ZA3020 ETC

Document overview

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Technical content

Features

/square4 2A Output Current /square4 0.18ȍ Internal Power MOSFET Switch /square4 Stable with Low ESR Output Ceramic capacitors /square4 Up to 95% Efficiency /square4 20µA Shutdown Mode /square4 Fixed 380kHz frequency /square4 Thermal Shutdown /square4 Cycle-by-cycle over current protection /square4 Wide 4.75 to 25V operating input range /square4 Output Adjustable from 1.22 to 21V /square4 Programmable under voltage lockout /square4 Frequency Synchronization Input /square4 Available in 8 pin SO package /square4 Evaluation Board Available

Applications

/square4 Distributed Power Systems /square4 Battery Charger /square4 Pre-Regulator for Linear Regulators Figure 1: Typical Application Circuit 00 . 511 . 52 Output Current (A) Efficiency (%) 5.0V 3.3V 2.5V SHUTDOWN IN BS FB COMPGND EN SNYC VIN 4.75 to 25V IN ENABLE OPEN VOUT 2.5V/2A NOT USED ZA3020 Efficiency versus Output Current and Voltage. VIN=10V SW ZA3020 2A Step-Down, PWM, Switch-Mode DC-DC Regulators ZA3020 Rev. 3. 5 2003-04- 22 w w w . v i m i c r o . c o m 1

Absolute Maximum Ratings (Note 1) Recommended Operating Conditions (Note 2) Supply Voltage (VIN) 28V Input Voltage (V IN) 4.75V to 25V Switch Voltage (VSW) -1V to V IN +1V Operating Temperature -40 to +125°C Boost Voltage V SW + 6V Feedback Voltage (VFB) –0.3 to 6V Enable/UVLO Voltage (VEN) –0.3 to 6V Comp Voltage (VCOMP) –0.3 to 6V Sync Voltage (VSYNC) –0.3 to 6V Package Thermal Characteristics Junction Temperature 150°C Thermal Resistance șJA (SOIC8) 105°C/W Lead Temperature 260°C Storage Temperature -65 to +150°C Electrical Characteristics (Unless otherwise specified VIN=12V, TA=25 C) Parameters Condition Min Typ Max Units Feedback Voltage 4.75V ≤ VIN ≤ 25V VCOMP < 2V 1.198 1.222 1.246 V Upper Switch On Resistance 0.18 ȍ Lower Switch On Resistance 10 ȍ Upper Switch Leakage V EN=0V; VSW=0V 0 10 µA Current Limit 2.4 2.85 3.3 A Current Limit Gain. Output Current to Comp Pin Voltage 1.95 A/V Error Amplifier Voltage Gain 400 V/V Error Amplifier Transconductance ∆IC = ±10 µA 500 770 1100 µMho Oscillator Frequency 342 380 418 KHz Short Circuit Frequency V FB = 0V 30 42 54 KHz Sync Frequency Sync Drive 0 to 2.7V 445 600 KHz Maximum Duty Cycle V FB = 1.0V 90 % Minimum Duty Cycle V FB = 1.5V 0 % Enable Threshold I CC > 100µA 0.7 1.0 1.3 V Enable Pull Up Current V EN = 0V 1.15 1.46 1.8 µA Under Voltage Lockout Threshold High Going 2.37 2.495 2.62 V Under Voltage Lockout Threshold Hysteresis 210 mV Supply current (quiescent) VEN ≤≤≤≤ 0.4V 23 36 µA Supply current (operating) VEN ≥ 2.6V; VFB =1.4V 1.0 1.2 mA Thermal Shutdown 160 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 2A Step-Down, PWM, Switch-Mode DC-DC Regulators ZA3020 Rev. 3. 5 2003-04- 22 w w w . v i m i c r o . c o m 2

Figure 2: Functional Block Diagram Σ 40/400KHz Oscillator Slope Compensation 1.8V Current Comparator Internal Regulators 1uA 2.30/2.53V 0.7V Shutdown Comparator Lockout Comparato r 10 ohm 0.2 ohm 1.22V Error Amplifier gm= 630uA/Volt IN SYNC EN COMP FB GND SW BS1 0.7VFrequency Foldback Comparator CLK S R Q Q Current Sense Amplifier 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 ȍ switch ensures that the bootstrap capacitor voltage is charged during light load conditions. External Schottky Diode D1 carries most of the inductor current. ZA3020 2A Step-Down, PWM, Switch-Mode DC-DC Regulators ZA3020 Rev. 3. 5 2003-04- 22 w w w . v i m i c r o . c o m 3

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 D SCH 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 V IN 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 11Kȍ 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 V IN. BS 1 IN SW GND SYNC EN COMP FB ZA3020 2A Step-Down, PWM, Switch-Mode DC-DC Regulators ZA3020 Rev. 3. 5 2003-04- 22 w w w . v i m i c r o . c o m 4

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/ʌ(R3 X C6). For R3=10Kȍ 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: V The maximum recommended value of R1 is 100Kȍ. Too high an impedance can make the Feedback node prone to noise injection particularly if unshielded inductors are used. 10Kȍ 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 0.1µF 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 V SW 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 V IN (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 2A Step-Down, PWM, Switch-Mode DC-DC Regulators ZA3020 Rev. 3. 5 2003-04- 22 w w w . v i m i c r o . c o m 5

Applications Information Continued Table 2: Diode Selection Guide VIN (Max) 1A Diodes 2A Diodes 15V 10BQ15 30BQ15 20V 1N5817 B120 SS12 B220 SK23 SR22 30V 1N5818 B130 MBRS130 SS13 20BQ030 B230 SK23 SR23 SS23 Table 3: Schottky Diode Manufacturers Vendor Web Site Diodes, Inc. www.diodes.com Fairchild Semiconductor www.fairchildsemi.com General Semiconductor www.gensemi.com International Rectifier www.irf.com On Semiconductor www.onsemi.com Pan Jit International www. panjit.com.tw 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. The Maximum current rating of the inductor should be above the peak operating current: I PEAK = ILOAD + (VOUT)(VIN-VOUT) 2(L)(F)(V IN) Example: VIN=12V VOUT=3.3V, L=15µH, ILOAD=1.2A 2(15u)(380KHz)(12) I PEAK = 1.809A Using Table 5 select a 15µH 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 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 R2 L1 minimum 1.22V 0ȍ 6.8µH 1.5V 2.32Kȍ 6.8µH 1.8V 4.75Kȍ 10µH 2.5V 10.5Kȍ 10µH 3.3V 16.9Kȍ 15µH 5.0V 30.9Kȍ 22µH ZA3020 2A Step-Down, PWM, Switch-Mode DC-DC Regulators ZA3020 Rev. 3. 5 2003-04- 22 w w w . v i m i c r o . c o m 6

Table 5. Inductor Selection Guide

2A Step-Down, PWM, Switch-Mode DC-DC Regulators ZA3020 Rev. 3. 5 2003-04-22 www.vimicro.com 9 /G01 /G05 /G01 /G33/G11/G28/G34/G23/G34/G01/G08/G03/G18/G0E/G01/G15/G0E/G06/G05/G21/G01/G25/G0A/G27/G03/G18/G06/G0D/G0B/G0A/G01 /G05 /G17/G2F/G1B/G21/G01/G32/G06/G0B/G07/G05/G01/G1B/G21/G01/G0A/G0B/G1B/G05/G01/G06/G0C/G1A/G01/G1A/G06/G01/G0B/G1D/G1D/G06/G20/G20/G06/G05/G0B/G1A/G03/G01/G20/G06/G21/G1A/G01/G1D/G06/G20/G20/G06/G04/G0A/G18/G01/G0C/G21/G03/G05/G01/G11/G04/G05/G0C/G1D/G1A/G06/G07/G21/G01/G0B/G04/G05/G01/G30/G0C/G1A/G19/G0C/G1A/G01/G14/G0B/G19/G0B/G1D/G1B/G1A/G06/G07/G21/G33/G01/G0B/G04/G05/G01/G1A/G06/G01/G32/G03/G01 /G19/G07/G06/G1F/G07/G0B/G20/G20/G03/G05/G01/G34/G06/G07/G01/G20/G06/G21/G1A/G01/G21/G1A/G0B/G04/G05/G0B/G07/G05/G01/G30/G0C/G1A/G19/G0C/G1A/G01/G02/G06/G0A/G1A/G0B/G1F/G03/G21/G25/G01/G01/G35/G06/G07/G01/G1A/G2F/G03/G01/G07/G03/G36/G0C/G1B/G07/G03/G05/G01/G30/G0C/G1A/G19/G0C/G1A/G01/G37/G06/G0A/G1A/G0B/G1F/G03/G01/G21/G06/G0A/G05/G03/G07/G01/G32/G0A/G06/G32/G01/G1A/G2F/G03/G01/G0B/G19/G19/G07/G06/G19/G07/G1B/G0B/G1A/G03/G01/G38/G2D/G39/G2B/G01 /G3A/G0C/G20/G19/G03/G07/G25/G01 STEP-DOWN CONVERTER EN /G01/G02/G03 /G04/G05/G06/G07/G08 /G09/G0A/G0B/G0C /G04 /G0C DC OUT /G0D/G02/G04 /G0E/G0F/G10/G02/G0C/G02 /G04 /G0C /G10 /G11 /G12 /G05 /G03 /G07 /G09/G02/G0C /G02/G06/G04/G13/G14 R02 /G09/G02/G12 /G04/G02/G02/G15/G14 1.222 + /G09/G02/G04/G04 /G04/G02/G13/G14/G16/G10/G12/G17 Vout= /G01/G02/G04 /G04/G02/G08 /G04 /G0C /G18/G02/G04 /G19/G0C/G10/G02 /G04 /G0C /G04 /G0C /G1A/G02/G04 /G04/G12/G13/G1B/G16/G0C/G0F /G09/G02/G11 /G0C/G0C/G1C/G14 4.75 ~ 28V to 1.2 ~ 21V /G09/G02/G03 /G0C/G0C/G13/G14/G16 /G09/G0A/G0B/G04 /G04 /G0C /G09/G02/G10 /G04/G02/G1C/G14 /G01/G02/G0C /G04/G02/G08 SYNC DC IN /G01/G02/G12 /G01 ZA3020 DC-DC /G04 /G0C R? + R02 /G01/G02/G05 /G01 (V) /G01/G02/G11 /G01 /G04 /G0C /G04 /G0C DEMO BOARD V1.0 /G09/G02/G07 /G02/G06/G04/G13/G14 R?=R03,R04,R05,R06,R07,R08 /G01/G02/G10 /G01 /G04 /G0C /G01/G02/G07 /G10/G04/G08 /G01 /G05 /G05 /G2F/G08/G09/G12/G05 /G30/G10/G07/G0C/G08/G03/G08/G18/G05 /G28/G09/G11/G09/G0F/G09/G0C/G0A/G09/G05 /G31/G07/G0F/G08/G05 /G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G32/G05 /G05 /G26/G05 /G21/G05 /G15/G1C/G19/G26/G05 /G23/G05/G31/G03/G0C/G05/G15/G0B/G0C/G0C/G09/G0A/G08/G0B/G0F/G05 /G05 /G05 /G15/G1C/G19/G21/G05 /G23/G05/G31/G03/G0C/G05/G15/G0B/G0C/G0C/G09/G0A/G08/G0B/G0F/G05 /G21/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G21/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G15/G1C/G21/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G1C/G13/G26/G10/G2A/G05 /G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G15/G1C/G1F/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G1C/G13/G26/G10/G2A/G05 /G22/G05 /G26/G05 /G15/G1C/G22/G05 /G26/G1C/G0C/G2A/G05/G05/G1C/G1E/G1C/G22/G05 /G23/G05 /G26/G05 /G15/G1C/G23/G05 /G21/G21/G0C/G2A/G05/G1C/G1E/G1C/G22/G05 /G25/G05 /G26/G05 /G15/G1C/G25/G05 /G26/G1C/G1C/G0E/G2A/G05/G1C/G1E/G1C/G22/G05 /G1E/G05 /G26/G05 /G15/G1C/G26/G26/G05 /G26/G1C/G10/G2A/G05/G22/G25/G14/G05/G26/G21/G26/G1C/G05 /G24/G05 /G26/G05 /G15/G1C/G24/G05 /G21/G21/G10/G2A/G05/G26/G1E/G14/G05/G33/G25/G14/G05/G26/G21/G26/G1C/G05 /G1F/G05 /G26/G05 /G2B/G1C/G26/G05 /G34/G21/G22/G1C/G35/G2C/G36/G05/G21/G2E/G05/G22/G1C/G14/G05/G2C/G0A/G02/G0B/G08/G08/G37/G18/G05 /G27/G05 /G26/G05 /G2D/G1C/G26/G05 /G26/G25/G10/G20/G05 /G26/G1C/G05 /G21/G05 /G28/G1C/G26/G05 /G26/G1C/G1D/G05/G26/G38/G05 /G05 /G05 /G28/G1C/G21/G05 /G26/G1C/G1D/G05/G26/G38/G05 /G26/G26/G05 /G26/G05 /G28/G1C/G22/G05 /G1C/G1D/G05/G26/G38/G05 /G26/G21/G05 /G26/G05 /G28/G1C/G23/G05 /G21/G13/G22/G21/G1D/G05/G26/G38/G05 /G26/G22/G05 /G26/G05 /G28/G1C/G25/G05 /G23/G13/G24/G25/G1D/G05/G26/G38/G05 /G26/G23/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G26/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G28/G1C/G1E/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G05/G26/G1C/G13/G25/G1D/G05/G26/G38/G05 /G26/G25/G05 /G26/G05 /G28/G1C/G24/G05 /G26/G1E/G13/G27/G1D/G05/G26/G38/G05 /G26/G1E/G05 /G26/G05 /G28/G1C/G1F/G05 /G22/G1C/G13/G27/G1D/G05/G26/G38/G05 /G26/G24/G05 /G26/G05 /G39/G1C/G26/G05 /G3A/G2E/G22/G1C/G21/G1C/G35/G2C/G29/G1F/G05 /G05/G05 /G05 /G05 /G05 /G33/G11/G28/G34/G23/G34/G01/G08/G03/G18/G0E/G01/G15/G0E/G06/G05/G21/G01/G15/G22/G1A

NOTE: 1) Control dimension is in inches. Dimension in bracket is millimeters. 2) Heat Slug Option Only (N Package) 0.016(0.410) 0.050(1.270) 0o-8o DETAIL "A" 0.011(0.280) 0.020(0.508) x 45o SEE DETAIL 0.0075(0.191) 0.0098(0.249) 0.229(5.820) 0.244(6.200) SEATING PLANE 0.001(0.030) 0.004(0.101) 0.189(4.800) 0.197(5.004) 0.053(1.350) 0.068(1.730) 0.049(1.250) 0.060(1.524) 0.150(3.810) 0.157(4.000) PIN 1 IDENT. 0.050(1.270)BSC 0.013(0.330) 0.020(0.508) ZA3020 2A Step-Down, PWM, Switch-Mode DC-DC Regulators 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 VIMICRO Corporation 2003-4-22 4/F T2-B Building, South District, High-Tech Industrial Park Shenzhen, Guangdong P.R.C. © 2003 VIMICRO Corp. Tel:+86-755-26719818 Fax:+86-755-26719539 Web:www.Vimicro.com