n Application l Notebook Systems and I/O Power l Digital Set Top Boxes l LCD Display, TV l Networking, XDSL Modem n Typical Application VIN 4.

Transcription

1 5297 n General Description The 5297 is a high frequency synchronous stepdown DC-DC converter with built internal power MOSFETs. That provides wide 4.5 to 18 input voltage range and 3A continuous load current capability. The 5297 has synchronous mode operation for higher efficiency over output current load range. The 5297 is current mode control scheme which provides fast transient reponse. Internal compensation function. n Features l Wide 4.5 to 18 Operating Input Range l 80mΩ/30mΩ Low R DS(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 0.8 l RoHS Compliant and Halogen Free 3A, 18, 500KHz Synchronous n Application n Typical Application EN 22uF 25 1uF l Notebook Systems and I/O Power l Digital Set Top Boxes l LCD Display, T l Networking, XDSL Modem 22nF CC SS 5297 EN/SYNC GND BST SW FB R4 10Ω 0.1uF L1 4.7uH R3 33K R1 40.2K R2 13K 3.3 3A 47uF 1

2 5297 3A, 18, 500KHz Synchronous n Functional Block Diagram CC CC Regulator M Current Sense Amplifer RSEN CC BST SS Oscillator HS Driver 1pF EN Reference 50pF 400k Current Limit Comparator Comparator On Time Control Logic Control CC SW 1MEG LS Driver FB Error Amplifer GND 2

3 5297 3A, 18, 500KHz Synchronous n Pin Configuration TSOT-23-8 Top iew AEAxxx 1. SS SW 4. GND 5. BST 6. EN 7. CC 8. FB * Die Attach: Conductive Epoxy n Pin Description Pin No. Pin Name Pin Description 1 SS 2 Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. Supply oltage. The 5297 operates from a +4.5 to +18 input rail. 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 5 BST 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. Bootstrap for High Side Gate Driver. Connect a 0.1µF or greater ceramic capacitor from BST to SW pins. 6 EN Enable. EN high to enable the CC Bias Supply. Decouple with a 1µF cap. 8 FB Feedback Input. It's used to regulate the output of the converter to a set value via an extermal resistive voltage divider. 3

4 5297 3A, 18, 500KHz Synchronous n Ordering Information x x x xxx x Special Feature Output oltage Number of Pins Package Type Pin Configuration Pin Configuration Package Type Number of Pins Output oltage Special Feature A 1. SS E: SOT-2X A: 8 ADJ: Adjustable L: TSOT-23-8 (Low Profile) SW 4. GND 5. BST 6. EN 7. CC 8. FB (TSOT-23-8) 4

5 5297 3A, 18, 500KHz Synchronous n Absolute Maximum Ratings Parameter Maximum Unit -0.3 to 19 SW BST -0.3 (-5 for 10ns) to 19 (20 for 5ns) SW +6 All Other Pins Junction Temperature Lead Temperature -0.3 to o C 260 o C Storage Temperature -65 to +150 o C n Recommended Operating Conditions Parameter Symbol Rating Unit Input oltage 4.5 to 18 Output oltage 0.8 to -3 Junction Temperature Range T J -40 to +125 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) TSOT-23-8 Conductive Epoxy θ JC 55 θ JA 100 o C / W Internal Power Dissipation P D 1250 mw Lead Temperature (Soldering 10sec)** 260 o C * Measure θ JC on backside center of molding compound if IC has no tab. ** MIL-STD-202G 210F 5

6 5297 3A, 18, 500KHz Synchronous n Electrical Specifications =12, unless otherwise noted. Typical values are at T A =25 o C. Parameter Symbol Test Condition Min Typ Max Units Supply Shutdown Current I EN =0 0.1 µa Supply Current I Q EN =2, FB =1, SS =3 0.7 ma Hihg Side Switch On-Resistance R DS(ON)1 BST-SW =5 80 mω Low Side Switch On-Resistance R RDS(ON)2 CC =5 30 mω Load Side Switch Leakage Current SW LKG EN =0, SW = µa Switch Current Limit A Oscillator Frequency f OSC FB = KHz Fold-back Frequency f FB FB <400m 0.25 f SW Maximum Duty Cycle D MAX FB =700m % Feedback oltage FB T A =25 o C -2% 800 2% m Feedback Current I FB FB =800m na EN Rising Threshold EN_RISG EN Falling Threshold EN_FALLG EN Input Current I EN EN =2 2 µa EN =0 0 µa EN Turn Off Delay EN TD-OFF 8 µs Input Under oltage Lockout Threshold Input Under oltage Lockout Hysteresis ULO 3.6 ULO 650 m CC Regulator CC 5 CC Load Regulation I CC =5mA 3 % Soft-Start Current I SS 11 µa Thermal Shutdown T SD 150 o C Thermal Hysteresis 20 o C 6

7 5297 n Detailed Descriptiion Internal CC Regulator The internal CC regulator is adjusted 5.0 to provide power to the internal circuits from input voltage. In order to maintain the CC voltage stably, a 1µF ceramic capacitor is recommended. 3A, 18, 500KHz Synchronous Thermal Shutdown The 5297 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 5297 is restarted under control of the soft start automatically when the junction temperature drops 20 o C 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 1.2 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 0 to its final value linearly. The soft start time can be calculated as follows: t SS 0.8 C = I SS SS 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 FB drops below 0.4, 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 5297 enters hiccup mode, the average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. Enternal Bootstrap Circuit Under oltage Lockout (ULO) The 5297 incorporates an under voltage lockout circuit to keep the device disabled when the input voltage is below the ULO start threshold voltage. During powering up, the internal circuits are held inactive and the soft start is grounded until the input voltage exceeds the ULO start threshold voltage. Once the ULO start threshold voltage is reached, the soft start is activated and the device begins to operate. The device operates until the input voltage falls below the ULO stop threshold voltage. The typical hysteresis in the ULO comparator is 650m. 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

8 5297 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 = f I L Where f is the oscillator frequency, is the input voltage, is the output voltage, and 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 Where OAD 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 1 LOAD + 2 f I 1 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: I C = I LOAD 1 L 3A, 18, 500KHz Synchronous At = 2, where I C = OAD /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: I = C Where C is the input capacitance value. Output Capacitor The output capacitor (C ) 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: Where R ESR is the equivalent series resistance (ESR) value of the output capacitor and C is the output capacitance value. f LOAD = 1 f L 1 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: = 8 f 2 L C R ESR f C 8

9 5297 3A, 18, 500KHz Synchronous When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: = 1 f L R ESR Setting the Output oltage 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: R 2 FB = R + R 1 2 The output voltage is: R1 + R = 0.8 R 2 2 n Typical Application Circuits 4.5~16 Ren1 18K C 2 NS C 1 22uF BST 5297 EN SW R4 10Ω 0.1uF L1 4.7uH 3.3/3A Ren2 10K 1uF C5 22nF CC SS GND FB R3 33K R1 40.2K R2 12.7K C6 15pF R5 0Ω C 1 22uF C 2 22uF () R1(KΩ) R2(KΩ) R3(KΩ) L(µH) C (µf) C (µf) x x x x x x2 9

10 5297 3A, 18, 500KHz Synchronous n Characterization Curve Load Transient Output oltage Ripple (200m/Div) =12, =3.3, I =0.5~3A (100m/Div) (20m/Div) =12, =3.3, I =3A SW (10/Div) Time(200us/Div) Time(2µs/Div) Power On from Input oltage Power On from Input oltage =12, =3.3 I =0A (2/Div) =12, =3.3 I =3A (2/Div) SW SW Power On from EN Power on from EN EN (2/Div) =12, =3.3 I =0A EN (2/Div) =12, =3.3 I =3A SW SW 10

11 5297 3A, 18, 500KHz Synchronous Power Off from Input oltage =12, =3.3, I =0A Power Off from Input oltage =12, =3.3 I =3A (2/Div) (2/Div) SW SW Time(50ms/Div) Power Off from EN Power Off from EN EN =12, =3.3, I =0A EN =12, =3.3, I =3A (2/Div) (2/Div) SW SW Time(2s/Div) Short Circuit Entry Short Circuit Recovery =12, =3.3, I =0A =12, =3.3, I =0A (1/Div) SW (10/Div) SS (1/Div) (5A/Div) (1/Div) SW (10/Div) SS (1/Div) (5AD/iv) 11

12 Efficiency (%) Efficiency (%) Efficiency (%) A, 18, 500KHz Synchronous Efficiency Efficiency =5, I =0~3A =3.3, I =0~3A Output Current (A) Output Current (A) Efficiency =1.2, I =0~3A Output Current (A) 12

13 5297 3A, 18, 500KHz Synchronous n Tape and Reel Dimension TSOT-23-8 P0 W P 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 ±0.1 mm 4.0±0.1 mm 4.0±0.1 mm 3000pcs 180±1 mm n Package Dimension TSOT-23-8 Top iew b D Side iew E1 E L 0.25 P 1 e e1 C Front iew A1 A2 A 13

14 Life Support Policy: These products of, Inc. are not authorized for use as critical components in life-support devices or systems, without 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., May 2016 Document: A018A-DS5297-A.07 Corporate Headquarter, Inc. 8F, 12, WenHu St., Nei-Hu Taipei 114, Taiwan. Tel: Fax: