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FEATURES
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LT8410/LT8410-1 Ultralow Power Boost Converter with Output Disconnect DESCRIPTION
The LT(R)8410/LT8410-1 are ultralow power boost converters with integrated power switch, Schottky diode and output disconnect circuitry. The parts control power delivery by varying both the peak inductor current and switch offtime. This control scheme results in low output voltage ripple as well as high efficiency over a wide load range. The quiescent current is a low 8.5A, which is further reduced to 0A in shutdown. The internal disconnect circuitry allows the output voltage to be blocked from the input during shutdown. High value (12.4M/0.4M) resistors are integrated on chip for output voltage detection, significantly reducing input referred quiescent current. The LT8410/-1 also features a comparator built into the SHDN pin, over voltage protection for the CAP and VOUT pins, built in soft-start and comes in a tiny 8-pin 2mm x 2mm DFN package.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 6580258, 6304066, 6127815, 6498466, 6611131.
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Ultralow Quiescent Current 8.5A in Active Mode 0A in Shutdown Mode Comparator Built into SHDN pin Low Noise Control Scheme Adjustable FB reference voltage Wide Input Range: 2.5V to 16V Wide Output Range : Up to 40V Integrated Power NPN Switch 25mA Current Limit (LT8410) 8mA Current Limit (LT8410-1) Integrated Schottky Diode Integrated Output Disconnect High Value (12.4M/0.4M) Feedback Resistors Integrated Built in Soft-Start (Optional Capacitor from VREF to GND) Overvoltage Protection for CAP and VOUT pins Tiny 8-Pin 2mm x 2mm DFN package
APPLICATIONS
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Sensor Power RF Mems Relay Power General Purpose Bias
TYPICAL APPLICATION
General Purpose Bias with Wide Input Voltage
VIN 2.5V to 16V 2.2F SW VCC CHIP ENABLE SHDN GND CAP VOUT 10 100H VOUT PEAK-TO-PEAK RIPPLE (mV) 0.1F VOUT = 16V 0.1F* 604K FBP 412K *HIGHER VALUE CAPACITOR IS REQUIRED WHEN THE VIN IS HIGHER THAN 5V
8410-1 TA01a
Output Voltage Ripple vs Load Current
100 VIN = 3.6V 8 EFFICIENCY (%) 90 80
Efficiency vs Load Current
VIN = 12V
VIN = 5V VIN = 3.6V
6
LT8410 VREF
70 60 50 40 0.01
4
0.1F
2
0 0.01
0.1 1 LOAD CURRENT (mA)
10
8410-1 TA02
0.1 1 10 LOAD CURRENT (mA)
100
8410-1 TA03
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LT8410/LT8410-1 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW SHDN 1 VCC 2 GND 3 SW 4 9 8 FBP 7 VREF 6 CAP 5 VOUT
VCC Voltage ................................................ -0.3V to 16V SW Voltage ................................................ -0.3V to 40V CAP Voltage ............................................... -0.3V to 40V VOUT Voltage .............................................. -0.3V to 40V SHDN Voltage ............................................ -0.3V to 16V VREF Voltage.............................................. -0.3V to 2.5V FBP Voltage .............................................. -0.3V to 2.5V Maximum Junction Temperature .......................... 125C Operating Temperature Range (Note 2)..-40C to 125C Storage Temperature Range...................-65C to 150C
DC PACKAGE 8-PIN (2mm 2mm) PLASTIC DFN TJMAX = 125C, JA = 88C/W EXPOSED PAD (PIN #9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LT8410EDC#PBF LT8410IDC#PBF LT8410EDC-1#PBF LT8410IDC-1#PBF TAPE AND REEL LT8410EDC#TRPBF LT8410IDC#TRPBF LT8410EDC-1#TRPBF LT8410IDC-1#TRPBF PART MARKING* LDQR LDQR LFCC LFCC 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 TEMPERATURE RANGE - 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/
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN =3.0V, VSHDN =VIN unless otherwise noted. (Note 2)
PARAMETER Minimum Operating Voltage Maximum Operating Voltage Reference Voltage VREF Current Limit VREF Discharge Time VREF Line Regulation Quiescent Current Quiescent Current in Shutdown Quiescent Current from VOUT and CAP Minimum Switch Off Time Switch Current Limit Not Switching VSHDN = 0V VOUT = 16V After Start-Up (Note 4) During Start-Up (Note 4) LT8410 LT8410-1
l l l l l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP 2.2
MAX 2.5 16 1.255
UNITS V V V A S %/V
1.220
1.235 10 70 0.01 8.5 0 3 240 600
(Note 3)
12 1
A A A nS nS
20 6
25 8
30 10
mA mA
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LT8410/LT8410-1 ELECTRICAL CHARACTERISTICS
PARAMETER Switch VCESAT Switch Leakage Current Schottky Forward Voltage Schottky Reverse Leakage PMOS Disconnect Current Limit PMOS Disconnect VCAP - VOUT VOUT Resistor Divider Ratio FBP Pin Bias Current SHDN Minimum Input Voltage High SHDN Input Voltage High Hysteresis SHDN Hysteresis Current SHDN Input Voltage Low SHDN Pin Bias Current VSHDN = 3V VSHDN = 16V 0 2 VFBP = 0.5V, Current Flows Out of Pin SHDN Rising CONDITIONS LT8410, ISW = 10mA LT8410-1, ISW = 4mA VSW = 5V IDIODE = 10mA VCAP - VSW = 5 VCAP - VSW = 40 LT8410 LT8410-1 IOUT = 1mA
l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN =3.0V, VSHDN =VIN unless otherwise noted. (Note 2)
MIN TYP 150 100 0 650 0 0 14 2.5 31.6 1.20 0.08 19 4 50 31.85 1.3 1.30 60 0.1 32.2 30 1.45 0.14 0.3 1 3 nA V mV A V A A 1 850 0.5 1 25 5 MAX UNITS mV mV A mV A A mA mA mV
(Note 3)
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 LT8410/LT8410-1 are guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over
the -40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: See applications section for more information. Note 4: Start-up mode occurs when VOUT is less than VFBP * 64/3.
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency vs Load Current
1000 OUTPUT VOLTAGE CHANGE (%) VCC = 3.6V VOUT = 16V FIGURE 4 CIRCUIT 0.6 0.4 0.2 0 -0.2 -0.4 -0.6
TA = 25C, unless otherwise noted.
Load Regulation
50 VCC = 3.6V VOUT = 16V FIGURE 4 CIRCUIT OUTPUT VOLTAGE (V)
VOUT vs FBP Voltage
SWITCHING FREQUENCY (kHz)
800
40
600
30
400
20
200
10
0
0
1 2 LOAD CURRENT (mA)
3
8410-1 G01
0
1 2 LOAD CURRENT (mA)
3
8410-1 G02
0
0
0.5
1 1.5 FBP VOLTAGE (V)
2
8410-1 G03
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LT8410/LT8410-1 TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Temperature
1 0.75 OUTPUT VOLTAGE CHANGE (%) 0.5 0.25 0 - 0.25 - 0.5 - 0.75 -1 - 40 0 40 80 TEMPERATURE (C) 120
8410-1 G04
Quiescent Current - Not Switching
12 10
Quiescent Current vs Temperature
QUIESCENT CURRENT (A)
8 6 4 2 0
QUIESCENT CURRENT (A)
VCC = 3.6V, VOUT = 16V LOAD = 0.5mA FIGURE 4 CIRCUIT
10
8
6
4
2 VCC = 3.6V
0
4
8 12 VCC VOLTAGE (V)
16
8410-1 G05
0 -40
0
40 80 TEMPERATURE (C)
120
8410-1 G06
Quiescent Current vs SHDN Voltage
10 1000
Quiescent Current in Regulation with No Load
2.5 VCC = 3.6V
SHDN Current vs SHDN Voltage
VCC = 3.6V SHDN PIN BIAS CURRENT (A) 2 1.5 1 0.5 0 -0.5
QUIESCENT CURRENT (A)
6
QUIESCENT CURRENT (A) VCC = 3.6V 0
8
100
4
2
0
1
2 3 SHDN VOLTAGE (V)
4
5
8410-1 G07
10
0
10 20 30 OUTPUT VOLTAGE (V)
40
8410-1 G08
0
4
8 12 SHDN VOLTAGE (V)
16
8410-1 G09
Peak Inductor Current vs Temperature (LT8410)
40 PEAK INDUCTOR CURRENT (mA) PEAK INDUCTOR CURRENT (mA) VCC = 3.6V VOUT = 16V FIGURE 4 CIRCUIT 15
Peak Inductor Current vs Temperature (LT8410-1)
1.235 VCC = 3.6V VOUT = 16V FIGURE 5 CIRCUIT
VREF Voltage vs Temperature
36
13
1.234 VREF VOLTAGE (V)
32
11
1.233
28
9
1.232
24
7
1.231 VCC = 3.6V
20 - 40
0
40 80 TEMPERATURE (C)
120
8410-1 G10
5 -40
0
40 80 TEMPERATURE (C)
120
8410-1 G11
1.23 -40
0
40 80 TEMPERATURE (C)
120
8410-1 G12
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LT8410/LT8410-1 TYPICAL PERFORMANCE CHARACTERISTICS
LT8410 Switching Waveform at No Load
VOUT VOLTAGE 2mV/DIV AC COUPLED VOUT VOLTAGE 10mV/DIV AC COUPLED SW VOLTAGE 10V/DIV INDUCTOR CURRENT 20mA/DIV VCC = 3.6V VOUT = 16V 50s/DIV
8410-1 G13
LT8410 Switching Waveform at 0.5mA Load
SW VOLTAGE 10V/DIV INDUCTOR CURRENT 10mA/DIV
VCC = 3.6V VOUT = 16V
2s/DIV
8410-1 G14
LT8410 Switching Waveform at 3mA Load
2.6 VOUT VOLTAGE 10mV/DIV AC COUPLED UVLO VOLTAGE (V) SW VOLTAGE 10V/DIV INDUCTOR CURRENT 20mA/DIV VCC = 3.6V VOUT = 16V 500ns/DIV
8410-1 G15
UVLO vs Temperature
2.4 VCC RISING 2.2 VCC FALLING 2 1.8 1.6 1.4 -40
0
40 80 TEMPERATURE (C)
120
8410-1 G16
Line Regulation
0.3 VOUT = 16V OUTPUT VOLTAGE CHANGE (%) 0.25 SHDN MINIMUM INPUT VOLTAGE HIGH (V) 0.2 0.15 0.1 0.05 0 1.4 1.5
SHDN Minimum Input Voltage High vs Temperature
SHDN RISING 1.3 SHDN FALLING 1.2
1.1
0
4
8 12 VCC VOLTAGE (V)
16
8410-1 G17
1 -40
0
40 80 TEMPERATURE (C)
120
8410-1 G18
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LT8410/LT8410-1 TYPICAL PERFORMANCE CHARACTERISTICS
Output Disconnect PMOS Current vs CAP to VOUT Voltage Difference
25 VCAP = 16V 20 PMOS CURRENT (mA) LT8410 SHDN VOLTAGE 5V/DIV INDUCTOR CURRENT 20mA/DIV
LT8410 Start-Up Waveforms Without Capacitor at VREF Pin
15 CAP VOLTAGE 5V/DIV VOUT VOLTAGE 5V/DIV VCC = 3.6V VOUT = 16V 0 0 4 8 12 16 CAP TO VOUT VOLTAGE DIFFERENCE (V)
8410-1 G19
10 LT8410-1
5
200s/DIV
8410-1 G20
LT8410 Start-Up Waveforms With 0.1F Capacitor at VREF Pin
SHDN VOLTAGE 5V/DIV INDUCTOR CURRENT 20mA/DIV VOUT VOLTAGE 200mV/DIV AC COUPLED INDUCTOR CURRENT 20mA/DIV LOAD CURRENT 0.5mA/DIV
LT8410 Transient Response 0.5mA1.5mA0.5mA Load Pulse
CAP VOLTAGE 5V/DIV VOUT VOLTAGE 5V/DIV VCC = 3.6V VOUT = 16V 2ms/DIV
8410-1 G21
VCC = 3.6V VOUT = 16V
2ms/DIV
8410-1 G22
SW Saturation Voltage vs Switch Current (LT8410)
300 250 SWITCH VCESAT (mV) 200 150 100 50 0
0
5
10 15 20 SWITCH CURRENT (mA)
25
8410-1 G24
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LT8410/LT8410-1 PIN FUNCTIONS
SHDN (Pin 1): Shutdown Pin. This pin is used to enable/ disable the chip. Drive below 0.3V to disable the chip. Drive above 1.4V to activate the chip. Do not float this pin. VCC (Pin 2): Input Supply Pin. Must be locally bypassed to GND. See typical applications section. GND (Pin 3 and Pin 9): Ground. Tie directly to local ground plane. Pin 9 is floating but must be grounded for proper shielding. SW (Pin 4): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. VOUT (Pin 5): Drain of Output Disconnect PMOS. Place a bypass capacitor from this pin to GND. CAP (Pin 6): This is the cathode of the internal Schottky Diode. Place a bypass capacitor from this pin to GND. VREF (Pin 7): Reference Pin. Soft-start can be achieved by placing a capacitor from this pin to GND. This cap will be discharged for 70s (typical) at the beginning of start-up and then be charged to 1.235V with a 10A current source. FBP(Pin 8): Positive Feedback Pin. This pin is the error amplifier's positive input terminal. To achieve the desired output voltage, choose the FBP pin voltage (VFBP) according to the following formula: VFBP = VOUT / 31.85 For protection purposes, the output voltage can not exceed 40V even if VFBP is driven higher than VREF .
BLOCK DIAGRAM
VCC 2 MAX 10A ENABLE CHIP SHDN 1 VOUT 5 CAP 6 SW 4
+ -
VREF 7
1.235V
12.4M
+
400K
-
DISCHARGE CONTROL
1.235V
OUTPUT DISCONNECT CONTROL
TIMING AND PEAK CURRENT CONTROL
SWITCH CONTROL
8 1.235V
+ +
FBP
-
VC
FB
+ -
9 GND 3 GND
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LT8410/LT8410-1 OPERATION
The LT8410 series utilizes a variable peak current, variable off-time control scheme to provide high efficiency over a wide output current range. The operation of the part can be better understood by referring to the Block Diagram. The part senses the output voltage by monitoring the internal FB node, and servoing the FB node voltage to be equal to the FBP pin voltage. The chip integrates an accurate high value resistor divider (12.4M/0.4M) from the VOUT pin. The output voltage is set by the FBP pin voltage, which in turn is set by an external resistor divider from the VREF pin. The FBP pin voltage can also be directly biased with an external reference, allowing full control of the output voltage during operation. The Switch Control block senses the output of the amplifier and adjusts the switching frequency as well as other parameters to achieve regulation. During the start-up of the circuit, special precautions are taken to ensure that the inductor current remains under control The LT8410 series also has a PMOS output disconnect switch. The PMOS switch is turned on when the part is enabled via the SHDN pin. When the part is in shutdown, the PMOS switch turns off, allowing the VOUT node to go to ground. This type of disconnect function is often required in power supplies. The differences between the LT8410 and LT8410-1 are the SW current limit and the output disconnect PMOS current limit. For the LT8410, the SW current limit and PMOS current limit are approximately 25mA and 19mA respectively, while those of the LT8410-1 are approximately 8mA and 4mA respectively.
APPLICATIONS INFORMATION
Inductor Selection Several inductors that work well with the LT8410 and LT8410-1 are listed in Table 1. The tables are not complete, and there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts, as many different sizes and shapes are available. Inductors with a value of 47H or higher are recommended for most LT8410 series designs. Inductors with low core losses and small DCR (copper wire resistance) are good choices for LT8410 series applications. For full output power, the inductor should have a saturation current rating higher than the peak inductor current. The peak inductor current can be calculated as: VIN * 150 * 10 - 6 mA L where the worst case ILIMIT is 30mA and 10mA for LT8410 and LT8410-1 respectively. L is the inductance value in Henrys and VIN is the input voltage to the boost circuit. IPK = ILIMIT +
Table 1. Recommended Inductors for LT8410/-1
PART LQH2MCN680K02 LQH32CN101K53 DO2010-683ML LPS3015-104ML LPS3015-154ML LPS3314-154ML L (H) 68 100 68 100 150 150 DCR () 6.6 3.5 8.8 3.4 6.1 4.1 SIZE (mm) VENDOR
2.0 x 1.6 x 0.9 Murata 3.2 x 2.5 x 2.0 www.murata.com 2.0 x 2.0 x 1.0 Coilcraft 3.0 x 3.0 x 1.4 www.coilcraft.com 3.0 x 3.0 x 1.4 3.3 x 3.3 x 1.3
Capacitor Selection The small size and low ESR of ceramic capacitors make them suitable for most LT8410 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 2.2F or higher input capacitor and a 0.1F to 1F output capacitor are sufficient for most applications. Always use a capacitor with a sufficient voltage rating. Many ceramic capacitors rated at 0.1F to 1F have greatly reduced capacitance when bias voltages are applied. Be sure to check actual capacitance at the desired output voltage. Generally a 0603
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LT8410/LT8410-1 APPLICATIONS INFORMATION
or 0805 size capacitor will be adequate. A 0.1F to 1F capacitor placed on the CAP node is recommended to filter the inductor current while a 0.1F to 1F capacitor placed on the VOUT node will give excellent transient response and stability. To make the VREF pin less sensitive to noise, putting a capacitor on the VREF pin is recommended, but not required. A 47nF to 220nF 0402 capacitor will be sufficient. Table 2 shows a list of several capacitor manufacturers. Consult the manufacturers for more detailed information and for their entire selection of related parts.
Table 2. Recommended Ceramic Capacitor Manufactures
MANUFACTURER Taiyo Yuden Murata AVX Kemet TDK PHONE (408) 573-4150 (814) 237-1431 (843) 448-9411 (408)986-0424 (847) 803-6100 WEBSITE www.t-yuden.com www.murata.com www.avxcorp.com www.kemet.com www.tdk.com
Connecting the Load to the CAP Node The efficiency of the converter can be improved by connecting the load to the CAP pin instead of the VOUT pin. The power loss in the PMOS disconnect circuit is then made negligible. No quiescent current will be consumed in the internal feedback resistor divider string during shutdown since the PMOS transistor will be open and the internal feedback resistor divider is connected at the VOUT pin. The disadvantage of this method is that the CAP node cannot go to ground during shutdown, but will be limited to around a diode drop below VCC. Loads connected to the part should only sink current. Never force external power supplies onto the CAP or VOUT pins. Maximum Output Load Current The maximum output current of a particular LT8410 series circuit is a function of several circuit variables. The following method can be helpful in predicting the maximum load current for a given circuit: Step 1. Calculate the peak inductor current: IPK = ILIMIT + VIN * 150 * 10 - 6 mA L
Setting Output Voltage The output voltage is set by the FBP pin voltage, and VOUT is equal to 31.85 * VFBP when the output is regulated, shown in Figure 1. Since the VREF pin provides a good reference (1.235V), the FBP voltage can be easily set by a resistor divider from the VREF pin to ground. The series resistance of this resistor divider should be kept larger than 200K to prevent loading down the VREF pin. The FBP pin can also be biased directly by an external reference. For over voltage protection, the output voltage is limited to 40V. Therefore, if VFBP is higher than 1.235V, the output voltage will stay at 40V.
50
where ILIMIT is 25mA and 8mA for LT8410 and LT8410-1 respectively. L is the inductance value in Henrys and VIN is the input voltage to the boost circuit. Step 2. Calculate the inductor ripple current: IRIPPLE
( VOUT + 1 - VIN ) * 200 * 10 - 6 mA =
L
40 OUTPUT VOLTAGE (V)
30
20
10
where VOUT is the desired output voltage. If the inductor ripple current is less than the peak current, then the circuit will only operate in discontinuous conduction mode. The inductor value should be increased so that IRIPPLE < IPK. An application circuit can be designed to operate only in discontinuous mode, but the output current capability will be reduced. Step 3. Calculate the average input current: IRIPPLE mA 2
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0
0.5
1 1.5 FBP VOLTAGE (V)
2
8410-1 F01
IIN(AVG) = IPK -
Figure 1. FBP to VOUT Transfer Curve
9
LT8410/LT8410-1 APPLICATIONS INFORMATION
Step 4. Calculate the nominal output current: IOUT(NOM) = IIN(AVG) * VIN * 0.7 VOUT mA this capacitor is first discharged for about 70s (providing protection against pin glitches and slow ramping), then an internal 10A current source pulls the VREF pin slowly to 1.235V. Since the VOUT voltage is set by the FBP pin voltage, the VOUT voltage will also slowly increase to the regulated voltage, which results in lower peak inductor current. The voltage ramp rate on the pin can be set by the value of the VREF pin capacitor. Output Disconnect The LT8410 series has an output disconnect PMOS that blocks the load from the input during shutdown. The maximum current through the PMOS is limited by circuitry inside the chip, helping the chip survive output shorts. SHDN Pin Comparator and Hysteresis Current An internal comparator compares the SHDN pin voltage with an internal voltage reference (1.3V) which gives a precise turn-on voltage level. The internal hysteresis of this turn-on voltage is about 60mV. When the chip is turned on, and the SHDN pin voltage is close to this turn-on voltage, 0.1A current flows out of the SHDN pin. This current is called SHDN pin hysteresis current, and will go away when the chip is off. By connecting the external resistors as in Figure 2, a user-programmable enable voltage function can be realized. The turn-on voltage for the configuration is: 1.30 * (1 + R1/R2) and the turn-off voltage is: - - (1.24 - R3 * 10 7) * (1 + R1/R2) - (R1 * 10 7) where R1, R2 and R3 are resistance value in .
ENABLE VOLTAGE
Step 5. Derate output current: IOUT = IOUT(NOM) * 0.8 For low output voltages the output current capability will be increased. When using output disconnect (load current taken from VOUT), these higher currents will cause the drop in the PMOS switch to be higher resulting in lower output current capability than predicted by the preceding equations. Inrush Current When VCC is stepped from ground to the operating voltage while the output capacitor is discharged, a high level of inrush current may flow through the inductor and Schottky diode into the output capacitor. Conditions that increase inrush current include a larger more abrupt voltage step at VCC, a larger output capacitor tied to the CAP pin and an inductor with a low saturation current. While the chip is designed to handle such events, the inrush current should not be allowed to exceed 0.3A. For circuits that use output capacitor values within the recommended range and have input voltages of less than 6V, inrush current remains low, posing no hazard to the device. In cases where there are large steps at VCC (more than 6V) and/or a large capacitor is used at the CAP pin, inrush current should be measured to ensure safe operation. Soft-Start The LT8410 series contains a soft-start circuit to limit peak switch currents during start-up. High start-up current is inherent in switching regulators in general since the feedback loop is saturated due to VOUT being far from its final value. The regulator tries to charge the output capacitor as quickly as possible, which results in large peak current. When the FBP pin voltage is generated by a resistor divider from the VREF pin, the start-up current can be limited by connecting an external capacitor (typically 47nF to 220nF) to the VREF pin. When the part is brought out of shutdown,
R1 R3 CONNECT TO SHDN PIN
R2
Figure 2. Programming Enable Voltage by Using External Resistors
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LT8410/LT8410-1 APPLICATIONS INFORMATION
Board Layout Considerations As with all switching regulators, careful attention must be paid to the PCB layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. The voltage signal of the SW pin has sharp rising and falling edges. Minimize the length and area of all traces connected to the SW pin and always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the FBP pin and VREF pin are sensitive to noise. Minimize the length and area of all traces to these two pins is recommended. Recommended component placement is shown in Figure 3.
VIN SHDN
SHDN
FBP
VCC
VREF
GND GND SW
CAP
VOUT
8410-1 F03
CAPACITOR GROUNDS MUST BE RETURNED DIRECTLY TO IC GROUND
Figure 3. Recommended Board Layout
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LT8410/LT8410-1 TYPICAL APPLICATIONS
VIN 2.5V to 16V C1 2.2F L1 100H C2 0.1F VOUT = 16V EFFICIENCY (%) C3 0.1F 604K GND FBP 412K C1: 2.2F, 16V, X5R, 0603 8410-1 TA05 C2: 0.1F, 25V, X5R, 0603 C3: 0.1F, 25V, X5R, 0603 * C4: 0.1F 16V, X7R, 0402 , L1: MURATA LQH32CN101K53 * HIGHER CAPACITANCE VALUE IS REQUIRED FOR C3 WHEN THE VIN IS HIGHER THAN 5V 50 40 0.01 C4 0.1F 80 VIN = 3.6V 70 60 VIN = 5V
Efficiency vs Load Current
100 90 VIN = 12V
SW VCC
CAP VOUT
TURN ON/OFF
LT8410 VREF SHDN
0.1 1 10 LOAD CURRENT (mA)
100
8410-1 TA07
Figure 4. 16V Output Converter with Wide Input Voltage 16V Output Converter with 2mm x 2mm Inductor
VIN 2.5V to 16V C1 2.2F L1 68H C2 0.1F VOUT = 16V C3 0.1F EFFICIENCY (%) R1 301K FBP R2 210K C1: 2.2F, 16V, X5R, 0603 8410 TA06 C2: 0.1F, 25V, X5R, 0603 C3: 0.1F, 25V, X5R, 0603 * C4: 0.1F, 16V, X7R, 0402 L1: COILCRAFT DO2010-683ML * HIGHER CAPACITANCE VALUE IS REQUIRED FOR C3 WHEN THE VIN IS HIGHER THAN 5V C4 0.1F 80
VIN (V) 3.6 5 12
IOUT (mA) 2.2 3.6 13
Efficiency vs Load Current
90 VIN = 12V VIN = 5V VIN = 3.6V
SW VCC
CAP VOUT
TURN ON/OFF
SHDN GND
LT8410 VREF
70
60
50
40 0.01
0.1 1 10 LOAD CURRENT (mA)
100
8410-1 TA08
LT8410 Maximum Output Current vs Output Voltage
VOUT (V) 40 35 30 25 20 15 10 5 RESISTOR DIVIDER FROM VREF R1 (k) / R2 ( k) NA 110/887 237/768 365/634 487/511 619/383 750/255 866/127 MAXIMUM OUTPUT CURRENT (mA) VIN = 2.8V 0.5 0.7 0.8 1.0 1.4 1.6 3.3 8.0 VIN = 3.6V 0.7 0.9 1.0 1.4 1.9 2.4 4.6 11 VIN = 5.0V 1.1 1.4 1.5 2.1 2.9 4.0 7.0 17 VIN = 12V 3.6 4.4 5.5 7.2 9.7 14 NA NA
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12
LT8410/LT8410-1 TYPICAL APPLICATIONS
34V Output Converter with Wide Input Voltage
VIN 2.5V to 16V C1 2.2F L1 150H C2 0.1F VOUT = 34V C3 0.1F 133K GND FBP 50 866K C1: 2.2F, 16V, X5R, 0603 8410-1 TA09 C2: 0.1F, 100V, X5R, 0603 C3: 0.1F, 100V, X5R, 0603 * C4: 0.1F, 16V, X7R, 0402 L1: COILCRAFT LPS3314-154ML * HIGHER CAPACITANCE VALUE IS REQUIRED FOR C3 WHEN THE VIN IS HIGHER THAN 8V 40 0.01 C4 0.1F EFFICIENCY (%) 90 VIN = 12V 80 VIN = 5V
Efficiency vs Load Current
SW VCC
CAP VOUT
70 VIN = 3.6V 60
TURN ON/OFF
LT8410 VREF SHDN
0.1 1 LOAD CURRENT (mA)
10
8410-1 TA10
VIN (V) 3.6 5 12
IOUT (mA) 0.8 1.2 4.0
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13
LT8410/LT8410-1 TYPICAL APPLICATIONS
VIN 2.5V to 16V C1 2.2F L1 220H C2 1.0F VOUT = 16V C3 10000F R1 604k R2 412k C1: 2.2F, 16V, X5R, 0603 8410-1 TA10a C2: 1.0F, 25V, X5R, 0603 * C3: 10000F, Electrolytic Capacitor C4: 0.1F, 16V, X7R, 0402 L1: COILCRAFT LPS3008-224ML * HIGHER CAPACITANCE VALUE IS REQUIRED FOR C2 WHEN THE VIN IS HIGHER THAN 12V C4 0.1F VOUT VOLTAGE 10V/DIV INPUT CURRENT 5mA/DIV INDUCTOR CURRENT 10mA/DIV VIN = 3.6V 20s/DIV
8410-1 G10b
Charging Waveforms
SHDN VOLTAGE 2V/DIV
SW VCC
CAP VOUT
TURN ON/OFF
LT8410-1 VREF SHDN GND FBP
Figure 5. Capacitor Charger with the LT8410-1 LT8410-1 Maximum Output Current vs Output Voltage
VOUT (V) 40 35 30 25 20 15 10 5 FEEDBACK RESISTOR DIVIDER R1 (k) / R2 ( k) NA 110/887 237/768 365/634 487/511 619/383 750/255 866/127 MAXIMUM OUTPUT CURRENT (mA) VIN = 2.8V 0.12 0.14 0.18 0.25 0.34 0.48 0.84 2.3 VIN = 3.6V 0.16 0.19 0.25 0.35 0.48 0.69 1.2 3.3 VIN = 5.0V 0.24 0.3 0.38 0.55 0.76 1.1 2.1 3.5 VIN = 12V 0.89 1.1 1.5 2 2.9 3.5 NA NA
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14
LT8410/LT8410-1 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 0.45 BSC 1.37 0.05 (2 SIDES)
0.05
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 BAR TOP MARK (SEE NOTE 6)
0.64 0.10 (2 SIDES)
PIN 1 NOTCH R = 0.20 OR 0.25 45 CHAMFER
(DC8) DFN 0106 REVO
4 0.200 REF 0.75 0.05 1.37 0.10 (2 SIDES) 0.00 - 0.05
1 0.23 0.45 BSC 0.05
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
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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.
15
LT8410/LT8410-1 TYPICAL APPLICATION
High Voltage Power Supply Doesn't Need a Transformer
DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY C3 0.1F VIN 2.5V to 16V C1 2.2F L1 100H C2 0.1F D1 C4 0.1F D2 C5 0.1F D3 C6 0.1F D4
SW VCC SHDN GND
CAP VOUT
TURN ON/OFF C1: 2.2F, 16V, X5R, 0603 C2 - C7: 0.1F, 100V, X5R, 0603 C8: 0.1F, 16V, X7R, 0402 D1 - D4: ON SEMI RB751S40T1G L1: MURATA LQH32CN101K53
LT8410 VREF 143K FBP 787K C8 0.1F
C7 0.1F
OUTPUT = 100V 0.4mA (VIN = 5V) 1.4mA (VIN = 12V)
8410-1 TA11
Output Voltage vs FBP Voltage
140 VIN = 5V 120 80 OUTPUT VOLTAGE (V) 100 EFFICIENCY (%) 80 60 40 20 0 50 70 90
Efficiency vs Load Current
VOUT = 100V VIN = 12V
VIN = 5V 60
0
0.5
1 1.5 FBP VOLTAGE (V)
2
8410-1 TA12
40 0.01
0.1 1 LOAD CURRENT (mA)
10
8410-1 TA13
RELATED PARTS
PART NUMBER LT1946/LT1946A LT3464 LT3471 LT3473/LT3473A LT3494/LT3494A DESCRIPTION 1.5A (ISW), 1.2MHz/2.7MHz, High Efficiency Step-Up DC/DC Converters 85mA (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky and PNP Disconnect Dual Output, Boost/Inverter, 1.3A (ISW), High Efficiency Boost-Inverting DC/DC Converter 1A (ISW), 1.2MHz, High Efficiency Step-Up DC/DC Converter with Integrated Schottky Diode and Output Disconnect 180mA/350mA (ISW), High Efficiency, Low Noise Step-Up DC/DC Converter with Output Disconnect COMMENTS VIN : 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD < 1A, 8-Lead MS Package VIN : 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25A, ISD < 1A, ThinSOTTM Package VIN : 2.4V to 16V, VOUT(MAX) = 40V, IQ = 2.5mA, ISD < 1A, DFN Package VIN : 2.2V to 16V, VOUT(MAX) = 36V, IQ = 100A, ISD < 1A, DFN Package VIN : 2.1V to 16V, VOUT(MAX) = 40V, IQ = 65A, ISD < 1A, DFN Package VIN : 2.3 V to 16V, VOUT(MAX) = 40V, IQ = 60A, ISD < 1A, DFN Package
LT3495/LT3495B/ 650mA/350mA (ISW), High Efficiency, Low Noise Step-Up LT3495-1/LT3495B-1 DC/DC Converter with Output Disconnect
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 1108 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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