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FEATURES

LT3502/LT3502A 1.1MHz/2.2MHz, 500mA Step-Down Regulators in 2mm x 2mm DFN and MS10 DESCRIPTION
The LT(R)3502/LT3502A are current mode PWM step-down DC/DC converters with an internal 500mA power switch, in tiny 8-lead 2mm x 2mm DFN and 10-lead MS10 packages. The wide input voltage range of 3V to 40V makes the LT3502/LT3502A suitable for regulating power from a wide variety of sources, including 24V industrial supplies and automotive batteries. Its high operating frequency allows the use of tiny, low cost inductors and capacitors, resulting in a very small solution. Constant frequency above the AM band avoids interfering with radio reception, making the LT3502A particularly suitable for automotive applications. Cycle-by-cycle current limit and frequency foldback provide protection against shorted outputs. Soft-start and frequency foldback eliminates input current surge during start-up. DA current sense provides further protection in fault conditions. An internal boost diode reduces component count.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

3V to 40V Input Voltage Range 500mA Output Current Switching Frequency: 2.2MHz (LT3502A), 1.1MHz (LT3502) 800mV Feedback Voltage Short-Circuit Robust Soft-Start Low Shutdown Current: <2A Internally Compensated Internal Boost Diode Thermally Enhanced 2mm x 2mm 8-Lead DFN and 10-lead MS10 Package
APPLICATIONS

Automotive Systems Battery-Powered Equipment Wall Transformer Regulation Distributed Supply Regulation
TYPICAL APPLICATION
3.3V Step-Down Converter
90 VIN 4.7V TO 40V BD VIN 1F SW LT3502A DA OFF ON SHDN GND 31.6k FB 10k 10F BOOST EFFICIENCY (%) 0.1F 6.8H VOUT 3.3V 500mA 80 5VOUT 70 60 50 40 30 20 10
3502 TA01a
LT3502A 12VIN Efficiency
3.3VOUT
0 0 0.1 0.3 0.2 LOAD CURRENT (A) 0.4 0.5
3502 TA01b
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LT3502/LT3502A ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Voltage (VIN) ....................................................40V BOOST Voltage .........................................................50V BOOST Pin Above SW Pin...........................................7V FB Voltage ...................................................................6V SHDN Voltage ...........................................................40V
BD Voltage ..................................................................7V Operating Junction Temperature Range (Note 2) LT3502AE, LT3502E ...........................-40C to 125C LT3502AI, LT3502I .............................-40C to 125C Storage Temperature Range...................-65C to 150C
PIN CONFIGURATION
TOP VIEW VIN 1 BD 2 FB 3 SHDN 4 9 8 SW 7 BOOST 6 DA 5 GND SW BOOST NC DA GND 1 2 3 4 5 TOP VIEW 10 9 8 7 6 VIN NC BD FB SHDN
DC PACKAGE 8-LEAD (2mm x 2mm) PLASTIC DFN JA = 102C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
MS PACKAGE 10-LEAD PLASTIC MSOP JA = 110C/W
ORDER INFORMATION
LEAD FREE FINISH LT3502EDC#PBF LT3502IDC#PBF LT3502AEDC#PBF LT3502AIDC#PBF LT3502EMS#PBF LT3502IMS#PBF LT3502AEMS#PBF LT3502AIMS#PBF TAPE AND REEL LT3502EDC#TRPBF LT3502IDC#TRPBF LT3502AEDC#TRPBF LT3502AIDC#TRPBF LT3502EMS#TRPBF LT3502IMS#TRPBF LT3502AEMS#TRPBF LT3502AIMS#TRPBF PART MARKING* LCLV LCLV LCLT LCLT LTDTR LTDTR LTDTS LTDTS PACKAGE DESCRIPTION 8-Lead 2mm x 2mm Plastic DFN 8-Lead 2mm x 2mm Plastic DFN 8-Lead 2mm x 2mm Plastic DFN 8-Lead 2mm x 2mm Plastic DFN 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP TEMPERATURE RANGE -40C to 125C -40C to 125C -40C to 125C -40C to 125C -40C to 125C -40C to 125C -40C to 125C -40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LT3502/LT3502A ELECTRICAL CHARACTERISTICS
PARAMETER Undervoltage Lockout Quiescent Current at Shutdown Quiescent Current Feedback Voltage VSHDN = 0V Not Switching 2mm x 2mm DFN 2mm x 2mm DFN MS10 MS10 (Note 5) IDA < 500mA (LT3502A) IDA < 500mA (LT3502A) IDA < 500mA (LT3502) IDA < 500mA (LT3502) 100mA Load (LT3502A) 100mA Load (LT3502) ISW = 500mA (Note 3) SW = 10V (Note 4) SW = 0V (Note 5) ISW = 500mA ISW = 500mA IOUT = 100mA 500 VSHDN = 5V VSHDN = 0V 2 0.3 0.75

The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 10V, VSHDN = 5V, VBOOST = 15V.
CONDITIONS MIN 2.6 TYP 2.8 0.5 1.5 0.785 0.79 0.780 0.786 0.8 0.8 0.8 0.8 0.005

MAX 3 2 2 0.813 0.81 0.816 0.813 50 2.7 2.8 1.3 1.4
UNITS V A mA V V V V %/V nA MHz MHz MHz MHz % % mV
Reference Voltage Line Regulation FB Pin Bias Current Switching Frequency 1.9 1.8 0.9 0.8 70 80
15 2.25 2.25 1.1 1.1 80 90 450 0.9 95 8 10 1.9 0.8 650 55
Maximum Duty Cycle Switch VCESAT Switch Current Limit Switch Active Current BOOST Pin Current Minimum BOOST Voltage Above Switch BOOST Schottky Forward Drop DA Pin Current to Stop OSC SHDN Bias Current SHDN Input Voltage High SHDN Input Voltage Low
1.1 130 30 13 2.2 1 80 1
A A A mA V V mA A A V V
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2. The LT3502EDC and LT3502AEDC are guaranteed to meet performance specifications from 0C to 125C junction temperature range. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3502IDC and LT3502AIDC are guaranteed over the - 40C to 125C operating junction temperature range. Note 3: Current limit guaranteed by design and/or correlation to static test. Slope compensation reduces current limit at higher duty cycle. Note 4: Current flows into pin. Note 5: Current flows out of pin.
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LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS
LT3502A 3.3VOUT Efficiency
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0 0.1 0.3 0.2 LOAD CURRENT (A) 0.4 0.5
3502 G01
(TA = 25C unless otherwise noted)
LT3502A 5VOUT Efficiency
90 100 90 12VIN 24VIN EFFICIENCY (%) 80 70 60 50 40 30 20 10 0 0 0.1 0.3 0.2 LOAD CURRENT (A) 0.4 0.5
3502 G02
LT3502 3.3VOUT Efficiency
5VIN
12VIN
80 70 EFFICIENCY (%) 60 50 40 30 20 10 0
24VIN
24VIN 12VIN
0
0.1
0.3 0.4 0.2 LOAD CURRENT (A)
0.5
3502 G03
LT3502 5VOUT Efficiency
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 0.1 0.3 0.4 0.2 LOAD CURRENT (A) 0.5
3502 G04
LT3502A Maximum Load Current VOUT = 3.3V, L = 6.8H
1.0 1.0 TYPICAL LOAD CURRENT (A) MINIMUM 0.9 0.9 0.8 LOAD CURRENT (A) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 10 20 VIN (V) 30 40
3502 G05
LT3502A Maximum Load Current VOUT = 5V, L = 10H
TYPICAL 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 10 20 VIN (V) 30 40
3502 G06
12VIN 24VIN
MINIMUM
LT3502 Maximum Load Current VOUT = 3.3V, L = 15H
0.9 0.8 0.7 LOAD CURRENT (A) 0.6 0.5 0.4 0.3 0.2 0.1 0 0 10 20 VIN (V)
3502 G07
LT3502 Maximum Load Current VOUT = 5V, L = 22H
0.9 700 TYPICAL 0.7 LOAD CURRENT (A) 0.6 0.5 0.4 0.3 0.2 0.1 100 0 0 10 20 VIN (V)
3502 G08
Switch Voltage Drop
600 500 VCE (mV) 400 300 200 25C 125C
TYPICAL MINIMUM
0.8 MINIMUM
-40C
30
40
0
30
40
0
0.2
0.4
0.6
0.8
1.0
3502 G09
SWITCH CURRENT (A)
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LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS
UVLO
3.5 3.0 FREQUENCY (MHz) 2.5 VIN (V) 2.0 1.5 1.0 0.5 0 -50 SWITCH CURRENT LIMIT (A) 2.0 2.5 LT3502A
(TA = 25C unless otherwise noted)
Switching Frequency
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 100 TEMPERATURE (C) 50 150
3502 G10
Soft-Start (SHDN)
1.5 LT3502 1.0
0.5
0 -50
-0.1 0 50 100 TEMPERATURE (C) 150
3502 G11
0
200 400 600 800 1000 1200 1400 1600 SHDN PIN VOLTAGE (mV)
3502 G12
SHDN Pin Current
300 250 SHDN PIN CURRENT (A) CURRENT LIMIT (A) 200 150 100 50 0 0 5 10 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 15 20 25 30 35 SHDN PIN VOLTAGE (V) 40 45
Switch Current Limit
1.2 1.0 CURRENT LIMIT (A)
Switch Current Limit
SW PEAK CURRENT LIMIT DA VALLEY CURRENT LIMIT
LT3502 0.8 0.6 0.4 0.2 0 0 50 DUTY CYCLE (%) 100
3502 G15
LT3502A
0 -50
0
50 100 TEMPERATURE (C)
150
3502 G14
3502 G13
LT3502A Maximum VIN for Full Frequency (VOUT = 3.3V)
45 40 35 30 VIN (V) 25 20 15 10 5 0 0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 TA = 85C VIN (V) TA = 25C 45 40 35 30
LT3502A Maximum VIN for Full Frequency (VOUT = 5V)
45 40 35 30 TA = 85C VIN (V) TA = 25C 25 20 15 10 5 0 0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7
LT3502 Maximum VIN for Full Frequency (VOUT = 3.3V)
25 20 15 10 5 0
TA = 25C TA = 85C
0
0.1
0.2 0.3 0.4 0.5 LOAD CURRENT (A)
0.6
0.7
3502 G16
3502 G17
3502 G18
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LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS
LT3502A Typical Minimum Input Voltage (VOUT = 3.3V)
7 6 5 VIN (V) VIN (V) 4 3 2 1 0 0.001 8 7 6 5 4 3 2 1 0.1 0.01 LOAD CURRENT (A) 1
3502 G19
(TA = 25C unless otherwise noted) LT3502 Typical Minimum Input Voltage (VOUT = 3.3V)
7 6 5 VIN (V) 4 3 2 1 0 0.001
LT3502A Typical Minimum Input Voltage (VOUT = 5V)
0 0.001
0.01 0.1 LOAD CURRENT (A)
1
3502 G20
0.1 0.01 LOAD CURRENT (A)
1
3502 G21
LT3502 Typical Minimum Input Voltage (VOUT = 5V)
8 7 6 5 VIN (V) 4 3 2 1 0 0.001 0.01 0.1 LOAD CURRENT (A) 1
3502 G22
Continuous Mode Waveform
VSW 5V/DIV VSW 5V/DIV
Discontinuous Mode Waveform
IL 200mA/DIV VOUT 20mV/DIV VIN = 12V VOUT = 3.3V L = 6.8H COUT = 10F IOUT = 250mA 200ns/DIV
3502 G23
IL 200mA/DIV VOUT 20mV/DIV VIN = 12V VOUT = 3.3V L = 6.8H COUT = 10F IOUT = 30mA 200ns/DIV
3502 G24
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LT3502/LT3502A PIN FUNCTIONS
(DFN/MS)
VIN (Pin 1/Pin 10): The VIN pin supplies current to the LT3502/LT3502A's internal regulator and to the internal power switch. This pin must be locally bypassed. BD (Pin 2/Pin 8): The BD pin is used to provide current to the internal boost Schottky diode. FB (Pin 3/Pin 7): The LT3502/LT3502A regulate their feedback pin to 0.8V. Connect the feedback resistor divider tap to this pin. Set the output voltage according to VOUT = 0.8(1 + R1/R2). A good value for R2 is 10k. SHDN (Pin 4/Pin 6): The SHDN pin is used to put the LT3502 in shutdown mode. Tie to ground to shut down the LT3502/LT3502A. Tie to 2V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. The SHDN pin also provides soft-start and frequency foldback. To use the soft-start feature, connect R3 and C4 to the SHDN pin. SHDN Pin voltage should not be higher than VIN.
GND (Pin 5/Pin 5): Ground Pin. DA (Pin 6/Pin 4): Connect the catch diode (D1) anode to this pin. This pin is used to provide frequency foldback in extreme situations. BOOST (Pin 7/Pin 2): The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. Connect a boost capacitor from this pin to SW Pin. SW (Pin 8/Pin 1): The SW pin is the output of the internal power switch. Connect this pin to the inductor, catch diode and boost capacitor.
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BLOCK DIAGRAM
LT3502/LT3502A
8
1 VIN INT REG AND UVLO BD 2
VIN
C2
ON OFF SLOPE COMP R S Q Q 4 SHDN DRIVER
BOOST
7
R3
C3 Q1 SW L1 8 C1 D1 VOUT
C4 OSC
FREQUENCY FOLDBACK VC gm
DA
6 GND
5 0.8V
3 R2
FB R1
3502 BD
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LT3502/LT3502A OPERATION
The LT3502/LT3502A are constant frequency, current mode step-down regulators. An oscillator enables an RS flip-flop, turning on the internal 500mA power switch Q1. An amplifier and comparator monitor the current flowing between the VIN and SW pins, turning the switch off when this current reaches a level determined by the voltage at VC. An error amplifier measures the output voltage through an external resistor divider tied to the FB pin and servos the VC node. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. An active clamp (not shown) on the VC node provides current limit. The VC node is also clamped to the voltage on the SHDN pin; soft-start is implemented by generating a voltage ramp at the SHDN pin using an external resistor and capacitor. The SHDN pin voltage during soft-start also reduces the oscillator frequency to avoid hitting current limit during start-up. An internal regulator provides power to the control circuitry. This regulator includes an undervoltage lockout to prevent switching when VIN is less than ~3V. The SHDN pin is used to place the LT3502/LT3502A in shutdown, disconnecting the output and reducing the input current to less than 2A. The switch driver operates from either VIN or from the BOOST pin. An external capacitor and the internal diode are used to generate a voltage at the BOOST pin that is higher than the input supply. This allows the driver to fully saturate the internal bipolar NPN power switch for efficient operation. A comparator monitors the current flowing through the catch diode via the DA pin and reduces the LT3502/ LT3502A's operating frequency when the DA pin current exceeds the 650mA valley current limit. This frequency foldback helps to control the output current in fault conditions such as shorted output with high input voltage. The DA comparator works in conjunction with the switch peak current limit comparator to determine the maximum deliverable current of the LT3502/LT3502A. The peak current limit comparator is used in normal current mode operations and is used to turn off the switch. The DA valley current comparator monitors the catch diode current and will delay switching until the catch diode current is below the 650mA limit. Maximum deliverable current to the output is therefore limited by both switch peak current limit and DA valley current limit.
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LT3502/LT3502A APPLICATIONS INFORMATION
FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the 1% resistors according to: R1= R2 VOUT -1 0.8V Note that this is a restriction on the operating input voltage for fixed frequency operation; the circuit will tolerate transient inputs up to the absolute maximum ratings of the VIN and BOOST pins. The input voltage should be limited to the VIN operating range (40V) during overload conditions. Minimum On Time The LT3502/LT3502A will still regulate the output at input voltages that exceed VIN(MAX) (up to 40V), however, the output voltage ripple increases as the input voltage is increased. As the input voltage is increased, the part is required to switch for shorter periods of time. Delays associated with turning off the power switch dictate the minimum on time of the part. The minimum on time for the LT3502/LT3502A is 60ns (Figure 1). When the required on time decreases below the minimum on time of 60ns, instead of the switch pulse width becoming narrower to accommodate the lower duty cycle requirement, the switch pulse width remains fixed at 60ns. The inductor current ramps up to a value exceeding the load current and the output ripple increases. The part then remains
R2 should be 20k or less to avoid bias current errors. Reference designators refer to the Block Diagram. Input Voltage Range The input voltage range for the LT3502/LT3502A applications depends on the output voltage and on the absolute maximum ratings of the VIN and BOOST pins. The minimum input voltage is determined by either the LT3502/LT3502A's minimum operating voltage of 3V, or by its maximum duty cycle. The duty cycle is the fraction of time that the internal switch is on and is determined by the input and output voltages: VOUT + VD DC = VIN - VSW + VD where VD is the forward voltage drop of the catch diode (~0.4V) and VSW is the voltage drop of the internal switch (~0.45V at maximum load). This leads to a minimum input voltage of: V +V VIN(MIN) = OUT D - VD + VSW DCMAX with DCMAX = 0.80 for the LT3502A and 0.90 for the LT3502. The maximum input voltage is determined by the absolute maximum ratings of the VIN and BOOST pins. For fixed frequency operation, the maximum input voltage is determined by the minimum duty cycle DCMIN: V +V VIN(MAX) = OUT D - VD + VSW DCMIN DCMIN = 0.15 for the LT3502A and 0.08 for the LT3502.
VSW 20V/DIV
IL 500mA/DIV VOUT 100mV/DIV VIN = 33V VOUT = 3.3V L = 6.8H COUT = 10F IOUT = 250mA 1s/DIV
3502 F01
Figure 1. Continuous Mode Operation Near Minimum On Time of 60ns
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LT3502/LT3502A APPLICATIONS INFORMATION
VSW 20V/DIV VSW 20V/DIV
IL 500mA/DIV VOUT 100mV/DIV VIN = 40V VOUT = 3.3V L = 6.8H COUT = 10F IOUT = 250mA 1s/DIV
3502 F02
IL 500mA/DIV VOUT 100mV/DIV VIN = 40V VOUT = 3.3V L = 6.8H COUT = 10F IOUT = 500mA 1s/DIV
3502 F03
Figure 2. Pulse Skip Occurs when Required On Time is Below 60ns
Figure 3. Pulse Skip with Large Load Current Will be Limited by the DA Valley Current Limit. Notice the Flat Inductor Valley Current and Reduced Switching Frequency
off until the output voltage dips below the programmed value before it begins switching again (Figure 2). Provided that the load can tolerate the increased output voltage ripple and that the components have been properly selected, operation above VIN(MAX) is safe and will not damage the part. As the input voltage increases, the inductor current ramps up quicker, the number of skipped pulses increases and the output voltage ripple increases. For operation above VIN(MAX) the only component requirement is that the components be adequately rated for operation at the intended voltage levels. Inductor current may reach current limit when operating in pulse skip mode with small valued inductors. In this case, the LT3502/LT3502A will periodically reduce its frequency to keep the inductor valley current to 650mA (Figure 3). Peak inductor current is therefore peak current plus minimum switch delay: VIN - VOUT * 60ns L The part is robust enough to survive prolonged operation under these conditions as long as the peak inductor current does not exceed 1.2A. Inductor current saturation and junction temperature may further limit performance during this operating regime. 900mA +
Inductor Selection and Maximum Output Current A good first choice for the inductor value is: L = 1.6(VOUT + VD) for the LT3502A L = 4.6(VOUT + VD) for the LT3502 where VD is the voltage drop of the catch diode (~0.4V) and L is in H. With this value there will be no subharmonic oscillation for applications with 50% or greater duty cycle. The inductor's RMS current rating must be greater than the maximum load current and its saturation current should be about 30% higher. For robust operation during fault conditions, the saturation current should be above 1.2A. To keep efficiency high, the series resistance (DCR) should be less than 0.1. Table 1 lists several vendors and types that are suitable. There are several graphs in the Typical Performance Characteristics section of this data sheet that show the maximum load current as a function of input voltage and inductor value for several popular output voltages. Low inductance may result in discontinuous mode operation, which is okay, but further reduces maximum load current. For details of the maximum output current and discontinuous mode operation, see Linear Technology Application Note 44.
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LT3502/LT3502A APPLICATIONS INFORMATION
Table 1
VENDOR Sumida URL www.sumida.com PART SERIES CDRH4D28 CDRH5D28 CDRH8D28 A916CY D585LC WE-TPC(M) WE-PD2(M) WE-PD(S) INDUCTANCE RATE (H) 1.2 to 4.7 2.5 to 10 2.5 to 33 2 to 12 1.1 to 39 1 to 10 2.2 to 22 1 to 27 SIZE (mm) 4.5 x 4.5 5.5 x 5.5 8.3 x 8.3 6.3 x 6.2 8.1 x 8 4.8 x 4.8 5.2 x 5.8 7.3 x 7.3
Toko Wurth Elektronik
www.toko.com www.we-online.com
Catch Diode A low capacitance 500mA Schottky diode is recommended for the catch diode, D1. The diode must have a reverse voltage rating equal to or greater than the maximum input voltage. The Phillips PMEG4005AEA is a good choice; it is related for 500mA continuous forward current and a maximum reverse voltage of 40V. Input Capacitor Bypass the input of the LT3502/LT3502A circuit with a 1F or higher value ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage and should not be used. A 1F ceramic is adequate to bypass the LT3502/LT3502A and will easily handle the ripple current. However, if the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT3502/LT3502A and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 1F capacitor is capable of this task, but only if it is placed close to the LT3502/LT3502A and the catch diode (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT3502/LT3502A. A ceramic input capacitor combined with trace or cable inductance forms a high
quality (underdamped) tank circuit. If the LT3502/LT3502A circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3502/LT3502A's voltage rating. This situation is easily avoided; see the Hot Plugging Safely section. Output Capacitor The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT3502/LT3502A to produce the DC output. In this role it determines the output ripple so low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3502/LT3502A's control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good value is: COUT = COUT = 33 for the LT3502A VOUT 66 for the LT3502 VOUT
where COUT is in F Use an X5R or X7R type and keep . in mind that a ceramic capacitor biased with VOUT will have less than its nominal capacitance. This choice will provide low output ripple and good transient response. Transient performance can be improved with a high value capacitor, but a phase lead capacitor across the feedback resistor, R1, may be required to get the full benefit (see the Compensation section).
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LT3502/LT3502A APPLICATIONS INFORMATION
For small size, the output capacitor can be chosen according to: 25 COUT = VOUT where COUT is in F. However, using an output capacitor this small results in an increased loop crossover frequency and increased sensitivity to noise. High performance electrolytic capacitors can be used for the output capacitor. Low ESR is important, so choose one that is intended for use in switching regulators. The ESR should be specified by the supplier and should be 0.1 or less. Such a capacitor will be larger than a ceramic capacitor and will have a larger capacitance, because the capacitor must be large to achieve low ESR. Table 2 lists several capacitor vendors. Figure 4 shows the transient response of the LT3502A with several output capacitor choices. The output is 3.3V. The load current is stepped from 150mA to 400mA and back to 150mA, and the oscilloscope traces show the output voltage. The upper photo shows the recommended value. The second photo shows the improved response (less voltage drop) resulting from a larger output capacitor and a phase lead capacitor. The last photo shows the response to a high performance electrolytic capacitor. Transient performance is improved due to the large output capacitance.
Table 2
VENDOR Panasonic PHONE (714) 373-7366 URL www.panasonic.com PART SERIES Ceramic Polymer, Tantalum Ceramic, Tantalum Ceramic Polymer, Tantalum Ceramic Ceramic, Tantalum Ceramic COMMENTS EEF Series T494,T495
BOOST Pin Considerations Capacitor C3 and the internal boost diode are used to generate a boost voltage that is higher than the input voltage. In most cases a 0.1F capacitor will work well. Figure 5 shows two ways to arrange the boost circuit. The BOOST pin must be at least 2.2V above the SW pin for best efficiency. For outputs of 3V and above, the standard circuit (Figure 5a) is best. For outputs less than 3V and above 2.5V, place a discrete Schottky diode (such as the BAT54) in parallel with the internal diode to reduce VD. The following equations can be used to calculate and minimize boost capacitance in F: 0.012/(VBD + VCATCH - VD - 2.2) for the LT3502A 0.030/(VBD + VCATCH - VD- 2.2) for the LT3502 VD is the forward drop of the boost diode, and VCATCH is the forward drop of the catch diode (D1). For lower output voltages the BD pin can be tied to an external voltage source with adequate local bypassing (Figure 5b). The above equations still apply for calculating the optimal boost capacitor for the chosen BD voltage. The absence of BD voltage during startup will increase minimum voltage to start and reduce efficiency. You must also be sure that the maximum voltage rating of BOOST pin is not exceeded.
Kemet Sanyo
(864) 963-6300 (408)794-9714
www.kemet.com www.sanyovideo.com
POSCAP
Murata AVX Taiyo Yuden
(404) 436-1300
www.murata.com www.avxcorp.com www.taiyo-yuden.com
TPS Series
(864) 963-6300
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LT3502/LT3502A APPLICATIONS INFORMATION
VOUT 32.4k FB 10k 10F IL 0.2A/DIV VOUT 0.1V/DIV AC COUPLED
10s/DIV
3502 F04a
VOUT 32.4k FB 10k 50pF 10F x2 IL 0.2A/DIV VOUT 0.1V/DIV AC COUPLED
10s/DIV
3502 F04b
VOUT 32.4k
+
FB 10k 100F SANYO 4TPB100M
IL 0.2A/DIV VOUT 0.1V/DIV AC COUPLED
10s/DIV
3502 F04c
Figure 4. Transient Load Response of the LT3502A with Different Output Capacitors as the Load Current is Stepped from 150mA to 400mA. VIN = 12V, VOUT = 3.3V, L = 6.8H
VDD BD BOOST VIN VIN LT3502 SW GND DA VOUT VIN BD BOOST VIN LT3502 SW GND VBOOST - VSW VIN MAX VBOOST 2VIN DA VOUT
VBOOST - VSW VOUT MAX VBOOST VIN + VOUT
3502 F05a
3502 F05b
(5a)
(5b)
Figure 5
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LT3502/LT3502A APPLICATIONS INFORMATION
The minimum operating voltage of an LT3502/LT3502A application is limited by the undervoltage lockout (3V) and by the maximum duty cycle as outlined above. For proper start-up, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3502/LT3502A is turned on with its SHDN pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly. This minimum load will depend on the input and output voltages, and on the arrangement of the boost circuit. The minimum load generally goes to
7 6 5 START VIN (V) VIN (V) 4 3 2 1 0 0.001 RUN
zero once the circuit has started. Figure 6 shows plots of minimum load to start and to run as a function of input voltage. In many cases the discharged output capacitor will present a load to the switcher which will allow it to start. The plots show the worst-case situation where VIN is ramping very slowly. At light loads, the inductor current becomes discontinuous and the effective duty cycle can be very high. This reduces the minimum input voltage to approximately 400mV above VOUT. At higher load currents, the inductor current is continuous and the duty cycle is limited by the maximum duty cycle of the LT3502/LT3502A, requiring a higher input voltage to maintain regulation.
8 7 6 5 4 3 2 1 0.1 0.01 LOAD CURRENT (A) 1
3502 G19
START RUN
0 0.001
0.01 0.1 LOAD CURRENT (A)
1
3502 G20
(6a) LT3502A Typical Minimum Input Voltage, VOUT = 3.3V
7 6 5 VIN (V)
(6b) LT3502A Typical Minimum Input Voltage, VOUT = 5V
8 7 6 START RUN
VIN (V)
4 3 2 1 0 0.001
RUN
START
5 4 3 2 1
0.1 0.01 LOAD CURRENT (A)
1
3502 G21
0 0.001
0.01 0.1 LOAD CURRENT (A)
1
3502 G22
(6c) LT3502 Typical Minimum Input Voltage, VOUT = 3.3V Figure 6
(6d) LT3502 Typical Minimum Input Voltage, VOUT = 5V
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15
LT3502/LT3502A APPLICATIONS INFORMATION
VSW 10V/DIV RUN SHDN GND
3502 F07a
IL 500mA/DIV
VOUT 2V/DIV VIN = 12V VOUT = 3.3V L = 6.8H COUT = 10F RUN 50k SHDN 0.1F GND
3502 F07b
5s/DIV
VSW 10V/DIV
IL 500mA/DIV VOUT 2V/DIV VIN = 12V VOUT = 3.3V L = 6.8H COUT = 10F 50s/DIV
3502 F07
Figure 7. To Soft Start the LT3502A, Add a Resistor and Capacitor to the SHDN Pin
Soft-Start The SHDN pin can be used to soft start the LT3502/LT3502A, reducing the maximum input current during start-up. The SHDN pin is driven through an external RC filter to create a voltage ramp at this pin. Figure 7 shows the start-up waveforms with and without the soft-start circuit. By choosing a large RC time constant, the peak start up current can be reduced to the current that is required to regulate the output, with no overshoot. Choose the value of the resistor so that it can supply 80A when the SHDN pin reaches 2V. Short and Reverse Protection If the inductor is chosen so that it won't saturate excessively, the LT3502/LT3502A will tolerate a shorted output. When operating in short-circuit condition, the LT3502/LT3502A will reduce their frequency until the valley current is 650mA (Figure 8a). There is another situation to consider in systems where the output will be held high when the input to the LT3502/LT3502A is absent. This may occur in
battery charging applications or in battery backup systems where a battery or some other supply is diode OR-ed with the LT3502/LT3502A's output. If the VIN pin is allowed to float and the SHDN pin is held high (either by a logic signal or because it is tied to VIN), then the LT3502/LT3502A's
VSW 10V/DIV
IL 500mA/DIV
VIN = 40V VOUT = 0V L = 6.8H COUT = 10F
2s/DIV
3502 F08a
Figure 8a. The LT3502A Reduces its Frequency to Below 500kHz to Protect Against Shorted Output with 40V Input
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16
LT3502/LT3502A APPLICATIONS INFORMATION
D4 VIN VIN BD BOOST SW LT3502A DA SHDN GND FB VOUT
+
3502 F08b
Figure 8b. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output; it Also Protects the Circuit from a Reversed Input. The LT3502/LT3502A Runs Only When the Input is Present
internal circuitry will pull its quiescent current through its SW pin. This is fine if your system can tolerate a few mA in this state. If you ground the SHDN pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LT3502/LT3502A can pull large currents from the output through the SW pin and the VIN pin. Figure 8b shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. Hot Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3502/LT3502A circuits. However, these capacitors can cause problems if the LT3502/LT3502A are plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion). The low loss ceramic capacitor combined with stray inductance in series with the power source forms an underdamped tank circuit, and the voltage at the VIN pin of the LT3502/LT3502A can ring to twice the nominal input voltage, possibly exceeding the LT3502/LT3502A's rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3502/LT3502A into an energized supply, the input network should be designed to prevent this overshoot. Figure 9 shows the waveforms that result when an LT3502/LT3502A circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The first plot is the response with a 2.2F ceramic capacitor at the
input. The input voltage rings as high as 35V and the input current peaks at 20A. One method of damping the tank circuit is to add another capacitor with a series resistor to the circuit. In Figure 9b an aluminum electrolytic capacitor has been added. This capacitor's high equivalent series resistance damps the circuit and eliminates the voltage overshoot. The extra capacitor improves low frequency ripple filtering and can slightly improve the efficiency of the circuit, though it is likely to be the largest component in the circuit. An alternative solution is shown in Figure 9c. A 1 resistor is added in series with the input to eliminate the voltage overshoot (it also reduces the peak input current). A 0.1F capacitor improves high frequency filtering. This solution is smaller and less expensive than the electrolytic capacitor. For high input voltages its impact on efficiency is minor, reducing efficiency less than one half percent for a 5V output at full load operating from 24V. Frequency Compensation The LT3502/LT3502A use current mode control to regulate the output. This simplifies loop compensation. In particular, the LT3502/LT3502A does not require the ESR of the output capacitor for stability allowing the use of ceramic capacitors to achieve low output ripple and small circuit size. Figure 10 shows an equivalent circuit for the LT3502/ LT3502A control loop. The error amp is a transconductance amplifier with finite output impedance. The power section, consisting of the modulator, power switch and inductor, is modeled as a transconductance amplifier generating an output current proportional to the voltage at the VC node. Note that the output capacitor integrates this current, and that the capacitor on the VC node (CC) integrates the error amplifier output current, resulting in two poles in the loop. RC provides a zero. With the recommended output capacitor, the loop crossover occurs above the RCCC zero. This simple model works well as long as the value of the inductor is not too high and the loop crossover frequency is much lower than the switching frequency. With a larger ceramic capacitor (very low ESR), crossover may be lower and a phase lead capacitor (CPL) across the feedback divider may improve the phase margin and transient response. Large electrolytic capacitors may have an ESR large enough to create an additional zero, and the phase lead may not be necessary.
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17
LT3502/LT3502A APPLICATIONS INFORMATION
CLOSING SWITCH SIMULATES HOT PLUG IIN VIN LT3502 DANGER! VIN 20V/DIV RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING OF THE LT3502
+
2.2F
LOW IMPEDANCE ENERGIZED 24V SUPPLY
STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR
IIN 5A/DIV 20s/DIV
(9a)
LT3502 VIN 20V/DIV
+
10F 35V AI.EI.
+
2.2F
IIN 5A/DIV
(9b)
1 LT3502 VIN 20V/DIV
20s/DIV
+
0.1F 2.2F
IIN 5A/DIV
(9c)
20s/DIV
3502 F09
Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LT3502 is Connected to a Live Supply
LT3502 0.5V
CURRENT MODE POWER STAGE SW gm = 1A/V R1 FB ESR gm = 100A/V CPL
VC RC 150k CC 70pF GND
ERROR AMPLIFIER 1M
Figure 10. Model for Loop Response
18
-
+
- +
OUT
800mV
+
C1 R2
C1
3502 F10
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LT3502/LT3502A APPLICATIONS INFORMATION
If the output capacitor is different than the recommended capacitor, stability should be checked across all operating conditions, including load current, input voltage and temperature. The LT1375 data sheet contains a more thorough discussion of loop compensation and describes how to test the stability using a transient load. PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 11 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT3502/LT3502A's VIN and SW pins, the catch diode (D1) and the input capacitor (C2). The loop formed by these components should be as small as possible and tied to system ground in only one place. These components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane below these components, and tie this ground plane to system ground at one location, ideally at the ground terminal of the output capacitor C1. The SW and BOOST nodes should be as small as possible. Finally, keep the FB node small so that the ground pin and ground traces will shield it from the SW and BOOST nodes. Include vias near the exposed GND pad of the LT3502/LT3502A to help remove heat from the LT3502/LT3502A to the ground plane. High Temperature Considerations The die temperature of the LT3502/LT3502A must be lower than the maximum rating of 125C. This is generally not a concern unless the ambient temperature is above 85C. For higher temperatures, care should be taken in the layout of the circuit to ensure good heat sinking of the LT3502/LT3502A. The maximum load current should be derated as the ambient temperature approaches 125C. The die temperature is calculated by multiplying the LT3502/LT3502A power dissipation by the thermal resistance from junction to ambient. Power dissipation within the LT3502/LT3502A can be estimated by calculating the total power loss from an efficiency measurement and subtracting the catch diode loss. Thermal resistance depends on the layout of the circuit board, but 102C/W and 110C/W are typical for the (2mm x 2mm) DFN and MS10 packages respectively. Outputs Greater Than 7V Note that for outputs above 7V, the input voltage range will be limited by the maximum rating of the BOOST pin. The sum of input and output voltages cannot exceed the BOOST pin's 50V rating. The 15V circuit (Figure 12) shows how to overcome this limitation using an additional zener diode. Other Linear Technology Publications Application notes AN19, AN35 and AN44 contain more detailed descriptions and design information for Buck regulators and other switching regulators. The LT1376 data sheet has a more extensive discussion of output ripple, loop compensation and stability testing. Design Note 100 shows how to generate a bipolar output supply using a buck regulator.
VIN 20V TO 40V BST R1 BD FB SHDN R2 DA D1 BD VIN C2 1F LT3502A DA GND OFF ON = VIA
3502 F11
VOUT C1
L1
C2 10V BOOST C3 0.1F SW 22pF R1 180k FB GND
3502 F12
VIN
C3
L1 33H
VOUT 15V 500mA
SHDN
R2 10k
C1 10F
Figure 11
Figure 12. 15V Step-Down Converter
3502fc
19
LT3502/LT3502A TYPICAL APPLICATIONS
0.8V Step-Down Converter
VBD 3V TO 7V 0.1F VIN 3V TO 40V BD C2 1F VIN BOOST SW LT3502A DA OFF ON SHDN GND C1: JMK212BJ476MG C3: HMK212BJ104MG L1: LQH43CN3R3M03 FB C1 47F
3502 TA02a
VBD 3V TO 7V VIN 3V TO 40V VOUT 0.8V 500mA
0.1F BD C2 1F VIN BOOST C3 0.1F SW LT3502 DA OFF ON SHDN GND C1: JMK316BJ107ML L1: LQH43CN100K03 FB C1 100F
3502 TA02b
L1 C3 0.1F 3.3H D1
L1 10H
D1
VOUT 0.8V 500mA
1.8V Step-Down Converter
VBD 3V TO 7V VIN 3V TO 40V VBD 3V TO 7V 0.1F BD C2 1F VIN BOOST SW LT3502A DA OFF ON SHDN GND FB R2 10k C1 22F
3502 TA03a
0.1F BD C2 1F VIN BOOST C3 0.1F SW LT3502 DA D1 R1 12.5k R2 10k C1 47F
3502 TA03b
L1 C3 0.1F 4.7H D1 R1 12.5k
VIN 3V TO 40V VOUT 1.8V 500mA
L1 15H
VOUT 1.8V 500mA
OFF ON
SHDN GND
FB
C1: JMK212BJ226MG L1: LQH43CN4R7M03
C1: JMK212BJ476MG L1: LQH55DN150M03
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20
LT3502/LT3502A TYPICAL APPLICATIONS
2.5V Step-Down Converter
VBD 3V TO 7V VIN 3.5V TO 40V VBD 3V TO 7V BD C2 1F VIN BOOST SW LT3502A DA OFF ON SHDN GND FB R2 10k C1 22F
3502 TA04a
0.1F
0.1F BD C2 1F VIN BOOST C3 0.1F SW LT3502 DA D1 R1 21.3k R2 10k C1 22F
3502 TA04b
L1 C3 0.1F 6.8H D1 R1 21.3k
VIN 3.5V TO 40V VOUT 2.5V 500mA
L1 15H
VOUT 2.5V 500mA
OFF ON
SHDN GND
FB
C1: JMK212BJ226MG L1: LQH43DN6R8M03
C1: JMK212BJ226MG L1: LQH55DN150M03
3.3V Step-Down Converter
VIN 4.7V TO 40V
BD VIN C2 1F LT3502A DA OFF ON SHDN GND FB R2 10k C1 10F
3502 TA05a
BOOST SW
L1 C3 0.1F 6.8H D1 R1 31.6k
VIN 4.5V TO 40V VOUT 3.3V 500mA
BD VIN C2 1F LT3502 DA OFF ON SHDN GND FB R2 10k C1 22F
3502 TA05b
BOOST C3 0.1F SW D1 R1 31.6k
L1 15H
VOUT 3.3V 500mA
C1: LMK316BJ106ML-BR L1: LQH43CN6R8M03
C1: JMK212BJ226MG L1: LQH55DN150M03
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21
LT3502/LT3502A PACKAGE DESCRIPTION
DC Package 8-Lead Plastic DFN (2mm x 2mm)
(Reference LTC DWG # 05-08-1719 Rev O)
0.70 0.05 2.55 0.05 1.15 0.05 0.64 0.05 (2 SIDES) PACKAGE OUTLINE
0.25 0.05 0.45 BSC 1.37 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.05 TYP 2.00 0.10 (4 SIDES)
R = 0.115 TYP 5
8 0.40 0.10 PIN 1 NOTCH R = 0.20 OR 0.25 x 45 CHAMFER
(DC8) DFN 0106 REVO
PIN 1 BAR TOP MARK (SEE NOTE 6)
0.64 0.10 (2 SIDES)
4 0.200 REF 0.75 0.05 1.37 0.10 (2 SIDES) 0.00 - 0.05
1 0.23 0.05 0.45 BSC
BOTTOM VIEW--EXPOSED PAD
NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
3502fc
22
LT3502/LT3502A PACKAGE DESCRIPTION
MS Package 10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
0.889 0.127 (.035 .005)
5.23 (.206) MIN
3.20 - 3.45 (.126 - .136) 3.00 0.102 (.118 .004) (NOTE 3)
0.50 0.305 0.038 (.0197) (.0120 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
10 9 8 7 6
0.497 0.076 (.0196 .003) REF
0.254 (.010) GAUGE PLANE
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE 4)
12345 0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) SEATING PLANE 0.17 -0.27 (.007 - .011) TYP 0.1016 0.0508 (.004 .002)
MSOP (MS) 0307 REV E
1.10 (.043) MAX
0.86 (.034) REF
NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.50 (.0197) BSC
3502fc
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.
23
LT3502/LT3502A TYPICAL APPLICATION
5V Step-Down Converter
VIN 6.7V TO 40V BD VIN C2 1F LT3502A DA OFF ON SHDN GND FB R2 10k C1 10F
3502 TA06a
BOOST C3 0.1F SW D1 R1 52.3k
L1 10H
VIN 6.4V TO 40V VOUT 5V 500mA
BD VIN C2 1F LT3502 DA OFF ON SHDN GND FB R2 10k C1 22F
3502 TA06b
BOOST C3 0.1F SW D1 R1 52.3k
L1 22H
VOUT 5V 500mA
C1: LMK316BJ106ML-BR L1: LQH43CN100K03
C1: LMK316BJ106ML-BR L1: LQH43CN100K03
RELATED PARTS
PART NUMBER LT1766 LT1933 LT1936 LT1940 LT1976/LT1977 LTC 3407/LTC3407-2 LT3434/LT3435 LT3437 LT3493 LT3501 LT3503 LT3505 LT3506/LT3506A LT3508 LT3510 LTC3548 DESCRIPTION 60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter 500mA (IOUT), 500kHz, Step-Down Switching Regulator in SOT-23 36V, 1.4A (IOUT), 500kHz, High Efficiency Step-Down DC/DC Converter Dual 25V, 1.4A (IOUT), 1.1MHz, High Efficiency Step-Down DC/DC Converter 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency StepDown DC/DC Converters with Burst Mode(R) Operation Dual 600mA/800mA, 1.5MHz/2.25MHz, Synchronous Step-DownDC/DC Converters 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency StepDown DC/DC Converters with Burst Mode Operation 60V, 400mA (IOUT), Micropower Step-Down DC/DC Converter with Burst Mode Operation 36V, 1.4A (IOUT), 750kHz, High Efficiency Step-Down DC/DC Converter Dual 25V, 3A (IOUT), 1.5MHz, High Efficiency Step-Down DC/DC Converter 20V, 1A (IOUT), 2.2MHz, High Efficiency Step-Down DC/DC Converter 36V, 1.2A (IOUT), 3MHz, High Efficiency Step-Down DC/DC Converter Dual 25V, 1.6A (IOUT), 575kHz/1.1MHz, High Efficiency Step-Down DC/DC Converters Dual 36V, 1.4A (IOUT), 2.5MHz, High Efficiency Step-Down DC/DC Converter Dual 25V, 2A (IOUT), 1.5MHz, High Efficiency Step-Down DC/DC Converter Dual 400mA + 800mA, 2.25MHz Synchronous Step-Down DC/DC Converter COMMENTS VIN: 5.5V to 60V, VOUT(MIN) = 1.2V, IQ = 2.5mA, ISD = 25A, TSSOP16/TSSOP16E Packages VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.6mA, ISD < 1A, ThinSOTTM Package VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.9mA, ISD < 1A, MS8E Package VIN: 3.6V to 25V, VOUT(MIN) = 1.20V, IQ = 3.8mA, ISD < 30A, TSSOP16E Package VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100A, ISD < 1A, TSSOP16E Package VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD <1A, 3mm x 3mm DFN, MS10E Package VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100A, ISD < 1A, TSSOP16E Package VIN: 3.3V to 60V, VOUT(MIN) = 1.25V, IQ = 100A, ISD < 1A, DFN Package VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1A, DFN Package VIN: 3.3V to 25V, VOUT(MIN) = 0.8V, IQ = 3.7mA, ISD < 10A, TSSOP20E Package VIN: 3.6V to 20V, VOUT(MIN) = 0.78V, IQ = 1.9mA, ISD < 1A, 2mm x 3mm DFN Package VIN: 3.6V to 36V, VOUT(MIN) = 0.78V, IQ = 2mA, ISD < 2A, 3mm x 3mm DFN, MS8E Packages VIN: 3.6V to 25V, VOUT(MIN) = 0.8V, IQ = 3.8mA, ISD < 30A, 4mm x 5mm DFN Package VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 4.3mA, ISD < 1A, 4mm x 4mm QFN, TSSOP16E Packages VIN: 3.3V to 25V, VOUT(MIN) = 0.8V, IQ = 3.7mA, ISD < 10A, TSSOP20E Package VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD < 1A, 3mm x 3mm DFN, MS10E Packages
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Burst Mode is a registered trademark of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.
24 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0908 REV C * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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