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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
General Description
The ZA3020 is a monolithic step down switch mode converter with a built in internal Power MOSFET. It achieves 2A continuous output current over a wide input supply range with excellent load and line regulation. Current mode operation provides fast transient response and eases loop stabilization. Fault condition protection includes cycle-bycycle current limiting and thermal shutdown. In shutdown mode the regulator draws 23A of supply current. The ZA3020 requires a minimum number of readily available standard external components. A synchronization pin allows the part to be driven to 600KHz.
Features
2A Output Current 0.18 Internal Power MOSFET Switch Stable with Low ESR Output Ceramic capacitors Up to 95% Efficiency 20A Shutdown Mode Fixed 380kHz frequency Thermal Shutdown Cycle-by-cycle over current protection Wide 4.75 to 25V operating input range Output Adjustable from 1.22 to 21V Programmable under voltage lockout Frequency Synchronization Input Available in 8 pin SO package Evaluation Board Available
Applications
Distributed Power Systems Battery Charger Pre-Regulator for Linear Regulators
Ordering Information
Part Number Package
ZA3020DS SOIC8
Temperature
-40 to +125 C
. For Tape & Reel use suffix - Z (e.g. ZA3020DS-Z)
Figure 1: Typical Application Circuit
Efficiency versus Output Current and Voltage. VIN=10V
VIN 4.75 to 25V
IN
95
IN
BS
90
5.0V
SW
Efficiency (%)
ENABLE SHUTDOWN OPEN NOT USED
EN SNYC
ZA3020
GND
VOUT 2.5V/2A
3.3V
85
FB COMP
2.5V
80
75
70 0 0.5 1 1.5 2
Output Current (A)
ZA3020
Rev. 3.5
2003-04-22
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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
Absolute Maximum Ratings (Note 1)
Supply Voltage (VIN) Switch Voltage (VSW ) Boost Voltage Feedback Voltage (VFB) Enable/UVLO Voltage (VEN) Comp Voltage (VCOMP) Sync Voltage (VSYNC) Junction Temperature Lead Temperature Storage Temperature 28V -1V to VIN +1V VSW + 6V -0.3 to 6V -0.3 to 6V -0.3 to 6V -0.3 to 6V 150C 260C -65 to +150C
Recommended Operating Conditions (Note 2)
Input Voltage (VIN) Operating Temperature 4.75V to 25V -40 to +125C
Package Thermal Characteristics
Thermal Resistance
JA
(SOIC8)
105C/W
Electrical Characteristics (Unless otherwise specified VIN=12V, TA=25 C)
Parameters
Feedback Voltage Upper Switch On Resistance Lower Switch On Resistance Upper Switch Leakage Current Limit Current Limit Gain. Output Current to Comp Pin Voltage Error Amplifier Voltage Gain Error Amplifier Transconductance Oscillator Frequency Short Circuit Frequency Sync Frequency Maximum Duty Cycle Minimum Duty Cycle Enable Threshold Enable Pull Up Current Under Voltage Lockout Threshold High Going Under Voltage Lockout Threshold Hysteresis Supply current (quiescent) Supply current (operating) Thermal Shutdown
Condition
4.75V VIN 25V VCOMP < 2V
Min
1.198
Typ
1.222 0.18 10 0 2.85 1.95
Max
1.246
Units
V
VEN=0V; VSW =0V 2.4
10 3.3
A A A/V
IC = 10 A VFB = 0V Sync Drive 0 to 2.7V VFB = 1.0V VFB = 1.5V ICC > 100A VEN = 0V VEN 0.4V VEN 2.6V; VFB =1.4V
500 342 30 445
400 770 380 42 90
1100 418 54 600 0 1.3 1.8 2.62 36 1.2
0.7 1.15 2.37
1.0 1.46 2.495 210 23 1.0 160
V/V Mho KHz KHz KHz % % V A V mV A mA C
Note 1. Exceeding these ratings may damage the device. Note 2. The device is not guaranteed to function outside its operating rating. Note 3. Measured on approximately 1" square of 1 oz. copper surrounding device leads.
ZA3020
Rev. 3.5
2003-04-22
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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
Figure 2: Functional Block Diagram
IN
2 Internal Regulators Slope Compensation Current Sense Amplifier 5V Q Q 3 1
BS
SYNC
8
Oscillator S 40/400KHz Shutdown Comparator CLK R Current Comparator
M1 0.2 ohm
SW
M2 10 ohm
0.7V
4 1uA 1.8V
GND
EN
7
2.30/2.53V
Lockout Comparato r
Frequency Foldback Comparator
0.7V 5
1.22V
FB
Error Amplifier gm= 630uA/Volt 6
COMP
Functional Description
The ZA3020 is a current mode r egulator. That is, the compensation pin voltage is proportional to the current delivered to the load. At the beginning of a cycle: the upper transistor M1 is off; the lower transistor M2 on; the COMP pin voltage is higher than the current sense amplifier output; and the current comparator's output is low. The rising edge of the 380KHz CLK signal sets the RS Flip-Flop. Its output turns off M2 and turns on M1 thus connecting the Switch pin and inductor to the Input supply. The increasing inductor current is sensed and amplified by the Current Sense Amplifier. Ramp compensation is summed to Current Sense Amplifier output and compared to the error amplifier output by the Current Comparator. When the Current Sense Amplifier plus Slope Compensation signal exceeds the Comp pin voltage, the RS Flip-Flop is reset and the chip reverts to its initial M1 off, M2 on state. If the Current Sense Amplifier plus Slope Compensation signal does not exceed the COMP voltage, then the falling edge of the CLK resets the Flip-Flop. The output of the Error amplifier integrates the voltage difference between the feedback and the 1.22V bandgap reference. The polarity is such that feedback pin voltages lower than 1.22V increases the COMP pin voltage. Since the COMP pin's voltage is proportional to the peak inductor current an increase in its voltage increases current delivered to the output. The lower 10 switch ensures that the bootstrap capacitor voltage is charged during light load conditions. External Schottky Diode D1 carries most of the inductor current.
ZA3020
Rev. 3.5
2003-04-22
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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
Pin Descriptions
BS 1
IN 2 SW 3 GND 4
8 SYNC 7 EN 6 COMP 5 FB
Pin 1: BS - Bootstrap - C5 This capacitor is needed to drive the power switch's gate above the supply voltage. It is connected between SW and Bootstrap pins to effect a floating supply across the power switch driver. The voltage across C5 is about 5V and is supplied by the internal +5V supply when the SW pin voltage is low. Pin 2: IN - Supply Voltage The ZA3020 operates from a +4.75V to +25V unregulated input. C1 is needed to prevent large voltage spikes from appearing at the input. Pin 3: SW - Switch This connects the inductor to either IN through M1 or to GND through M2. Pin 4: GND - Ground This pin is the voltage reference for the regulated voltage. For this reason care must be taken in its layout. This node should be placed outside of the DSCH to C1 ground path to prevent switching current spikes to induce voltage noise into the part. Pin 5: FB - Feedback An external resistor divider from the output voltage to GND, tapped to the FB pin sets the output voltage. To prevent current limit run away during a short circuit fault condition the frequency fold back comparator lowers the oscillation frequency when the FB voltage is below 650mV.
Pin 6: COMP - Compensation This node is the output of the transconductance error amplifier and the input to the current comparator. Frequency compensation is done at this node by connecting a series R-C to ground. See the compensation section for exact details. Pin 7: EN - Enable/UVLO A voltage greater than 2.495V enables operation. Leave the input unconnected if unused. An Under Voltage Lockout (UVLO) function can be implemented by the addition of a resistor divider from VIN to GND. For complete low current shutdown its needs to be less than 0.7V. Pin 8: SYNC - Synchronization Input This pin is used to synchronize the internal oscillator frequency to an external source. There is an internal 11K pull down resistor to GND hence leave the input unconnected if unused. Sync Pin Operation The SYNC pin driving waveform should be a square wave with a rise time of less than 20ns. Minimum Hi voltage level is 2.7V. Low level is less than 0.8V. The frequency of the external Sync signal needs to be greater than 445 KHz. A rising edge on the SYNC pin forces a reset of the oscillator. The upper DMOS is switched off immediately if it is not already off. 250nS later the upper DMOS turns on connecting SW to VIN.
ZA3020
Rev. 3.5
2003-04-22
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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
Applications Information
Bootstrap Capacitor - C6 This bypasses the upper switch gate drive. Its value should be > 4.7nF. For simplicity of design this capacitor can be the same value as Compensation cap C3. Compensation Capacitor - C3 This is the system compensation cap that is in series with R3. Using a ceramic 10nF, 50V, X7R capacitor allows it to match C5. Auxiliary Compensation Capacitor - C6 This is the system compensation cap that connects between the COMP and GND pin. This capacitor rolls off the high frequency noise and gain that can cause duty cycle jitter. On well laid out boards using low ESR Output capacitor (C2) C6 may not be necessary. It -3DB frequency is set by 1/ (R3 X C6). For R3=10K and C6=100pF the cut-off frequency is 159KHz which filters out the 400KHz switching noise and yet is above the GBW target of 10KHz to 80KHz Use a ceramic 100pF, 50V, X7 capacitor. Compensation Resistor - R3 The loop compensation gain is directly proportional to R3's value. The higher it's value the higher the gain. Calculation of its value is discussed in detail in the Loop Compensation section. Refer Table 4 for recommended values that accompany a surface mount ceramic and special polymer output capacitor. Feedback Divider Resistors - R2, R1 The Output voltage is set by R2 and R3: VOUT = 1.22V [1 + (R2 / R1)] The maximum recommended value of R1 is 100K . Too high an impedance can make the Feedback node prone to noise injection particularly if unshielded inductors are used. 10K is a good standard value. Input Bypass Capacitor - C1 C1 is the bulk supply capacitor whose value should be 10uF. The capacitor can be electrolytic, tantalum or ceramic. However since it absorbs the input switching current it requires an adequate ripple current rating. Its RMS current rating should be greater than approximately 1/2 of the output current. For insuring stable operation C1 should be placed as close to the IC as possible. Alternately a smaller high quality ceramic 0.1F capacitor may be placed closer to the IC and the bulk C1 placed further away. However if using this technique some caution is needed if the bulk C1 is also a high quality ceramic capacitor. Large voltage excursions caused by resonant energy oscillation between the two is possible. Schottky Catch Diode - D1 D1 supplies most of the current to inductor L1 when VSW is low. The lower the forward Schottky voltage drop (VSCH) the higher the regulator efficiency. Tables 2 provides the Schottky part numbers based on the maximum input voltage and current rating. Table 3 lists manufacturer's websites. D1's maximum reverse voltage rating should be greater than the maximum input voltage VIN (Max). The diode's average current rating must be above the average load current: IDIODE (AVG) = ILOAD X [VIN -(VOUT+VSCH)] /VIN Example: VIN= 12V, VOUT= 3.3V, ILOAD= 1.2A, VSCH =0.5V. IDIODE (AVG) = 1.2A X [12-(3.3+0.5)] / 12V = 0.82A In this case a 1A diode can be used.
ZA3020
Rev. 3.5
2003-04-22
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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
Applications Information Continued
Table 2: Diode Selection Guide VIN (Max) 15V 20V 1A Diodes 10BQ15 1N5817 B120 SS12 1N5818 B130 MBRS130 SS13 2A Diodes 30BQ15 B220 SK23 SR22 20BQ030 B230 SK23 SR23 SS23 The Maximum current rating of the inductor should be above the peak operating current: IPEAK = ILOAD + (VOUT)(VIN-VOUT) 2(L)(F)(VIN) Example: VIN=12V VOUT=3.3V, L=15H, ILOAD=1.2A IPEAK = 1.6 + (3.3)(12-3.3) 2(15u)(380KHz)(12) IPEAK Table 3: Schottky Diode Manufacturers
Vendor Diodes, Inc. Fairchild Semiconductor General Semiconductor International Rectifier On Semiconductor Pan Jit International Web Site www.diodes.com www.fairchildsemi.com www.gensemi.com www.irf.com www.onsemi.com www.panjit.com.tw
30V
= 1.809A
Using Table 5 select a 15H inductor with a Max IDC rating of > 1.809A. Output Capacitor - C2 The selection of the output capacitor is the most critical component of a switching regulator. Its electrical value and equivalent series resistance (ESR) directly affect: * * * System stability Loop compensation components R3 and C3 Output ripple voltage
Inductor - L1 Optimal inductor selection involves trade-offs in electrical value, current rating and mechanical sizing. Table 4 lists the recommended minimum inductor values for common output voltage values. Table 5 Selection guide lists inductors by manufacturer, electrical value, maximum output current, DC resistance, core type, core material and mechanical sizing.
Moreover C2 is frequently the most expensive component of a switching regulator. Figures 3 and 4 along with Table 4 are schematics for two C2 components that have low ESR value.
Table IV. Recommended components for standard output voltages VOUT
1.22V 1.5V 1.8V 2.5V 3.3V 5.0V
ZA3020 Rev. 3.5
R2
0 2.32K 4.75K 10.5K 16.9K 30.9K
2003-04-22
L1 minimum
6.8H 6.8H 10H 10H 15H 22H
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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
Figure 3: ZA3020 with Murata 22F / 10V Ceramic Output
INPUT 4.75 to 25V C5 10nF IN
C1 10F/35V
BS SW
L1 15H
EN
ZA3020
FB GND COMP
OUTPUT 2.5V/3A
D1
OPEN NOT USED
SYNC
R2 10.5K C2 22F/10V Ceramic
C6 100pF
C3 22nF R3 10K
R1 10K
Figure 4: ZA3020 with Panasonic 47F / 6.3V Special Polymer Output Capacitor
C5 10nF INPUT 4.75 to 25V C1 10F/50V
IN
BS SW
L1 15H OUTPUT 2.5V/3A D1 FB R2 10.5K C2 47F/6.3V Panasonic SP R1 10K
EN
ZA3020
GND COMP
OPEN NOT USED
SYNC
C6 100pF
C3 22nF R3 4.99K
Note 1: For VOUT<2.5V R3 = 4.7K
ZA3020
Rev. 3.5
2003-04-22
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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
Table 5. Inductor Selection Guide
Vendor/Model Sumida
CR75 CR75 CR75 CDH74 CDH74 CDH74 CDRH5D28 CDRH5D28 CDRH5D28 CDRH6D28 CDRH6D28 CDRH6D28 CDRH6D28 CDRH6D38 CDRH6D38 CDRH6D38 CDRH6D38 CDRH104R CDRH104R CDRH104R CDRH104R 10 15 22 10 15 22 6.8 10 15 6.8 10 15 22 6.8 10 15 22 6.8 10 15 22 6.8 10 15 22 6.8 10 15 22 10 16 22 10 15 22 10 15 22 10 15 22 2003-04-22 2.3 1.8 1.5 2.75 2.1 1.7 1.6 1.3 1.1 2.3 1.7 1.6 1.3 2.3 2.0 1.6 1.3 4.8 4.4 3.6 2.9 2.01 1.77 1.40 1.15 1.79 1.63 1.33 1.09 4.3 3.3 2.5 2.26 2.00 1.83 2.4 2.0 1.6 3.8 3.0 2.6 0.070 0.090 0.110 0.056 0.083 0.130 0.053 0.065 0.103 0.031 0.065 0.057 0.096 0.031 0.038 0.057 0.096 0.027 0.035 0.050 0.073 0.068 0.090 0.142 0.208 0.050 0.055 0.081 0.115 0.0265 0.0492 0.0265 0.051 0.066 0.100 0.030 0.040 0.050 0.030 0.040 0.050 Open Open Open Open Open Open Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite
Value (H)
Max IDC (A)
Max DCR ()
Core Type
Core Material
Package Dimensions (mm) W L H
7.0 7.0 7.0 7.3 7.3 7.3 5.5 5.5 5.5 6.7 6.7 6.7 6.7 6.7 6.7 6.7 6.7 10.1 10.1 10.1 10.1 5.0 5.0 5.0 5.0 7.6 7.6 7.6 7.6 10.0 10.0 10.0 9.7 9.7 9.7 9.4 9.4 9.4 9.4 9.4 9.4
7.8 7.8 7.8 8.0 8.0 8.0 5.7 5.7 5.7 6.7 6.7 6.7 6.7 6.7 6.7 6.7 6.7 10.0 10.0 10.0 10.0 5.0 5.0 5.0 5.0 7.6 7.6 7.6 7.6 10.0 10.0 10.0 11.5 11.5 11.5 13.0 13.0 13.0 13.0 13.0 13.0
5.5 5.5 5.5 5.2 5.2 5.2 5.5 5.5 5.5 3.0 3.0 3.0 3.0 4.0 4.0 4.0 4.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 5.1 5.1 5.1 5.1 4.3 4.3 4.3 4.0 4.0 4.0 3.0 3.0 3.0 5.1 5.1 5.1
8
Toko
D53LC Type A D53LC Type A D53LC Type A D53LC Type A D75C D75C D75C D75C D104C D104C D104C D10FL D10FL D10FL
Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Open Open Open Open Open Open Open Open Open
Coilcraft
DO3308 DO3308 DO3308 DO3316 DO3316 DO3316 ZA3020 Rev. 3.5
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ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
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ZA3020 DC-DC DEMO BOARD V1.0
STEP-DOWN CONVERTER 4.75 ~ 28V to 1.2 ~ 21V
Vout= 1.222
R? + R02 (V) R02
R?=R03,R04,R05,R06,R07,R08
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9
ZA3020
2A Step-Down, PWM, Switch-Mode DC-DC Regulators
Packaging
SOIC8
PIN 1 IDENT.
0.229(5.820) 0.244(6.200)
0.150(3.810) 0.157(4.000)
0.0075(0.191) 0.0098(0.249)
SEE DETAIL
0.013(0.330) 0.020(0.508) 0.050(1.270)BSC 0.011(0.280) x 45 o 0.020(0.508)
0.189(4.800) 0.197(5.004) 0.053(1.350) 0.068(1.730) 0.049(1.250) 0.060(1.524)
0o-8o
0.016(0.410) 0.050(1.270)
DETAIL "A"
SEATING PLANE 0.001(0.030) 0.004(0.101) NOTE: 1) Control dimension is in inches. Dimension in bracket is millimeters. 2) Heat Slug Option Only (N Package)
Notice: Vimicro Corporation believes the information in this document to be accurate and reliable. However, it is subject
to change without notice. Please Contact the factory for current specifications No Responsibility is assumed by Vimicro Corporation for its use or fit to any application, nor for infringement of patent or rights of third parties. ZA3020 Rev. 3.5 2003-4-22 (c) 2003 VIMICRO Corp. VIMICRO Corporation
4/F T2-B Building, South District, High-Tech Industrial Park Shenzhen, Guangdong P.R.C.
Tel:+86-755-26719818 Fax:+86-755-26719539 Web:www.Vimicro.com

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