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MIC22601
4 MHz, 6A Integrated Switch Synchronous Buck Regulator
General Description
The Micrel MIC22601 is a high efficiency 6A Integrated switch synchronous buck (step-down) regulator. The MIC22601 is optimized for highest efficiency (greater than 90%), while still switching at 4MHz over a broad load range with only 0.22H inductor and down to 22F 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. A full range of sequencing and tracking options is available with the MIC22601. The enable/delay pin, combined with the power good PG/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 MIC22601 is available in a 24-pin 4mm x 4mm MLF(R) package with a junction operating temperature 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 4MHz PWM frequency Adjustable output voltage option down to 0.7V Output current to 6A Small Passive components: 0.22H and 22F Full sequence and tracking ability Power On Reset/Power Good Ultra fast transient response - Easy RC compensation 100% maximum duty cycle Fully integrated MOSFET switches Micro power shutdown Thermal shutdown and current limit protection 24-pin 4mmx4mm MLF(R) package -40C to +125C junction temperature range
Applications
* * * * * * High power density point of load conversion Servers and routers Blu-ray/DVD players and recorders Computer peripherals Base stations FPGA, DSP and low voltage ASIC power
_____________________________________________________________________________________________________________________________________
Typical Application
Efficiency vs. Load Current
100 90 80 70 60 50 40 0
VIN = 3.6V
VIN = 5V
VOUT = 3.3V TA = 25C L = 470nF 1 2 3 4 5 OUTPUT CURRENT (A) 6
Figure 1. Typical Application Circuit, 6A 4MHz Synchronous Output Converter
Ramp Control is a trademark of Micrel, Inc. MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.
Sequencing & Tracking
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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MIC22601
Ordering Information
Part Number MIC22601YML
(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 PVIN
24-Pin 4mm x 4mm MLF(R) (ML)
Pin Description
Pin Number 1, 6, 13, 18 17 2 Pin Name PVIN SVIN EN Pin Name Power Supply Voltage (Input): Requires bypass capacitor to GND. Signal Power Supply Voltage (Input): Requires bypass capacitor-toGND. Enable/Delay (Input): This pin has a 1.24V band gap reference. When the pin is pulled higher than this 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: A capacitor-to-ground from this pin determines the slew rate of the 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, refer to the 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. High when the Power is Good Power Ground (Signal): Ground Signal Ground (Signal): Ground Delay (Input): Add a capacitor to set the delay from FB reaching 90% nominal to POR asserting high. 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
FB COMP POR/PG
7, 12, 19, 24 16 3 8, 9, 10, 11, 20, 21, 22, 23 EP
PGND SGND DELAY SW GND
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Absolute Maximum Ratings(1)
Supply Voltage (VIN) .........................................................6V Output Switch Voltage (VSW) ............................................6V Output Switch Current (ISW).......................Internally Limited Logic Input Voltage (VEN, VLQ)........................... VIN to -0.3V Storage Temperature (Ts) .........................-65C to +150C Lead Temperature (soldering 10sec.)........................ 260C EDS Rating(3) ................................................................+2kV
Operating Ratings(2)
Supply Voltage (VIN)......................................... 2.6V to 5.5V Junction Temperature (TJ) ..................-40C TJ +125C Thermal Resistance 4mm x 4mm MLF-24 (JC) ................................. 14C/W 4mm x 4mm 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 22601 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 = 0.9*VNOM VOUT 1.8V; VIN = 2.6 to 5.5V, ILOAD= 100mA 100mA < ILOAD < 6000mA, 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 1 10 0.2 0.2 0.03 0.025 4 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 6
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
3.2 1.14 0.7 0.7
4.8 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 INPUT CURRENT (A) 9 8 7 6 5 4 3 2 1 TA = 25C 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 INPUT VOLTAGE (V)
Shutdown Current vs. Input Voltage
INPUT CURRENT (A)
10 9 8 7 6 5 4 3 2 1 -40
Shutdown Current vs. Temperature
INPUT CURRENT (mA)
Quiescent Current vs. Input Voltage
1.2
Not Switching FB = 1V
1.0 0.8 0.6 0.4 0.2 0 2.5
TA = 25C
VIN = 3.3V
-20
0
20
40
60
80
100
TEMPERATURE (C)
Quiescent Current vs. Temperature
1.0 REFERENCE VOLTAGE (V) INPUT CURRENT (mA) 0.9 Not Switching FB = 1V 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -40 -20 20 40 0 VIN = 3.3V 60 80 100 120 0.710 0.708 0.706 0.704 0.702 0.700 0.698 0.696 0.694 0.692 0.690 2.5
Reference Voltage vs. Input Voltage
REFERENCE VOLTAGE (V)
120
0
3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V)
5.5
0.710 0.708 0.706 0.704 0.702 0.700 0.698 0.696 0.694 0.692 -40 0.690
Reference Voltage vs. Temperature
TA = 25C 3 3.5 4 4.5 5 5.5 INPUT VOLTAGE (V) 6
VIN = 3.3V
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
1.3 1.28 ENABLE VOLTAGE (V) 1.26 1.24 1.22 1.2 1.18 1.16 1.14 1.12 1.1 2.5
Enable Level vs. Input Voltage
ENABLE VOLTAGE (V)
1.30 1.28 1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12 -40 -20
Enable Voltage vs. Temperature
4.8 4.6 FREQUENCY (MHz) 4.4 4.2 4 3.8 3.6 3.4 120 3.2 2.5
Switching Frequency vs. Input Voltage
TA = 25C 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5
VIN = 5.5V 0 20 40 60 80 100
TCASE = 25C
1.10
3
TEMPERATURE (C)
3.5 4 4.5 5 INPUT VOLTAGE (V)
5.5
4.8 4.6 FREQUENCY (MHz) 4.4
Switching Frequency vs. Temperature
P-Channel RDSON
45 40 35 RDSON (mO) 30 25 20 15 10 5 120 0 2.5 3 TCASE = 90C 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5
vs. Input Voltage
OUTPUT VOLTAGE (V)
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0
Output Voltage vs VRC
4.2 4.0 3.8 3.6 3.4 -40 -20 0 20 40 3.2
VIN = 3.3V
V
OUT
= 1.8V
60
80
TEMPERATURE (C)
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0.2
0.4 0.6 VRC (V)
0.8
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Typical Characteristics (continued)
100 90 80 70 60 50 40 0 VOUT = 3.3V TA = 25C L = 470nF 1 2 3 4 5 OUTPUT CURRENT (A) 6 VIN = 3.6V VIN = 5V
Efficiency vs. Load Current
100 90 80 70 60 50 40 0
Efficiency vs. Output Current
VIN = 2.5V VIN = 3.6V
100 90 80
Efficiency vs. Output Current
VIN = 3.3V
VIN = 5V
70 60 VOUT = 1.8V TA = 25C L = 470nF 50 6 40 0
VIN = 5V
VOUT = 1V L = 470nF 1 2 3 4 5 OUTPUT CURRENT (A) 6
1 2 3 4 5 OUTPUT CURRENT (A)
50 40 30 GAIN (dB) 20 10 0
Bode (5V to 1.8V - 6A) 470nH and 47F
Phase
180 144 108 72 GAIN (dB) 36 0
50 40 30 20 10 0
Bode (3.3V to 1.8V - 6A) 470nH and 47F
Phase
180 144 108 72 GAIN (dB) 36 0
50 40 30 20 10 0
Bode (5V to 3.3V - 6A) 470nH and 47F
Phase
180 144 108 72 36 0
Gain
Gain
Gain
100F OSCON on VIN 1 10 100 1000 10000 FREQUENCY (kHz) 1
100F OSCON on VIN 10 100 1000 10000 FREQUENCY (kHz) 1
100F OSCON on VIN 10 100 1000 10000 FREQUENCY (kHz)
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Functional Characteristics
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Typical Circuits and Waveforms
Sequencing Circuit and Waveform
Tracking Circuit and Waveform
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Functional Diagram
Figure 2. IC Block Diagram
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MIC22601 FB The feedback pin provides a 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 47k 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 CDELAY. 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 source 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. In order to achieve the highest efficiency and reduce internal losses, connect a Schottky diode directly from this pin-to-ground as close to the package as possible. SGND Internal signal ground for all low power sections. PGND Internal ground connection to the source of the internal N-Channel MOSFETs.
Functional Description
PVIN 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 10F 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-toground. 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 MIC22601 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 when using low value, low ESR ceramic capacitors.
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MIC22601 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, which 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 1uA out of the IC to allow a startup delay to be implemented. The delay time is simply the time it takes 1uA to charge CDLY to 1.24V. Therefore:
TDLY = 1.24 C DLY 1 10 -6
Application Information
The MIC22601 is a 6A Synchronous step down regulator IC with a fixed 4MHz, voltage mode PWM control scheme. The other features include tracking and sequencing control for controlling multiple output power systems. Power-on-reset and easy RC compensation are other features as well.
Component selection
Input Capacitor A minimum 10F 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 MIC22601 was designed specifically for the use of ceramic output capacitors. 47F can be increased to improve transient performance. Since the MIC22601 is 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 MIC22601. 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 MIC22601 is designed for use with a 0.22H 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 1A to the output current level. The RMS rating should be chosen to be equal or greater than the Current Limit of the MIC22601 to prevent overheating in a fault condition. For best electrical May 2009 10
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, 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 V.I (during flywheel diode conduction time) or I2R (during MOSFET conduction time). 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 4Mhz frequency and the switching transitions make up the switching losses. Although one is not required, a Schottky diode rated for 2A continuous current, connected between SW and GND can add up to 5% to efficiency. This is achieved by preventing forward biasing of the internal MOSFET body
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Micrel, Inc. diodes between switching transitions. The MOSFET body diode is less efficient for these short current pulses. Figure 3 shows an efficiency curve. The non-shaded 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 3.6V to 1.8V
100 90 80 70 60 50 40 0 1 2 3 4 5 OUTPUT CURRENT (A) 6
MIC22601 Compensation The MIC22601 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 4Mhz ramp signal and using the output of the error amplifier to modulate the pulse width of the switch node, maintaining output voltage regulation. With a typical gain bandwidth of 100-200 kHz, the MIC22601 is capable of extremely fast transient responses. The MIC22601 is designed to be stable with a typical application using a 0.22H inductor and a 47F ceramic (X5R) output capacitor. These values can be varied dependant on the tradeoff between size, cost and efficiency, keeping the LC natural frequency 1 ( ) ideally less than 34kHz to ensure stability 2 LC can be achieved. The minimum recommended inductor value is 0.22H 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 0.22H 0.47H 1H 2.2H
* VOUT > 1.2V, VOUT > 1V
L = 470nH (3mm x 3mm)
Figure 3. Efficiency Curve
The dashed region, 1A to 6A, efficiency loss is dominated by MOSFET RDS(ON) and inductor DC losses. Higher input supply voltages will increase the Gate-toSource threshold on the internal MOSFETs, reducing the internal RDS(ON). 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; LPD = IOUT2 x DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows: Efficiency Loss = 1 -
VOUT IOUT x 100 (VOUT IOUT ) + LPD
22-47F 4.7pF 0*-10pF 0-15pF 15-33pF
47F100F 10pF 22pF 15-22pF 33-47pF
100F470F 15pF 33pF 33pF 100-220pF
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.
Feedback The MIC22601 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. To calculate the resistor divider network for the desired output is as follows:
R2 = R1 VOUT - 1 V REF
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Micrel, Inc. Where VREF is 0.7V, R1 is the upper resistor, R2 is the lower resistor 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 decoupling capacitor (50pF - 100pF) across the lower resistor (R2) can reduce noise pick-up by providing a low impedance path to the ground. PWM Operation The MIC22601 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 MIC22601 will run at 100% duty cycle. The MIC22601 provides constant switching at 4MHz with synchronous internal MOSFETs. The internal 30m 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 lowside N-Channel MOSFET provides the current during the off cycle, a freewheeling Schottky diode from the switch node to ground is not required. 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 MIC22601 provides additional pins to provide up/down sequencing and tracking capability for connecting multiple voltage regulators together. 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 1st up, last down power sequence. May 2009 12
MIC22601 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 DELAY matched at TPOR = 1 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 MIC22601 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 rate of the output voltage. The rate is 0.7 C RC where TRAMP is the time given by TRAMP = 1 10 -6 from 0% to 100% nominal output voltage. Tracking & Sequencing examples There 4 distinct variations which are easily implemented using the MIC22601. The 2 Sequencing variations are Delayed and windowed. The 2 tracking variants are ratio metric and Normal. The following diagrams illustrate methods for connecting two MIC22601's to achieve these requirements.
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MIC22601
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MIC22601 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.
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Micrel, Inc. Current limit The MIC22601 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 I.R 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 on the RDSON value. Current limit is set to 9A nominal. 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. Where *
MIC22601
PDISS is the power dissipated within the MLF(R) package and is typically 1.8W at 6A load. This has been calculated for a 0.47H inductor and details can be found in table 1 below for reference. VIN 3 1 1.2 1.8 2.5 3.3 1.67 1.68 1.70 1.72 3.5 1.71 1.72 1.74 1.76 1.78 4 1.76 1.77 1.79 1.80 1.82 4.5 1.81 1.81 1.74 1.85 1.86 5 1.85 1.86 1.84 1.89 1.91
VOUT @5A
Table 1. Power dissipation (W) for 5A output
*
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.
* TA is the Operating Ambient temperature. Example The Evaluation board has 2 copper planes contributing to an RCA of approximately 25C/W. The worst case RJC of the MLF(R) 4x4 is 14C/W. RJA = RJC + RCA
Figure 4. Current Limit Detail
RJA = 14 + 25 = 39C/W To calculate the junction temperature for a 50C ambient: TJ = TAMB+PDISS. RJA TJ = 50 + (1.8 x 39) TJ = 120C This is below our maximum of 125C.
Thermal considerations The MIC22601 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 = TA + PD * RJA
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Schematic
U1 MIC22601YML
J1 +VIN J2 GND J3 EN SVIN C1 22F C2 22F C4 22F C5 SVIN
1 6 13 18 17 2 4 3
C3 22F/6.3V
PVIN PVIN PVIN PVIN SVIN EN RC Delay POR EP
22F/6.3V C6 1nF C7 10nF
SW SW SW SW SW SW SW SW
8 9 10 11 20 21 22 23
L1 0.22H D1 C10 47F/6.3V C11 47F/6.3V
J7 +VOUT 1.8V@6A
C8 1nF
FB Comp
14 15
R1 R2 698 1.1k C12 100pF J8 GND
PGND
PGND
PGND
SGND
PGND
7
5
12
19
24
16
C9 15pF
R4 20k
SVIN
R3 47.5k J11 POR
Bill of Materials
Item C1, C2, C3, C4, C5 C6 C7 C8 C9 C10, C11 C12 D1 L1 R1 R2 R3 R4 U1
Notes: 1. TDK: www.tdk.com 2. AVX: www.avx.com 3. Murata: www.murata.com 4. Vishay: www.vishay.com 5. Diodes, Inc.: www.diodes.com 6. Micrel: www.micrel.com
Part Number C2012X5R0J226M 08056D226MAT GRM21BR60J226ME39L Open GRM188R71H103KA01D VJ0603Y102KXQCW1BC C1005COG1H150J C3216X5R0J476M GRM31CR60J476ME19 GRM31CC80G476ME19L VJ0402A101KXQCW1BC SS2P2L DFLS220 IHLP1616ABERR22M01 CRCW06031101FKEYE3 CRCW04026980FKEYE3 CRCW06034752FKEYE3 CRCW04022002FKEYE3 MIC22601YML
Manufacturer TDK
(1)
Description 22F/6.3V, 0805 Ceramic Capacitor Open, 0603 Ceramic Capacitor
Qty 5 NA 1 1 1 2 1 1 1 1 1 1 1 1
AVX(2) Murata NA Murata
(3) (3)
10nF, 0603 Ceramic Capacitor 1nF, 0603 Ceramic Capacitor 15pF, 0402 Ceramic Capacitor 47F/6.3V, 1206 Ceramic Capacitor 100pF, 0603 Ceramic Capacitor
(5)
Vishay(4) TDK(1) TDK
(1) (3) (3)
Murata
Murata Visyay
Vishay(4)
(4)
Diodes, Inc. Vishay(4) Vishay Vishay
(4) (4)
2A, 20V Schottky Diode 0.22H, 9.5A 1.1k, 0603 Resistor 698, 0603 Resistor 47.5k, 0603 Resistor 20k, 0402 Resistor Integrated 6A Synchronous Buck Regulator
Vishay(4) Vishay(4) Micrel
(6)
May 2009
16
M9999-050509-A
Micrel, Inc.
MIC22601
PCB Layout Recommendation
Top Assembly
Top Layer
May 2009
17
M9999-050509-A
Micrel, Inc.
MIC22601
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.
May 2009
18
M9999-050509-A

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