIO S
5V to 5V SEPIC
L1 22H C3 0.22F
D1
VIN 3V TO 10V C1 1F
VIN LT3460 SHDN GND
SW
L2 22H
30k
50pF C2 1F
EFFICIENCY (%)
FB 10k
C1, C2: TAIYO YUDEN X5R LMK107BJ105 C3: TAIYO YUDEN X7R LMK107BJ224 D1: ON SEMICONDUCTOR MBR0520 L1, L2: MURATA LQH32CN-220 OR EQUIVALENT
RELATED PARTS
PART NUMBER LT1613 LT1615/LT1615-1 LT1944/LT1944-1 LT1945 LT1961 LTC3400/LTC3400B LTC3401/LTC3402 LT3461/LT3461A LT3464 LT3465/LT3465A DESCRIPTION 550mA (ISW), 1.4MHz, High Efficiency Step-Up DC/DC Converter 300mA/80mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter Dual Output 350mA/100mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter Dual Output, Pos/Neg, 350mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter 600mA (ISW), 1.2MHz, Synchronous Step-Up DC/DC Converter 1A/2A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter 0.3A (ISW), 1.3MHz/3MHz, High Efficiency Step-Up DC/DC Converter with Integrated Schottky 0.08A (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky, Output Disconnect Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED Boost Regulator with Integrated Schottky Diode COMMENTS VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD <1A, ThinSOT Package VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20A, ISD <1A, ThinSOT Package VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20A, ISD <1A, MS Package VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20A, ISD <1A, MS Package VIN: 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD <6A, MS8E Package VIN: 0.85V to 5V, VOUT(MAX) = 5V, IQ = 19A/300A, ISD <1A, ThinSOT Package VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38A, ISD <1A, MS Package VIN: 2.5V to 16V, VOUT(MAX) = 38V, IQ = 2.8mA, ISD <1A, SC70, ThinSOT Packages VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25A, ISD <1A, ThinSOT Package VIN: 2.7V to 16V, VOUT(MAX) = 30V, IQ = 1.9mA, ISD <1A, ThinSOT Package
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
U
Efficiency
80
VOUT 5V 50mA
VIN = 6.5V VIN = 5V
75 VIN = 4V 70 65 60 55
3460 TA06
50
0
100 50 LOAD CURRENT (mA)
150
3460 TA06a
3460f LT/TP 0204 1K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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