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MIC2619
1.2MHz PWM Boost Converter with OVP
General Description
The MIC2619 is a 1.2MHz pulse width modulated (PWM) step-up switching regulator that is optimized for low power, high output voltage applications. With a maximum output voltage of 35V, and a switch current of over 350mA, the MIC2619 can easily supply most high voltage bias applications, such as TV tuners. The MIC2619 implements a constant frequency 1.2MHz PWM current-mode control scheme. The high frequency PWM operation saves board space by reducing external component sizes. The additional benefit of the constant frequency PWM control scheme as opposed to variable frequency control schemes is lower output noise and smaller input ripple injected back to the battery source. The MIC2619 has programmable overvoltage protection to ensure output protection in case of fault condition. The MIC2619 is available in a low profile Thin SOT-23 6pin package. The MIC2619 has a junction temperature range of -40C to +125C. All support documentation can be found on Micrel's web site at: www.micrel.com.
Features
* * * * * * * * * * * * 2.8V to 6.5V Input Voltage 350mA Switch Current Output Voltage up to 35V 1.2MHz PWM Operation 1.265V Feedback Voltage Programmable Over-Voltage Protection (OVP) <1% Line Regulation <1A Shutdown Current Over-Temperature Protection Under-Voltage Lock Out (UVLO) Low Profile Thin SOT-23-6 Package -40C to +125C Junction Temperature Range
Applications
* Bias Supply Applications: - Tuner Varactor Bias - High Voltage Bias Supplies - Avalanche Photo Diode - High Voltage Display Bias * DSL/Broadband applications * Constant Current Power Supplies
_________________________________________________________________________________________________________________________
Typical Application
1.2MHz Boost Converter with OVP in Thin SOT-23-6
Micrel Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel +1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com
March 2010
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Micrel, Inc.
MIC2619
Ordering Information
Part Number MIC2619YD6
Note: 1. Under bar( ) symbol may not be to scale.
Marking(1) 2619
Overvoltage Protection Programmable
Junction Temp. Range -40C to +125C
Package Thin SOT-23-6
Lead Finish Lead Free
Pin Configuration
6-Pin TSOT-23 (YD6)
Pin Description
Pin Number 1 2 3 4 5 6 Pin Name SW GND FB EN OVP VIN Pin Function Switch Node (Input): Internal power bipolar collector. Ground. Feedback (Input): Output voltage sense node. Connect external resistor network to set output voltage. Nominal feedback voltage is 1.265V. Enable (Input): Logic high enables regulator. Logic low shuts down regulator. Do not leave floating. Over-Voltage Protection (Input): Programmable to 35V, adjustable through resistor divider network. Supply (Input): 2.8V to 6.5V for internal circuitry. Requires a minimum 1.0F ceramic capacitor.
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Absolute Maximum Ratings(1)
Supply Voltage (VIN) .........................................................7V Switch Voltage (VSW)....................................... -0.3V to 40V Enable Pin Voltage (VEN)..................................... -0.3 to VIN Feedback Voltage (VFB), (VOVP)........................................6V Ambient Storage Temperature (TS)...........-65C to +150C ESD Rating (3) ................................................................. 2kV
Operating Ratings(2)
Supply Voltage (VIN)......................................... 2.8V to 6.5V Output Voltage (VOUT) .......................................... VIN to 35V Junction Temperature Range (TJ)............. -40C to +125C Package Thermal Impedance Thin SOT-23-6 (JA).........................................177C/W
Electrical Characteristics (4)
TA = 25C, VIN = VEN = 3.6V, VOUT = 10V, IOUT = 10mA, unless otherwise noted. Bold values indicate -40C TJ 125C.
Parameter Supply Voltage Range Under Voltage Lockout Quiescent Current Shutdown Current Feedback Voltage Feedback Input Current Line Regulation Load Regulation Maximum Duty Cycle Switch Current Limit Switch Saturation Voltage Switch Leakage Current Enable Threshold
Condition
Min 2.8 1.8
Typ
Max 6.5
Units V V mA A V nA
2.1 2.1 0.04
2.4 5 1 1.303
VFB > 1.265V, (not switching) VEN = 0V
1.227
1.265 -450 0.2 0.3
VFB = 1.265V 2.8V VIN 6.5V 5mA IOUT 20mA
85
1
% % % mA
90
VIN = 3.6V
(5)
350 400 0.01 1.5 0.4 14 1.2 1.202 1.265 -200 150 1.328 40 1
VIN = 3.6V, ISW = 300mA VEN = 0V, VSW = 10V TURN ON TURN OFF
mV A V A MHz V nA C C
Enable Pin Current Oscillator Frequency Overvoltage Protection OVP Input Current Overtemperature Threshold Shutdown
Notes:
VEN = 6.5V
VOVP = 1.265V Hysteresis
10
1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(max), the junction-to-ambient thermal resistance, JA, and the ambient temperature, TA. The maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. 2. This device is not guaranteed to operate beyond its specified operating ratings. 3. Devices are inherently ESD sensitive. Handling precautions required. Human body model: 1.5k in series with 100pF. 4. Specification for packaged product only. 5. Guaranteed by design.
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Typical Characteristics
Efficiency V OUT = 5V
100% 90% 80% EFFICIENCY (%)
EFFICIENCY (%) 90% 80% 70%
Efficiency V OUT = 10V
90% 80% 70% EFFICIENCY (%)
V IN =5V V IN =3.3V
Efficiency V OUT = 12V
70% 60% 50% 40% 30% 20% 10% 0% 0 50 100 150 LOAD CURR ENT (mA) 200
L = 10H C = 1F V IN =3.6V V IN =3V V IN =4.2V
60% 50% 40% 30% 20% 10% 0% 0 20 40
60% 50% 40% 30% 20% 10% 0%
L = 10H C = 1F V IN =5V V IN =3.3V
L = 10H C = 1F
60
80
100
0
LOAD CURRENT (mA)
20 40 60 LOAD CUR RENT (mA)
80
Efficiency V OUT = 35V
70% 60% EFFICIENCY (%) 50% 40% 30% 20% 10% 0% 0 4 8 12 LOAD CURRENT (mA) 16
L = 10H C = 1F V IN =6.5V V IN =5V
Load Regulation (V OUT =10V)
10.10 10.08 OUTPUT VOLTAGE (V) OUTPU T VOLTAGE (V) 10.06 10.04 10.02 10.00 9.98 9.96 9.94 9.92 9.90 0 10 20 30 40 50 60 LOAD CURR ENT (mA) 70
V IN = 3.6V L = 10H C = 1F
Load Regulation (V OUT =35V)
35.5 35.4 35.3 35.2 35.1 35.0 34.9 34.8 34.7 34.6 34.5 0 2 4 6 8 10 LOAD CURR ENT (mA) 12
V IN = 5V L = 10H C = 1F
Line Regulation (V OUT =12V)
12.20 12.16 OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V) 35.5 35.4 35.2 35.1 35.0 34.9 34.8 34.7 34.6 34.5 35.3
Line Regulation (V OUT =35V)
1.50 1.45 1.40 1.35 1.30 1.25 1.20 1.15 1.10 1.05 1.00 0.95 0.90 3 3.5
Frequency vs. Input Voltage
12.12 12.08 12.04 12.00 11.96 11.92 11.88 11.84 11.80 3 3.5 4 4.5 5 5.5 6 INPUT VOLTAGE (V) 6.5
IOU T = 40mA L = 10H C = 1F
FREQUENCY (MHz)
IOU T = 10mA L = 10H C = 1F
V OU T = 12V L = 10H C = 1F ILOAD = 40mA
4.5
4.9 5.3 5.7 6.1 INPUT VOLTAGE (V)
6.5
4 4.5 5 5.5 6 INPUT VOLTAGE (V)
6.5
Switch Current Limit vs. Input Voltage
1100 1000 CU RRENT LIMIT (mA)
C URRENT LIMIT (mA) 900 800 700 600 500 400 300 200 100 0
Switch Current Limit vs. T emperature
3.50 3.25 3.00 2.75 2.50 2.25 2.00 1.75 1.50 1.25 1.00 0.75 0.50
Quiescent Current vs. Input Voltage
900 800 700 600 500 400 300 200 3 3.5 4 4.5 5 5.5 6 IN PU T VOLTAGE (V) 6.5
V OU T = 12V L = 10H C = 1F
V IN = 3.6V V OU T = 12V L = 10H C = 1F
QUIESCENT CURRENT (mA)
V F B = 3V No Switching
-40 -20
0
20 40 60 80 100 120
TEMPERATUR E (C)
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 INPUT VOLTAGE (V)
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Typical Characteristics (Continued)
Feedback Voltage vs. T emperature
1.34
SWITCHING FREQUENCY (M Hz)
Switching Frequency vs. T emperature
1.40 1.35 1.30 1.25 1.20 1.15 1.10 1.05 1.00 0.95 0.90 -40 -20
V IN = 3.6V V OU T = 12V IOU T = 25mA L = 10H C = 1F
1.32 FEEDB ACK VOLTAGE (V) 1.30 1.28 1.26 1.24 1.22 1.20 1.18 -40 -20 0 20 40 60 80 100 120 TEMPER ATURE (C)
V IN = 3.6V V OU T = 12V IOU T = 25mA L = 10H C = 1F
0 20 40 60 80 100 120 Temperature (C)
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Functional Characteristics
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Functional Characteristics (Continued)
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Functional Diagram
MIC2619 Block Diagram
Functional Description
The MIC2619 is a constant frequency, PWM current mode boost regulator. It is composed of an oscillator, slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, and bipolar output transistor. The oscillator generates a 1.2MHz clock which triggers the PWM generator to turn on the output transistor and resets the slope compensation ramp generator. The current amplifier is used to measure switch current by amplifying the voltage signal from the internal sense resistor. The output of the current amplifier is summed with the output of the slope compensation ramp generator. This summed currentloop signal is then fed to one of the inputs of the PWM generator. The gm error amplifier measures the feedback voltage through the external feedback resistors and amplifies the error between the detected signal and the 1.265V reference voltage. The output of the gm error amplifier provides the voltage-loop signal that is fed to the other input of the PWM generator. When the current-loop signal exceeds the voltage loop signal, the PWM generator turns off the bipolar output transistor. The next clock period initiates the next switching cycle, maintaining the constant frequency current-mode PWM control.
VIN VIN provides power to the control and reference circuitry as well as the switch mode regulator MOSFETs. Due to the high speed switching, a 1F capacitor is recommended as close as possible to the VIN and GND pin. EN The enable pin provides a logic level control of the output. In the off state, supply current of the device is greatly reduced (typically <0.1A). Also, in the off state, the output drive is placed in a "tri-stated" condition, where the bipolar output transistor is in an "off" state or non-conducting state. OVP The OVP pin provides over-voltage protection on the output of the MIC2619. When the OVP circuit is tripped, the output voltage remains at the set OVP voltage. Because the OVP circuit operates at a lower frequency than the feedback circuit, output ripple will be higher while in an OVP state. OVP requires a resistor divider network to the output and GND to set the OVP voltage. If the output voltage overshoots the set OVP voltage, then the MIC2619 OVP circuit will shut off the switch; saving itself and other sensitive circuitry downstream. The accuracy of the OVP pin is 5% and therefore should be set above the output voltage to ensure noise or other variations will not cause a false triggering of the OVP circuit.
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MIC2619 voltage associated with this pin, the switch node should be routed away from sensitive nodes. GND The ground pin is the ground path for high current PWM mode. The current loop for the power ground should be kept as small as possible.
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Application Information
DC-to-DC PWM Boost Conversion The MIC2619 is a constant-frequency boost converter. It can convert a low DC input voltage to a higher DC output voltage. Figure 1 shows a typical circuit. Boost regulation is achieved by turning on an internal switch, which draws current through the inductor. When the switch turns off, the inductor's magnetic field collapses. This causes the current to be discharged into the output capacitor through an external Schottky diode (D1). The Functional Characteristics show Input Voltage ripple, Output Voltage ripple, SW Voltage, and Inductor Current for 10mA load current. Regulation is achieved by modulating the pulse width i.e., pulse-width modulation (PWM).
The duty cycle required for voltage conversion should be less than the maximum duty cycle of 85%. Also, in light load conditions where the input voltage is close to the output voltage, the minimum duty cycle can cause pulse skipping. This is due to the energy stored in the inductor causing the output to slightly overshoot the regulated output voltage. During the next cycle, the error amplifier detects the output as being high and skips the following pulse. This effect can be reduced by increasing the minimum load or by increasing the inductor value. Increasing the inductor value also reduces the peak current.
Input Capacitors A 1F ceramic capacitor is recommended on the VIN pin for bypassing. Increasing input capacitance will improve performance and provide greater noise immunity. The input capacitor should be as close as possible to the inductor and the MIC2619, with short traces for good noise performance. X5R or X7R dielectrics are recommended for the input capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore not recommended. Also, tantalum and electrolytic capacitors alone are not recommended because of their reduced RMS current handling, reliability, and ESR increases. Output Capacitors Output capacitor selection is also a trade-off between performance, size, and cost. The minimum recommended output capacitor is 1F. Increasing output capacitance will lead to an improved transient response but also an increase in size and cost. X5R or X7R dielectrics are recommended for the output capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore not recommended. Inductor Inductor selection will be determined by the following (not necessarily in order of importance);
Figure 1. Typical Application Circuit
Duty Cycle Considerations Duty cycle refers to the switch on-to-off time ratio and can be calculated as follows for a boost regulator:
D = 1- VIN VOUT
However at light loads, the inductor will completely discharge before the end of a switching cycle. The current in the inductor reaches 0A before the end of the switching cycle. This is known as discontinuous conduction mode (DCM). DCM occurs when:
IOUT < VIN IPEAK VOUT 2
* * * *
Inductance Rated current value Size requirements
Where
IPEAK =
(VOUT
- VIN ) VIN V Lf OUT

In DCM, the duty cycle is smaller than in continuous conduction mode. In DCM the duty cycle is given by:
D=
f 2 L IOUT (VOUT - VIN ) VIN
DC resistance (DCR) The MIC2619 was designed for use with a 10H inductor. Proper selection should ensure the inductor can handle the maximum average and peak currents required by the load. Maximum current ratings of the inductor are generally given in two methods; permissible DC current and saturation current. Permissible DC current can be rated either for a 40C temperature rise or a 10 to 20% loss in inductance. Ensure the inductor selected can handle the maximum operating current. When saturation current is specified, make sure that there is enough margin so that the peak current will not
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1 - VOUT VIN IPEAK = IOUT + VOUT 2 x f x L
MIC2619
Diode Selection The MIC2619 requires an external diode for operation. A Schottky diode is recommended for most applications due to their lower forward voltage drop and reverse recovery time. Ensure the diode selected can deliver the peak inductor current and the maximum reverse voltage is rated greater than the output voltage. Soft-start Feed-forward capacitors can be used to provide softstart for the MIC2619. Figure 2 shows a typical circuit for soft-start applications. Typically a 0.22nF feedforward capacitor will yield 5ms in rise time.
As shown by the previous calculation, the peak inductor current is inversely proportional to the switching frequency and the inductance; the lower the switching frequency or the inductance the higher the peak current. As input voltage increases the peak current also increases. The size of the inductor depends on the requirements of the application. DC resistance (DCR) is also important. While DCR is inversely proportional to size, DCR can represent a significant efficiency loss. Refer to the Efficiency Considerations. To maintain stability, increasing inductor size will have to be met with an increase in output capacitance. This is due to the unavoidable "right half plane zero" effect for the continuous current boost converter topology. The frequency at which the right half plane zero occurs can be calculated as follows:
Frequency = VOUT VIN L IOUT 2
2
Figure 2. Soft-start Circuit
The right half plane zero has the undesirable effect of increasing gain, while decreasing phase. This requires that the loop gain is rolled off before this has significant effect on the total loop response. This can be accomplished by either reducing inductance (increasing RHPZ frequency) or increasing the output capacitor value (decreasing loop gain).
Feedback resistors The MIC2619 utilizes a feedback pin to compare the output to an internal reference. The output voltage is adjusted by selecting the appropriate feedback resistor network values. Using the evaluation board schematic as a reference, the desired output voltage can be calculated as follows:
R VOUT = VREF 4 + 1 R 5
Where VREF is equal to 1.265V. Over-voltage Protection uses the same equation as the feedback pin.
R VOVP = VREF 1 + 1 R 2
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MIC2619 Evaluation Board Schematic
Bill of Materials
Item C1 Part Number C1608X5R1A105K GRM185R61A105KE36D 0603ZD105KT2A C2 C3 TAJA106M010R C1608X7R11H223K GRM188R71H223KA01D 06035C223JAT2A C4 08055D105MAT2A GRM21BR71H105KA12L CL21B105KBFNNNE D1 L1 SK14 B140/B C1G22L100MNE VLF3012ST-100MR59 LQH32PN100MN0L R1 R2, R5 R3 R4 U1
Notes: 1. TDK: www.tdk.com 2. Murata: www.murata.com 3. AVX: www.avx.com 4. Samsung: www.sem.samsung.com 5. MCC: www.mccsemi.com 6. Diode, Inc.: www.diodes.com 7. Vishay: www.vishay.com 8. Micrel, Inc.: www.micrel.com
Manufacturer TDK
(1) (2)
Description Capacitor, 1.0F, 10V, X5R, 0603 size Capacitor, 1.0F, 10V, X5R, 0603 size Capacitor, 1.0F, 10V, X5R, 0603 size Capacitor, 10.0F, 10V, A Case Capacitor, 22nF, 50V, X7R, 0603 size Capacitor, 22nF, 50V, X7R, 0603 size Capacitor, 22nF, 50V, X7R, 0603 size Capacitor, 1.0F, 50V, X5R, 0805 size Capacitor, 1.0F, 50V, X5R, 0805 size Capacitor, 1.0F, 50V, X7R, 0805 size Schottky Diode, 1A, 40V Schottky Diode, 1A, 40V Inductor, 10.0H, 0.8A, 2.5 x 2.0 x 1.0mm Inductor, 10.0H, 0.59A, 2.8 x 3.0 x 1.2mm Inductor, 10.0H, 0.7A, 3.2 x 2.5 x 1.55mm Resistor, 267k, 1%, 1/16W, 0603 size Resistor, 10k, 1%, 1/16W, 0603 size Resistor, 100k, 1%, 1/16W, 0603 size Resistor, 226k, 1%, 1/16W, 0603 size 1.2MHz PWM Boost Converter with OVP
Qty. 1 1 1
Murata AVX TDK
AVX(3)
Murata AVX AVX Murata Samsung(4) MCC(5) Diode, Inc. TDK Murata Vishay
(7) (6)
1
1
Samsung
1 1 2 1 1 1
CRCW0603267KFKEA CRCW060310K0FKEA CRCW0603100KFKEA CRCW0603226KFKEA MIC2619YD6
Vishay Vishay Vishay Micrel, Inc.(8)
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Recommended Layout
Top Layout
Bottom Layout
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Package Information
6-Pin TSOT (YD6)
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Recommended Land Pattern
6-Pin TSOT (YD6)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2009 Micrel, Incorporated.
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