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LT3436 3A, 800kHz Step-Up Switching Regulator
FEATURES

DESCRIPTIO
Constant 800kHz Switching Frequency Wide Operating Voltage Range: 3V to 25V High Efficiency 0.1/3A Switch 1.2V Feedback Reference Voltage 2% Overall Output Voltage Tolerance Uses Low Profile Surface Mount External Components Low Shutdown Current: 11A Synchronizable from 1MHz to 1.4MHz Current-Mode Control Constant Maximum Switch Current Rating at All Duty Cycles* Available in a Small Thermally Enhanced TSSOP-16 Package
The LT(R)3436 is an 800kHz monolithic boost switching regulator. A high efficiency 3A, 0.1 switch is included on the die together with all the control circuitry required to complete a high frequency, current-mode switching regulator. Current-mode control provides fast transient response and excellent loop stability. New design techniques achieve high efficiency at high switching frequencies over a wide operating range. A low dropout internal regulator maintains consistent performance over a wide range of inputs from 24V systems to LiIon batteries. An operating supply current of 1mA maintains high efficiency, especially at lower output currents. Shutdown reduces quiescent current to 11A. Maximum switch current remains constant at all duty cycles. Synchronization capability allows an external logic level signal to increase the internal oscillator from 1MHz to 1.4MHz. Full cycle-by-cycle switch current limit protection and thermal shutdown are provided. High frequency operation allows the reduction of input and output filtering components and permits the use of tiny chip inductors. The LT3436 is available in an exposed pad, 16-pin TSSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. *Protectd by U.S. Patents including 6535042, 6611131, 6498466
APPLICATIO S

DSL Modems Portable Computers Battery-Powered Systems Distributed Power
TYPICAL APPLICATIO
3.9H
5V to 12V Boost Converter
B220A INPUT 5V 4.7F CERAMIC OPEN OR HIGH = ON VIN LT3436 SHDN SYNC FB VSW 90.9k VC
EFFICIENCY (%)
OUTPUT 12V 0.9A
GND
10nF 470pF 4.7k
MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING.
10k 1%
22F CERAMIC
3436 TA01
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Efficiency vs Load Current
90 85 80 75 70 65 60 VIN = 5V VOUT = 12V 0 0.1 0.2 0.3 0.4 0.5 0.6 LOAD CURRENT (A) 0.7 0.8
3436 TA01b
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LT3436
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW GND VIN SW SW GND GND NC GND 1 2 3 4 5 6 7 8 17 16 GND 15 NC 14 SYNC 13 VC 12 FB 11 SHDN 10 NC 9 GND
Input Voltage .......................................................... 25V Switch Voltage ......................................................... 35V SHDN Pin ............................................................... 25V FB Pin Current ....................................................... 1mA SYNC Pin Current .................................................. 1mA Operating Junction Temperature Range (Note 2) LT3436E .......................................... - 40C to 125C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LT3436EFE FE PART MARKING 3436EFE
FE PACKAGE 16-LEAD PLASTIC TSSOP EXPOSED PAD IS GND (PIN 17), MUST BE SOLDERED TO PCB
TJMAX = 125C, JA = 45C/W, JC(PAD) = 10C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER Recommended Operating Voltage Maximum Switch Current Limit Oscillator Frequency Switch On Voltage Drop VIN Undervoltage Lockout VIN Supply Current VIN Supply Current/ISW Shutdown Supply Current Feedback Voltage FB Input Current FB to VC Voltage Gain FB to VC Transconductance VC Pin Source Current VC Pin Sink Current VC Pin to Switch Current Transconductance VC Pin Minimum Switching Threshold VC Pin 3A ISW Threshold Maximum Switch Duty Cycle SHDN Threshold Voltage SHDN Input Current (Shutting Down) SHDN Threshold Current Hysteresis SYNC Threshold Voltage SYNC Input Frequency SYNC Pin Resistance ISYNC = 1mA Duty Cycle = 0% 0.4V < VC < 0.9V IVC = 10A VFB = 1V VFB = 1.4V 3.3V < VIN < 25V ISW = 3A (Note 3) ISW = 0A ISW = 3A CONDITION
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 15V, VC = 0.8V, SHDN, SYNC and switch open unless otherwise noted.
MIN

TYP 4 800 330 2.6 1 15 11
MAX 25 6 960 550 2.73 1.3 25 45 1.218 1.224 - 0.4 1300 - 165 165
UNITS V A kHz mV V mA mA/A A A V V A Mho A A A/V V V % %
3 3 640 2.47
VSHDN = 0V, VIN = 25V, VSW = 25V
3V < VIN < 25V, 0.4V < VC < 0.9V

1.182 1.176 0 150 500 - 85 70
1.2 - 0.2 350 850 - 120 110 4.8 0.3 0.9
VC = 1.2V, ISW = 350mA VC = 1.2V, ISW = 1A SHDN = 60mV Above Threshold SHDN = 100mV Below Threshold

85 80 1.28 -7 4 1
90 1.35 -10 7 1.5 20 1.42 -13 10 2.2 1.4
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V A A V MHz k
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ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3436E is guaranteed to meet performance specifications from 0C to 125C. Specifications over the - 40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Minimum input voltage is defined as the voltage where the internal regulator enters lockout. Actual minimum input voltage to maintain a regulated output will depend on output voltage and load current. See Applications Information.
TYPICAL PERFORMANCE CHARACTERISTICS
FB Voltage
1.220 1.215
SWITCH VOLTAGE (mV)
400 1.210
FB VOLTAGE (V)
350 300 250 200 150 100 50 0
TA = 25C
OSCILLATOR FREQUENCY (kHz)
1.205 1.200 1.195 1.190 1.185 1.180 -50 -25 0 25 50 75 100 125
TEMPERATURE (C)
3436 G01
SHDN Threshold
1.40 14 12 1.38
SHDN THRESHOLD (V) VIN CURRENT (A)
SHDN INPUT CURRENT (A)
1.36
1.34
1.32 2 1.30 -50 -25 0 0 25 50 75 100 125 0 5 TEMPERATURE (C)
3436 G04
UW
Switch On Voltage Drop
500 450 TA = 125C 920 890 860 830 800 770 740 710 0 0.5 1.5 2.0 1.0 SWITCH CURRENT (A) 2.5 3.0
3436 G02
Oscillator Frequency
TA = -40C
680 -50 -25
0
25
50
75
100
125
TEMPERATURE (C)
3436 G03
SHDN Supply Current
-12 TA = 25C SHDN = 0V -10
SHDN Input Current
10 8 6 4
SHUTTING DOWN -8 -6 -4 -2 0 -50 -25 STARTING UP
10 15 20 INPUT VOLTAGE (V)
25
30
3436 G05
50 25 75 0 TEMPERATURE (C)
100
125
3436 G06
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LT3436 TYPICAL PERFOR A CE CHARACTERISTICS
SHDN Supply Current
300 250
VIN CURRENT (A)
TA = 25C VIN = 15V
SWITCH PEAK CURRENT (A)
VIN CURRENT (A)
200 150 100 50 0
0
0.2
0.4 0.6 0.8 1.0 SHDN VOLTAGE (V)
PIN FUNCTIONS
GND (Pins 1, 5, 6, 8, 9, 16, 17): Short GND pins 1, 5, 6,8, 9, 16 and the exposed pad (pin 17) on the PCB. The GND is the reference for the regulated output, so load regulation will suffer if the "ground" end of the load is not at the same voltage as the GND of the IC. This condition occurs when the load current flows through the metal path between the GND pins and the load ground point. Keep the ground path short between the GND pins and the load and use a ground plane when possible. Keep the path between the input bypass and the GND pins short. The exposed pad should be attached to a large copper area to improve thermal performance. VIN (Pin 2): This pin powers the internal circuitry and internal regulator. Keep the external bypass capacitor close to this pin. SW (Pins 3, 4): The switch pin is the collector of the onchip power NPN switch and has large currents flowing through it. Keep the traces to the switching components as short as possible to minimize radiation and voltage spikes. SHDN (Pin 11): The shutdown pin is used to turn off the regulator and to reduce input drain current to a few microamperes. The 1.35V threshold can function as an accurate undervoltage lockout (UVLO), preventing the regulator from operating until the input voltage has reached a predetermined level. Float or pull high to put the regulator in the operating mode. FB (Pin 12): The feedback pin is used to set output voltage using an external voltage divider that generates 1.2V at the pin with the desired output voltage. If required, the current limit can be reduced during start up when the FB pin is below 0.5V (see the Current Limit Foldback graph in the Typical Performance Characteristics section). An impedance of less than 5k at the FB pin is needed for this feature to operate. VC (Pin 13): The VC pin is the output of the error amplifier and the input of the peak switch current comparator. It is normally used for frequency compensation, but can do double duty as a current clamp or control loop override. This pin sits at about 0.3V for very light loads and 0.9V at maximum load. SYNC (Pin 14): The sync pin is used to synchronize the internal oscillator to an external signal. It is directly logic compatible and can be driven with any signal between 20% and 80% duty cycle. The synchronizing range is equal to initial operating frequency, up to 1.4MHz. See Synchronization section in Applications Information for details. When not in use, this pin should be grounded.
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1.2 1.4
3436 G07
Input Supply Current
1200 1000 800 600 400 200 0 MINIMUM INPUT VOLTAGE TA = 25C 4.0 3.5
Current Limit Foldback
TA = 25C SWITCH CURRENT 3.0 2.5 2.0 1.5 1.0 0.5 10 20 30 40
FB INPUT CURRENT (A)
0
5
10 15 20 INPUT VOLTAGE (V)
25
30
3436 G08
0
0
0.2
1.0 0.4 0.6 0.8 FEEDBACK VOLTAGE (V)
0 1.2
3436 G09
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LT3436
BLOCK DIAGRAM
The LT3436 is a constant frequency, current-mode boost converter. This means that there is an internal clock and two feedback loops that control the duty cycle of the power switch. In addition to the normal error amplifier, there is a current sense amplifier that monitors switch current on a cycle-by-cycle basis. A switch cycle starts with an oscillator pulse which sets the RS flip-flop to turn the switch on. When switch current reaches a level set by the inverting input of the comparator, the flip-flop is reset and the switch turns off. Output voltage control is obtained by using the output of the error amplifier to set the switch current trip point. This technique means that the error
INPUT
2.5V BIAS REGULATOR
SYNC
SHUTDOWN COMPARATOR
1.35V
3A ERROR AMPLIFIER gm = 850Mho
VC
Figure 1. Block Diagram
-
SHDN
+
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amplifier commands current to be delivered to the output rather than voltage. A voltage fed system will have low phase shift up to the resonant frequency of the inductor and output capacitor, then an abrupt 180 shift will occur. The current fed system will have 90 phase shift at a much lower frequency, but will not have the additional 90 shift until well beyond the LC resonant frequency. This makes it much easier to frequency compensate the feedback loop and also gives much quicker transient response. A comparator connected to the shutdown pin disables the internal regulator, reducing supply current.
INTERNAL VCC SLOPE COMP
0.3V
800kHz OSCILLATOR
S CURRENT COMPARATOR RS FLIP-FLOP R CURRENT SENSE AMPLIFIER VOLTAGE GAIN = 40 DRIVER CIRCUITRY
SW Q1 POWER SWITCH
+ -
7A
+
0.005
-
+
-
FB
1.2V GND
3436 F01
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LT3436
APPLICATIONS INFORMATION
FB RESISTOR NETWORK The suggested resistance (R2) from FB to ground is 10k 1%. This reduces the contribution of FB input bias current to output voltage to less than 0.2%. The formula for the resistor (R1) from VOUT to FB is:
R1 = R2(VOUT - 1. 2) 1.2 - R2(0.2A)
LT3436 ERROR AMPLIFIER
VSW OUTPUT
+ -
1.2V FB R1
+
R2 10k
3436 F02
VC
GND
Figure 2. Feedback Network
OUTPUT CAPACITOR Step-up regulators supply current to the output in pulses. The rise and fall times of these pulses are very fast. The output capacitor is required to reduce the voltage ripple this causes. The RMS ripple current can be calculated from: IRIPPLE(RMS) = IOUT
(VOUT - VIN ) / VIN
The LT3436 will operate with both ceramic and tantalum output capacitors. Ceramic capacitors are generally chosen for their small size, very low ESR (effective series resistance), and good high frequency operation, reducing output ripple voltage. Their low ESR removes a useful zero in the loop frequency response, common to tantalum capacitors. To compensate for this, the VC loop compensation pole frequency must typically be reduced by a factor of 10. Typical ceramic output capacitors are in the 4.7F
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to 22F range. Since the absolute value of capacitance defines the pole frequency of the output stage, an X7R or X5R type ceramic, which have good temperature stability, is recommended. Tantalum capacitors are usually chosen for their bulk capacitance properties, useful in high transient load applications. ESR rather than absolute value defines output ripple at 800kHz. Values in the 22F to 100F range are generally needed to minimize ESR and meet ripple current ratings. Care should be taken to ensure the ripple ratings are not exceeded.
Table 1. Surface Mount Solid Tantalum Capacitor ESR and Ripple Current E Case Size ESR (Max, ) Ripple Current (A)
AVX TPS, Sprague 593D D Case Size AVX TPS, Sprague 593D C Case Size AVX TPS 0.2 (typ) 0.5 (typ) 0.1 to 0.3 0.7 to 1.1 0.1 to 0.3 0.7 to 1.1
INPUT CAPACITOR Unlike the output capacitor, RMS ripple current in the input capacitor is normally low enough that ripple current rating is not an issue. The current waveform is triangular, with an RMS value given by: IRIPPLE(RMS) = 0.29(VIN )(VOUT - VIN ) (L)( f)(VOUT )
At higher switching frequency, the energy storage requirement of the input capacitor is reduced so values in the range of 2.2F to 10F are suitable for most applications. Y5V or similar type ceramics can be used since the absolute value of capacitance is less important and has no significant effect on loop stability. If operation is required close to the minimum input voltage required by either the output or the LT3436, a larger value may be necessary. This is to prevent excessive ripple causing dips below the minimum operating voltage resulting in erratic operation.
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LT3436
APPLICATIONS INFORMATION
INDUCTOR CHOICE AND MAXIMUM OUTPUT CURRENT When choosing an inductor, there are 2 conditions that limit the minimum inductance; required output current, and avoidance of subharmonic oscillation. The maximum output current for the LT3436 in a standard boost converter configuration with an infinitely large inductor is: The recommended minimum inductance is:
LMIN = (VIN )2 (VOUT - VIN ) 0.4(VOUT )2 (IOUT )(f)
IOUT (MAX) = 3A
VIN * VOUT
Where = converter efficiency (typically 0.87 at high current). As the value of inductance is reduced, ripple current increases and IOUT(MAX) is reduced. The minimum inductance for a required output current is given by:
LMIN =
VIN (VOUT - VIN ) (V )(I ) 2VOUT (f) 3 - OUT OUT VIN *
The second condition, avoidance of subharmonic oscillation, must be met if the operating duty cycle is greater than 50%. The slope compensation circuit within the LT3436 prevents subharmonic oscillation for inductor ripple currents of up to 1.4AP-P, defining the minimum inductor value to be:
LMIN = VIN (VOUT - VIN ) 1.4VOUT (f)
These conditions define the absolute minimum inductance. However, it is generally recommended that to prevent excessive output noise, and difficulty in obtaining stability, the ripple current is no more than 40% of the average inductor current. Since inductor ripple is:
IP -P RIPPLE =
VIN (VOUT - VIN ) VOUT (L)(f)
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The inductor value may need further adjustment for other factors such as output voltage ripple and filtering requirements. Remember also, inductance can drop significantly with DC current and manufacturing tolerance. The inductor must have a rating greater than its peak operating current to prevent saturation resulting in efficiency loss. Peak inductor current is given by:
ILPEAK =
(VOUT )(IOUT ) VIN (VOUT - VIN ) + VIN * 2VOUT (L)(f)
Also, consideration should be given to the DC resistance of the inductor. Inductor resistance contributes directly to the efficiency losses in the overall converter. Suitable inductors are available from Coilcraft, Coiltronics, Dale, Sumida, Toko, Murata, Panasonic and other manufactures.
Table 2
PART NUMBER Coilcraft DO1608C-222 Sumida CDRH3D16-1R5 CDRH4D18-1R0 CDC5D23-2R2 CR43-1R4 CDRH5D28-2R6 CDRH6D38-3R3 CDRH6D28-3R0 Toko (D62F)847FY-2R4M (D73LF)817FY-2R2M 2.4 2.2 2.5 2.7 0.037 0.03 2.7 3.0 1.5 1.0 2.2 1.4 2.6 3.3 3.0 1.6 1.7 2.2 2.5 2.6 3.5 3.0 0.043 0.035 0.03 0.056 0.013 0.02 0.024 1.8 2.0 2.5 3.5 3.0 4.0 3.0 2.2 2.4 0.07 2.9 VALUE (H) ISAT(DC) (Amps) DCR () HEIGHT (mm)
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LT3436
APPLICATIONS INFORMATION
CATCH DIODE The suggested catch diode (D1) is a B220A Schottky. It is rated at 2A average forward current and 20V reverse voltage. Typical forward voltage is 0.5V at 2A. The diode conducts current only during switch off time. Peak reverse voltage is equal to regulator output voltage. Average forward current in normal operation is equal to output current. SHUTDOWN AND UNDERVOLTAGE LOCKOUT Figure 4 shows how to add undervoltage lockout (UVLO) to the LT3436. Typically, UVLO is used in situations where the input supply is current limited, or has a relatively high source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops. This looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. UVLO prevents the regulator from operating at source voltages where these problems might occur.
LT3436 INPUT R1 SHDN R2 GND
3436 F04
IN 3A
7A 1.35V VCC
C1
Figure 4. Undervoltage Lockout
An internal comparator will force the part into shutdown below the minimum VIN of 2.6V. This feature can be used to prevent excessive discharge of battery-operated systems. If an adjustable UVLO threshold is required, the
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shutdown pin can be used. The threshold voltage of the shutdown pin comparator is 1.35V. A 3A internal current source defaults the open pin condition to be operating (see Typical Performance Graphs). Current hysteresis is added above the SHDN threshold. This can be used to set voltage hysteresis of the UVLO using the following:
R1 = R2 = VH - VL 7A 1.35V (VH - 1.35V) + 3A R1
VH - Turn-on threshold VL - Turn-off threshold Example: switching should not start until the input is above 4.75V and is to stop if the input falls below 3.75V. VH = 4.75V VL = 3.75V
4.75V - 3.75V = 143k 7A 1.35V R2 = = 50.4k (4.75V - 1.35V) + 3A 143k R1 =
Keep the connections from the resistors to the SHDN pin short and make sure that the interplane or surface capacitance to the switching nodes are minimized. If high resistor values are used, the SHDN pin should be bypassed with a 1nF capacitor to prevent coupling problems from the switch node.
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APPLICATIONS INFORMATION
SYNCHRONIZATION The SYNC pin, is used to synchronize the internal oscillator to an external signal. The SYNC input must pass from a logic level low, through the maximum synchronization threshold with a duty cycle between 20% and 80%. The input can be driven directly from a logic level output. The synchronizing range is equal to initial operating frequency up to 1.4MHz. This means that minimum practical sync frequency is equal to the worst-case high self-oscillating frequency (960kHz), not the typical operating frequency of 800kHz. Caution should be used when synchronizing above 1.1MHz because at higher sync frequencies the amplitude of the internal slope compensation used to prevent subharmonic switching is reduced. Higher inductor values will tend to eliminate this problem. See Frequency Compensation section for a discussion of an entirely different cause of subharmonic switching before assuming that the cause is insufficient slope compensation. Application Note 19 has more details on the theory of slope compensation. LAYOUT CONSIDERATIONS As with all high frequency switchers, when considering layout, care must be taken to achieve optimal electrical, thermal and noise performance. For maximum efficiency, switch rise and fall times are typically in the nanosecond range. To prevent noise both radiated and conducted, the high speed switching current path, shown in Figure 5, must be kept as short as possible. This is implemented in the suggested layout of Figure 6. Shortening this path will also reduce the parasitic trace inductance of approximately 25nH/inch. At switch off, this parasitic inductance produces a flyback spike across the LT3436 switch. When operating at higher currents and output voltages, with poor layout, this spike can generate voltages across the LT3436 that may exceed its absolute maximum rating. A ground plane should always be used under the switcher circuitry to prevent interplane coupling and overall noise. The VC and FB components should be kept as far away as possible from the switch node. The LT3436 pinout has been designed to aid in this. The ground for these components should be separated from the switch current path. Failure to do so will result in poor stability or subharmonic like oscillation. Board layout also has a significant effect on thermal resistance. The exposed pad is the copper plate that runs under the LT3436 die. This is the best thermal path for heat out of the package. Soldering the pad onto the board will reduce die temperature and increase the power capability of the LT3436. Provide as much copper area as possible around this pad. Adding multiple solder filled feedthroughs under and around the pad to the ground plane will also help. Similar treatment to the catch diode and inductor terminations will reduce any additional heating effects.
C3 SW LT3436 VIN
Figure 5. High Speed Switching Path
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L1 D1 VOUT
HIGH FREQUENCY SWITCHING PATH
C1 LOAD
GND
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LT3436
APPLICATIONS INFORMATION
L1 3.9H D1 B220A INPUT 5V C3 4.7F CERAMIC VIN OPEN OR HIGH = ON LT3436 SHDN SYNC FB R2 10k 1% C1 22F CERAMIC VSW R1 90.9k VC
MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING.
L1 C3
D1
MINIMIZE LT3436, C1, D1 LOOP VOUT
KELVIN SENSE VOUT
Figure 6. Typical Application and Suggested Layout (Topside Only Shown)
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OUTPUT 12V 0.8A
GND
C2 10nF R3 4.7k
C4 470pF
INPUT GND R3
C4
C2 KEEP FB AND VC COMPONENTS AWAY FROM HIGH FREQUENCY, HIGH INPUT COMPONENTS
U1 C1 GND
R2
R1
PLACE FEEDTHROUGHS AROUND GROUND PIN FOR GOOD THERMAL CONDUCTIVITY
SOLDER EXPOSED GROUND PAD TO BOARD
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APPLICATIONS INFORMATION
The inductor must have a rating greater than its peak operating current to prevent saturation resulting in efficiency loss. Peak inductor current is given by: thermal resistance number and add in worst-case ambient temperature: TJ = TA + JA (PTOT) If a true die temperature is required, a measurement of the SYNC to GND pin resistance can be used. The SYNC pin resistance across temperature must first be calibrated, with no device power, in an oven. The same measurement can then be used in operation to indicate the die temperature. FREQUENCY COMPENSATION Loop frequency compensation is performed on the output of the error amplifier (VC pin) with a series RC network. The main pole is formed by the series capacitor and the output impedance (500k) of the error amplifier. The pole falls in the range of 2Hz to 20Hz. The series resistor creates a "zero" at 1kHz to 5kHz, which improves loop stability and transient response. A second capacitor, typically one-tenth the size of the main compensation capacitor, is sometimes used to reduce the switching frequency ripple on the VC pin. VC pin ripple is caused by output voltage ripple attenuated by the output divider and multiplied by the error amplifier. Without the second capacitor, VC pin ripple is:
ILPEAK =
(VOUT )(IOUT ) VIN (VOUT - VIN ) + VIN * 2VOUT (L)(f)
Also, consideration should be given to the DC resistance of the inductor. Inductor resistance contributes directly to the efficiency losses in the overall converter. THERMAL CALCULATIONS Power dissipation in the LT3436 chip comes from four sources: switch DC loss, switch AC loss, drive current, and input quiescent current. The following formulas show how to calculate each of these losses. These formulas assume continuous mode operation, so they should not be used for calculating efficiency at light load currents.
DC, duty cycle = ISW (VOUT - VIN ) VOUT (V )(I ) = OUT OUT VIN
Switch loss: VIN loss: (VIN )(ISW )(DC ) + 1mA(VIN ) 50 RSW = Switch resistance ( 0.16 hot) PVIN =
PSW = (DC )(ISW )2 (RSW ) + 17n(ISW ) VOUT ( f)
(
)
Example: VIN = 5V, VOUT = 12V and IOUT = 0.8A Total power dissipation = 0.34 + 0.31 + 0.11 + 0.005 = 0.77W Thermal resistance for LT3436 package is influenced by the presence of internal or backside planes. With a full plane under the package, thermal resistance will be about 40C/W. To calculate die temperature, use the appropriate
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VC Pin Ripple =
1.2(VRIPPLE)(gm)(RC) (VOUT)
VRIPPLE = Output ripple (VP-P) gm = Error amplifier transconductance (850mho) RC = Series resistor on VC pin VOUT = DC output voltage
To prevent irregular switching, VC pin ripple should be kept below 50mVP-P. Worst-case VC pin ripple occurs at maximum output load current and will also be increased if poor quality (high ESR) output capacitors are used. The addition of a 150pF capacitor on the VC pin reduces switching frequency ripple to only a few millivolts. A low value for RC will also reduce VC pin ripple, but loop phase margin may be inadequate.
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LT3436
TYPICAL APPLICATIO S
Load Disconnects in Shutdown
D3 1N4148 L1 3.9H C6 0.1F D2 1N4148 C5 0.1F R4 1M
VIN 5V
OFF ON
3V to 20VIN 5VOUT SEPIC with Either Two Inductors or a Transformer
L1 CDRH6D28-100 VIN 3V TO 20V D1 B220A C6 OPT VOUT 5V
+
C1 OPT SHDN
GND
OPTION: REPLACE L1, L2 WITH TRANSFORMER CTX5-1A, CTX8-1A, CTX10-2A
Maximum Load Current Increases with Input Voltage
2.0 1.8 100 90 80
MAXIMUM LOAD CURRENT (A)
1.6
EFFICIENCY (%)
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 2 4 6 8 10 12 14 16 18 20 VIN (V)
3436 TA02c
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D1 B220A VIN C3 4.7F LT3436 SHDN SYNC GND FB VC C2 10nF R3 4.7k VSW
Q1 C1 Si2306DS 4.7F R1 90.9k R2 10k 1% C4 470pF
VOUT 12V C7 0.8A 22F
LT3436 * TA02
VIN SHDN LT3436
SW FB
C7 1F, X5R, 25V CERAMIC C3 10nF
C5 OPT
R1 31.6K 1%
SYNC
SYNC VC GND GND
L2 CDRH6D28-100 R3 2.2k R2 10K 1%
C1 4.7F X5R 25V CERAMIC
C4 470pF
C2 22F X5R 10V CERAMIC
GND
3436 TA02b
Efficiency
12VIN 3.3VIN 5VIN
70 60 50 40 30 20 10 0 0 500 1.0k 1.5k LOAD CURRENT (mA) 2.0k
3436 TA02d
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TYPICAL APPLICATIO S
4V-9VIN to 5VOUT SEPIC Converter**
VIN** 4V TO 9V L1A* 15H VIN OFF ON SHDN LT3436 VSW
+
C1 4.7F 20V
Boost Converter Drives Luxeon III 1A 3.6V White LED with 70% Efficiency
0.05 1% 1A CONSTANT CURRENT 49.9 1% VIN VIN LED ON SHDN LT3436 SW FB LXHL-PW09 EMITTER VOUT = VIN + VLED L1 UPS120
VIN 3.3V TO 4.2V
4.7F X5R 6.3V CERAMIC 8.2k GND
Q1: MMBT2222A Q2: FMMT3906 L1: CDRH6D28-3R0
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C2 4.7F
D1 B220A R2 31.6k 1%
VOUT 5V
FB GND VC
*
L1B* 15H
+
R3 10k 1%
C3 47F 10V
R1 2.2k C4 15nF
C5 470pF
MAX I OUT
LT3436 * TA03
* COILTRONICS CTX15-4 ** INPUT VOLTAGE MAY BE GREATER OR LESS THAN OUTPUT VOLTAGE
IOUT 0.84A 1.03A 1.18A 1.29A 1.50A
VIN 4V 5V 6V 7V 9V
+
LT1783
-
VOUT Q1 0.1F 4.99k 1.21k 1%
3436 TA03b
SYNC VC GND GND
Q2
78.7k
22F X5R 10V CERAMIC
3436fa
13
LT3436
TYPICAL APPLICATIO S
Single Li-Ion Cell to 5V
L1 4.7H D1 B220A VOUT 5V R1 31.6k 1%
+
SEPIC Converter Drives 5W LumiLEDs Luxeon V White LEDs at 70% Efficiency
D1 B130A CCOUP 2.2F, X5R, 25V CERAMIC VIN LED ON VIN SHDN LT3436 C1 4.7F X5R 25V CERAMIC 8.2k GND
3436 TA04b
VIN 3.6V TO 17V
Q1: DIODES, INC. MMBT2222A L1: CDRH6D28 10H 1.7A L2: CDRH4D28 10H 1A D2: LUMILEDS LXHL-PW03 EMITTER OR LXHL-LW6C STAR
14
U
VIN OFF SINGLE Li-Ion CELL ON SHDN LT3436 VSW
+
C1 10F
FB GND C2 3.3nF R3 1.5k VC R2 10k 1% C3 470pF
+
C4 47F 10V
LT3436 * TA04
IOUT VIN 1.5A 2.7V 1.86A 3.3V 2.0A 3.6V
VOUT L2 D2
L1
SW FB R5 23.7k Q1 R7 124k
+
LT1783
700mA
-
SYNC VC GND GND C4 0.1F
VOUT R6 4.99k
R4 1k 1%
R2 0.068 1%
C2 22F X5R 16V CERAMIC
3436fa
LT3436
PACKAGE DESCRIPTION
FE Package 16-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
3.58 (.141)
6.60 0.10 4.50 0.10
SEE NOTE 4
0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
4.30 - 4.50* (.169 - .177)
0.09 - 0.20 (.0035 - .0079)
0.50 - 0.75 (.020 - .030)
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE
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
Exposed Pad Variation BB
4.90 - 5.10* (.193 - .201) 3.58 (.141) 16 1514 13 12 1110 9
2.94 (.116) 0.45 0.05 1.05 0.10 2.94 6.40 (.116) (.252) BSC
12345678 1.10 (.0433) MAX
0 - 8
0.25 REF
0.65 (.0256) BSC
0.195 - 0.30 (.0077 - .0118) TYP
0.05 - 0.15 (.002 - .006)
FE16 (BB) TSSOP 0204
4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE
3436fa
15
LT3436
TYPICAL APPLICATIO
L1 5 4 1
150 MUR405
VIN 12V TO 25V
+
2.2F
RELATED PARTS
PART NUMBER LT1310 LT1370/LT1370HV LT1371/LT1371HV LT1613 LT1618 LT1946/LT1946A LT1961 LTC3400/LTC3400B LTC3401 LTC3402 DESCRIPTION 1.5A (ISW), 4.5 MHz, High Efficiency Step-Up DC/DC Converter with PLL 6A (ISW), 500kHz, High Efficiency Step-Up DC/DC Converter 3A (ISW), 500kHz, High Efficiency Step-Up DC/DC Converter 550mA (ISW), 1.4MHz, High Efficiency Step-Up DC/DC Converter 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter 1.5A (ISW), 1.2MHz/2.7MHz, 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 (ISW), 3MHz, Synchronous Step-Up DC/DC Converter 2A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter COMMENTS VIN = 2.75V to 18V, VOUT(MAX) = 35V, IQ = 12mA, ISD = <1A, MSE Package VIN = 2.7V to 30V, VOUT(MAX) = 35V/42V, IQ = 4.5mA, ISD = <12A, DD, TO220-7 Packages VIN = 2.7V to 30V, VOUT(MAX) = 35V/42V, IQ = 4mA, ISD = <12A, DD,TO220-7,S20 Packages 90% Efficiency, VIN = 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD = <1A, ThinSOT Package 90% Efficiency, VIN = 1.6V to 18V, VOUT(MAX) = 35V, IQ = 1.8mA, ISD = <1A, MS Package VIN = 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD = <1A, MS8 Package 90% Efficiency, VIN = 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD = 6A, MS8E Package 92% Efficiency, VIN = 0.85V to 5V, VOUT(MAX) = 5V, IQ = 19A/300A, ISD = <1A, ThinSOT Package 97% Efficiency, VIN = 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38A, ISD = <1A, MS Package 97% Efficiency, VIN = 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38A, ISD = <1A, MS Package
3436fa LT/LWI/LT 0505 REV A * PRINTED IN USA
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
U
High Voltage Laser Power Supply
0.01F 5kV 1800pF 10kV 47k 5W 1800pF 10kV 11 2 8 3 HV DIODES LASER
+
2.2F Q1 0.47F Q2
L2 10H
VSW VIN LT3436 VC GND FB
10k 0.1F
10k VIN 1N4002 (ALL) 190 1% L1 = TBD Q1, Q2 = ZETEX ZTX849 0.47F = WIMA 3X 0.15F TYPE MKP-20 HV DIODES = SEMTECH-FM-50 LASER = HUGHES 3121H-P COILTRONICS (407) 241-7876
+
10F
LT3436 * TA05
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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