AME AME5297 n General Description 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter n Application The AME5297 is a high frequency synchronous stepdown DC-DC converter with built internal power MOSFETs. That provides wide 4.5V to 18V input voltage range and 3A continuous load current capability. The AME5297 has synchronous mode operation for higher efficiency over output current load range. The AME5297 is current mode control scheme which provides fast transient reponse. Internal compensation function. l l l l n Typical Application VIN 4.5-18V C1 22uF 25V n Features l Wide 4.5V to 18V Operating Input Range l 80mΩ/30mΩ Low RDS(ON) internal Power MOSFETs l Proprietary Switching Loss Reduction Techn -ique l High Efficiency Synchronous Mode Operation l Fixed 500KHz Switching Frequency l External Programmable Soft Start l OCP and Hiccup l Thermal Shutdown l Output Adjustable from 0.8V l RoHS Compliant and Halogen Free Rev. A.05 Notebook Systems and I/O Power Digital Set Top Boxes LCD Display, TV Networking, XDSL Modem IN BST R4 10Ω C4 0.1uF VCC SW C3 1uF 3.3V 3A VOUT L1 4.7uH AME5297 R1 40.2K SS C4 22nF EN C2 47uF EN/SYNC GND FB R3 33K R2 13K 1 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 n Functional Block Diagram IN VCC VCC Regulator M RSEN Current Sense Amplifer VCC SS BST Oscillator HS Driver 1pF EN Reference 50pF 400k SW Current Limit Comparator Comparator On Time Control Logic Control VCC LS Driver 1MEG FB Error Amplifer 2 GND Rev. A.05 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 n Pin Configuration TSOT-23-8 Top View 8 7 6 5 AME5297 1 2 3 4 AME5297-AEAxxx 1. SS 2. IN 3. SW 4. GND 5. BST 6. EN 7. VCC 8. FB * Die Attach: Conductive Epoxy n Pin Description Pin No. Pin Name 1 SS Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. 2 IN Supply Voltage. The AME5297 operates from a +4.5V to +18V input rail. C1 is needed to decouple the input rail. Use wide PCB trace to make the connection. 3 SW Switch Node. Connect this pin to an external L-C filter. 4 GND System Ground. This pin is the reference ground of the regulated output voltage. For this reason care must be taken in PCB layout. Suggested to be connected to GND with copper and vias. 5 BST Bootstrap for High Side Gate Driver. Connect a 0.1µF or greater ceramic capacitor from BST to SW pins. 6 EN 7 VCC 8 FB Rev. A.05 Pin Description Enable. EN high to enable the AME5297. Bias Supply. Decouple with a 0.1µF-to-1µF cap. Feedback Input. It's used to regulate the output of the converter to a set value via an extermal resistive voltage divider. 3 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 n Ordering Information AME5297 - x x x xxx x Special Feature Output Voltage Number of Pins Package Type Pin Configuration Pin Configuration A (TSOT-23-8) 4 1. SS 2. IN 3. SW 4. GND 5. BST 6. EN 7. VCC 8. FB Package Type Number of Pins Output Voltage Special Feature E: SOT-2X A: 8 ADJ: Adjustable L: TSOT-23-8 (Low Profile) Rev. A.05 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 n Absolute Maximum Ratings Parameter Maximum Unit VIN -0.3 to 19 V VSW -0.3V (-5V for 10ns) to 19V (20V for 5ns) V VBST VSW +6V V All Other Pins -0.3 to 6 V Junction Temperature 150 o C Lead Temperature 260 o C -65 to +150 o C Storage Temperature n Recommended Operating Conditions Parameter Symbol Rating VIN 4.5V to 18V VOUT 0.8V to VIN-3V Junction Temperature Range TJ -40 to +125 Ambient Temperature Range TA -40 to +85 Input Voltage Output Voltage Unit V o C n Thermal Information Parameter Package Die Attach Thermal Resistance* (Junction to Case) Thermal Resistance (Junction to Ambient) Symbol Maximum θJ C 55 Unit o TSOT-23-8 Conductive Epoxy Internal Power Dissipation Lead Temperature (Soldering 10sec)** θJA 100 PD 1250 260 C/W mW o C * Measure θJC on backside center of molding compound if IC has no tab. ** MIL-STD-202G 210F Rev. A.05 5 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 n Electrical Specifications VIN=12V, unless otherwise noted. Typical values are at TA=25oC. Parameter Symbol Test Condition Supply Shutdown Current IIN VEN=0V 0.1 µA Supply Current IQ VEN=2V, VFB=1V, VSS=3V 0.7 mA Hihg Side Switch On-Resistance RDS(ON)1 VBST-SW=5V 80 mΩ Low Side Switch On-Resistance RRDS(ON)2 VCC=5V 30 mΩ SW LKG VEN=0V, VSW=12V 0.15 µA 4.2 5 A 440 500 Load Side Switch Leakage Current Switch Current Limit Oscillator Frequency fOSC VFB=0.75V Fold-back Frequency fFB VFB<400mV Maximum Duty Cycle DMAX VFB=700mV Feedback Voltage VFB TA=25 C Feedback Current IFB VFB=800mV Typ Max 580 Units KHz 0.25 fSW 90 95 % -2% 800 2% mV 10 50 nA EN Rising Threshold VEN_RISING 1.2 1.4 1.6 V EN Falling Threshold VEN_FALLING 1.1 1.25 1.4 V EN Input Current EN Turn Off Delay IEN VEN=2V 2 µA VEN=0V 0 µA 8 µs ENTD-OFF Input Under Voltage Lockout Threshold VUVLO Input Under Voltage Lockout Hysteresis VCC Regulator 3.6 V ∆VUVLO 650 mV VCC 5 V 3 % µA VCC Load Regulation ICC=5mA Soft-Start Current ISS 11 Thermal Shutdown TSD 150 o C 20 o C Thermal Hysteresis 6 o Min Rev. A.05 AME AME5297 n Detailed Descriptiion Internal VCC Regulator The internal VCC regulator is adjusted 5.0V to provide power to the internal circuits from input voltage VIN. In order to maintain the VCC voltage stably, a 0.1µ F-to-1µF ceramic capacitor is recommended. 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter Thermal Shutdown The AME5297 protects itself from overheating with an internal thermal shutdown circuit. If the junction temperature exceeds the thermal shutdown threshold, the voltage reference is grounded and the shutdown mode is activated. The AME5297 is restarted under control of the soft start automatically when the junction temperature drops 20oC below the thermal shutdown threshold. Enable and Soft Start The EN pin provides electrical on/off control of the regulator. When the EN pin voltage exceeds the lockout threshold voltage, the regulator starts to operate and the soft start begins to charge the external capacitor. If the EN pin voltage is pulled below the lockout threshold voltage, the regulator stops switching and the soft start resets. Connecting the EN pin to ground or to any voltage less than 1.2V will disable the regulator and activate the shutdown mode. To limit the start-up inrush current, a soft-start circuit is used to ramp up the reference voltage from 0V to its final value linearly. The soft start time can be calculated as follows: t SS = 0.8 × CSS ISS Under Voltage Lockout (UVLO) The AME5297 incorporates an under voltage lockout circuit to keep the device disabled when the input voltage VIN is below the UVLO start threshold voltage. During powering up, the internal circuits are held inactive and the soft start is grounded until the input voltage VIN exceeds the UVLO start threshold voltage. Once the UVLO start threshold voltage is reached, the soft start is activated and the device begins to operate. The device operates until the input voltage VIN falls below the UVLO stop threshold voltage. The typical hysteresis in the UVLO comparator is 650mV. Rev. A.05 Over-Current Protection and Hiccup Mode The over-current limiting is implemented by cycle-bycycle monitoring the current through the high side MOSFET. If the peak current exceeds the over-current limit threshold, the high side MOSFET is turned off. When the feedback voltage VFB drops below 0.4V, the oscillator frequency is reduced to about 1/4 of the normal frequency to ensure that the inductor current has more time to decay, thereby preventing runaway. Meanwhile, the AME5297 enters hiccup mode, the average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. Enternal Bootstrap Circuit The external bootstrap circuit contains a capacitor and a resistor. A bootstrap capacitor provides power for the high side MOSFET driver. In order to supply the AC current and maintain the BST-SW voltage stably at the switching condition of the high side MOSFET, a 0.1µF low ESR ceramic capacitor is recommended. The bootstrap resistor which suggests placing 10Ω is utilized to reduce switching spike voltage and noise. 7 AME AME5297 n Application Information Inductor Selection For most applications, the inductance range is chosen based on the desired ripple current. A larger inductance reduces ripple current; meanwhile, the output ripple voltage decreases. Determine inductance is to allow the peakto-peak ripple current to be approximately 30% of the maximum load current. The inductance value can be calculated by: L= V VOUT × 1 − OUT VIN f × IL Where f is the oscillator frequency, VIN is the input voltage, VOUT is the output voltage, and ∆IL is the peak-to-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current, calculated by: I LPEAK = I LOAD + VOUT V × 1 − OUT 2 × f × IL VIN Where ILOAD is the load current. The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI constraints. The input current to the buck converter is discontinuous; therefore an input capacitor is required to supply the AC current while maintaining the DC input voltage. In order to prevent large voltage drop, a low ESR capacitors is recommended for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors will also be suggested. Choose X5R or X7R dielectrics when using ceramic capacitors. Since the input capacitor absorbs the input switching current, it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: 8 At VIN = 2VOUT, where ICIN = ILOAD/2 is the worst-case condition occurs. For simplification, use an input capacitor with a RMS current rating greater than half of the maximum load current. When using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input. When using electrolytic or tantalum capacitors, a high quality, small ceramic capacitor, i.e. 0.1µF, should be placed as close to the IC as possible. The input voltage ripple for low ESR capacitors can be estimated by: VIN = I LOAD VOUT V × × 1 − OUT C IN × f VIN VIN Where CIN is the input capacitance value. Output Capacitor The output capacitor (COUT) is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by: VOUT = Input Capacitor I CIN = I LOAD × 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter VOUT V × 1 − OUT VIN VIN VOUT V 1 × 1 − OUT × R ESR + f ×L VIN 8 × f × COUT Where RESR is the equivalent series resistance (ESR) value of the output capacitor and COUT is the output capacitance value. When using ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance which is the main cause for the output voltage ripple. For simplification, the output voltage ripple can be estimated by: VOUT = VOUT V × 1 − OUT 8 × f × L × COUT VIN 2 Rev. A.05 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: VOUT = VOUT V × 1 − OUT × R ESR f ×L VIN Setting the Output Voltage The output voltage is using a resistive voltage divider connected from the output voltage to feedback pin. It divides the output voltage down to the feedback voltage by the ratio: VFB = VOUT × R2 R1 + R 2 The output voltage is: VOUT = 0.8 × R1 + R 2 R2 n Typical Application Circuits VIN 4.5V~16V Ren1 18K IN CIN2 NS CIN1 22uF BST C3 1uF C5 22nF Rev. A.05 C4 0.1uF AME5297 L1 4.7uH VOUT 3.3V/3A SW EN Ren2 10K R4 10Ω VCC R1 40.2K SS FB R3 33K C6 15pF COUT 1 22uF COUT2 22uF R5 0Ω R2 12.7K GND VOUT(V) R1(KΩ) R2(KΩ) R3(KΩ) L(µH) CIN(µF) COUT(µF) 1.0 20.5 82.0 82 1.5 22 22x2 1.2 30.1 60.4 82 1.5 22 22x2 1.8 40.2 32.4 56 2.2 22 22x2 2.5 40.2 19.1 33 3.3 22 22x2 3.3 40.2 12.7 33 4.7 22 22x2 5.0 40.2 7.68 33 6.8 22 22x2 9 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 n Characterization Curve Load Transient VIN=12V, VOUT=3.3V, IOUT=0.5~3A IL (2A/Div) Output Voltage Ripple V IN (100mV/Div) V OUT (20mV/Div) VSW (10V/Div) VOUT (200mV/Div) C4 IL (2A/Div) C3 VIN=12V, VOUT=3.3V, IOUT=3A C1 C2 C3 C4 Time(2µs/Div) Time(200µF/Div) Power On from Input Voltage Power On from Input Voltage V IN (5V/Div) VOUT (2V/Div) VIN=12V, VOUT=3.3V IOUT=0A C2 V SW (5V/Div) C3 IL (2A/Div) C4 VEN (5V/Div) V OUT (2V/Div) VIN (5V/Div) VOUT (2V/Div) C1 VSW (5V/Div) C3 IL (2A/Div) C4 Time(5ms/Div) Power On from EN Power on from EN VIN=12V, VOUT=3.3V IOUT=0A VEN (5V/Div) VOUT (2V/Div) V SW (5V/Div) V SW (5V/Div) IL (2A/Div) C1 C2 VIN=12V, VOUT=3.3V IOUT=3A C3 C3 IL (2A/Div) C4 Time(5ms/Div) 10 C1 C2 Time(5ms/Div) C1 C2 VIN=12V, VOUT=3.3V IOUT=3A C4 Time(5ms/Div) Rev. A.05 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 Power Off from Input Voltage Power Off from Input Voltage VIN=12V, VOUT=3.3V IOUT=3A VIN=12V, VOUT=3.3V, IOUT=0A VIN (5V/Div) C1 V OUT (2V/Div) C2 VSW (5V/Div) IL (2A/Div) V IN (5V/Div) V OUT (2V/Div) VSW (5V/Div) C3 IL (2A/Div) C4 VEN (5V/Div) C1 VOUT (2V/Div) C1 C2 C3 C4 Time(50ms/Div) Time(5ms/Div) Power Off from EN Power Off from EN VEN (5V/Div) C1 C2 V OUT (2V/Div) C2 V SW (5V/Div) C3 VSW (5V/Div) C3 IL (2A/Div) C4 IL (2A/Div) C4 VIN=12V, VOUT=3.3V, IOUT=0A Time(2s/Div) Time(5ms/Div) Short Circuit Entry Short Circuit Recovery VIN=12V, VOUT=3.3V, IOUT=0A VIN=12V, VOUT=3.3V, IOUT=0A VOUT (1V/Div) V SW (10V/Div) V SS (1V/Div) IL (5A/Div) C3 C2 C1 C4 Time(5ms/Div) Rev. A.05 VIN=12V, VOUT=3.3V, IOUT=3A VOUT (1V/Div) C3 VSW (10V/Div) C2 VSS (1V/Div) C1 IL (5AD/iv) C4 Time(5ms/Div) 11 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 Efficiency 12V 18V VOUT =5V, IOUT =0~3A 100 100 90 90 80 80 Efficiency (%) Efficiency (%) 18V Efficiency 70 60 50 40 30 20 5V VOUT =3.3V, IOUT=0~3A 70 60 50 40 30 20 10 10 0 12V 0 0. 0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Output Current (A) Output Current (A) Efficiency 5V 12V 100 18V VOUT=1.2V, IOUT =0~3A Efficiency (%) 90 80 70 60 50 40 30 20 10 0 0.0 0. 5 1.0 1. 5 2. 0 2.5 3. 0 Output Current (A) 12 Rev. A.05 AME 3A, 18V, 500KHz Synchronous Step-Down DC/DC Converter AME5297 n Tape and Reel Dimension TSOT-23-8 P0 W AME AME PIN 1 P Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Pitch (P0) Part Per Full Reel Reel Size TSOT-23-8 8.0±0.1 mm 4.0±0.1 mm 4.0±0.1 mm 3000pcs 180±1 mm n Package Dimension TSOT-23-8 Top View Side View D L b E E1 0.25 PIN 1 e C e1 A A1 A2 Front View Rev. A.05 13 www.ame.com.tw E-Mail: [email protected] Life Support Policy: These products of AME, Inc. are not authorized for use as critical components in life-support devices or systems, without the express written approval of the president of AME, Inc. AME, Inc. reserves the right to make changes in the circuitry and specifications of its devices and advises its customers to obtain the latest version of relevant information. AME, Inc. , October 2014 Document: A018A-DS5297-A.05 Corporate Headquarter AME, Inc. 8F, 12, WenHu St., Nei-Hu Taipei 114, Taiwan . Tel: 886 2 2627-8687 Fax: 886 2 2659-2989