AME. 40V CC/CV Buck Converter AME5244. n General Description. n Typical Application. n Features. n Functional Block Diagram.

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1 5244 n General Description n Typical Application The 5244 is a specific 40 H buck converter that operates in either C/CC mode supports an put voltage range of 0.8 to 2 and support constant put current at 200KHz switching frequency. Protection features include under voltage protection, over voltage protection, current limit, thermal shutdown, and short circuit protection. The device is available in SOP-8/PP package with exposed pad for low thermal resistance. n Features IN= 8~40 C 47uF C4 3.3nF C5 Optional R3 8.2K IN 5244 COMP BS GND R4 C3 0Ω 22nF SW FB L 47uH D SK R 34 0K R2 20K C2 470uF BUS GND l 40 Maximum Rating for Input Power l 200KHz Switching Frequency l CC/C Mode Function l Internal Soft Start l UP, Input/Output OP, OTP, SCP l Available in SOP-8/PP Package l RoHS Compliant and Halogen Free 5244-AZAADJ-24 n Functional Block Diagram IN n Application Oscillator EMI Control BS l Car Charger l Wall Adapter ref & S/D Control PWM Controller 0.8 SW FB CC Control COMP GND

2 5244 n Pin Configuration SOP-8/PP Top iew GND AZAADJ. IN 2. COMP 3. NC 4. NC 5. FB 6. GND 7. SW 8. BS * Die Attach: Conductive Epoxy n Pin Description Pin No. Pin Name Pin Description IN Input power. 2 COMP Compensation Node. 3, 4 NC No connection. 5 FB Feedback Input. 6 GND Ground. 7 SW Power Switching Output 8 BS High Side. Gate Drive Boost Input. 9 Exposed Pad Ground. 2

3 5244 n Ordering Information x x x xxx - xx Special Feature Output oltage Number of Pins Package Type Pin Configuration Pin Configuration Package Type Number of Pins Output oltage Special Feature A. IN Z: SOP/PP A: 8 ADJ: Adjustable 0 (SOP-8/PP) 2. COMP NC 4. NC 5. FB 6. GND 7. SW 8. BS 3

4 5244 n Absolute Maximum Ratings Input oltage Parameter Maximum -0.3 to 40 Unit Switch oltage - to IN + Boost Switch oltage All Other Pins SW to SW to 7 Electrostatic Discharge (HBM) Junction Temperature Storage Temperature ESD Classification o C -65 to +50 o C HBM 2 k MM 50 n Recommended Operating Conditions Parameter Symbol Rating Unit Input oltage IN 8 to 40 Output oltage OUT 0.8 to 2 Junction Temperature Range T J -40 to +25 Ambient Temperature Range T A -40 to +85 o C n Thermal Information Parameter Package Die Attach Symbol Maximum Unit Thermal Resistance* (Junction to Case) Thermal Resistance (Junction to Ambient) SOP-8/PP Conductive Epoxy θ JC 9 θ JA 84 o C / W Power Dissipation P D 450 mw 4 Lead Temperature ( soldering 0 sec)** * Measure θ JC on backside center of molding compound if IC has no tab. ** MIL-STD-202G 20F 260 o C

5 5244 n Electrical Specifications Typical values IN =2 with typical T A =25 o C, unless otherwise specified. Parameter Symbol Test Condition Min Typ Max Units Input oltage Operating Range IN 8 40 IN ULO Rising Threshold oltage ULO Input oltage Rising 7 IN ULO Hysteresis ULO_YHS Input oltage Falling Standby Current OUT =5, No load 3 ma Feedback oltage FB 0.8 Feedback oltage Accuracy FB % Internal Soft Start Time T SS 0 ms Hith Site Switch ON-Resistance R DS(ON)_HI 20 mω Max. Duty Cycle D MAX 85 % Switching Frequency f OSC FB = KHz Constant Current I CC 5244-AZAADJ-0.6 A 5244-AZAADJ A Thermal Shutdown T SD 50 o C Thermal Shutdown Hysteresis T SD 20 o C Output OP O-OUT OUT x.06 OUT x.6 Input OP O-IN Input OP Hysteresis 2 Short Current Limit 2 A 5

6 5244 n Detailed Description 6 Under oltage Lock (ULO) The 5244 incorporates an under voltage lock circuit to keep the device disabled when IN (the input voltage) is below the ULO rising threshold voltage. Once the ULO rising threshold voltage is reached,the device start-up begins. The device operates until IN falls below the ULO falling threshold voltage. The typical hysteresis in the ULO comparator is. Over oltage Protection The 5244 has input and put over-voltage protections. The thresholds of input and put OP circuit include are typicapl 35 and minimum 06% x OUT, respectively. Once the input voltage or put voltage is higher than the threshold, the high-side MOSFET is turned off. When the input voltage or put voltage drops lower than the threshold, the high-side MOSFET will be enabled again. Over Current Protection The 5244 cycle-by-cycle limits the peak inductor current to protect embedded switch from dameage. Highside switch current limiting is implemented by monitoring the current through the high side MOSFET. Thermal Shutdown The 5244 protects itself from overheating with an internal thermal shutdown circuit. If the junction temperature exceeds the thermal shutdown trip point, the highside MOSFET is turned off. The part is restarted when the junction temperature drops 20 o C below the thermal shutdown trip point Setting the Output oltage The put voltage is using a resistive voltage divider connected from the put voltage to FB. It divides the put voltage down to the feedback voltage by the ratio: FB = R2 R + R 2 the put voltage is: R R = 0.8 R + Inductor Selection The inductor is required to supply contant current to the load while being driven by the switched input voltage. A larger value inductor will have a larger physical size and higher series resistance. It will result in less ripple current that will in turn result in lower put ripple voltage. Make sure that the peak inductor current is below the maximum switch current limit. Determine inductance is to allow the peak-to-peak ripple current to be approximately 30% of the maximum load current. The inductance value can be calculated by: L = fs I L in Where f S is the switching frequency, IN is the input voltage, OUT is the put voltage, and Ι L is the peakto-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current, calculated by: Where I LOAD is the load current. The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI constraints. Input Capacitor 2 I = + LPK I LOAD 2 fs L 2 The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the AC current while maintaining the DC input voltage. Use low ESR capacitors 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. in

7 5244 Since the input capacitor (C) absorbs the input switching current, it requires an adequate ripple current tating. The RMS current in the input capacitor can be esimated by: I C I LOAD in At IN =2 OUT, where I C = I LOAD /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.µF, should be placed as close to the IC as possible. The input voltage ripple for low ESR capacitors can be estimated by: I LOAD I = C C fs in Where C is the input capacitance value. Output Capacitor The put capacitor (C2) is required to maintain the DC put voltage. Ceramic, tantalum, or low ESR electrolutic capacitors are recommended. Low ESR capacitors are preferred to keep the put voltage ripple low. The put voltage ripple can be estimated by: Where R ESR is the equivalent series resistance (ESR) value of the put capacitor and C2 is the put capacitance value. When using ceramic capacitors, the impandance at the switching frequency is dominated by the capacitance which is the main cause for the put voltage ripple. For simplification, the put voltage ripple can be estimated by: = in = fs L in R = 2 8 fs L C2 in ESR in + 8 fs C2 When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the put ripple can be approximated to: = fs L in The characteristics of the put capacitor also affect the stability of the regulation system. Rectifier Diode Use a Schottky diode as the rectifier to conduct current when the High-Side MOSFET is turned off. The Schottky diode must have current rating higher than the maximum put current and a reverse voltage rating higher than the maximum input voltage. Compensation Components 5244 has current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the COMP pin. COMP is the put of the internal transconductance error amplifier. A series capacitor-resistor combination sets a pole-zero combination to govern the characteristics of the control system. The DC gain of the voltage feedback loop is given by: FB A DC = RLOAD GCS AEA ESR Where FB is the feedback voltage (0.8), A EA is the error amplifier voltage gain, G CS is the current sense transconducductance and R LOAD is the load resistor value. The system has two poles of importance. One is due to the put capacitor and the load resistor, and the other is due to the compansation capacitor (C4) and the put resistor of the error amplifier. These poles are located at: f f P P2 GEA = 2 π C4 A = 2 π C2 R EA LOAD R 7

8 5244 Where G EA is the error amplifier transconducductance. The system has one zero of importance, due to the compensation capacitor (C4) and the compensation resistor (R3). This zero is located at: f = Z 2 π C4 R3 The system may have another zero of importance, if the put capacitor has a large capacitance and/or a high ESR value. The zero, due to the ESR and capacitance of the put capacitor, is located at: f ESR = 2 π C2 R ESR In this case, a third pole set by the second compensation capacitor (C5) and the compensation resistor (R3) is used to compensate the effect of the ESR zero on the loop gain. This pole is located at: f 3 = P 2 π C5 R3 The goal of compensation design is to shape the converter transfer function to get a desired loop gain. The system crossover frequency where the feedback loop has the unity gain is important. Lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies could cause system instability. A good standard is to set the crossover frequency below one-tenth of the switching frequency. To optimize the compensation components, the following procedure can be used. 2. Choose the compensation capacitor (C4) to achieve the desired phase margin. For applications with typical inductor values, setting the compensation zero (f Z ) below one-forth of the crossover frequency provides sufficient phase margin. Determine C4 by the floolwing equation: 4 C4 > 2 π R3 f c Where R3 is the compensation resistor. 3. Determine if the second compensation capacitor (C5) is required. It is required if the ESR zero of the put capacitor is located at less than half of the switching frequency, or the following relationship is valid: 2 π C2 R If this is the case, then add the second compensation capacitor (C5) to set the pole f P3 at the location of the ESR zero. Determine C5 by the equation: C2 R C5 = R3 s ESR ESR f < 2. Choose the compensation resistor (R3) to set the desired crossover frequency. Determine R3 by the following equation: 2 C2 f 3 = G G c c R EA CS FB 2 C2 0. f < G G EA CS FB Where f C is the desired crossover frequency which is typically below one tenth of the switching frequency. 8

9 5244 PC Board Lay Guidance When laying the printed circuit board, the following checklist should be uesd to ensure proper operation of the IC. ) Arrange the power components to reduce the AC loop size consisting of C IN, IN pin, SW pin and the sckottky diode. 2) Place input decoupling ceramic capacitor C IN as close to IN pin as possible. C IN is connected power GND with vias or short and wide path. 3) Return FB and COMP to signal GND pin, and connect the singal GND to power GND at a single point for the best noise immunity. Connect exposed pad to power ground copper area with copper and vias. 4) Use copper plane for power GND for best heat disspation and noise immunity. 5) Please feedback resistor close to FB pin. Top Layer Bottom Layer 9

10 5244 n Radiated EMI Data (ertical) n Radiated EMI Data (Horizontal) 0

11 5244 n Characterization Curve Efficiency vs. Output Current Power ON from IN Efficiency (%) IN (0/div) OUT (2/div) SW (5/div) Output Current (A) Time (0.0ms/div) Power Off from IN I- Curve Output oltage OUT () Load Current I OUT (A) Full Load Ripple Load Transient Response SW (5/div) OUT (20m/div) Time (2.0µs/div)

12 5244 n Characterization Curve (Contd.) Load Transient Response Load Transient Response Input oltage vs. Constant Current 0A Short 2.9 Constant Current (A) Input oltage () 2A Short 2

13 5244 n Characterization Curve 0.82 FB S Temperature 5.00 Stanby Current vs. Temperature FB() Standby Current (ma) Temperature( C) Temperature ( C) Frequency (KHz) Frequency vs. Temperature Temperature ( C) CC Current (A) CC Current vs. Temperature Temperature ( C) Input OP vs. Temperature Input OP () Temperature ( C) 3

14 5244 n Tape and Reel Dimension SOP-8/PP P PIN W Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size SOP-8/PP 2.0±0. mm 4.0±0. mm 2500pcs 330± mm n Package Dimension SOP-8/PP TOP IEW D SIDE IEW SYMBOLS MILLIMETERS INCHES MIN MAX MIN MAX A E2 E E L A A C PIN D C E E L b b e FRONT IEW A2 A A D e.270 BSC BSC θ 0 o 8 o 0 o 8 o E D

15 Life Support Policy: These products of, Inc. are not authorized for use as critical components in life-support devices or systems, with the express written approval of the president of, Inc., 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., Inc., June 203 Document: A06A-DS5244-A.03 Corporate Headquarter, Inc. 8F, 2, WenHu St., Nei-Hu Taipei 4, Taiwan. Tel: Fax: