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MIC3385
8MHz Inductorless Buck Regulator with LDO Standby Mode
General Description
The Micrel MIC3385 is a high-efficiency inductorless buck regulator that features a LOWQ(R) LDO standby mode that draws only 18A of quiescent current. The MIC3385 requires no external inductor enabling an ultra-low noise, small size, and high efficiency solution for portable power applications. In PWM mode, the MIC3385 operates with a constant frequency 8MHz PWM control. Under light load conditions, such as in system sleep or standby modes, the PWM switching operation can be disabled to reduce switching losses. In this light load LOWQ(R) mode, the LDO maintains the output voltage and draws only 18A of quiescent current. The LDO mode of operation saves battery life while not introducing spurious noise and high ripple as experienced with pulse skipping or bursting mode regulators. The MIC3385 operates from 2.7V to 5.5V input and features internal power MOSFETs that can supply up to 600mA output current in PWM mode. It can operate with a maximum duty cycle of 100% for use in low-dropout conditions. The MIC3385 is available in the 14-pin 3mm x 3.5mm MLF(R) package with a junction operating range from -40C to +125C. Data sheets and support documentation can be found on Micrel's web site at: www.micrel.com.
Features
* 2.7 to 5.5V supply voltage * Light load LOWQ(R) LDO mode - 18A quiescent current - Low noise, 75Vrms * 8MHz PWM mode - Output current to 600mA - >90% efficiency - 100% maximum duty cycle * Adjustable output voltage option down to 1V * Ultra-fast transient response * NO external inductor required * Enables sub 1mm profile solution * Fully integrated MOSFET switches * Micropower shutdown * Thermal shutdown and current limit protection (R) * Pb-free 14-pin 3x3.5x0.9mm MLF package * -40C to +125C junction temperature range
Applications
* * * * * * Slim digital cameras MP3 players Portable power applications Cellular phones PDAs USB peripherals
Typical Application
2.5V OUT Efficiency
100 90 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 600 OUTPUT CURRENT (mA) VIN =3.2V VIN =3.6V VIN =4.2V
(R) Adjustable Output Buck Regulator with LOWQ Mode
LOWQ is a registered trademark of Micrel, Inc. MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc. Micrel Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel +1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com
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MIC3385
Ordering Information
Part Number MIC3385YHL MIC3385-1.5YHL
Notes: 1. 2. MLF(R) is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free. Other voltage options available. Please contact Micrel for details.
Voltage Adj. 1.5V
Temperature Range -40 to +125C -40 to +125C
Package 14-Pin 3mm x 3.5mm MLF
(R)
Lead Finish Pb-free Pb-free
14-Pin 3mm x 3.5mm MLF(R)
Pin Configuration
FB VIN LOWQ EN OUT OUT OUT 1 2 3 4 5 6 7 14 BIAS 13 LDO 12 AVIN 11 GND 10 SW 9 8 SW SW
14- Pin 3mm x 3.5mm MLF(R) (HL)
Pin Description
Pin Number 1 2 3 4 5,6,7 8,9,10 11 12 13 14 Pin Name FB VIN LOWQ EN OUT SW GND AVIN LDO BIAS Pin Function Feedback. Input to the error amplifier. Connect to the external resistor divider network to set the output voltage. Supply Voltage (Input): Supply voltage for the internal switches and drivers. Enable LDO Mode (Input): Logic low enables the internal LDO and disables the PWM operation. Logic high enables the PWM mode and disables the LDO mode. Enable (Input). Logic low will shut down the device, reducing the quiescent current to less than 5A. Switch Output after inductor. Switch (Output): Internal power MOSFET output switches before Inductor Power Ground. Requires input capacitor to GND. Analog Supply Voltage (Input): Supply voltage for the analog control circuitry and LDO input power. Requires bypass capacitor to GND. LDO Output (Output): Connect to VOUT for LDO mode operation. Internal circuit bias supply. Must be de-coupled to signal ground with a 0.1F capacitor and should not be loaded.
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Absolute Maximum Ratings(1)
Supply Voltage (VIN) .......................................................+6V Output Switch Voltage (VSW). .........................................+6V Output Switch Current (ISW)..............................................2A Logic Input Voltage (VEN, VLOWQ)....................... -0.3V to VIN Storage Temperature (Ts) .........................-60C to +150C EDS Rating(3) .................................................................. 3kV
Operating Ratings(2)
Supply Voltage (VIN)..................................... +2.7V to +5.5V Logic Input Voltage (VEN, VLOWQ)....................... -0.3V to VIN Junction Temperature (TJ) ........................ -40C to +125C Junction Thermal Resistance 3x3.5 MLF(R)-14 (JA)...........................................55C/W
Electrical Characteristics(4)
VIN = VEN = VLOWQ =3.6V; L = 0.47H; COUT = 10F; TA = 25C, unless noted. Bold values indicate -40C< TJ < +125C.
Parameter Supply Voltage Range Under-Voltage Lockout Threshold UVLO Hysteresis Quiescent Current, PWM mode Quiescent Current, LDO mode Shutdown Current [Adjustable] Feedback Voltage FB pin input current Current Limit in PWM Mode Output Voltage Line Regulation Output Voltage Load Regulation, PWM Mode Output Voltage Load Regulation, LDO Mode Maximum Duty Cycle PWM Switch ON-Resistance Oscillator Frequency LOWQ threshold voltage LOWQ Input Current Enable Threshold Enable Input Current LDO Dropout Voltage IOUT = 50mA, Note 5 0.5 VFB = 0.9 * VNOM VOUT > 2V; VIN = VOUT+300mV to 5.5V; ILOAD= 100mA VOUT < 2V; VIN = 2.7V to 5.5V; ILOAD= 100mA 20mA < ILOAD < 300mA 100A < ILOAD < 50mA VLOWQ = 0V VFB 0.4V ISW = 50mA VFB = 0.7VFB_NOM (High Side Switch) ISW = -50mA VFB = 1.1VFB_NOM (Low Side Switch) 7.2 0.5 100 0.4 0.4 8 0.85 0.1 0.85 0.1 110 8.8 1.3 2 1.3 2 0.75 VFB = 0.9 * VNOM (not switching) VLOWQ = 0V;IOUT = 0mA VEN = 0V 1% 2% (over temperature) 0.99 0.98 (turn-on) Condition Min. 2.7 2.45 2.55 100 690 16 0.01 1 1 1 0.13 0.2 0.1 1.85 900 29 5 1.01 1.02 Typ. Max. 5.5 2.65 Units V V mV A A A V V nA A % % % % MHz V A V A mV
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Electrical Characteristics(4) (Continued)
VIN = VEN = VLOWQ =3.6V; L = 0.47H; COUT = 10F; TA = 25C, unless noted. Bold values indicate -40C< TJ < +125C.
Parameter Output Voltage Noise LDO Current Limit Over-Temperature Shutdown Over-Temperature Hysteresis Internal Inductor
Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5k in series with 100pF. 4. Specification for packaged product only. 5. Dropout voltage is defined as the input-to-output differential at which the output voltage drops 2% below its nominal value that is initially measured at a 1V differential. For outputs below 2.7V, the dropout voltage is the input-to-output voltage differential with a minimum input voltage of 2.7V.
Condition LOWQ = 0V; COUT = 10F, 10Hz to 100kHz LOWQ = 0V; VOUT = 0V (LDO Mode)
Min.
Typ. 75
Max.
Units Vrms mA C C H
60
120 160 20 0.47
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Typical Characteristics PWM Mode
2.5V OUT Efficiency
100 90 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 600 OUTPUT CURRENT (mA) V IN =3.2V VIN =3.6V VIN =4.2V
1.8V OUT Efficiency
100 V IN =3.2V 90 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 600 OUTPUT CURRENT (mA) VIN =3.6V VIN =4.2V
1.5V OUT Efficiency
100 90 V IN =3.2V 80 70 60 50 40 30 20 10 0 0 VIN =3.6V VIN =4.2V
100 200 300 400 500 600 OUTPUT CURRENT (mA)
1.2V OUT Efficiency
100 90 V IN =3.2V 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 600 OUTPUT CURRENT (mA) VIN =3.6V VIN =4.2V
1.0V OUT Efficiency
100 90 V IN =3.2V 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 600 OUTPUT CURRENT (mA) VIN =3.6V VIN =4.2V
1.018 1.014 1.010 1.006 1.002 0.998 0.994 0.990 0
Load Regulation
VIN =3.6V /LowQ=V IN
100 200 300 400 500 600 OUTPUT CURRENT (mA)
1100 1000 900
Quiescent Current vs. Input Voltage
9.0
Frequency vs. Input Voltage
8.5
8.0 800 700 600 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 INPUT VOLTAGE (V) 7.5
7.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 INPUT VOLTAGE (V)
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Typical Characteristics LDO Mode
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Typical Characteristics LDO Mode (cont.)
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Functional Characteristics
Load Transient PWM Mode
Load Transient LDO Mode
Output Voltag e AC Coupled (50mV/div)
Load (100mA/div)
COUT = 10F
Load (25mA/div)
Output Voltag e AC Coupled (50mV/div)
COUT = 10F
Time (100s/div )
Time (100s/div )
Enable Transient PWM Mode
Enable Transient LDO Mode
Output Voltag e (1.5V/div)
Enable (2V/div)
COUT = 10F
Enable (2V/div)
Output Voltag e (1.5V/div)
COUT = 10F
Time (40s/div )
Time (40s/div )
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Functional Diagram
MIC3385 Block Diagram
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MIC3385 BIAS The BIAS pin supplies the power to the internal power to the control and reference circuitry. The bias is powered from input voltage through an RC lowpass filter. The RC lowpass filter frequency is:
1 2 (20 )(100nF )
Functional Description
VIN VIN provides power to the MOSFETs for the switch mode regulator section, along with the current limiting sensing. Due to the high switching speeds, a 1F capacitor is recommended to ground (GND) pin for bypassing. Please refer to layout recommendations. AVIN Analog VIN (AVIN) provides power to the LDO subsection and the bias through an internal 6 resistor. AVIN and VIN must be tied together. Careful layout should be considered to ensure that high frequency switching noise caused by VIN is reduced before reaching AVIN. LDO The LDO pin is the output of the linear regulator and should be connected to the output. In LOWQ mode (LOWQ < 1.5V), the LDO provides the output voltage. In PWM mode (LOWQ > 1.5V) the LDO pin is high impedance. 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 <1A). Also, in the off state, the output drive is placed in a "tri-stated" condition, where both the high side P-channel MOSFET and the low-side N-channel are in an "off" or non-conducting state. Do not drive the enable pin above the supply voltage. LOWQ The LOWQ pin provides a logic level control between the internal PWM mode and the low noise linear regulator mode. With LOWQ pulled low (<0.5V), quiescent current of the device is greatly reduced by switching to a low noise linear regulator mode that has a typical IQ of 18A. In linear (LDO) mode the output can deliver 60mA of current to the output. By placing LOWQ high (>1.5V), this transitions the device into a constant frequency PWM buck regulator mode. This allows the device the ability to efficiently deliver up to 600mA of output current at the same output voltage.
FB The feedback pin (FB) provides the control path to control the output. For adjustable versions, a resistor divider connecting the feedback to the output is used to adjust the desired output voltage. The output voltage is calculated as follows:
R1 VOUT = VREF x + 1 R2
where VREF is equal to 1.0V. A feedforward capacitor is recommended for most designs using the adjustable output voltage option. To reduce battery current draw, a 100K feedback resistor is recommended from the output to the FB pin (R1). Also, a feedforward capacitor should be connected between the output and feedback (across R1). The large resistor value and the parasitic capacitance of the FB pin can cause a high frequency pole that can reduce the overall system phase margin. By placing a feedforward capacitor, these effects can be significantly reduced. Feedforward capacitance (CFF) can be calculated as follows:
CFF = 1 2 x R1x 160kHz
For fixed options a feedforward capacitor from the output to the FB pin is required. Typically a 100pF small ceramic capacitor is recommended SW The switch (SW) pin connects directly to the inductor and provides the switching current necessary to operate in PWM mode. Due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes. GND Combines PGND and SGND Power ground (PGND) is the ground path for the high current PWM mode. Signal ground (SGND) is the ground path for the biasing and control circuitry.
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MIC3385 Input Capacitor A minimum 1F ceramic is recommended on the VIN pin for bypassing. X5R or X7R dielectrics are recommended for the input capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore, not recommended. A minimum 1F is recommended close to the VIN and PGND pins for high frequency filtering. Smaller case size capacitors are recommended due to their lower ESR and ESL. Please refer to layout recommendations for proper layout of the input capacitor. Output Capacitor The MIC3385 is optimized for a 10F output capacitor. A larger value can be used to improve transient response The MIC3385 utilizes type III internal compensation and utilizes an internal high frequency zero to compensate for the double pole roll off of the LC filter. For this reason, larger output capacitors can create instabilities. X5R or X7R dielectrics are recommended for the output capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore, not recommended. In addition to a 10F, a small 10nF is recommended close to the load for high frequency filtering. Smaller case size capacitors are recommended due to there lower ESR and ESL.
Application Information
The MIC3385 is a 600mA PWM power supply that utilizes a LOWQ light load mode to maximize battery efficiency in light load conditions. This is achieved with a LOWQ control pin that when pulled low, shuts down all the biasing and drive current for the PWM regulator, drawing only 18A of operating current. This allows the output to be regulated through the LDO output. It is capable of providing 60mA of output current. This method has the advantage of producing a clean, low current, ultra low noise output in LOWQ mode. During LOWQ mode, the SW node becomes high impedance, blocking current flow. Other methods of reducing quiescent current, such as pulse frequency modulation (PFM) or bursting techniques create large amplitude, low frequency ripple voltages that can be detrimental to system operation. When more than 60mA is required, the LOWQ pin can be forced high, causing the MIC3385 to enter PWM mode. In this case, the LDO output makes a "hand-off" to the PWM regulator with virtually no variation in output voltage. The LDO output then turns off allowing up to 600mA of current to be efficiently supplied through the PWM output to the load.
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Layout Recommendations
Top Layer
Bottom Layer
Note: The above figures demonstrate the recommended layout for the MIC3385 adjustable option.
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Vin J1 Vin 5.5 Max
R4 10K 1 2 C1 10F/6.3V 12
U1 MIC3385YHL VIN AVin OUT SW LDO EN LOWQ FB
1 R2 Option 14 5, 6, 7 8, 9, 10
J5 OUT
C4 10F/3.6V C3 82pF/50V
JP1 1X2 2
13 R1 Option
J4 EN
4
J3 LOWQ Vin
R5 10K R3
3
BIAS
GND
11
C2 0.1F/6.3V
J2 GND
J6 GND
MIC3385 Adjustable Output Schematic
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1608X5R0J106K C1, C4 JMK107BJ106MA-T GRM188R60J106M C1005X5R0J104M C2 04026D104MAT2A VJ0402Y104KXQPW1BC C3 R1 R2 R3 R4, R5
U1
Notes: 1. TDK: www.tdk.com. 2. Taiyo Yuden, Inc.: www.t-yuden.com. 3. Murata: www.murata.com. 4. AVX: www.avxcorp.com. 5. Vishay: www.website.com. 6. Micrel, Inc.: www.micrel.com.
TDK
(1)
Taiyo Yuden(2) Murata(3) TDK
(1)
10F Ceramic Capacitor X5R, 6.3V 10F Ceramic Capacitor X7R, 6.3V 1F Ceramic Capacitor X5R, 6.3V 1F Ceramic Capacitor X7R, 6.3V 82pF Ceramic Capacitor COG, 50V 82pF Ceramic Capacitor COG, 10V 100K, 1% 0402, 1/16W (Optional) 124K, 1% 0402, 1/16W (Optional) 20, 1% 0603, 1/16W 10K, 1% 0603, 1/16W
8MHz Power System Module w/LDO Standby Mode
2 2 1 1 1 1 1 1 1 1
1
AVX(4) Vishay(5) TDK
(1) (5)
C1005COG1H820J VJ0402A80KXQPW1BC CRCW04021003FKEYE3 CRCW04021243FKEYE3 CRCW060320R0FKEYE3 CRCW06031002FKEYE3
MIC3385YHL
Vishay
Vishay(5) Vishay(5) Vishay
(5)
Vishay(5)
Micrel, Inc.(6)
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Package Information
14-Pin 3mm x 3.5mm MLF(R) (HL)
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) 2006 Micrel, Incorporated.
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