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MIC22700
1MHz, 7A Integrated Switch High Efficiency Synchronous Buck Regulator
General Description
The Micrel MIC22700 is a high efficiency 7A Integrated switch synchronous buck (step-down) regulator. The MIC22700 is optimized for highest efficiency, achieving more than 95% efficiency while still switching at 1MHz over a broad range. The device works with a small 1H inductor and 100F output capacitor. The ultra-high speed control loop keeps the output voltage within regulation even under extreme transient load swings commonly found in FPGAs and low voltage ASICs. The output voltage can be adjusted down to 0.7V to address all low voltage power needs. The MIC22700 offers a full range of sequencing and tracking options. The Enable/Delay pin combined with the Power Good/POR pin allows multiple outputs to be sequenced in any way during turn-on and turn-off. The RC (Ramp ControlTM) pin allows the device to be connected to another product in the MIC22xxx and/or MIC68xxx family, to keep the output voltages within a certain V on start up. The MIC22700 is available in a 24-pin 4mm x 4mm MLF(R) 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
* * * * * * * * * * * * * Input voltage range: 2.6V to 5.5V Output voltage adjustable down to 0.7V Output load current up to 7A Full sequencing and tracking capability Power on Reset/Power Good output Efficiency > 95% across a broad load range Ultra fast transient response - Easy RC compensation 100% maximum duty cycle Fully integrated MOSFET switches Micropower shutdown Thermal shutdown and current limit protection 24-pin 4mm x 4mm MLF(R) -40C to +125C junction temperature range
Applications
* * * * * * High power density point of load conversion Servers and routers DVD recorders / Blu-Ray players Computing peripherals Base stations FPGAs, DSP and low voltage ASIC power
Typical Application
Efficiency @ 3.3VOUT
100 95 90 85 80 75 70 65 60 55 VIN = 5.5V 1 2 3 4 5 6 LOAD CURRENT (A) 7
MIC22700 7A 1MHz Synchronous Output Converter
50 0
Sequencing & Tracking
Ramp Control 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
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MIC22700
Ordering Information
Part Number MIC22700YML
(R)
Voltage Adj.
Junction Temp. Range -40 to +125C
Package 24-Pin 4x4 MLF
(R)
Lead Finish Pb-Free
Note: MLF is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configuration
PGND PGND PVIN SVIN EP SGND COMP FB PVIN SW SW SW PGND SW PGND SW SW SW SW
PVIN EN DELAY RC POR/PG PVIN
24-Pin 4mm x 4mm MLF(R) (ML)
Pin Description
Pin Number 1, 6, 13, 18 17 2 Pin Name PVIN SVIN EN Description Power Supply Voltage (Input): Requires bypass capacitor to GND. Signal Power Supply Voltage (Input): Requires bypass capacitor-to-GND. Enable/Delay (Input): When this pin is pulled higher than the enable threshold, the part will start up. Below this voltage the device is in its low quiescent current mode. The pin has a 1A current source charging it to VIN. By adding a capacitor to this pin a delay may easily be generated. The enable function will not operate with an input voltage lower than the min specified. Ramp Control: Capacitor to ground from this pin determines slew rate of output voltage during start-up. This can be used for tracking capability as well as soft start. Feedback: Input to the error amplifier, connect to the external resistor divider network to set the output voltage. Compensation pin (Input): Place a RC to GND to compensate the device, see applications section. Power On Reset (Output): Open-drain output device indicates when the output is out of regulation and is active after the delay set by the delay pin. Power Ground: Ground Signal Ground: Ground Delay (Input): Capacitor to ground sets internal delay timer. Timer delays poweron reset (POR) output at turn-on and ramp down at turn-off. Switch (Output): Internal power MOSFET output switches. Exposed Pad (Power): Must make a full connection to a GND plane for full output power to be realized.
4
RC
14 15 5 7, 12, 19, 24 16 3 8, 9, 10, 11, 20, 21, 22, 23 EP
FB COMP POR/PG PGND SGND DELAY SW GND
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Absolute Maximum Ratings(1)
Supply Voltage (VIN) .......................................... -0.3V to 6V Output Switch Voltage (VSW) ............................. -0.3V to 6V Output Switch Current (ISW).......................Internally Limited Logic Input Voltage (VEN VFLG) .......................... -0.3V to VIN Storage Temperature (Ts) .........................-65C to +150C ESD Rating(3) .................................................................. 2kV Lead Temperature (Soldering 10sec) ........................ 260C
Operating Ratings(2)
Supply Voltage (VIN)......................................... 2.6V to 5.5V Junction Temperature (TJ) ..................-40C TJ +125C Thermal Resistance 4x4 MLF-24 (JC) ...............................................14C/W 4x4 MLF-24 (JA) ...............................................40C/W
Electrical Characteristics(4)
TA = 25C with VIN = VEN = 3.3V; VOUT = 1.8V, unless otherwise specified. Bold values indicate -40C< TJ < +125C.
Parameter Supply Voltage Range Under-Voltage Lockout Threshold UVLO Hysteresis Quiescent Current, PWM Mode Shutdown Current [Adjustable] Feedback Voltage FB Pin Input Current Current Limit Output Voltage Line Regulation Output Voltage Load Regulation Maximum Duty Cycle Switch ON-Resistance PFET Switch ON-Resistance NFET Oscillator Frequency EN/DLY Threshold Voltage EN/DLY Source Current RC Pin IRAMP Power On Reset IPG(LEAK) Power On Reset VPG(LO) Power On Reset VPG Over-Temperature Shutdown Over-Temperature Shutdown Hysteresis
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. 4. Specification for packaged product only.
Condition (turn-on) VEN =>1.34V; VFB = 0.9V (not switching) VEN = 0V 2% (over temperature) VFB = 0.5 VOUT 1.8V; VIN = 2.6 to 5.5V, ILOAD= 100mA 100mA < ILOAD < 7A, VIN = 3.3V VFB 0.5V ISW = 1000mA; VFB=0.5V ISW = 1000mA; VFB=0.9V
Min 2.6 2.4
Typ 2.5 280 850 5 0.7 1 10.5 0.2 0.2 0.03 0.025 1 1.24 1 1
Max 5.5 2.6 1300 10 0.714 14
Units V V mV A A V nA A % % % MHz V A A A A mV
0.686 7
100
VIN = 2.6 to VIN = 5.5V Ramp Control Current VPORH = 5.5V; POR = High Output Logic-Low Voltage (undervoltage condition), IPOR = 5mA Threshold, % of VOUT below nominal Hysteresis
0.8 1.14 0.7 0.7
1.2 1.34 1.3 1.3 1 2
130 7.5 10 2 160 20 12.5
% % C C
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Typical Characteristics
10 SHUTDOWN CURRENT (A) 8 6 4 2 0
Shutdown Current vs. Temperature
QUIESCENT CURRENT (A)
FEEDBACK VOLTAGE (V)
EN = 0V VIN = 3.3V
900
Quiescent Current vs. Temperature
EN > 1.34V 890 V = 0.9V FB 880 V = 3.3V IN 870 No Switching 860 850 840 830 820 810 -40 -25 -10 5 20 35 50 65 80 95 110 125 800
0.6990 0.6989 0.6988 0.6987 0.6986 0.6985 0.6984 0.6983 0.6982 0.6981
Feedback Voltage vs. Input Voltage
EN = V V
IN IN
= 3.3V
AMB = 25C
-40 -25 -10 5 20 35 50 65 80 95 110 125
0.6980 2.5
TEMPERATURE (C)
TEMPERATURE (C)
3 3.5 4 4.5 5 INPUT VOLTAGE (V)
5.5
0.701 FEEDBACK VOLTAGE (V) 0.700 0.699 0.698 0.697 0.696 0.695 V
IN
Feedback Voltage vs. Temperature
1.245 ENABLE VOLTAGE (V) 1.244 1.243 1.242 1.241 1.24 1.239 1.238 1.237 1.236 1.235
Enable Voltage vs. Temperature
ENABLE HYSTERESIS (V) VIN = 3.3V
0.0100 0.0095 0.0090 0.0085 0.0080 0.0075 0.0070 0.0065 0.0060 0.0055
Enable Hysteresis vs. Temperature
V
IN
= 3.3V
= 3.3V
IN
EN = V
-40 -25 -10 5 20 35 50 65 80 95 110 125
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (C)
TEMPERATURE (C)
1020 1015 FREQUENCY (kHz) 1010 1005 1000 995 990 985
Frequency vs. Temperature
VIN = 3.3V EN = V
IN
Frequency vs. Input Voltage
1040 FREQUENCY (kHz) 1030 1020 1010 1000 990 980 2.5 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5 EN = V
IN
-40 -25 -10 5 20 35 50 65 80 95 110 125
980
TEMPERATURE (C)
40 EN = VIN 38 36 34 32 30 28 26 24 22 20 2.5 3 3.5 4 4.5 5 INPUT VOLTAGE (V)
RDSON (mOhm)
Quiescent Current vs. Input Voltage
1200 QUIESCENT CURRENT (A) 1100 1000 900 800 700 600 2.5 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5 SHUTDOWN CURRENT (A) EN > 1.34V VFB = 0.9V No Switching
7.0 6.5 6.0 5.5 5.0 4.5 4.0 2.5
Shutdown Current vs. Input Voltage
EN = 0V
3 3.5 4 4.5 5 INPUT VOLTAGE (V)
5.5
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-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
0.0050
P-Channel R DSON vs. Input Voltage
5.5
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Typical Characteristics (continued)
Efficiency @ 1.2V OUT
100 95 90 85 80 75 70 65 60 55 50 0 2.6VIN 3.3VIN 5.5VIN 100 95 90 85 80 75 70 65 60 55 50 0
Efficiency @ 1.8V OUT
2.6VIN 5.5VIN 3.3VIN 100 95 90 85 80 75 70 65 60
Efficiency @ 3.3VOUT
1
2 3 4 5 6 LOAD CURRENT (A)
7
1
2 3 4 5 6 LOAD CURRENT (A)
7
55 VIN = 5.5V 50 0 1 2 3 4 5 6 LOAD CURRENT (A)
7
100 80 60 40 20 0 -20 -40 -60 -80 -100 100
Bode Plot (VIN - 3.6V, VO - 1.8V)
250 200 150 100 50 0 -50 -100 -150 -200
100 80 60 40 20 0 -20 -40 -60 -80 -100 100
Bode Plot (VIN - 5.5V, VO - 1.8V)
250 200 150 100 50 0 -50 -100 -150 -200
100 80 60 40 20 0 -20 -40 -60 -80 -100 100
Bode Plot (VIN - 5.0V, VO - 3.3V)
250 200 150 100 50 0 -50 -100 -150 -200 -250 1M
1k 10k 100k FREQUENCY (Hz)
-250 1M
1k 10k 100k FREQUENCY (Hz)
-250 1M
1k 10k 100k FREQUENCY (Hz)
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Functional Characteristics
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Functional Characteristics (continued)
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Typical Circuits and Waveforms
Sequencing Circuit and Waveform
Tracking Circuit and Waveform
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Functional Diagram
Figure 1. MIC22700 Block Diagram
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Functional Description
PVIN, SVIN PVIN is the input supply to the internal 30m P-Channel Power MOSFET. This should be connected externally to the SVIN pin. The supply voltage range is from 2.6V to 5.5V. A 22F ceramic is recommended for bypassing each PVIN supply. EN/DLY This pin is internally fed with a 1A current source to VIN. A delayed turn on is implemented by adding a capacitor to this pin. The delay is proportional to the capacitor value. The internal circuits are held off until EN/DLY reaches the enable threshold of 1.24V. RC RC allows the slew rate of the output voltage to be programmed by the addition of a capacitor from RC to ground. RC is internally fed with a 1A current source and VOUT slew rate is proportional to the capacitor and the 1A source. Delay Adding a capacitor to this pin allows the delay of the POR signal. When VOUT reaches 90% of its nominal voltage, the Delay pin current source (1A) starts to charge the external capacitor. At 1.24V, POR is asserted high. Comp The MIC22700 uses an internal compensation network containing a fixed frequency zero (phase lead response) and pole (phase lag response) which allows the external compensation network to be much simplified for stability. The addition of a single capacitor and resistor will add the necessary pole and zero for voltage mode loop stability using low value, low ESR ceramic capacitors. FB The feedback pin provides the control path to control the output. A resistor divider connecting the feedback to the output is used to adjust the desired output voltage. Refer to the feedback section in the "Applications Information" for more detail. POR This is an open drain output. A 47.5k resistor can be used for a pull up to this pin. POR is asserted high when output voltage reaches 90% of nominal set voltage and after the delay set by CDLY. POR is asserted low without delay when enable is set low or when the output goes below the -10% threshold. For a Power Good (PG) function, the delay can be set to a minimum. This can be done by removing the Delay capacitor. SW This is the connection to the drain of the internal PChannel MOSFET and drain of the N-Channel MOSFET. This is a high frequency high power connection; therefore traces should be kept as short and as wide as practical. SGND Internal signal ground for all low power sections. PGND Internal ground connection to the source of the internal N-Channel MOSFETs.
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MIC22700 performance, the inductor should be placed very close to the SW nodes of the IC. For this reason, the heat of the inductor is somewhat coupled to the IC, so it offers some level of protection if the inductor gets too hot. It is important to test all operating limits before settling on the final inductor choice. The size requirements refer to the area and height requirements that are necessary to fit a particular design. Please refer to the inductor dimensions on their datasheet. DC resistance is also important. While DCR is inversely proportional to size, DCR can represent a significant efficiency loss. Refer to the "Efficiency Considerations" below for a more detailed description. Enable/DLY Capacitor Enable/DLY sources 1A out of the IC to allow a startup delay to be implemented. The delay time is simply the time it takes 1A to charge CDLY to 1.25V. Therefore:
TDLY = 1.24 C DLY 1 x 10 -6
Application Information
The MIC22700 is a 7A Synchronous step down regulator IC with a fixed 1 MHz, voltage mode PWM control scheme. The other features include tracking and sequencing control for controlling multiple output power systems, power on reset.
Component selection
Input Capacitor A minimum 22F ceramic is recommended on each of the PVIN pins for bypassing. X5R or X7R dielectrics are recommended for the input capacitor. Y5V dielectrics, aside from losing most of their capacitance over temperature, they also become resistive at high frequencies. This reduces their ability to filter out high frequency noise. Output Capacitor The MIC22700 was designed specifically for the use of ceramic output capacitors. 100F can be increased to improve transient performance. Since the MIC22700 is in voltage mode, the control loop relies on the inductor and output capacitor for compensation. For this reason, do not use excessively large output capacitors. The output capacitor requires either an X7R or X5R dielectric. Y5V and Z5U dielectric capacitors, aside from the undesirable effect of their wide variation in capacitance over temperature, become resistive at high frequencies. Using Y5V or Z5U capacitors can cause instability in the MIC22700. Inductor Selection Inductor selection will be determined by the following (not necessarily in the order of importance): * * * * Inductance Rated current value Size requirements
Efficiency considerations Efficiency is defined as the amount of useful output power, divided by the amount of power consumed.
V xI Efficiency % = OUT OUT V xI IN IN x 100
DC resistance (DCR) The MIC22700 is designed for use with a 0.47H to 4.7H inductor. 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% 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 that the peak current will not saturate the inductor. The ripple can add as much as 1.2A to the output current level. The RMS rating should be chosen to be equal or greater than the Current Limit of the MIC22700 to prevent overheating in a fault condition. For best electrical July 2009 11
Maintaining high efficiency serves two purposes. It decreases power dissipation in the power supply, reducing the need for heat sinks and thermal design considerations and it decreases consumption of current for battery powered applications. Reduced current draw from a battery increases the devices operating time, critical in hand held devices. There are mainly two loss terms in switching converters: static losses and switching losses. Static losses are simply the power losses due to VI or I2R. For example, power is dissipated in the high side switch during the on cycle. Power loss is equal to the high side MOSFET RDS(ON) multiplied by the RMS Switch Current squared (ISW2). During the off cycle, the low side N-Channel MOSFET conducts, also dissipating power. Similarly, the inductor's DCR and capacitor's ESR also contribute to the I2R losses. Device operating current also reduces efficiency by the product of the quiescent (operating) current and the supply voltage. The current required to drive the gates on and off at a constant 1MHz or 4MHz frequency and the switching transitions make up the switching losses.
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Micrel, Inc. Figure 2 shows an efficiency curve. The portion, from 0A to 1A, efficiency losses are dominated by quiescent current losses, gate drive and transition losses. In this case, lower supply voltages yield greater efficiency in that they require less current to drive the MOSFETs and have reduced input power consumption.
Efficiency
100 95 90 85 80 75 70 65 60 55 50 0 1 2 3 4 5 6 LOAD CURRENT (A) 7 VIN = 3.3V VOUT = 1.8V
MIC22700
Efficiency vs. Inductance
95 90 85 80 75 70 65 60 55 50 0
L = 1H L = 4.7H
200 400 600 800 OUTPUT CURRENT (mA)
Figure 3. Efficiency vs. Inductance
Figure 2. Efficiency Curve
The region, 1A to 7A, efficiency loss is dominated by MOSFET RDS(ON) and inductor DC losses. Higher input supply voltages will increase the Gate-to-Source voltage on the internal MOSFETs, reducing the internal RDS(ON). This improves efficiency by decreasing 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; LPD = IOUT2 x DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows:
VOUT I OUT Efficiency Loss = 1 - (V OUT I OUT ) + LPD 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. Alternatively, under lighter loads, the ripple current due to the inductance becomes a significant factor. When light load efficiencies become more critical, a larger inductor value maybe desired. Larger inductances reduce the peak-to-peak inductor ripple current, which minimize losses. The following graph in Figure 3 illustrates the effects of inductance value at light load.
Compensation The MIC22700 has a combination of internal and external stability compensation to simplify the circuit for small, high efficiency designs. In such designs, voltage mode conversion is often the optimum solution. Voltage mode is achieved by creating an internal 1MHz ramp signal and using the output of the error amplifier to modulate the pulse width of the switch node, thereby maintaining output voltage regulation. With a typical gain bandwidth of 100-200 kHz, the MIC22700 is capable of extremely fast transient responses. The MIC22700 is designed to be stable with a typical application using a 1H inductor and a 100F ceramic (X5R) output capacitor. These values can be varied dependant upon the tradeoff between size, cost and efficiency, keeping the LC natural frequency 1 ( ) ideally less than 26 kHz to ensure 2x x L C stability can be achieved. The minimum recommended inductor value is 0.47H and minimum recommended output capacitor value is 22F. The tradeoff between changing these values is that with a larger inductor, there is a reduced peak-to-peak current which yields a greater efficiency at lighter loads. A larger output capacitor will improve transient response by providing a larger hold up reservoir of energy to the output. The integration of one pole-zero pair within the control loop greatly simplifies compensation. The optimum values for CCOMP (in series with a 20k resistor) are shown below.
C L 0.47H 1H 2.2H
22-47F 0*-10pF 0 -15pF 15-33pF
47F100F 22pF 15-22pF 33-47pF
100F470F 33pF 33pF 100-220pF
* VOUT > 1.2V, VOUT > 1V
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Micrel, Inc. Feedback The MIC22700 provides a feedback pin to adjust the output voltage to the desired level. This pin connects internally to an error amplifier. The error amplifier then compares the voltage at the feedback to the internal 0.7V reference voltage and adjusts the output voltage to maintain regulation. The resistor divider network for a desired VOUT is given by:
R2 = R1 VOUT - 1 V REF
MIC22700 Enable/DLY pin The Enable pin contains a trimmed, 1A current source which can be used with a capacitor to implement a fixed desired delay in some sequenced power systems. The threshold level for power on is 1.24V with a hysteresis of 20mV. Delay Pin The Delay pin also has a 1A trimmed current source and a 1A current sink which acts with an external capacitor to delay the operation of the Power On Reset (POR) output. This can be used also in sequencing outputs in a sequenced system, but with the addition of a conditional delay between supplies; allowing a first up, last down power sequence. After Enable is driven high, VOUT will start to rise (rate determined by RC capacitor). As the FB voltage goes above 90% of its nominal set voltage, Delay begins to rise as the 1A source charges the external capacitor. When the threshold of 1.24V is crossed, POR is asserted high and Delay continues to charge to a voltage VDD. When FB falls below 90% of nominal, POR is asserted low immediately. However, if enable is driven low, POR will fall immediately to the low state and Delay will begin to fall as the external capacitor is discharged by the 1A current sink. When the threshold of VDD1.24V is crossed, VOUT will begin to fall at a rate determined by the RC capacitor. As the voltage change in both cases is 1.24V, both rising and falling delays are 1.24 C DLY matched at TPOR = 1 x 10 - 6 RC pin The RC pin provides a trimmed 1A current source/sink similar to the Delay Pin for accurate ramp up (soft start) and ramp down control. This allows the MIC22700 to be used in systems requiring voltage tracking or ratio-metric voltage tracking at startup. There are two ways of using the RC pin: 1. Externally driven from a voltage source 2. Externally attached capacitor sets output ramp up/down rate In the first case, driving RC with a voltage from 0V to VREF will program the output voltage between 0 and 100% of the nominal set voltage. In the second case, the external capacitor sets the ramp up and ramp down time of the output voltage. The time 0.7 C RC where TRAMP is the time is given by TRAMP = 1 x 10 - 6 from 0 to 100% nominal output voltage.
where VREF is 0.7V and VOUT is the desired output voltage. A 10k or lower resistor value from the output to the feedback is recommended since large feedback resistor values increase the impedance at the feedback pin, making the feedback node more susceptible to noise pick-up. A small capacitor (50pF - 100pF) across the lower resistor can reduce noise pick-up by providing a low impedance path to ground. PWM Operation The MIC22700 is a voltage mode, pulse width modulation (PWM) controller. By controlling the ratio of on-to-off time, or duty cycle, a regulated DC output voltage is achieved. As load or supply voltage changes, so does the duty cycle to maintain a constant output voltage. In cases where the input supply runs into a dropout condition, the MIC22700 will run at 100% duty cycle. The MIC22700 provides constant switching at 1MHz with synchronous internal MOSFETs. The internal MOSFETs include a high-side P-Channel MOSFET from the input supply to the switch pin and an N-Channel MOSFET from the switch pin-to-ground. Since the low-side NChannel MOSFET provides the current during the off cycle, very low power is dissipated during the off period. PWM control provides fixed frequency operation. By maintaining a constant switching frequency, predictable fundamental and harmonic frequencies are achieved. Other methods of regulation, such as burst and skip modes, have frequency spectrums that change with load that can interfere with sensitive communication equipment. Sequencing and tracking The MIC22700 provides additional pins to provide up/down sequencing and tracking capability for connecting multiple voltage regulators together.
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Micrel, Inc. Sequencing & Tracking examples There are four distinct variations which are easily implemented using the MIC22700. The two sequencing variations are Delayed and Windowed. The two tracking variants are Normal and Ratio Metric. The following diagrams illustrate methods for connecting two MIC22700's to achieve these requirements. Sequencing: Normal Tracking:
MIC22700
Ratio Metric Tracking:
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MIC22700 Current Limit The MIC22700 is protected against overload in two stages. The first is to limit the current in the P-channel switch; the second is over temperature shutdown. Current is limited by measuring the current through the high side MOSFET during its power stroke and immediately switching off the driver when the preset limit is exceeded. The circuit in Figure 4 describes the operation of the current limit circuit. Since the actual RDSON of the PChannel MOSFET varies part-to-part, over temperature and with input voltage, simple IR voltage detection is not employed. Instead, a smaller copy of the Power MOSFET (Reference FET) is fed with a constant current which is a directly proportional to the factory set current limit. This sets the current limit as a current ratio and thus, is not dependant upon the RDSON value. Current limit is set to nominal value. Variations in the scale factor K between the Power PFET and the reference PFET used to generate the limit threshold account for a relatively small inaccuracy.
An alternative method here shows an example of a VDDQ & VTT solution for a DDR memory power supply. Note that POR is taken from Vo1 as POR2 will not go high. This is because POR is set high when FB > 0.9VREF. In this example, FB2 is regulated to 1/2VREF.
Figure 4. Current Limit Detail
Thermal Considerations The MIC22700 is packaged in the MLF(R) 4mm x 4mm, a package that has excellent thermal performance equaling that of the larger TSSOP packages. This maximizes heat transfer from the junction to the exposed pad (ePAD) which connects to the ground plane. The size of the ground plane attached to the exposed pad determines the overall thermal resistance from the junction to the ambient air surrounding the printed circuit board. The junction temperature for a given ambient temperature can be calculated using: TJ = TAMB + PDISS * RJA Where * PDISS is the power dissipated within the MLF(R) package and is typically 1.5W at 7A load. This has been calculated for a 1H inductor and details can be found in table 1 below for reference.
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MIC22700 Example: The Evaluation board has two copper planes contributing to an RJA of approximately 25C/W. The worst case RJC of the MLF 4x4 is 14oC/W. RJA = RJC + RCA RJA = 14 + 25 = 39oC/W To calculate the junction temperature for a 50C ambient: TJ = TAMB+PDISS . RJA TJ = 50 + (1.5 x 39) TJ = 109C This is below the maximum of 125C.
*
RJA is a combination of junction to case thermal resistance (RJC) and Case-to-Ambient thermal resistance (RCA), since thermal resistance of the solder connection from the ePAD to the PCB is negligible; RCA is the thermal resistance of the ground plane to ambient, so RJA = RJC + RCA.
VIN 2.6V 2.073 2.133 2.207 -- -- 3.3V 1.884 1.896 1.934 1.953 -- 3.6V 1.836 1.853 1.873 1.881 1.423 4.5V 1.784 1.786 1.814 1.797 1.79 5.5V 1.791 1.796 1.826 1.803 1.789
VOUT @7A 0.7V 1.2V 1.8V 2.5V 3.3V
Table 1. Power Dissipation (W) for 7A output
*
TAMB is the Operating Ambient temperature.
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Evaluation Board Schematic
Bill of Materials
Item C1, C2, C3, C4, C5 C7, C13 C6 Part Number C2012X5R0J226M 08056D226MAT GRM21BR60J226ME39L GRM188R71H103KA01D Open(VJ0603Y102KXQCW1BC) Open(GRM188R71H102KA01D) Open(C1608C0G1H102J) VJ0603Y102KXQCW1BC C8 GRM188R71H102KA01D C1608C0G1H102J C9 GRM1555C1H390JZ01D VJ0402A390KXQCW1BC C3216X5R0J476M C10, C11 GRM31CR60J476ME19 GRM31CC80G476ME19L C12 D1 L1 R1 VJ0402A101KXQCW1BC GRM1555C1H101JZ01D SS2P2L DFLS220 SPM6530T-1R0M120 HCP0704-1R0-R CRCW06031101FKEYE3 Manufacturer TDK(1) AVX(2) Murata
(3)
Description 22F/6.3V, 0805, Ceramic Capacitor 10nF, 0603, Ceramic Capacitor 1nF, 0603, Ceramic Capacitor 1000pF/50V, X7R, 0603, Ceramic Capacitor 1000pF/50V, COG, 0603, Ceramic Capacitor 1nF, 0603, Ceramic Capacitor, 1000pF/50V, X7R, 0603, Ceramic Capacitor 1000pF/50V, COG, 0603, Ceramic Capacitor 39pF/50V, COG, 0402, Ceramic Capacitor
Qty 5 1 1
Murata Vishay(4) Murata TDK Vishay Murata TDK Murata BC components TDK Murata Murata Vishay Murata Vishay Diodes, Inc.(6) TDK Coiltronics Vishay
(7) (5)
1
39pF /10V, 0402, Ceramic Capacitor 47F/6.3V, X5R, 1206, Ceramic Capacitor 47F/6.3V, X5R, 1206, Ceramic Capacitor 47F/4V, X6S, 1206, Ceramic Capacitor 100pF, 0603, Ceramic Capacitor 100pF/50V, COG, 0402, Ceramic Capacitor Schottky Diode, 2A, 20V 1H, 12A, size 7x6.5x3mm 1H, 12A, size 6.8x6.8x4.2mm Resistor, 1.1k, 0603, 1%
1
2
1 1 1 1
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Micrel, Inc.
Item R2 R3 R4 R5 Q1 Open(CMDPM7002A) U1
Notes:
1. 2. 3. 4. 5. 6. 7. 8. 9. TDK: www.tdk.com AVX: www.avx.com Murata: www.murata.com Vishay: www.vishay.com BC Components: www.bccomponents.com Diodes, Inc.: www.diodes.com Coiltronics:coiltronics.com Central Semiconductor: www.centralsemi.com
MIC22700
Part Number CRCW04026980FKEYE3 CRCW06034752FKEYE3 CRCW04022002FKEYE3 Open(CRCW06031003FRT1) Open(2N7002E) Manufacturer Vishay Vishay Vishay Vishay Vishay Central Semiconductor(8) Micrel(9) Signal MOSFET - SOT-23-6 Integrated 7A Synchronous Buck Regulator 1 1 Description Resistor, 698, 0603, 1% Resistor, 47.5k, 0603, 1% Resistor, 20k, 0402, 1% Resistor, 100k, 0603, 1% Qty 1 1 1 1
MIC22700YML
Micrel, Inc.: www.micrel.com
July 2009
18
M9999-072209-B
Micrel, Inc.
MIC22700
PCB Layout Recommendations
Top Silk
Top Layer
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Micrel, Inc.
MIC22700
Bottom Silk
Bottom Layer
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Micrel, Inc.
MIC22700
Package Information
24-Pin 4mm x 4mm MLF(R) (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) 2009 Micrel, Incorporated.
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