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MIC22400
4A Integrated Switch Synchronous Buck Regulator with Frequency Programmable up to 4MHz
General Description
The Micrel MIC22400 is a high efficiency 4A integrated switch synchronous buck (step-down) regulator. The MIC22400 is optimized for highest efficiency and achieves over 90% efficiency while still switching at 1MHz over a broad load range. 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 sequence options are available with the MIC22400. The enable/delay pin combined with the power good pin allows multiple outputs to be sequenced in any way on turn on and turn off. The RC (Ramp ControlTM) pin allows the device to be connected to another MIC22400 family of products to keep the output voltages within a certain V on start up. The MIC22400 is available in a 20-pin 3mm x 4mm MLF(R) and thermally enhanced 20-pin e-TSSOP 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 current up to 4A Full sequencing and tracking ability Power on reset Efficiency > 90% across a broad load range Programmable frequency 800kHz to 4MHz Easy RC compensation Ultra fast transient response 100% maximum duty cycle Fully integrated MOSFET switches Micropower shutdown Thermal shutdown and current limit protection 20-pin 3mm x 4mm MLF(R) 20-pin e-TSSOP -40C to +125C junction temperature range
Applications
* * * * * * High power density point of load conversion Servers and routers DVD recorders Computing peripherals Base stations FPGAs, DSP and low voltage ASIC power
Typical Application
Efficiency V O = 3.3V
100 95 90 85 80 75 70 65 60 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 OUTPUT CURRENT (A)
MIC22400 4A Synchronous Buck Regulator
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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MIC22400
Ordering Information
Part Number MIC22400YML MIC22400YTSE* Voltage Adj. Adj. Junction Temp. Range -40 to +125C -40 to +125C Package 20-Pin 3x4 MLF
(R)
Lead Finish Pb-Free Pb-Free
20-Pin e-TSSOP
* Contact Micrel Marketing for YTSE availability.
Pin Configuration
DELAY PVIN RC EN
EN DELAY 1 2 3 4 5 6 7 8 9 20 PVIN 19 NC 18 PGND 17 SW 16 SW 15 SW 14 SW 13 PGND 12 NC 11 PVIN
POR CF NC COMP NC FB SVIN SGND PVIN NC
PGND SW SW SW SW PGND
RC POR CF COMP NC FB SGND
SVIN 10
20-Pin 3mm x 4mm MLF(R) (ML)
20-Pin e-TSSOP (TS)
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Pin Description
Pin Number MLF-20
1 2 3, 5, 9 4 6 7 8 10, 17 11, 16 12, 13, 14, 15 18
Pin Number e-TSSOP-20
4 5 7, 12, 19 6 8 9 10 11, 20 13, 18 14, 15, 16, 17 1
Pin Name
POR CF NC COMP FB SGND SVIN PVIN PGND SW EN
Description
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. Adjustable frequency with external capacitor. Not connected internally. Compensation pin (Input): Place a RC to GND to compensate the device, see applications section. Feedback: Input to the error amplifier, connect to the external resistor divider network to set the output voltage. Signal Ground (Signal): Ground Signal Power Supply Voltage (Input): Requires bypass capacitor to GND. Power Supply Voltage (Input): Requires bypass capacitor to GND. Power Ground (Signal): Ground Switch (Output): Internal power MOSFET output switches. Enable (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. Delay (Input): Capacitor-to-ground sets internal delay timer. Timer delays poweron reset (POR) output at turn-on and ramp down at turn-off. 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. Exposed Pad (Power): Must make a full connection to a GND plane for full output power to be released.
19 20
2 3
DELAY RC
EP
EP
GND
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Absolute Maximum Ratings(1)
Supply Voltage (VIN) .........................................................6V Output Switch Voltage (VSW) ............................................6V Output Switch Current (ISW)..............................................6A Logic Input Voltage (VEN, VLQ)........................... VIN to -0.3V Storage Temperature (Ts) .........................-65C to +150C ESD Rating(3) .................................................................. 2kV
Operating Ratings(2)
Supply Voltage (VIN)......................................... 2.6V to 5.5V Junction Temperature (TJ) ..................-40C TJ +125C Thermal Resistance 3x4 MLF-20 (JA) ...............................................45C/W e-TSSOP-20 (JA) ...........................................32.2C/W
Electrical Characteristics(4)
TA = 25C with VIN = VEN = 3.3V; VOUT = 1.2V, COSC = 400pF, 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 Oscillator Current FB Pin Input Current Current Limit in PWM Mode 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 1% 2% (over temperature)
Min 2.6 2.4
Typ
2.5 280 1.3 5 0.7 400 1 6 0.2 0.2 0.060 0.035 1 1.24 1 1
Max 5.5 2.6 2.0 10 0.707 0.714 480 100 7.5
Units
V V mV mA A V V A nA A % % % MHz V A A A A mV
0.693 0.686 320
VFB = 0.5V VOUT 1.2V; VIN = 2.6 to 5.5V, ILOAD= 100mA 100mA < ILOAD < 4000mA, VIN = 3.3V VFB 0.5V ISW = 1000mA; VFB=0.5V ISW = 1000mA; VFB=0.9V
4.4
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
135
7.5
10 2.7 150 10
12.5
% %
C C
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Typical Characteristics
10 8 6 4 2 0 2.5 25C
Shutdown Current vs. Input Voltage
10 8 6 4 2 0
Shutdown Current vs. Temperature
2.0 1.6 1.2 0.8 0.4
Operating Current vs. Input Voltage
No Switching
VIN = 3.3V TEMPERATURE (C)
3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V)
5.5
0 2.5
FB = 0.9V 25C 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V)
2.0 1.6 1.2
Operating Current vs. Temperature
0.710
Reference Voltage vs. Input Voltage
0.710
Reference Voltage vs. Temperature
0.705
0.705
0.700 0.8 0.4 0
No Switching
25C
0.700
0.695
0.695 VIN = 3.3V TEMPERATURE (C)
FB = 0.9V VIN = 3.3V TEMPERATURE (C)
0.690 2.5
3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V)
5.5
0.690
1.30 1.26 1.22 1.18 1.14 1.10
Enable Voltage vs. Temperature
8 7 6 5 4 3 2
Enable Hysterisis vs. Temperature
1060 1040 1020 1000 980 960 940
Frequency vs. Temperature
VIN = 3.3V TEMPERATURE (C)
1 0
VIN = 3.3V TEMPERATURE (C)
920 900 TEMPERATURE (C)
65 63 61 59 57 55
P-Channel RDSON vs. Temperature
40 38 36 34 32 30
N-Channel RDSON vs. Temperature
TEMPERATURE (C)
TEMPERATURE (C)
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Typical Characteristics (continued)
Efficiency V O = 3.3V
100 95 90 85 80 75 70 65 VIN = 5V 100 95 90 85 80 75 70 65 60 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 OUTPUT CURRENT (A) VIN - 5V
Efficiency V O = 1.8V
VIN - 3.3V
100 95 90 85 80 75 70 65
Efficiency V O = 1.2V
VIN - 3.3V
VIN - 5V
60 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 OUTPUT CURRENT (A)
60 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 OUTPUT CURRENT (A)
V IN = 5.0V, VOUT = 1.2V
60 40 Phase @ 4A 20 0 -20 -40 -60 1 10 100 FREQUENCY (kHz) Gain @ 4A 200 150 100 50 0 -50 -100 -150 -200 1,000 -40 -60 1 20 0 -20 60 40
V IN = 3.3V, VOUT = 1.2V
200 Phase @ 4A 150 100 50 Gain @ 4A 0 -50 -100 -150 10 100 FREQUENCY (kHz) -200 1,000
-40 -60 1 20 0 -20 60 40
VIN = 3.3V, VOUT = 1.8V
200 Phase @ 4A 150 100 50 0 Gain @ 4A -50 -100 -150 10 100 FREQUENCY (kHz) -200 1,000
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Functional Characteristics
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Functional Characteristics (continued)
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Tracking Circuit and Waveform
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Functional Diagram
Figure 1. MIC22400 Block Diagram
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Functional Description
PVIN PVIN is the input supply to the internal 60m 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 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 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 MIC22400 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 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 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. CF Adding a capacitor to this pin can adjust switching frequency from 800kHz to 4MHz. 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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MIC22400 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 Capacitor Enable 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 1.10 - 6
Application Information
The MIC22400 is a 4A Synchronous step down regulator IC with an adjustable switching frequency from 800kHz to 4MHz, 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 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 MIC22400 was designed specifically for the use of ceramic output capacitors. 100F can be increased to improve transient performance. Since the MIC22400 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 MIC22400. 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 MIC22400 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 MIC22400 to prevent overheating in a fault condition. For best electrical February 2008 12
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 in the frequency range from 800kHz to 4Mhz and the switching transitions make up the switching losses.
M9999-022108-A
Micrel, Inc. Figure 2 shows an efficiency curve. The portion, from 0A to 0.2A, 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 V O = 1.2V
100 95 90 85 80 75 70 65 VIN = 3.3V
MIC22400
Efficiency vs. Inductance
4.7H
94 92 90 88 86 84 82 80 78 76 0
1H
VIN = 3.3V 0.2 0.4 0.6 0.8 1.0 1.2 OUTPUT CURRENT (A)
Figure 3. Efficiency vs. Inductance
60 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 OUTPUT CURRENT (A)
Figure 2. Efficiency Curve
The region, 0.2A to 4A, 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 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:
VOUT I OUT Efficiency Loss = 1 - (V OUT I OUT ) + LPD x 100
Compensation The MIC22400 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 100-200kHz, the MIC22400 is capable of extremely fast transient responses. The MIC22400 is designed to be stable with a typical application using a 1H inductor and a 47F ceramic (X5R) output capacitor. These values can be varied dependant upon the tradeoff between size, cost and efficiency, keeping the LC natural frequency
(
1 2 L C
) ideally less than 26 kHz to ensure stability
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 may be 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.
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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Feedback The MIC22400 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
Enable 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 = 1.10 - 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 MIC22400 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 = 1.10 - 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 MIC22400 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 MIC22400 will run at 100% duty cycle. The MIC22400 provides constant switching from 800kHz to 4MHz with synchronous internal MOSFETs. The internal MOSFETs include a 60m high-side P-Channel MOSFET from the input supply to the switch pin and a 30m N-Channel MOSFET from the switch pin-toground. Since the low-side 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 MIC22400 provides additional pins to provide up/down sequencing and tracking capability for connecting multiple voltage regulators together.
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Sequencing & Tracking examples There are four distinct variations which are easily implemented using the MIC22400. The two sequencing variations are Windowed and Delayed. The two tracking variants are Normal and Ratio Metric. The following diagrams illustrate methods for connecting two MIC22400's to achieve these requirements. Sequencing:
Normal Tracking:
Ratio Metric Tracking:
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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.
Current Limit The MIC22400 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. Figure 4 describes the operation of the current limit circuit. Since the actual RDSON of the P-Channel 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 6A 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.
Figure 4. Current Limit Detail
Thermal Considerations The MIC22400 is packaged in the MLF(R) 3mm 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 0.89W at 3A load. This has been calculated for a 1H inductor and details can be found in table 1 below for reference.
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Micrel, Inc. * 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 VOUT @3A 1 1.2 1.8 2.5 3.3 3 0.732 0.741 0.825 0.894 - 3.5 0.689 0.691 0.764 0.813 0.817 4 0.672 0.668 0.732 0.776 0.816 4.5 0.668 0.662 0.720 0.762 0.801 5 0.670 0.665 0.720 0.765 0.800
MIC22400
Example: To calculate the junction temperature for a 50C ambient:
TJ = TAMB+PDISS . RJA TJ = 50 + 0.894 x 45 TJ = 90.2C This is below the maximum of 125C.
Table 1. Power Dissipation (W) for 4A Output
*
TAMB is the Operating Ambient temperature.
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Package Information
20-Pin 3mm x 4mm MLF(R) (ML)
20-Pin e-TSSOP (TS)
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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) 2008 Micrel, Incorporated.
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