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MIC2296
High Power Density 1.2A Boost Regulator
General Description
The MIC2296 is a 600kHz, PWM dc/dc boost switching regulator available in a 2mm x 2mm MLFTM package option. High power density is achieved with the MIC2296's internal 34V / 1.2A switch, allowing it to power large loads in a tiny footprint. The MIC2296 is a version of the MIC2295 1.2MHz, PWM dc/dc boost switching regulator, that offers improved efficiency resulting from 600kHz operation. The MIC2296 implements constant frequency 600kHz PWM current mode control. The MIC2296 offers internal compensation that offers excellent transient response and output regulation performance. The high frequency operation saves board space by allowing small, low-profile external components. The fixed frequency PWM scheme also reduces spurious switching noise and ripple to the input power source. The MIC2296 is available in a low-profile Thin SOT23 5lead package and a 2mm x2mm 8-lead MLFTM leadless package. The 2mm x 2mm MLFTM package option has an output over-voltage protection feature. The MIC2296 has an operating junction temperature range of -40C to +125C
Features
* * * * * * * * * * * * * 2.5V to 10V input voltage range Output voltage adjustable to 34V 1.2A switch current 600kHz PWM operation Stable with small size ceramic capacitors High efficiency Low input and output ripple <1A shutdown current UVLO Output over-voltage protection (MIC2296BML) Over temperature shutdown 2mm x 2mm leadless 8-lead MLFTM package option -40oC to +125oC junction temperature range
Applications
* * * * * * * * Organic EL power supplies 3.3V to 5V/500mA conversion TFT-LCD bias supplies Positive and negative output regulators SEPIC converters Positive to negative Cuk converters 12V supply for DSL applications Multi-output dc/dc converters
L1 10H VOUT 5V/400mA 1000 pF
10H
VOUT 15V/100mA
VIN 1-Cell Li Ion 3V to 4.2V
C1 2.2F
MIC2296BML SW VIN OVP FB EN AGND PGND R2 901
MIC2296 BD5
R1 10k 2.2F
VIN VIN 1-Cell Li Ion C1 2.2F EN
SW FB
R1 10k 10F R2 3.3k
GND
MLF and MicroLeadFrame is a trademark of Amkor Technology 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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MIC2296
Ordering Information
Part Number Standard MIC2296BML MIC2296BD5* Lead-Free MIC2296YML MIC2296YD5* Output Over Voltage Protection 34V Marking Code Standard WDA WDAA Lead-Free WDA WDAA Junction Temperature Range -40C to 125C -40C to 125C Package 2mm x2mm MLF-8L Thin SOT-23-5
* Contact factory for availability.
Pin Configuration
FB GND SW 1 3 2
OVP VIN EN 1 2 3 4 EP 8 7 6 5 PGND SW FB NC
4 EN
5 VIN
AGND
TSOT-23-5 (BD5)
8-pin MLFTM (BML)
Pin Description
MIC2296BD5 Thin SOT-23-5 -- 5 4 -- -- 3 1 -- 2 -- MIC2296BML 2x2 MLF-8L 1 2 3 4 5 6 7 8 -- EP Pin Name OVP VIN EN AGND N/C FB SW PGND GND GND Pin Function Output Over-Voltage Protection (Input): Tie this pin to VOUT to clamp the output voltage to 34V maximum in fault conditions. Tie this pin to ground if OVP function is not required. Supply (Input): 2.5V to 10V input voltage. Enable (Input): Logic high enables regulator. Logic low shuts down regulator. Analog ground No connect. No internal connection to die. Feedback (Input): 1.24V output voltage sense node. VOUT = 1.24V ( 1 + R1/R2) Switch Node (Input): Internal power BIPOLAR collector. Power ground Ground (Return): Ground. Ground (Return). Exposed backside pad.
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Absolute Maximum Rating (1)
Supply voltage (VIN)........................................................12V Switch voltage (VSW) ........................................ -0.3V to 34V Enable pin voltage (VEN)....................................... -0.3 to VIN FB Voltage (VFB)...............................................................6V Switch Current (ISW) ......................................................2.5A Ambient Storage Temperature (TS)............-65C to +150C ESD Rating(3) ................................................................. 2KV
Operating Range (2)
Supply Voltage (VIN).......................................... 2.5V to 10V Junction Temperature Range (TJ)..............-40C to +125C Package Thermal Impedance JA 2x2 MLF-8L lead ..........................................93C/W
Electrical Characteristics (4)
TA=25 C, VIN =VEN = 3.6V, VOUT = 15V, IOUT = 40mA, unless otherwise noted. Bold values indicate -40C TJ 125C.
o
Symbol
VIN VUVLO IVIN ISD VFB IFB
Parameter
Supply Voltage Range Under-Voltage Lockout Quiescent Current Shutdown Current Feedback Voltage Feedback Input Current Line Regulation Load Regulation
Condition
Min 2.5 1.8
Typ
2.1 2.8 0.1
Max 10 2.4
5
Units
V V mA A V nA
VFB = 2V (not switching) VEN = 0V (+/-1%) (+/-2%) (Over Temp) VFB = 1.24V 3V VIN 5V 5mA IOUT 40mA
(5)
1
1.252
1.227
1.24 -450 0.04 0.5
1.215
1.265
1
% % %
DMAX ISW VSW ISW VEN IEN fSW VOVP TJ
Notes: 1.
Maximum Duty Cycle Switch Current Limit Switch Saturation Voltage Switch Leakage Current Enable Threshold Enable Pin Current Oscillator Frequency Output over-voltage protection Over-Temperature Threshold Shutdown Note 5 ISW = 0.5A VEN = 0V, VSW = 10V TURN ON TURN OFF VEN = 10V VIN = 3.6V MIC2296BML only Hysteresis
90 1.2
95 1.7 250 0.01
2.5 1 0.4
A mV A V A kHz V
1.5
20 525 30 600 32 150 10
40
675 34
C C
2. 3. 4. 5.
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. This device is not guaranteed to operate beyond its specified operating rating. IC devices are inherently ESD sensitive. Handling precautions required. Human body model rating: 1.5K in series with 100pF. Specification for packaged product only. ISD = IVIN.
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Typical Characteristics
84 82 80 78 76 74 72 0 50 100 150 200 250 OUTPUT CURRENT (mA)
VIN = 3.2V VIN = 3.6V
12V Output with L = 4.7H
VIN = 4.2V
90 88 86 84 82 80 78 76 74 72 70
5V Output with L = 4.7H
VIN = 4.2V
300 290 280 270 260 250 240 230 220 210 200
Switch Saturation Voltage vs. Input Voltage
VIN = 3.2V
VIN = 3.6V
0
200 400 600 800 1000 OUTPUT CURRENT (mA)
10 Input Voltage (V)
800
Frequency vs. Input Voltage
100 98 96
Max Duty Cycle vs. Input Voltage
2 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1 2.5
Current Limit vs. Input Voltage
600
400
94
200
92 90 2.5
0 2.5
5 7.5 INPUT VOLTAGE (V)
10
5 7.5 INPUT VOLTAGE (V)
10
5 7.5 INPUT VOLTAGE (V)
10
12.2 OUTPUT VOLTAGE (V) 12.15 12.1 12.05 12 11.95 11.9 11.85 11.8 0
Load Regulation
FEEDBACK VOLTAGE (V) 1.30 1.28 1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12
Feedback Voltage vs. Temperature
FEEDBACK CURRENT (nA)
700 600 500 400 300 200 100
FB Pin Current vs. Temperature
V 25
IN
= 3.6V
50 75 100 125 150 LOAD (mA)
1.10 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
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Functional Characteristics
Enable Characteristics
Output Voltage (5V/div)
Output Voltage (50mV/div)
Step Load Response
Enable Voltage (2V/div)
VIN = 3.6V VOUT = 12V IOUT = 150mA
Load Current (100mA/div)
VIN = 3.6V VOUT = 12V IOUT = 50mA to 150mA
TIME (2s/div)
TIME (100s/div)
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MIC2296 slope compensation ramp generator. This summed current-loop signal is 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 1.24V 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 constant frequency current-mode PWM control
EN
Functional Description
The MIC2296 is a high power density, PWM dc/dc boost regulator. The block diagram is shown in Figure 1. The MIC2296 is composed of an oscillator, slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, and a 1.2A bipolar output transistor. The oscillator generates a 600kHz clock. The clock's two functions are to trigger the PWM generator that turns on the output transistor, and to reset the slope compensation ramp generator. The current amplifier is used to measure the 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
VIN FB OVP*
MIC2296
OVP* SW gm
VREF
PWM Generator
1.24V CA
600kHz Oscillator *OVP available on MLFTM package option only.
Ramp Generator
GND
MIC2296 Block Diagram Figure 1
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voltage condition is detected saving itself and other sensitive circuitry downstream.
Application Information
DC to DC PWM Boost Conversion The MIC2296 is a constant frequency boost converter. It operates by taking a DC input voltage and regulating a higher DC output voltage. Figure 2 shows a typical circuit.
VIN L1 10H VOUT
Component Selection
Inductor Inductor selection is a balance between efficiency, stability, cost, size and rated current. For most applications a 10H is the recommended inductor value. It is usually a good balance between these considerations. Efficiency is affected by inductance value in that larger inductance values reduce the peak to peak ripple current. This has an effect of reducing both the DC losses and the transition losses. There is also a secondary effect of an inductors DC resistance (DCR). The DCR of an inductor will be higher for more inductance in the same package size. This is due to the longer windings required for an increase in inductance. Since the majority of input current (minus the MIC2296 operating current) is passed through the inductor, higher DCR inductors will reduce efficiency. Also, 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;
Frhpz = VIN 2 VOUT x L x IOUT x 2
VIN EN
SW OVP FB R1 C2 10F R2 GND
U1 MIC2296-BML
GND
GND
Figure 2
Boost regulation is achieved by turning on an internal switch, which draws current through the inductor (L1). 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 Schottkey diode (D1). Voltage regulation is achieved my modulating the pulse width or pulse width modulation (PWM). Duty Cycle Considerations Duty cycle refers to the switch on-to-off time ratio and can be calculated as follows for a boost regulator; V D = 1- IN VOUT
The duty cycle required for voltage conversion should be less than the maximum duty cycle of 90%. 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 overshoot slightly over 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 reduces peak current, which in turn reduces energy transfer in each cycle.
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).
Over Voltage Protection For MLF package of MIC2296, there is an over voltage protection function. If the feedback resistors are disconnected from the circuit or the feedback pin is shorted to ground, the feedback pin will fall to ground potential. This will cause the MIC2296 to switch at full duty-cycle in an attempt to maintain the feedback voltage. As a result the output voltage will climb out of control. This may cause the switch node voltage to exceed its maximum voltage rating, possibly damaging the IC and the external components. To ensure the highest level of protection, the MIC2296 OVP pin will shut the switch off when an overApril 2005
Output Capacitor Output capacitor selection is also a trade-off between performance, size and cost. Increasing output capacitance will lead to an improved transient response, but also an increase in size and cost. X5R or X7R dielectric ceramic capacitors are recommended for designs with the MIC2296. Y5V values may be used, but to offset their tolerance over temperature, more capacitance is required. The following table shows the recommended ceramic (X5R) output capacitor value vs. output voltage. Output Voltage
<6V <16V <34V
Recommended Output Capacitance
10F 4.7F 2.2F
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Diode Selection The MIC2296 requires an external diode for operation. A Schottkey 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. Input Capacitor A minimum 1F ceramic capacitor is recommended for designing with the MIC2296. Increasing input capacitance will improve performance and greater noise immunity on the source. The input capacitor should be as close as possible to the inductor and the MIC2296, with short traces for good noise performance. Feedback Resistors The MIC2296 utilizes a feedback pin to compare the output to an internal reference. The output voltage is adjusted by selecting the appropriate feedback resistor values. The desired output voltage can be calculated as follows; R1 + 1 VOUT = VREF x R2
Where VREF is equal to 1.24V.
Capacitor Selection Multi-layer ceramic capacitors are the best choice for input and output capacitors. They offer extremely low ESR, allowing very low ripple, and are available in very small, cost effective packages. X5R dielectrics are preferred. A 4.7F to 10F output capacitor is suitable for most applications. Diode Selection For maximum efficiency, Schottky diode is recommended for use with MIC2296. An optimal component selection can be made by choosing the appropriate reverse blocking voltage rating and the average forward current rating for a given application. For the case of maximum output voltage (34V) and maximum output current capability, a 40V / 1A Schottky diode should be used. Open-Circuit Protection For MLF package option of MIC2296, there is an output over-voltage protection function that clamps the output to below 34V in fault conditions. Possible fault conditions may include: if the device is configured in a constant current mode of operation and the load opens, or if in the standard application the feedback resistors are disconnected from the circuit. In these cases the FB pin will pull to ground, causing the MIC2296 to switch with a high duty-cycle. As a result, the output voltage will climb out of regulation, causing the SW pin to exceed its maximum voltage rating and possibly damaging the IC and the external components. To ensure the highest level of safety, the MIC2296 has a dedicated pin, OVP, to monitor and clamp the output voltage in over-voltage conditions. The OVP function is offered in the 2mm x 2mm MLF-8L package option only. To disable OVP function, tie the OVP pin to ground
Duty-Cycle The MIC2296 is a general-purpose step up DC-DC converter. The maximum difference between the input voltage and the output voltage is limited by the maximum duty-cycle (Dmax) of the converter. In the case of MIC2296, DMAX = 85%. The actual duty cycle for a given application can be calculated as follows: V D = 1- IN VOUT
The actual duty-cycle, D, cannot surpass the maximum rated duty-cycle, Dmax.
Output Voltage Setting The following equation can be used to select the feedback resistors R1 and R2 (see figure 1). V R1 = R 2 OUT - 1 1.24V
A high value of R2 can increase the whole system efficiency, but the feedback pin input current (IFB) of the gm operation amplifier will affect the output voltage. The R2 resistor value must be less than or equal to 5k (R2 5k).
Inductor Selection In MIC2296, the switch current limit is 1.2A. The selected inductor should handle at least 1.2A current without saturating. The inductor should have a low DC resistor to minimize power losses. The inductor's value can be 4.7H to 10H for most applications.
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MIC2296
V IN 3V to 4.2V
L1 4.7H
D1
VOUT 5V @ 400mA 470 pF
V IN 3V to 4.2V
L1 4.7H
D1
VOUT 9V @ 180mA 560 pF
MIC2296BML C1 4.7F 6.3V VIN SW OVP EN GND GND FB R1 5.62k
MIC2296BML C2 22F 6.3V C1 2.2F 10V VIN SW OVP EN GND GND GND FB R2 5k R1 31.6k C2 4.7F 16V
R2 1.87k
GND
3VIN to 4.2VOUT @ 400mA
3VIN - 4.2VIN to 9VOUT @ 180mA
V IN 3V to 4.2V
L1 15H
D1
VOUT 12V @ 120mA 1200 pF
V IN 5V
L1 15H
D1
VOUT 24V @160mA
MIC2296BML C1 2.2F 10V VIN SW OVP EN GND GND FB R2 5k R1 43.2k C2 4.7F 16V C1 2.2F 10V
MIC2296BML VIN SW OVP EN GND GND GND FB R2 2.32k R1 43.2k C2 2.2F 25V
GND
3VIN - 4.2Vin to 12VOUT @ 120mA
5VIN to 24VOUT @ 160mA
V IN 3V to 4.2V
L1 15H
D1
VOUT 24V@80mA 1200 pF
MIC2296BML C1 2.2F 10V VIN SW OVP EN GND GND FB R2 2.32k R1 43.2k C2 2.2F 25V
GND
3VIN to 4.2VIN to 24VOUT @ 80mA
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MIC2296
Package Information
8-Pin Package MLF (ML)
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) 2005 Micrel, Incorporated.
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