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3A Step-Down Switching Regulator with Programmable Soft Start
POWER MANAGEMENT Description
The SC4521 is a current mode switching regulator with an integrated switch, operating at 600kHz with programmable soft start and enable functions. The integrated switch allows for cost effective low power solutions (peak switch current 3 amps). High frequency operation allows for very small passive components. Current mode operation allows for fast dynamic response and instantaneous duty cycle adjustment as the input varies (ideal for CPE applications where the input is a wall plug power). The low shutdown current makes it ideal for portable applications where battery life is important. The SC4521 is an 600kHz switching regulator with a low pin count. The SC4521 allows customers to use large capacitive loads because its programmable soft start limits the dv/ dt of the output at start up.
SC4521
Features
Wide operating voltage range: 4.4V to 24V Integrated 3 Amp switch 600kHz frequency of operation Programmable soft start funchion Current mode control Precision enable threshold SO-8 EDP Lead-free package, fully WEEE and RoHS compliant
Applications
XDSL modems CPE equipment DC-DC point of load applications Portable equipment Digtial consumer electronics
Typical Application Circuit
D1
1 VIN Enable C3 2 5 8 BST IN EN SS SW 3 6
C1 L1 VOUT
SC4521
GND 4
FB COMP
R1 7 D2 R2 C2
C6
C4 R3
Revision: October 5, 2007
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SC4521
POWER MANAGEMENT Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device reliability.
Parameter Input Supply Voltage Boost Pin Above VSW Boost Pin Voltage EN Pin Voltage FB Pin Voltage FB Pin Current SS Pin Voltage Thermal Impedance Junction to Ambient (1) Maximum Junction Temperature Storage Temperature Range Lead Temperature (Soldering) 10 sec ESD Rating (Human Body Model)
Symbol VIN (VBST - VSW) V BST V EN V FB IFB V SS JA TJ TSTG TLEAD ESD
Limits -0.3 to +28 16 -0.3 to +32 -0.3 to +24 -0.3 to +6 1 +3 36.5 150 -65 to +150 300 2
Units V V V V V mA V C/W C C C kV
Note: (1) ThetaJA is calculated from a package in still air, mounted to 3" x 4.5", 4 layer FR4 PCB with thermal vias under exposed pad per JESD51 standards.
Electrical Characteristics
Unless specified: VIN = 12V, VCOMP = 0.8V, VBST = VIN + 5V, EN = tied to VIN, SW = open. TA = TJ = -40C to 125C.
Parameter Operating Input Voltage Maximum Switch Current Limit Oscillator Frequency Switch On Voltage Drop VIN Rising Undervoltage Lockout VIN UVLO Hysteresis VIN Supply Current Standby Current Thermal Shutdown Trip Point Thermal Shutdown Hysteresis
Symbol VIN ISW fOSC VD(SW) VUVLO VHYST IQ IQ(OFF)
Conditions
Min
Typ
Max 24
Units V A kHz mV
TA = 25C, D = 50%
3.5 500 600 220 3.9 60
5.5 700
ISW = 3A TJ = 0C to 85C
4.4
V mV
V FB = 1V V E N = 0V
3 250 155 10
5.5
mA A C C
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SC4521
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: VIN = 12V, VCOMP = 0.8V, VBST = VIN + 5V, EN = tied to VIN, SW = open. TA = TJ = -40C to 125C.
Parameter FB Input Current Feedback Voltage Feedback Voltage Line Regulation FB to VCOMP Voltage Gain(2) FB to VCOMP Transconductance(2) VCOMP Pin Source Current VCOMP Pin Sink Current VCOMP Pin to Switch Current Transconductance VCOMP Pin Maximum Switching Threshold VCOMP OCP Threshold VCOMP Hiccup Retry Threshold Maximum Switch Duty Cycle Minimum Boost Voltage Above Switch(2) Boost Current
Symbol IFB V FB
Conditions
Min
Typ -0.25
Max -1 0.816
Units A V mV/V V/V
0.784 4.4V < VIN < 24V(1) 0.9V VCOMP 2.0V ICOMP = 10A VFB = 0.6V VFB = 1.0V VCOMP = 1.25V Duty cycle = 0% VCOMP rising VCOMP falling 150 500
0.8 +3 350 850 70 -70 4.3 0.6 2 0.25
1300 110 -110
Mho A A A/V V V V %
DMAX
VCOMP = 1.2V, ISW = 400mA
85 2.7
V 15 45 1.5 V A A A mA mA
ISW = 1A ISW = 3A
10 30 1.1 1.27 8 10 16 -2
Enable Input Threshold Voltage Enable Output Bias Current
VETH IEOL IEOH EN = 50mV below threshold EN = 50mV below threshold V SS = 0
Soft Start Charging Current (3) Soft Start Discharging Current
ISS ISS
Notes: (1) The required minimum input voltage for a regulated output depends on the output voltage and load condition. (2) Guaranteed by design. (3) See Application Information.
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SC4521
POWER MANAGEMENT Pin Configurations Ordering Information
Part Number (1)(2) SC4521SETRT P ackag e SOIC-8L-EDP EVALUATION BOARD
TOP VIEW
BST IN SW GND 1 2 3 4 8 7 6 5 SS COMP FB EN
S C 4521E V B
Notes: (1) Only available in tape and reel packaging. A reel contains 2500 devices. (2) Lead free product. This product is WEEE and RoHS compliant.
(SOIC-8L-EDP)
Pin Descriptions
Pin # 1 2 3 4 5 Pin Name Pin Function BST IN SW GND EN This pin provides power to the internal NPN switch. The minimum turn on voltage for this switch is 2.7V. Pin IN delivers all power required by control and power circuitry. This pin sees high di/dt during switching. A decoupling capacitor should be attached to this pin as close as possible. Pin SW is the emitter of the internal switch. The external freewheeling diode should be connected as close as possible to this pin. All voltages are measured with respect to this pin. The decoupling capacitor and the freewheeling diode should be connected to GND as short as possible. This is the chip enable input. The regulator is switched on if EN is high, and it is off if EN is low. The regulator is in standby mode when EN is low, and the input supply current is reduced to a few microamperes. Feedback input for adjustable output controllers. Thi s i s the output of the i nternal error ampli fi er and i nput of the peak current comparator. A compensation network is connected to this pin to achieve the specified performance. Soft start pin. An external capacitor connected from this pin to GND sets the soft start time.
6 7 8 -
FB COMP SS
THERMAL P ad for heatsi nki ng purposes. C onnect to ground plane usi ng multi ple vi as. Not connected PAD internally.
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SC4521
POWER MANAGEMENT Block Diagram
+ +
SLOPE 40m
Is
+
ISEN
IN
COMP FB
BST
-
+
EA
PWM
S R
Q
POWER TRANSISTOR
SW
Is
EN
1.6V INTERNAL SUPPLY
REFERENCE
UVLO
HICCUP
OL
GND
SS
SLOPE SLOPE COMP OSCILLATOR FB
FREQUENCY
CLK
Typical Characteristic - OCP Limit
SC4519H OCP Limit vs Duty Cycle
7 6.5 6 5.5 Current Limit (A) 5 4.5 4 3.5 3 2.5 2 0 20 40 60 80 100 Duty Cycle (%) ILIM @-40C ILIM @25C ILIM @125C
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SC4521
POWER MANAGEMENT Application Information
The SC4521 is a current mode buck converter regulator. The SC4521 uses two feedback loops that control the duty cycle of the internal power switch. The error amplifier functions like that of the voltage mode converter. The output of the error amplifier works as a switch current reference. This technique effectively removes one of the double poles in the voltage mode system. With this, it is much simpler to compensate a current mode converter to have better performance. Soft Start Internally, connected to the SS pin is a 100K pull-up resistor from an internal 1.6V regulator and the collector of an NPN pull-down transistor from SS to GND. The NPN transistor is "on" when the Enable pin is low or when a fault is detected (Input UVLO, Over-Current, or Over Temp). When the SC4521 is disabled or when a fault is detected, the NPN transistor pulls the SS pin low. The SS charging time is controlled by the internal 100k resistor and external soft-start cap. This is a closed-loop soft-start which effectively "ramps the reference". The SS process completes when the SS pin voltage is exceeds the internal reference voltage, 0.8V. The SS pin continues to charge up to 1.6V, well above the reference voltage to ensure it does not interfere with normal operation. The governing SS equation is:
TSS = 69000 * CSS For example, a 22nF SS cap would give a SS time of approximately 1.5mS.
about 2V. When an OCP fault is detected, the switch is turned off and the external COMP capacitor is gradually discharged at the rate of dv/dt=3A/Ccomp. Ccomp is the total capacitance value attached to COMP. At the same time, the soft start cap CSS is quickly discharged. Once the COMP voltage has fallen below 250mV, the part enters a normal startup cycle. In the case of sustained overcurrent or dead-short, the part will continually cycle through the retry sequence as described above. Enable Pulling and holding the EN pin below 0.4V activates the shut down mode of the SC4521 which reduces the input supply current to 250A. During the shut down mode, the switch is turned off. The SC4521 is turned on if the EN pin is pulled high. Oscillator Its internal free running oscillator sets the PWM frequency at 600kHz for the SC4521 without any external components to program the frequency. UVLO When the EN pin is pulled and held above 1.8V, the voltage on Pin IN determines the operation of the SC4521. As VIN increases during power up, the internal circuit senses VIN and keeps the power transistor off until VIN reaches 4.4V. Load Current The peak current IPEAK in the switch is internally limited. For a specific application, the allowed load current IOMAX will change if the input voltage drifts away from the original design as given for continuous current mode:
IOMAX = 3 - VO (1 - D) 2 L fs
However, when VI is higher than about 13V, the SC4521 requires a pull-up resistor from the SS pin to VI for normal operation. The softstart time can be estimated as:
TSS = R SS C SS [ - Ln (1 - 0 .8 )] VI
Where: Rss = pull-up resistance from SS pin to VI, Css = capacitance from SS pin to GND, and VI = input voltage. Overcurrent Protection The current sense amplifier in the SC4521 monitors the switch current during each cycle. Overcurrent protection (OCP) is triggered when the current limit exceeds the upper limit of 3A, detected by a voltage on COMP greater than
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Where: fs = switching frequency, Vo = output voltage and D = duty ratio, VO/VI VI = input voltage.
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SC4521
POWER MANAGEMENT Application Information (Cont.)
Figure 2 shows the theoretical maximum load current for the specific cases. In a real application, however, the allowed maximum load current also depends on the layout and the air cooling condition. Therefore, the maximum load current may need to be degraded according to the thermal situation of the application.
L= VO (VI - VO ) VI f s IOMAX
Maximum Load Current vs Input Voltage L=10uH
2.900 2.880 2.860 2.840 2.820 2.800 2.780 2.760 2.740 2.720 2.700 4 6 8 10 12 14 16 18 Vi (V)
Where: fs = switching frequency, = ratio of the peak to peak inductor current to the output load current and VO = output voltage. The peak to peak inductor current is:
I p - p = * I OMAX
Iomax (A)
Vo=2.5V Vo=3.3V Vo=5V
After the required inductor value is selected, the proper selection of the core material is based on the peak inductor current and efficiency specifications. The core must be able to handle the peak inductor current IPEAK without saturation and produce low core loss during the high frequency operation.
IPEAK = IOMAX + Ip - p 2
Figure 2. Theoretical maximum load current curves Inductor Selection The factors for selecting the inductor include its cost, efficiency, size and EMI. For a typical SC4521 application, the inductor selection is mainly based on its value, saturation current and DC resistance. Increasing the inductor value will decrease the ripple level of the output voltage while the output transient response will be degraded. Low value inductors offer small size and fast transient responses while they allow large ripple currents, poor efficiencies and require more output capacitance for low output ripple. The inductor should be able to handle the peak current without saturating and its copper resistance in the winding should be as low as possible to minimize its resistive power loss. A good trade-off among its size, loss and cost is to set the inductor ripple current to be within 15% to 30% of the maximum output current. The inductor value can be determined according to its operating point under its continuous mode and the switching frequency as follows:
The power loss for the inductor includes its core loss and copper loss. If possible, the winding resistance should be minimized to reduce inductor's copper loss. The core must be able to handle the peak inductor current IPEAK without saturation and produce low core loss during the high frequency operation. The core loss can be found in the manufacturer's datasheet. The inductor's copper loss can be estimated as follows:
PCOPPER = I 2LRMS R WINDING
Where: ILRMS is the RMS current in the inductor. This current can be calculated as follows:
ILRMS = IOMAX 1 + 12 12
Output Capacitor Selection Basically there are two major factors to consider in selecting the type and quantity of the output capacitors. The first one is the required ESR (Equivalent Series Resistance) which should be low enough to reduce the output voltage deviation during load changes. The second one is the required capacitance, which should be high enough to hold up the output voltage. Before the SC4521 regulates the inductor current to a new value during a
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SC4521
POWER MANAGEMENT Application Information (Cont.)
load transient, the output capacitor delivers all the additional current needed by the load. The ESR and ESL of the output capacitor, the loop parasitic inductance between the output capacitor and the load combined with inductor ripple current are all major contributors to the output voltage ripple. Surface mount ceramic capacitors are recommended. Input Capacitor Selection The input capacitor selection is based on its ripple current level, required capacitance and voltage rating. This capacitor must be able to provide the ripple current drawn by the converter. For the continuous conduction mode, the RMS value of the input capacitor current ICIN(RMS) can be calculated from:
ICIN (RMS) = I OMAX VO (VI - VO ) V
2 I
TW =
1 D max fs
Where: fs = the switching frequency and Dmax = maximum duty ratio, 0.85 for the SC4521. The required minimum capacitance for the boost capacitor will be:
C boost = IB TW VD
Where: IB = the boost current and VD= discharge ripple voltage. With fs = 600kHz, VD = 0.5V and IB = 0.045A, the required minimum capacitance for the boost capacitor is:
Cboost = IB 1 0.045 1 Dmax = 0.85 = 128nF 0.5 600k VD fs
This current gives the capacitor's power loss through its RCIN(ESR) as follows:
PCIN = I2CIN (RMS) * R CIN(ESR)
The input ripple voltage mainly depends on the input capacitor's ESR and its capacitance for a given load, input voltage and output voltage. Assuming that the input current of the converter is constant, the required input capacitance for a given voltage ripple can be calculated by:
C IN = IOMAX D (1 - D) fs ( VI - IOMAX R CIN (ESR) )
The internal driver of the switch requires a minimum 2.7V to fully turn on that switch to reduce its conduction loss. If the output voltage is less than 2.7V, the boost capacitor can be connected to either the input side or an independent supply with a decoupling capacitor. But the Pin BST should not see a voltage higher than its maximum rating. Freewheeling Diode Selection This diode conducts during the switch's off-time. The diode should have enough current capability for full load and short circuit conditions without any thermal concerns. Its maximum repetitive reverse block voltage has to be higher than the input voltage of the SC4521. A low forward conduction drop is also required to increase the overall efficiency. The freewheeling diode should be turned on and off fast with minimum reverse recovery because the SC4521 is designed for high frequency applications. SS23 Schottky rectifier is recommended for certain applications. The average current of the diode, ID_AVG can be calculated by:
Where: VI = the given input voltage ripple. Because the input capacitor is exposed to the large surge current, attention is needed for the input capacitor. If tantalum capacitors are used at the input side of the converter, one needs to ensure that the RMS and surge ratings are not exceeded. For generic tantalum capacitors, it is suggested to derate their voltage ratings at a ratio of about two to protect these input capacitors. Boost Capacitor and its Supply Source Selection The boost capacitor selection is based on its discharge ripple voltage, worst case conduction time and boost current. The worst case conduction time T w can be estimated as follows:
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ID- AVG = Iomax (I - D)
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SC4521
POWER MANAGEMENT Application Information (Cont.)
Thermal Considerations There are three major power dissipation sources for the SC4521. The internal switch conduction loss, its switching loss due to the high frequency switching actions and the base drive boost circuit loss. These losses can be estimated as:
Ptotal = Io R on D + 10.8 10 -3 Io VI +
2
Where: RL - Load and C - Output capacitor. The goal of the compensation design is to shape the loop to have a high DC gain, high bandwidth, enough phase margin, and high attenuation for high frequency noises. Figure 3 gives a typical compensation network which offers 2 poles and 1 zero to the power stage:
1
10 Io D (Vboost ) 1000
Where: IO = load current; Ron = on-equivalent resistance of the switch; VBOOST = input voltage or output based on the boost circuit connection. The junction temperature of the SC4521 can be further determined by:
TJ = TA + JA Ptotal
SC4521
3 SW FB 6 7
IN 5 8 EN SS
BST
2
L1
Vout
R1 C
GND 4
COMP
C4 C5 R3 D2
R2
JA is the thermal resistance from junction to ambient. Its value is a function of the IC package, the application layout and the air cooling system. The freewheeling diode also contributes a significant portion of the total converter loss. This loss should be minimized to increase the converter efficiency by using Schottky diodes with low forward drop (VF).
Pdiode = VF Io (1 - D)
Figure 3. Compensation network provides 2 poles and 1 zero. The compensation network gives the following characteristics:
s R2 Z GCOMP (s) = 1 gm s R1 + R2 s (1 + ) P2 1+
Loop Compensation Design The SC4521 has an internal error amplifier and requires a compensation network to connect between the COMP pin and GND pin as shown in Figure 3. The compensation network includes C4, C5 and R3. R1 and R2 are used to program the output voltage according to:
VO = 0.8 * (1 + R1 ) R2
Where:
1 = Z = P2 = 1 C 4 + C5 1 R 3 C4
C 4 + C5 R 3 C 4 C5
Assuming the power stage ESR (equivalent series resistance) zero is an order of magnitude higher than the closed loop bandwidth, which is typically one tenth of the switching frequency, the power stage control to output transfer function with the current loop closed (Ridley model) for the SC4521 will be as follows:
G VD (s) = 4.3 R L s 1+ 1 RL C
The loop gain will be given by:
R R2 1 T(s) = GCOMP (s) G VD (s) = 3.655 10 L C4 R1 + R 2 s
-3
1+ (1 +
s s ) (1 + ) P1 P2
s Z
Where:
p1 = 1 RL C
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SC4521
POWER MANAGEMENT Application Information (Cont.)
One integrator is added at origin to increase the DC gain. Z is used to cancel the power stage pole P1 so that the loop gain has -20dB/dec rate when it reaches 0dB line. P2 is placed at half switching frequency to reject high frequency switching noises. Figure 4 gives the asymptotic diagrams of the power stage with current loop closed and its loop gain. 2. Start the PCB layout by placing the power components first. Arrange the power circuit to achieve a clean power flow route. Put all power connections on one side of the PCB with wide copper filled areas if possible. 3. The VIN bypass capacitor should be placed next to the VIN and GND pins. 4. The trace connecting the feedback resistors to the output should be short, direct and far away from any noise sources such as switching node and switching components. 5. Minimize the loop including input capacitor, the SC4521 and freewheeling diode D2. This loop passes high di/dt current. Make sure the trace width is wide enough to reduce copper losses in this loop. 6. Maximize the trace width of the loop connecting the inductor, freewheeling diode D 2 and the output capacitor. 7. Connect the ground of the feedback divider and the compensation components directly to the GND pin of the SC4521 by using a separate ground trace. 8. Connect Pin 4 to a large copper area to remove the IC heat and increase the power capability of the SC4521. A few feedthrough holes are required to connect this large copper area to a ground plane to further improve the thermal environment of the SC4521. The traces attached to other pins should be as wide as possible for the same purpose.
Loop gain T(s) p1 Power stage C Z P2
Figure 4. Asymptotic diagrams of power stage with current loop closed and its loop gain. The design guidelines for the SC4521 applications are as following: 1. Set the loop gain crossover corner frequency C for given switching corner frequency C = 2fC 2. Place an integrator at the origin to increase DC and low frequency gains. 3. Select Z such that it is placed at P1 to obtain a -20dB/dec rate to go across the 0dB line. 4. Place a high frequency compensator pole P2 (P2 = fs) to get the maximum attenuation of the switching ripple and high frequency noise with the adequate phase lag at C. Layout Guidelines: In order to achieve optimal electrical and thermal performance for high frequency converters, special attention must be paid to the PCB layouts. The goal of layout optimization is to identify the high di/dt loops and minimize them. The following guidelines should be used to ensure proper operation of the converters. 1. A ground plane is suggested to minimize switching noises and trace losses and maximize heat transferring.
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SC4521
POWER MANAGEMENT Application Information (Cont.)
Design Example 1: 5V to 1V at 2A
D1
C1 0.22u 1 L1 SW FB GND COMP 3 3.9uH 6 7 C4 18n C5 560p R1 2.49k BST 2
VI = 5V
0
R0 C3 10u
Vo=1V @2A
Co 470u
IN EN SS
5 8 Css 100n
SC4521
4
R2 10k
R3 20k
D2
Note: The bottom pad needs a big copper area to remove the heat.
Bill of Materials
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Qty 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1 Co C3 C4 C5 D1 D2 L1 R0 R1 R2 R3 R4 C ss U1 Reference Value 0.22uF, 25V, 0805, X7R 470uF, 10V, ZA 10uF 18nF, 0805, X7R, 25V 560pF, 50V, 0805 1N4148SW, SOD323 E C 30LA 02 3.9uH 0, 0805 2.49k, 1%, 0805 10k, 1%, 0805 20k, 1%, 0805 not used, 0805 100nF S C 4521 Semtech SMTZONE Nihon Inter Electronics Corp. Sumida: RCR875DNP-3R9L Part No./Manufacturer Vishay: VJ0805Y224KXX Rubicon TDK: C3216OJ106MT Vishay Vishay
Unless specified, all resistors have 1% precision with 0805 package. Resistors are +/-1% and all capacitors are +/-20%
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SC4521
POWER MANAGEMENT Application Information (Cont.)
Design Example 2: 6.2V to 1.5V at 1.5A
D1
C1 0.22u 1 L1 SW FB GND COMP 3 4.7uH 6 7 C4 18n C5 560p R1 8.66k BST 2
VI = 6.2V
0
R0 C3 10u
Vo=1.5V
Co 100u
IN EN SS
5 8 Css 100n
SC4521
4
R2 10k
R3 4.87k
D2
Note: The bottom pad needs a big copper area to remove the heat.
Bill of Materials
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Qty 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1 Co C3 C4 C5 D1 D2 L1 R0 R1 R2 R3 R4 C ss U1 Reference Value 0.22uF, 25V, 0805, X7R 100uF 10uF 18nF, 0805, X7R, 25V 560pF, 50V, 0805 1N4148SW, SOD323 MBRA210LT3 4.7uH 0, 0805 8.66k, 1%, 0805 10k, 1%, 0805 4.87k, 0805 not used, 0805 100nF S C 4521 Semtech ON Toko: 919AS-4R7 Vishay Vishay Vishay Vishay Part No./Manufacturer Vishay: VJ0805Y224KXX Sanyo TDK: C3216OJ106MT Vishay Vishay
Unless specified, all resistors have 1% precision with 0805 package. Resistors are +/-1% and all capacitors are +/-20%
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SC4521
POWER MANAGEMENT Application Information (Cont.)
Design Example 3: 13V ~ 21V to 3.3V at 1A
C1 0.22u
D3 L1
VI
1
R0 0 C3 4.7u
IN EN
BST
2 Rss 200k 5 8 Css 330n
SW FB
3 10uH 6 7 C4 18n R2 8.25k R1 24.9k
Vo=3.3V
C2 10u
SS
GND 4
COMP
SC4521
C5 560p
R3 3.83k
D2
Note: The bottom pad needs a big copper area to remove the heat.
Bill of Materials
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Qty 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1 C2 C3 C4 C5 D2 D3 L1 R0 R1 R2 R3 Rss C ss U1 1N4148WS, SOD323 10uH 0, 0805 24.9k, 1%, 0805 8.25k, 1%, 0805 3.83k, 1%, 0805 2 0 0 k, 0 8 0 5 330nF, 0805 S C 4521 Semtech SMTZONE SMTZONE SMTZONE Sumida: CDRH6D38NP-100NC Reference Value 0.22uF, 25V, 0805, X7R 10uF 4.7uF, 1206, 25V, X5R 18nF, 0805, X7R, 25V 560pF, 50V, 0805 Part No./Manufacturer Vishay: VJ0805Y224KXX Taiyo-Yuden: EDK316BJ106MF-T Panasonic Vishay Vishay Nihon-International: EC31QS04
Unless specified, all resistors have 1% precision with 0805 package. Resistors are +/-1% and all capacitors are +/-20%
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SC4521
POWER MANAGEMENT Application Information (Cont.)
Design Example 4: 13V ~ 21V to 5V at 1.5A
C1 0.22u
D3 L1
VI
1
R0 0 C3 4.7u
IN EN
BST
2 Rss 200k 5 8 Css 470n
SW FB
3 10uH 6 7 C4 18n R2 10k R1 51.1k
Vo=5V
C2 10u
SS
GND 4
COMP
SC4521
C5 560p
R3 4.87k
D2
Note: The bottom pad needs a big copper area to remove the heat.
Bill of Materials
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Qty 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1 C2 C3 C4 C5 D2 D3 L1 R0 R1 R2 R3 Rss C ss U1 1N4148WS, SOD323 10uH 0, 0805 51.1k, 1%, 0805 10k, 1%, 0805 4.87k, 1%, 0805 2 0 0 k, 0 8 0 5 470nF, 0805 S C 4521 Semtech SMTZONE SMTZONE SMTZONE Sumida: CDRH6D38NP-100NC Reference Value 0.22uF, 25V, 0805, X7R 10uF 4.7uF, 1206, 25V, X5R 18nF, 0805, X7R, 25V 560pF, 50V, 0805 Part No./Manufacturer Vishay: VJ0805Y224KXX Taiyo-Yuden: EDK316BJ106MF-T Panasonic Vishay Vishay Nihon-International: EC31QS04
Unless specified, all resistors have 1% precision with 0805 package. Resistors are +/-1% and all capacitors are +/-20%
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SC4521
POWER MANAGEMENT Application Information (Cont.)
(PCB - TOP)
(PCB - BOTTOM)
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SC4521
POWER MANAGEMENT Application Information (Cont.)
(Componet Side - TOP)
(Componet Side - TOP)
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SC4521
POWER MANAGEMENT Outline Drawing - SOIC-8L EDP
A N 2X E/2 E1 E 1 ccc C 2X N/2 TIPS 2 e/2 B D aaa C SEATING PLANE A2 A C bxN bbb F EXPOSED PAD H H GAGE PLANE 0.25 L (L1) h A1 C A-B D e D
DIM
A A1 A2 b c D E1 E e F H h L L1 N 01 aaa bbb ccc
DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX
.069 .053 .005 .000 .065 .049 .012 .020 .010 .007 .189 .193 .197 .150 .154 .157 .236 BSC .050 BSC .116 .120 .130 .085 .095 .099 .010 .020 .016 .028 .041 (.041) 8 0 8 .004 .010 .008 1.75 1.35 0.13 0.00 1.65 1.25 0.31 0.51 0.25 0.17 4.80 4.90 5.00 3.80 3.90 4.00 6.00 BSC 1.27 BSC 2.95 3.05 3.30 2.15 2.41 2.51 0.25 0.50 0.40 0.72 1.04 (1.05) 8 8 0 0.10 0.25 0.20
h
c
01
SEE DETAIL SIDE VIEW
NOTES: 1.
A
DETAIL
A
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 4. REFERENCE JEDEC STD MS-012, VARIATION BA.
2007 Semtech Corp.
17
www.semtech.com
SC4521
POWER MANAGEMENT Land Pattern - SOIC-8L-EDP
E D
SOLDER MASK
DIM
(C) F G Z C D E F G P X Y Z
DIMENSIONS INCHES MILLIMETERS
(.205) .134 .201 .101 .118 .050 .024 .087 .291 (5.20) 3.40 5.10 2.56 3.00 1.27 0.60 2.20 7.40
Y THERMAL VIA O 0.36mm
NOTES: 1.
P X
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET.
2. REFERENCE IPC-SM-782A, RLP NO. 300A. 3. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD SHALL BE CONNECTED TO A SYSTEM GROUND PLANE. FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE.
Contact Information
Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804
2007 Semtech Corp. 18 www.semtech.com

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