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MIC23250
4MHz Dual 400mA Synchronous Buck Regulator with HyperLight LoadTM
General Description
Features
The MIC23250 is a high efficiency 4MHz dual 400mA * Input voltage: 2.7V to 5.5V HyperLight LoadTM synchronous buck regulator with HyperLight LoadTM mode. * Dual output current 400mA/400mA HyperLight LoadTM provides very high efficiency at light * Up to 94% peak efficiency and 85% efficiency at 1mA loads and ultra-fast transient response which is perfectly * 33A dual quiescent current suited for supplying processor core voltages. An additional * 1H inductor with a 4.7F capacitor benefit of this proprietary architecture is very low output * 4MHz in PWM operation ripple voltage throughout the entire load range with the use of small output capacitors. The fixed output MIC23250 has * Ultra fast transient response a tiny 2mm x 2mm Thin MLF(R) package that saves * Low voltage output ripple precious board space by requiring only 6 additional * 20mVpp in HyperLight LoadTM mode external components to drive both outputs up to 400mA * 3mV output voltage ripple in full PWM mode each. * 0.01A shutdown current The device is designed for use with a 1H inductor and a * Fixed output:10-pin 2mm x 2mm Thin MLF(R) 4.7F output capacitor that enables a sub-1mm height. * Adjustable output:12-pin 2.5mm x 2.5mm Thin MLF(R) The MIC23250 has a very low quiescent current of 33A * -40C to +125C junction temperature range with both outputs enabled and can achieve over 85% efficiency at 1mA. At higher loads the MIC23250 provides a constant switching frequency around 4MHz while providing Applications peak efficiencies up to 94%. * Mobile handsets The MIC23250 fixed output voltage option is available in a * Portable media players (R) 10-pin 2mm x 2mm Thin MLF . The adjustable output (R) * Portable navigation devices (GPS) options is available in a 12-pin 2.5mm x 2.5mm Thin MLF . * WiFi/WiMax/WiBro modules The MIC23250 is designed to operate over the junction * Digital cameras operating range from -40C to +125C. * Wireless LAN cards Data sheets and support documentation can be found on * USB Powered Devices Micrel's web site at: www.micrel.com. ____________________________________________________________________________________________________________
Typical Application
Efficiency V OUT = 1.8V
100 VIN = 3.0V 90 VIN = 2.7V 80 70 VIN = 4.2V 60 50 40 30 20 10 0 11 L = 1H COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA) VIN = 3.6V
HyperLight Load is a 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
June 2010
M9999-061110-E
Micrel, Inc.
MIC23250
Ordering Information
Part Number Marking Code WV3 WV2 WV4 WV5 1WV WV1 5WV 4WV Nominal Output Voltage 1 0.9V 1.2V 1.2V 1.2V 1.2V 1.575V 2.6V ADJ Nominal Output Voltage 2 1.1V 1.0V 1.6V 1.8V 3.3V 1.8V 3.3V ADJ Junction Temp. Range -40 to +125C -40 to +125C -40 to +125C -40 to +125C -40 to +125C -40 to +125C -40 to +125C -40 to +125C Package Lead Finish Pb-Free Pb-Free Pb-Free Pb-Free Pb-Free Pb-Free Pb-Free
(R)
MIC23250-3BYMT MIC23250-C4YMT MIC23250-W4YMT MIC23250-G4YMT MIC23250-S4YMT MIC23250-GFHYMT MIC23250-SKYMT MIC23250-AAYMT
Notes: 1) 2)
10-Pin 2mm x 2mm Thin MLF(R) 10-Pin 2mm x 2mm Thin MLF
(R)
10-Pin 2mm x 2mm Thin MLF(R) 10-Pin 2mm x 2mm Thin MLF 10-Pin 2mm x 2mm Thin MLF
(R) (R)
10-Pin 2mm x 2mm Thin MLF(R) 10-Pin 2mm x 2mm Thin MLF
(R)
12-Pin 2.5mm x 2.5mm Thin MLF
Pb-Free
Additional voltage options available (0.8V to 3.3V). Contact Micrel for details. Thin MLF is GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
(R)
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MIC23250
Pin Configuration
SNS1 EN1 AGND SW1 PGND 1 2 3 4 5 10 SNS2 9 8 7 6 EN2 AVIN SW2 VIN
FB1 SNS1 EN1 AGND SW1 PGND
1 2 3 4 5 6
12 FB2 11 SNS2 10 EN2 9 8 7 AVIN SW2 VIN
10-Pin 2mm x 2mm Thin MLF(R) (MT) Fixed Output (Top View)
12-Pin 2.5mmx2.5mm Thin MLF(R) (MT) Adjustable Output (Top View)
Pin Description
Pin Number (Fixed) Pin Number (Adjustable) Pin Name Pin Function
- 1 2 3 4 5 6 7 8 9 10 -
1 2 3 4 5 6 7 8 9 10 11 12
FB1 SNS1 EN1 AGND SW1 PGND VIN SW2 AVIN EN2 SNS2 FB2
Feedback VOUT1 (Input): Connect resistor divider at this node to set output voltage. Resistors should be selected based on a nominal VFB of 0.72V. Sense 1 (Input): Error amplifier input. Connect to feedback resistor network to set output 1 voltage. Enable 1 (Input): Logic low will shut down output 1. Logic high powers up output 1. Do not leave unconnected. Analog Ground. Must be connected externally to PGND. Switch Node 1 (Output): Internal power MOSFET output. Power Ground. Supply Voltage (Power Input): Requires close bypass capacitor to PGND. Switch Node 2 (Output): Internal power MOSFET output. Supply Voltage (Power Input): Analog control circuitry. Connect to VIN. Enable 2 (Input): Logic low will shut down output 2. Logic high powers up output 2. Do not leave unconnected. Sense 2 (Input): Error amplifier input. Connect to feedback resistor network to set output 2 voltage. Feedback VOUT2 (Input): Connect resistor divider at this node to set output voltage. Resistors should be selected based on a nominal VFB of 0.72V.
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MIC23250
Absolute Maximum Ratings(1)
Supply Voltage (VIN) .........................................................6V Output Switch Voltage (VSW) ............................................6V Logic Input Voltage (VEN1, VEN2) ........................ -0.3V to VIN Storage Temperature Range (Ts)..............-65C to +150C ESD Rating(3) .................................................................. 2kV
Operating Ratings(2)
Supply Voltage (VIN)......................................... 2.7V to 5.5V Logic Input Voltage (VEN1, VEN2) ............................. 0V to VIN Junction Temperature (TJ) ..................-40C TJ +125C Thermal Resistance 2mm x 2mm Thin MLF-10 (JA) .........................70C/W 2.5mm x 2.5mm Thin MLF-12 (JA) ...................65C/W
Electrical Characteristics(4)
TA = 25C with VIN = VEN1 = VEN2 = 3.6V; L = 1H; COUT = 4.7F; IOUT = 20mA; only one channel power is enabled, unless otherwise specified. Bold values indicate -40C< TJ < +125C.
Parameter Condition Min Typ Max Units
Under-Voltage Lockout Threshold UVLO Hysteresis Quiescent Current Shutdown Current Output Voltage Accuracy Feedback Voltage (Adj only) Current Limit in PWM Mode Output Voltage Line Regulation Output Voltage Load Regulation
(turn-on) VOUT1, 2 (both Enabled), IOUT1, 2 = 0mA , VSNS1,2 >1.2 * VOUT1, 2 Nominal VEN1, 2 = 0V; VIN = 5.5V VIN = 3.6V if VOUTNOM < 2.5V, ILOAD = 20mA VIN = 4.5V if VOUTNOM 2.5V, ILOAD = 20mA SNS = 0.9*VOUT NOM VIN = 3.6V to 5.5V if VOUTNOM < 2.5V, ILOAD = 20mA VIN = 4.5V to 5.5V if VOUTNOM 2.5V, ILOAD = 20mA 20mA < ILOAD < 400mA, VIN = 3.6V if VOUTNOM < 2.5V 20mA < ILOAD < 400mA, VIN = 5.0V if VOUTNOM 2.5V ISW = 100mA PMOS ISW = -100mA NMOS ILOAD = 120mA VOUT = 90%
2.45
2.55 60 33 0.01
2.65 50
4 +2.5 +2.5 1
V mV A A % % V A %/V %/V % % MHz s V A
C C
-2.5 -2.5 0.410
PWM Switch ON-Resistance Frequency Soft Start Time Enable Threshold Enable Input Current Over-temperature Shutdown Over-temperature Shutdown Hysteresis
0.5
0.720 0.65 0.4 0.4 0.5 0.5 0.6 0.8 4 260 0.8 0.1 160 40
1.2 2
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.
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MIC23250
Typical Characteristics
50 45 40 35 30 25 20 15 10 5 L = 1H COUT = 4.7F 0.01 11 1
Quiescent Current vs. Input Voltage
10
4MHz
Switching Frequency vs. Output Current
10
4MHz
Switching Frequency vs. Output Current
L = 4.7H
VIN = 3.0V
1 L = 1H
0.1
VIN = 4.2V VOUT = 1.8V L = 1H COUT = 4.7F
L = 2.2H 0.1 VIN = 3.6V VOUT = 1.8V COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA)
0 2.7 3.2 3.7 4.2 4.7 5.2 5.7 INPUT VOLTAGE (V)
VIN = 3.6V 0 100 1000 OUTPUT CURRENT (mA)
0.01 11
5.0
Frequency vs. Temperature
1.90 1.88 1.86 1.84 1.82 1.80 1.78 1.76 1.74 1.72 1.70 11
Output Voltage vs. Output Current
4.5
VIN = 3.0V VIN = 4.2V VIN = 3.6V
1.90 L = 1H 1.88 COUT = 4.7F 1.86 1.84 1.82 1.80
Load = 10mA
Output Voltage vs. Input Voltage
Load = 1mA
4.0
3.5
3.0
L = 1H COUT = 4.7F Load = 120mA 20 40 60 80 TEMPERATURE (C)
1.78 Load = 300mA 1.76 Load = 50mA Load = 400mA 1.74
Load = 150mA
0 100 1000 OUTPUT CURRENT (mA)
1.72 1.70 2.7 3.2 3.7 4.2 4.7 5.2 5.7 INPUT VOLTAGE (V)
1.9
Output Voltage vs. Temperature
VOUT2 = 1.8V
1.2
Enable Threshold vs. Temperature
1.000 0.975
Enable Threshold vs. Input Voltage
1.0 VIN = 3.6V 0.8 VIN = 2.7V
1.8
VIN = 5.5V
0.950 0.925 0.900 0.875 0.850
Enable ON Enable OFF
1.7
L = 1H COUT = 4.7F Load = 120mA VOUT1 = 1.575V
0.6 0.4 0.2 L = 1H COUT = 4.7F 20 40 60 80 TEMPERATURE (C)
1.6
0.825
1.5
20 40 60 80 TEMPERATURE (C)
0
0.800 2.7 3.2 3.7 4.2 4.7 5.2 5.7 INPUT VOLTAGE (V)
VIN = 3.6V VOUT = 1.8V Load = 150mA
700
Current Limit vs. Input Voltage
Efficiency V OUT = 1.2V
100 VIN = 3.0V 90 VIN = 2.7V 80 70 VIN = 3.6V 60 VIN = 4.2V 50 40 30
100
Efficiency V OUT = 1.575V
90 VIN = 2.7V 80 70 VIN = 4.2V 60 50 40 30 20 10 0 11 VIN = 3.0V
650
VIN = 3.6V
600 L = 1H COUT = 4.7F 5.7
20 10 0 11
550 2.7 3.2 3.7 4.2 4.7 5.2 INPUT VOLTAGE (V)
L = 1H COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA)
L = 1H COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA)
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MIC23250
Typical Characteristics (Continued)
Efficiency V OUT = 1.8V
100 VIN = 3.0V 90 VIN = 2.7V 80 70 VIN = 4.2V 60 50 40 30 20 10 0 11 L = 1H COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA) VIN = 3.6V 100 90 80
Efficiency V OUT = 2.5V
VIN = 2.7V
100 90 80 70 60 50 40 30 20
Efficiency V OUT = 3.3V
VIN = 4.2V VIN = 5.0V VIN = 5.5V
VIN = 3.6V 70 VIN = 4.2V VIN = 3.0V 60 50 40 30 20 10 0 11 L = 1H COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA)
10 0 11
L = 1H COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA)
100 90 80 70 60 50 40 30 20 10 0 11
Efficiency V OUT = 1.8V With Various Inductors
L = 1.5H L = 1.0H
Dual Output Efficiency
100 90 80 70 60 50 VIN = 3.3V VIN = 4.2V
L = 0.47H
VIN = 3.6V
VIN = 3.6V COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA)
40 VOUT1 = 1.575V 30 VOUT2 = 1.8V 20 Load1 = Load2 L1 = L2 = 1H 10 COUT1 = COUT2 = 4.7F 0 11 0 100 1000 OUTPUT CURRENT (mA)
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MIC23250
Functional Characteristics
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Micrel, Inc.
MIC23250
Functional Characteristics (Continued)
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Micrel, Inc.
MIC23250
Functional Characteristics (Continued)
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MIC23250
Functional Diagram
MIC23250 Simplified Fixed Output Block Diagram
VIN AVIN
EN1
ENABLE LOGIC ENABLE LOGIC
EN2
SW1
GATE DRIVES
GATE DRIVES
SW2
ISENSE
Zero X Current Limit
CONTROL LOGIC TON TIMER & SOFT START
CONTROL LOGIC TON TIMER & SOFT START
Zero X Current Limit
ISENSE
UVLO
UVLO
+
FB1 SNS1
REF1
REF2
+
ERROR COMPARATOR
-
ERROR COMPARATOR
FB2 SNS2
PGND
AGND
MIC23250 Simplified Adjustable Output Block Diagram
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Micrel, Inc.
MIC23250
Functional Description
VIN The VIN provides power to the internal MOSFETs for the switch mode regulator along with the current limit sensing. The VIN operating range is 2.7V to 5.5V so an input capacitor with a minimum of 6.3V voltage rating is recommended. Due to the high switching speed, a minimum of 2.2F bypass capacitor placed close to VIN and the power ground (PGND) pin is required. Based upon size, performance and cost, a TDK C1608X5R0J475K, size 0603, 4.7F ceramic capacitor is highly recommended for most applications. Refer to the layout recommendations for details. AVIN The analog VIN (AVIN) provides power to the analog supply circuitry. AVIN and VIN must be tied together. Careful layout should be considered to ensure high frequency switching noise caused by VIN is reduced before reaching AVIN. A 0.01F bypass capacitor placed as close to AVIN as possible is recommended. See layout recommendations for details. EN1/EN2 The enable pins (EN1 and EN2) control the on and off states of outputs 1 and 2, respectively. A logic high signal on the enable pin activates the output voltage of the device. A logic low signal on each enable pin deactivates the output. MIC23250 features built-in soft-start circuitry that reduces in-rush current and prevents the output voltage from overshooting at start up. SW1/SW2 The switching pin (SW1 or SW2) connects directly to one end of the inductor (L1 or L2) and provides the current path during switching cycles. The other end of the inductor is connected to the load and SNS pin. Due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes. SNS1/SNS2 The SNS pin (SNS1 or SNS2) is connected to the output of the device to provide feedback to the control circuitry. A minimum of 2.2F bypass capacitor should be connected in shunt with each output. Based upon size, performance and cost, a TDK C1608X5R0J475K, size 0603, 4.7F ceramic capacitor is highly recommended for most applications. In order to reduce parasitic inductance, it is good practice to place the output bypass capacitor as close to the inductor as possible. The SNS connection should be placed close to the output bypass capacitor. Refer to the layout recommendations for more details. PGND The power ground (PGND) is the ground path for the high current in PWM mode. The current loop for the power ground should be as small as possible and separate from the Analog ground (AGND) loop. Refer to the layout recommendations for more details. AGND The signal ground (AGND) is the ground path for the biasing and control circuitry. The current loop for the signal ground should be separate from the Power ground (PGND) loop. Refer to the layout recommendations for more details. FB1/FB2 (Adjustable Output Only) The feedback pins (FB1/FB2) are two extra pins that can only be found on the MIC23250-AAYMT devices. It allows the regulated output voltage to be set by applying an external resistor network. The internal reference voltage is 0.72V and the recommended value of RBOTTOM is within 10% of 442k. The RTOP resistor is the resistor from the FB pin to the output of the device and RBOTTOM is the resistor from the FB pin to ground. The output voltage is calculated from the equation below. See Compensation under the Applications Information section for recommended feedback component values.
RTOP VOUT = 0.72V + 1 R BOTTOM
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Micrel, Inc.
MIC23250
Applications Information
The MIC23250 is designed for high performance with a small solution size. With a dual 400mA output inside a tiny 2mm x 2mm Thin MLF(R) package and requiring only six external components, the MIC23250 meets today's miniature portable electronic device needs. While small solution size is one of its advantages, the MIC23250 is big in performance. Using the HyperLight LoadTM switching scheme, the MIC23250 is able to maintain high efficiency throughout the entire load range while providing ultra-fast load transient response. Even with all the given benefits, the MIC23250 can be as easy to use as linear regulators. The following sections provide an over view of implementing MIC23250 into related applications Input Capacitor A minimum of 2.2F ceramic capacitor should be placed close to the VIN pin and PGND pin for bypassing. A TDK C1608X5R0J475K, size 0603, 4.7F ceramic capacitor is recommended based upon performance, size and cost. A X5R or X7R temperature rating is recommended for the input capacitor. Y5V temperature rating capacitors, aside from losing most of their capacitance over temperature, can also become resistive at high frequencies. This reduces their ability to filter out high frequency noise. Output Capacitor The MIC23250 was designed for use with a 2.2F or greater ceramic output capacitor. Increasing the output capacitance will lower output ripple and improve load transient response but could increase solution size or cost. A low equivalent series resistance (ESR) ceramic output capacitor such as the TDK C1608X5R0J475K, size 0603, 4.7F ceramic capacitor is recommended based upon performance, size and cost. Either the X7R or X5R temperature rating capacitors are recommended. The Y5V and Z5U temperature rating capacitors, aside from the undesirable effect of their wide variation in capacitance over temperature, become resistive at high frequencies. Inductor Selection Inductor selection will be determined by the following (not necessarily in the order of importance); * * * Inductance Rated current value Size requirements
RBOTTOM
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 of the inductor does not cause it to saturate. Peak current can be calculated as follows:
1 - VOUT / VIN I PEAK = I OUT + VOUT 2 x f x L
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. Refer to the Application Circuit and Bill of Material for details. 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. Compensation The MIC23250 is designed to be stable with a 0.47H to 4.7H inductor with a minimum of 2.2F ceramic (X5R) output capacitor. For the adjustable MIC23250, the total feedback resistance should be kept around 1M to reduce current loss down the feedback resistor network. This helps to improve efficiency. A feed-forward capacitor (CFF) of 120pF must be used in conjunction with the external feedback resistors to reduce the effects of parasitic capacitance that is inherent of most circuit board layouts. Figure 1 and Table 1 shows the recommended feedback resistor values along with the recommended feed-forward capacitor values for the MIC23250 adjustable device.
RTOP
CFF
* DC resistance (DCR) The MIC23250 was designed for use with an inductance range from 0.47H to 4.7H. Typically, a 1H inductor is recommended for a balance of transient response, efficiency and output ripple. For faster transient response a 0.47H inductor may be used. For lower output ripple, a 4.7H is recommended.
Figure 1. Feedback Resistor Network
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MIC23250
VOUT (V) 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3
RTOP (k) 49 111 172 233 295 356 417 479 540 602 663 724 786 847 909 970 1031 1093 1154 1216 1277 1338 1400 1461 1522 1584
RBOTTOM (k) 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442 442
CFF (pF) 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120 120
There are two types of losses in switching converters; DC losses and switching losses. DC losses are simply the power dissipation of I2R. Power is dissipated in the high side switch during the on cycle. Power loss is equal to the high side MOSFET RDSON multiplied by the Switch Current squared. During the off cycle, the low side N-channel MOSFET conducts, also dissipating power. Device operating current also reduces efficiency. The product of the quiescent (operating) current and the supply voltage is another DC loss. The current required driving the gates on and off at a constant 4MHz frequency and the switching transitions make up the switching losses.
Efficiency V OUT = 1.8V
100 80 60 40 20 0 0.1 VIN = 2.7V VIN = 3.6V VIN = 3.3V
VOUT = 1.8V L = 1H 11 0 100 LOAD (mA) 1000
Table 1. Recommended Feedback Component Values
Efficiency Considerations Efficiency is defined as the amount of useful output power, divided by the amount of power supplied.
V x I OUT Efficiency % = OUT V xI IN IN
x 100
The Figure above shows an efficiency curve. From no load to 100mA, efficiency losses are dominated by quiescent current losses, gate drive and transition losses. By using the HyperLight LoadTM mode the MIC23250 is able to maintain high efficiency at low output currents. Over 100mA, efficiency loss is dominated by MOSFET RDSON and inductor losses. Higher input supply voltages will increase the Gate-to-Source threshold on the internal MOSFETs, thereby reducing the internal RDSON. This improves efficiency by reducing DC losses in the device. All but the inductor losses are inherent to the device. In which case, inductor selection becomes increasingly critical in efficiency calculations. As the inductors are reduced in size, the DC resistance (DCR) can become quite significant. The DCR losses can be calculated as follows: DCR Loss = IOUT2 x DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows:
Maintaining high efficiency serves two purposes. It reduces power dissipation in the power supply, reducing the need for heat sinks and thermal design considerations and it reduces consumption of current for battery powered applications. Reduced current draw from a battery increases the devices operating time and is critical in hand held devices. June 2010
VOUT x I OUT Efficiency Loss = 1 - V x I OUT + L _ PD OUT
x 100
Efficiency loss due to DCR is minimal at light loads and gains significance as the load is increased. Inductor selection becomes a trade-off between efficiency and size in this case.
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Micrel, Inc. HyperLight Load ModeTM The MIC23250 uses a minimum on and off time proprietary control loop (patented by Micrel). When the output voltage falls below the regulation threshold, the error comparator begins a switching cycle that turns the PMOS on and keeps it on for the duration of the minimumon-time. This increases the output voltage. If the output voltage is over the regulation threshold, then the error comparator turns the PMOS off for a minimum-off-time until the output drops below the threshold. The NMOS acts as an ideal rectifier that conducts when the PMOS is off. Using a NMOS switch instead of a diode allows for lower voltage drop across the switching device when it is on. The asynchronous switching combination between the PMOS and the NMOS allows the control loop to work in discontinuous mode for light load operations. In discontinuous mode, the MIC23250 works in pulse frequency modulation (PFM) to regulate the output. As the output current increases, the off-time decreases, thus providing more energy to the output. This switching scheme improves the efficiency of MIC23250 during light load currents by only switching when it is needed. As the load current increases, the MIC23250 goes into continuous conduction mode (CCM) and switches at a frequency centered at 4MHz. The equation to calculate the load when the MIC23250 goes into continuous conduction mode may be approximated by the following formula:
(V - VOUT ) x D I LOAD > IN 2L x f
MIC23250 As shown in the previous equation, the load at which MIC23250 transitions from HyperLight LoadTM mode to PWM mode is a function of the input voltage (VIN), output voltage (VOUT), duty cycle (D), inductance (L) and frequency (f). This is illustrated in the graph below. Since the inductance range of MIC23250 is from 0.47H to 4.7H, the device may then be tailored to enter HyperLight LoadTM mode or PWM mode at a specific load current by selecting the appropriate inductance. For example, in the graph below, when the inductance is 4.7H the MIC23250 will transition into PWM mode at a load of approximately 5mA. Under the same condition, when the inductance is 1H, the MIC23250 will transition into PWM mode at approximately 70mA.
Switching Frequency vs. Output Current
L = 4.7H
10
4MHz
1 L = 1H L = 2.2H 0.1 VIN = 3.6V VOUT = 1.8V COUT = 4.7F 0 100 1000 OUTPUT CURRENT (mA)
0.01 11
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MIC23250
MIC23250 Typical Application Circuit (Fixed Output)
Bill of Materials
Item Part Number Manufacturer Description Qty
C1, C2, C3 C4 R1, R2
C1608X5R0J475K VJ0603Y103KXXAT CRCW06031002FKEA LQM21PN1R0MC0D LQH32CN1R0M33 LQM31PN1R0M00
TDK
(1) (2)
4.7F Ceramic Capacitor, 6.3V, X5R, Size 0603 0.01F Ceramic Capacitor, 25V, X7R, Size 0603 10k, 1%, 1/16W, Size 0603 1H, 0.8A, 190m, L2mm x W1.25mm x H0.5mm 1H, 1A, 60m, L3.2mm x W2.5mm x H2.0mm 1H, 1.2A, 120m, L3.2mm x W1.6mm x H0.95mm 1H, 0.8A, 100m, L2.5mm x W1.8mm x H1.35mm 0.47H, 1.4A, 80m, L3.2mm x W1.6mm x H0.85mm 1.5H, 1.5A, 70m, L2.5mm x W2mm x H1.0mm
(5)
3 1 Optional
Vishay
Vishay(2) Murata(3) Murata TDK FDK
(3)
Murata(3)
(1) (3)
L1, L2
GLF251812T1R0M LQM31PNR47M00 MIPF2520D1R5 EPL2010-102
2
Murata
(4)
Coilcraft
1.0H, 1.0A, 86m, L2.0mm x W1.8mm x H1.0mm
4MHz Dual 400mA Fixed Output Buck Regulator with HyperLight LoadTM Mode 1
U1
MIC23250-xxYMT
Micrel, Inc.(6)
Notes: 1. TDK: www.tdk.com. 2. Vishay: www.vishay.com. 3. Murata: www.murata.com. 4. FDK: www.fdk.co.jp. 5. Coilcraft: www.coilcraft.com. 6. Micrel, Inc: www.micrel.com.
June 2010
15
M9999-061110-E
Micrel, Inc.
MIC23250
PCB Layout Recommendations (Fixed Output)
Top Layer
Bottom Layer
June 2010
16
M9999-061110-E
Micrel, Inc.
MIC23250
MIC23250 Typical Application Circuit (Adjustable Output)
Bill of Materials
Item Part Number Manufacturer Description Qty
C1, C2, C3 C4 C5, C6 R1, R2 R3, R5 R4, R6
C1608X5R0J475K VJ0603Y103KXXAT VJ0603Y121KXAAT CRCW06031002FKEA CRCW06036653FKEA CRCW06034423FKEA LQM21PN1R0MC0D LQH32CN1R0M33 LQM31PN1R0M00
TDK(1) Vishay
(2) (2)
4.7F Ceramic Capacitor, 6.3V, X5R, Size 0603 0.01F Ceramic Capacitor, 25V, X7R, Size 0603 120pF Ceramic Capacitor, 50V, X7R, Size 0603 10k, 1%, 1/16W, Size 0603 665k, 1%, 1/16W, Size 0603 442k, 1%, 1/16W, Size 0603 1H, 0.8A, 190m, L2mm x W1.25mm x H0.5mm 1H, 1A, 60m, L3.2mm x W2.5mm x H2.0mm 1H, 1.2A, 120m, L3.2mm x W1.6mm x H0.95mm 1H, 0.8A, 100m, L2.5mm x W1.8mm x H1.35mm 0.47H, 1.4A, 80m, L3.2mm x W1.6mm x H0.85mm 1.5H, 1.5A, 70m, L2.5mm x W2mm x H1.0mm
(5)
3 1 2 Optional 2 2
Vishay
Vishay(2) Vishay(2) Vishay
(2) (3)
Murata Murata TDK
Murata(3)
(3) (1)
L1, L2
GLF251812T1R0M LQM31PNR47M00 MIPF2520D1R5 EPL2010-102
2
Murata(3) FDK(4) Coilcraft
1.0H, 1.0A, 86m, L2.0mm x W1.8mm x H1.0mm
4MHz Dual 400mA Adjustable Output Buck Regulator with HyperLight LoadTM Mode 1
U1
Notes:
MIC23250-AAYMT
Micrel, Inc.(6)
1. TDK: www.tdk.com. 2. Vishay: www.vishay.com. 3. Murata: www.murata.com. 4. FDK: www.fdk.co.jp. 5. Coilcraft: www.coilcraft.com. 6. Micrel, Inc: www.micrel.com.
June 2010
17
M9999-061110-E
Micrel, Inc.
MIC23250
PCB Layout Recommendations (Adjustable Output)
Top Layer
Bottom Layer
June 2010
18
M9999-061110-E
Micrel, Inc.
MIC23250
Package Information (Fixed Output)
10-Pin 2mm x 2mm Thin MLF (MT)
(R)
June 2010
19
M9999-061110-E
Micrel, Inc.
MIC23250
Package Information (Adjustable Output)
(R) 12-Pin 2.5mm x 2.5mm Thin MLF (MT)
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) 2007 Micrel, Incorporated.
June 2010
20
M9999-061110-E

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