A S1 3 4 1 6 50 m A , U lt r a lo w Ri p p le S te p Do w n D C/ DC Co n v e r te r 1 General Description 2 Key Features The AS1341 is a high-efficiency step-down converter with adjustable output voltages from 1.25V to VIN using supply voltages of up to 20V. Output Voltages: Fixed 5V or Adjustable An integrated current-limited 0.4Ω MOSFET delivers load currents up to 600mA. Output Current: Up to 600mA The AS1341 also includes a 100% duty cycle LDO mode with a low dropout of only 250mV for high efficiency if input voltages is in the range of the output voltage. Input Voltage Range: 4.5V to 20V 1.25V Lowest Output Voltage Efficiency: up to 96% The AS1341 has a low quiescent current (12µA) to improve lightload efficiency and minimize battery use, and draws only 0.8µA in shutdown mode. Quiescent Supply Current: 12µA High switching frequencies (up to 200kHz) allow the use of small surface-mount inductors and output capacitors. Internal 0.4Ω P-Channel MOSFET Power-OK Output Shutdown Current: 0.8µA The device is available in a TDFN-8 3x3mm pin package. 100% Maximum Duty Cycle for Low Dropout Current-Limited Architecture Thermal Shutdown TDFN-8 3x3mm Package 3 Applications The device is ideal for notebook computers, distributed power systems, keep-alive supplies, and any other battery-operated, portable device. Figure 1. AS1341 - Typical Application VIN 4.5V to 20V CIN 5 4 IN LX L1 VOUT = 5V D1 7 COUT + SHDNN 6 AS1341 ILIMIT 8 OUT RPULL 3 POK 1 2 GND www.ams.com/DC-DC_Step-Up/AS1341 FB Revision 1.09 Indicates High-Power Trace 1 - 18 AS1341 Datasheet - P i n A s s i g n m e n t s 4 Pin Assignments Figure 2. Pin Assignments (Top View) FB 1 8 OUT GND 2 7 SHDNN AS1341 POK 3 LX 4 6 ILIMIT 9 5 IN 4.1 Pin Descriptions Table 1. Pin Descriptions Pin Number Pin Name 1 FB 2 GND 3 POK 4 5 LX IN 6 ILIMIT 7 SHDNN 8 OUT 9 NC Description Feedback Input. For the fixed 5V output connect this pin to GND. For adjustable output, connect to a resistive divider between VOUT and GND to set the output voltage between 1.25V and VIN. Ground Power OK. Active-low open-drain reset output. Note: Connect pin POK to GND when the Power-Ok feature is not used. Inductor Connection. Connect this pin to an external inductor. 4.5V to 20V Input Supply Voltage Peak Current Control Input. Connect this pin to IN or GND to set peak current limit (see Setting Current Limit on page 11). Shutdown Input. A low on this pin puts the AS1341 into shutdown mode. Supply current is reduced to 0.8µA and LX goes high-impedance. Regulated Output Voltage High-Impedance Sense Input. For the fixed 5V output connect this pin to VOUT. For adjustable output connect this pin to GND. Exposed Pad. This pad is not connected internally. Connect to GND or do not connect. www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 2 - 18 AS1341 Datasheet - A b s o l u t e M a x i m u m R a t i n g s 5 Absolute Maximum Ratings Stresses beyond those listed in Table 2 may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in Electrical Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Table 2. Absolute Maximum Ratings Parameter Min Max Units IN to GND -0.3 +23 V LX to GND -2 VIN + 0.3 V FB to GND -0.3 +5 V ILIMIT, SHDNN, OUT, POK to GND -0.3 VIN + 0.3 V 2 A 36.3 ºC/W +150 ºC +150 ºC Comments Electrical Parameters Peak Input Current Temperature Ranges and Storage Conditions Thermal Resistance ΘJA Storage Temperature Range -55 Junction Temperature Package Body Temperature Humidity non-condensing Moisture Sensitive Level www.ams.com/DC-DC_Step-Up/AS1341 5 +260 ºC 85 % 1 on PCB The reflow peak soldering temperature (body temperature) specified is in accordance with IPC/ JEDEC J-STD-020 “Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices”. The lead finish for Pb-free leaded packages is matte tin (100% Sn). Represents a max. floor life time of unlimited Revision 1.09 3 - 18 AS1341 Datasheet - E l e c t r i c a l C h a r a c t e r i s t i c s 6 Electrical Characteristics VIN = +12V, SHDNN = VIN, Typical values are at TAMB = +25ºC (unless otherwise specified). Specifications based on circuit shown in Figure 1 on page 1. Table 3. Electrical Characteristics Symbol Parameter Max Units TAMB Operating Temperature Range -45 85 °C VIN Input Voltage Range 4.5 20 V Output Voltage (Preset Output) VOUT Conditions FB = GND Output Voltage (Adjustable) VDROPOUT Dropout Voltage 5.00 5.15 VIN V IOUT = 600mA, ILIMIT = VIN 250 mV Line Regulation VIN = 6V to 20V, 200Ω load 0.1 %/V Load Regulation ILIMIT = VIN, IOUT = 0 to 500mA 1 % Feedback Set Voltage (Adjustable Output) IIN Input Supply Current IINDROP Input Supply Current in Dropout Input Shutdown Current Input Undervoltage Lockout Threshold VIN rising IFB 4.85 Typ 1.25 VFB VUVLO Min 1.212 1.25 1.288 V 12 18 µA No load 45 60 µA SHDNN = GND 0.8 3 µA 3.6 4.0 4.4 VIN falling 3.5 3.9 4.3 OUT Bias Current VOUT = 5.5V 2 3.5 5 µA FB Bias Current VFB = 1.3V -25 +25 nA 150 mV No load FB Threshold Low Thermal Shutdown 50 10ºC hysteresis 100 145 V ºC DC-DC Switches tOFFMIN LX Switch Minimum Off-Time tONMAX LX Switch Maximum On-Time RLX LX Switch On-Resistance ILXPEAK LX Current Limit VFB = 1.3V LX Switch Leakage Current 0.4 0.6 µs 8 10 12 µs VIN = 6V 0.4 VIN = 4.5V 0.5 Ω ILIMIT = GND, L = 39µH 500 700 900 ILIMIT = IN, L = 10µH 1000 1400 1800 LX Zero-Crossing Threshold Zero-Crossing Timeout 0.2 -75 LX does not rise above the threshold +75 30 mA mV µs VIN = 20V, LX = GND, TAMB = +25ºC 0.1 VIN = 20V, LX = GND 1 µA Control Inputs Digital Input Level SHDNN, ILIMIT = GND 0.8 SHDNN, ILIMIT = IN 2.4 Digital Input Leakage Current VSHDNN, VILIMIT = 0 to 20V, VIN = 20V -100 Power-OK Threshold Falling edge, relative to VOUT 90 POK Output Voltage Low V +100 nA 95 % IPOK = 1mA 0.4 V VIN, VPOK = 16V, TAMB = 25°C 0.1 VIN, VPOK = 16V 1 Power-OK POK Output Leakage Current 92.5 µA Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality Control) methods. www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 4 - 18 AS1341 Datasheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s 7 Typical Operating Characteristics VOUT = 5V, TAMB = +25ºC (unless otherwise specified). Figure 4. Efficiency vs. IOUT Figure 3. Efficiency vs. IOUT 100 100 ILIMIT = high 95 85 VIN = 20V 80 VIN = 6V VIN = 12V 90 VIN = 12V Efficiency (%) . Efficiency (%) . 90 ILIMIT = low 95 VIN = 6V 75 70 65 85 75 70 65 60 60 55 55 50 VIN = 20V 80 50 0.1 1 10 100 1000 0.1 1 Output Current (mA) Figure 5. Efficiency vs. IOUT; VOUT = 3.3V 100 ILIMIT = high 95 95 90 90 VIN = 4.5V 85 80 VIN = 20V 75 VIN = 12V 70 65 ILIMIT = low VIN = 4.5V VIN = 12V 80 VIN = 20V 75 70 65 60 55 55 50 50 0.1 1 10 100 0.1 1000 1 10 100 1000 Output Current (mA) Output Current (mA) Figure 7. Efficiency vs. IOUT; VIN = 12V Figure 8. Efficiency vs. IOUT; VIN = 12V 95 ILIMIT = high 90 ILIMIT = low 90 Efficiency (%) . Efficiency (%) . 1000 85 60 95 100 Figure 6. Efficiency vs. IOUT; VOUT = 3.3V Efficiency (%) . Efficiency (%) . 100 10 Output Current (mA) 85 80 75 70 22uH 85 80 75 70 10uH 10uH 39uH 4.1uH 65 22uH 65 0.1 1 10 100 1000 0.1 Output Current (mA) www.ams.com/DC-DC_Step-Up/AS1341 1 10 100 1000 Output Current (mA) Revision 1.09 5 - 18 AS1341 Datasheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s Figure 9. Efficiency vs. Input Voltage Figure 10. Output Voltage vs. Input Voltage 100 5.15 IOUT = 1mA IOUT = 100mA 95 IOUT = 300mA 5.1 IOUT = 500mA Efficiency (%) . IOUT = 600mA 90 VOUT (V) . 5.05 85 80 5 4.95 VOUT=3.3V, IOUT=500mA 75 4.9 VOUT=5V, IOUT=500mA VOUT=3.3V, IOUT=250mA VOUT=5V, IOUT=250mA 70 4.85 5 8 11 14 17 20 5 8 Input Voltage (V) 11 14 17 20 Input Voltage (V) Figure 11. Output Voltage vs. Input Voltage; VOUT = 3.3V Figure 12. Peak Switch Current vs. Input Voltage; VOUT = 3.3V 1.8 3.4 IOUT = 100mA . IOUT = 1mA 1.6 ILIMIT = high L=10µH 1.4 ILIMIT = high L=39µH IOUT = 500mA VOUT (V) . 3.35 3.3 3.25 Peak Switch Current (A) IOUT = 300mA 1.2 1 ILIMIT = low L=10µH 0.8 ILIMIT = low L=39µH 0.6 0.4 0.2 0 3.2 4 6 8 10 12 14 16 18 5 20 8 Figure 13. Switching Frequency vs. Output Current; VIN = 12V, VOUT = 5V, L = 10µH 14 17 20 Figure 14. Switching Frequency vs. Output Current; VIN = 12V, VOUT = 3.3V, L = 10µH 250 250 . . ILIMIT = low 200 Switching Frequency (kHz) Switching Frequency (kHz) 11 Input Voltage (V) Input Voltage (V) 150 100 ILIMIT = high 50 0 200 ILIMIT = low 150 100 ILIMIT = high 50 0 0 100 200 300 400 500 600 0 Output Current (mA) www.ams.com/DC-DC_Step-Up/AS1341 100 200 300 400 500 600 Output Current (mA) Revision 1.09 6 - 18 AS1341 Datasheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s Figure 15. Load Regulation, VOUT vs. IOUT; VIN = 12V, VOUT = 5V Figure 16. Load Regulation, VOUT vs. IOUT; VIN = 12V, VOUT = 3.3V 5.15 3.4 5.05 Output Voltage (V) . Output Voltage (V) . 5.1 ILIMIT = high 5 ILIMIT = low 4.95 3.35 ILIMIT = high ILIMIT = high 3.3 ILIMIT = low ILIMIT = low 3.25 4.9 4.85 3.2 200 300 400 500 600 0 Output Current (mA) 300 500 600 10V/Div 50mV/Div ILX VLX VOUT 100mV/Div 500mA ILOAD 1A/Div VOUT 15V 10V 200µs/Div 10mA 10µs/Div 10V/Div 50mV/Div VSHDNN 5V/Div VOUT VLX VOUT ILX Figure 20. Startup Waveform; RLOAD = 100Ω 1A/Div Figure 19. LX Waveform; VIN = 20V, IOUT = 500mA 2µs/Div www.ams.com/DC-DC_Step-Up/AS1341 400 Figure 18. Load Transient Response VIN ILX 200 Output Current (mA) Figure 17. Line Transient Response; IOUT = 500mA IL 100 1A/Div 100 1A/Div 0 5V 0V 100µs/Div Revision 1.09 7 - 18 AS1341 Datasheet - D e t a i l e d D e s c r i p t i o n 8 Detailed Description The AS1341 step-down converter was specifically designed for battery-powered portable devices, including laptop computers, PDAs, and MP3/ DVD/CD players. The advanced current-limited control scheme provides high-efficiency over a wide range of output loads. The highly-efficient operation (up to 100% duty cycle) allows extremely low dropout voltage, increasing the usable supply voltage range. In no-load conditions the AS1341 draws only 12µA; in shutdown mode it draws only 0.8µA to further reduce power consumption and extend battery life. The AS1341 features an integrated 20V switching MOSFET, internal current sensing, and a high switching frequency, for minimal PCB space and external component requirements. Figure 21. AS1341 - Block Diagram - 5V fixed Output Voltage 3 + + – – + POK – RPULL L1 5 4 IN LX 8 CIN AS1341 OUT COUT + 1 Q 7 R FB SHDNN + S 6 ILIMIT D1 – Current Limit Control Maximum OnTime Delay Minimum Off-Time Delay – 100mV + VSET 1.25V + – + – 2 GND 8.1 Current-Limit Control The AS1341 uses a proprietary current-limiting control scheme with operation up to 100% duty cycle. The DC-DC converter pulses as needed to maintain regulation, resulting in a variable switching frequency that increases with the load. This eliminates the high-supply currents associated with conventional constant-frequency pulse-width-modulation (PWM) controllers that unnecessarily switch the MOSFET. When the output voltage is too low, the error comparator sets a flip-flop, which turns on the internal P-channel MOSFET and begins a switching cycle. The inductor current ramps up linearly, storing energy in a magnetic field while charging the output capacitor and servicing the load (see Figure 19 on page 7). The MOSFET turns off when the peak current limit is reached, or when the maximum on-time of 10µs is exceeded and the output voltage is in regulation. If the output is out of regulation and the peak current is never reached, the MOSFET remains on, allowing a duty cycle up to 100%. This feature ensures the lowest possible dropout voltage. Once the MOSFET turns off, the flip-flop resets, the inductor current is pulled through D1 (see Figure 21), and the current through the inductor ramps back down, transferring the stored energy to the output capacitor and load. The MOSFET remains off until the 0.4µs minimum off-time expires, and the output voltage goes out of regulation. www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 8 - 18 AS1341 Datasheet - D e t a i l e d D e s c r i p t i o n 8.2 Dropout Voltage A buck converter’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In batterypowered systems, this limits the useful end-of-life battery voltage. To maximize battery life, the AS1341 operates with duty cycles up to 100%, which minimizes the dropout voltage and eliminates switching losses while in dropout. When the supply voltage approaches the output voltage, the P-channel MOSFET remains on continuously to supply the load. Note: Dropout voltage is defined as the difference between the input and output voltages when the input is low enough for the output to drop out of regulation. For a step-down converter with 100% duty cycle, dropout is related to the MOSFET drain-to-source on-resistance (RDSON) and inductor series resistance (RINDUCTOR), and thus it is proportional to the load current: VDROPOUT = IOUT x (RDSON + RINDUCTOR) (EQ 1) 8.3 Shutdown A logic low on pin SHDNN shuts down the AS1341; a logic high on SHDNN powers on the device. In shutdown mode the supply current drops to 0.8µA to maximize battery life, and the internal P-channel MOSFET turns off to isolate the output from the input. The output capacitance and load current determine the output voltage decay rate. Note: Pin SHDNN should not be left floating. If the shutdown feature is not used, connect SHDNN to IN. 8.4 Power-OK Output The AS1341 provides a Power OK output (POK) that goes high-impedance when the output reaches 92.5% of its regulation point. POK goes low when the output is below 92.5% of the regulation point and the AS1341 is turned on (IN ≥ 4.5V and SHDNN ≥ 2.4V). A 12kΩ to 1MΩ pullup resistor between pin POK and pin IN or pin OUT or another voltage (≤ IN) can provide a microprocessor logic control signal. Note: Connect pin POK to GND when the Power-Ok feature is not used. 8.5 Thermal-Overload Protection Integrated thermal-overload protection limits total power dissipation in the AS1341. During continuous thermal-overload conditions, when the AS1341 junction temperature exceeds TJ = +145ºC, the internal thermal sensor turns off the pass transistor, allowing the AS1341 to cool down. When the AS1341 junction temperature cools by 10ºC, the thermal sensor turns the pass transistor on again resulting in a pulsed output. www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 9 - 18 AS1341 Datasheet - A p p l i c a t i o n I n f o r m a t i o n 9 Application Information 9.1 Adjusting Output Voltage The AS1341 feedback input features dual-mode operation. Connect FB to GND for the 5.0V preset output voltage (see Figure 21 on page 8). Adjust the output voltage by connecting a voltage-divider from the output to GND (see Figure 22). Figure 22. Adjustable Output Voltage Circuit VIN 4.5V to 20V 5 4 IN LX 1.25V to VIN D1 7 CIN L1 + RPULL SHDNN AS1341 6 COUT 3 R1 POK 1 ILIMIT FB 2 R2 8 GND OUT Indicates High-Power Trace Select a value for R2 between 10k and 1MΩ. Calculate R1 as: VOUT R 1 = R 2 ⋅ ------------- – 1 VFB (EQ 2) Where: VFB = 1.25V. VOUT may range from 1.25V to VIN. 9.2 Negative Output Voltage VIN may range from 4.5V to (20V-VOUT). Therefore the maximum negative output voltage is -15V. Figure 23. Adjustable Negative Output Voltage Circuit VIN 4.5V to (20V-VOUT) 5 4 IN LX 7 3 SHDNN 6 CIN ILIMIT 2 GND AS1341 POK L1 D1 R1 1 + FB 8 COUT R2 OUT VOUT = -1.25V to -15V Indicates High-Power Trace www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 10 - 18 AS1341 Datasheet - A p p l i c a t i o n I n f o r m a t i o n 9.3 Setting Current Limit The AS1341 adjustable peak current limit is set by connecting ILIMIT as shown in Table 4. Table 4. Setting Peak Current Limit Current Limit ILIMIT Connected To 700mA GND 1400mA IN The current limit chosen should reflect the maximum load current. The maximum output current is half of the peak current limit. Choosing a lower current limit allows using an inductor with a lower current rating, however, it requires a higher inductance (see Inductor Selection) and does not allow for reduced inductor package size. 9.4 Inductor Selection The AS1341 operates with a wide range of inductance values. For most applications, values between 10µH and 47µH work best with the controller’s high switching frequency. Larger inductor values will reduce the switching frequency and thereby improve efficiency and EMI. Note: The four key factors in inductor selection are inductance value, saturation rating, series resistance, and size. The trade-off for improved efficiency is a higher output ripple and slower transient response. On the other hand, low-value inductors respond faster to transients, improve output ripple, offer smaller physical size, and minimize cost. If the inductor value is too small, the peak inductor current exceeds the current limit due to current-sense comparator propagation delay, potentially exceeding the inductor’s current rating. Calculate the minimum inductance value as follows: LMIN = ((VINMAX - VOUTPUT) x tONMIN/ILXPEAK (EQ 3) Where: tONMIN = 1µs The inductor saturation current rating must be greater than the peak switch current limit, plus the overshoot due to the 250ns current-sense comparator propagation delay. Saturation occurs when the magnetic flux density of the inductor reaches the maximum level the core can support and the inductance starts to fall. Choose an inductor with a saturation rating greater than IPEAK in the following equation: IPEAK = (ILXPEAK + (VIN - VOUTPUT) x 250ns)/L (EQ 4) Inductor series resistance affects both efficiency and dropout voltage (see Dropout Voltage on page 9). High series resistance limits the maximum current available at lower input voltages, and increases the dropout voltage. For optimum performance, select an inductor with the lowest possible DC resistance that fits in the allotted dimensions. Table 5. Recommended Inductors Part Number L DCR Current Rating MSS6132-103ML 10µH 85mΩ 1.4A LPS4018-472ML 4.7µH 125mΩ 1.8A MSS6132-393ML 39µH 345mΩ 0.8A LPS4018-223ML 22µH 360mΩ 0.7A CDRH6D28NP-150 15µH 62mΩ 1.4A CDRH5D18NP-4R1 4.1µH 57mΩ 1.95A CDRH6D28NP-470 47µH 176mΩ 0.8A CDRH5D18NP-220 22µH 215mΩ 0.8A LQH66SN-100M03 10µH 36mΩ 1.6A LQH55DN-150M03 15µH 150mΩ 1.4A LQH66SN-470M03 47µH 170mΩ 0.8A LQH55DN-470M03 47µH 400mΩ 0.8A www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 Manufacturer Coilcraft www.coilcraft.com Sumida www.sumida.com Murata www.murata.com 11 - 18 AS1341 Datasheet - A p p l i c a t i o n I n f o r m a t i o n 9.5 Maximum Output Current The AS1341 output current determines the regulator’s switching frequency. When the converter approaches continuous mode, the output voltage falls out of regulation. For the typical application, the maximum output current is approximately: ILOADMAX = 1/2 x ILXPEAKMIN (EQ 5) For low-input voltages, the maximum on-time may be reached and the load current is limited by: ILOAD = (1/2 x (VIN - VOUT) x 10µs)/L (EQ 6) 9.6 Output Capacitor Choose the output capacitor to service the maximum load current with acceptable voltage ripple. The output ripple has two components: variations in the charge stored in the output capacitor with each LX pulse, and the voltage drop across the capacitor’s equivalent series resistance (ESR) caused by the current into and out of the capacitor: VRIPPLE ≅ VRIPPLEESR + VRIPPLEC (EQ 7) The output voltage ripple as a consequence of the ESR and output capacitance is: VRIPPLEESR = ESR x IPEAK (EQ 8) VRIPPLEC = (L x (IPEAK - IOUTPUT)2)/(2 x (COUT x VOUTPUT)) x VIN/(VIN - VOUTPUT) (EQ 9) Where: IPEAK is the peak inductor current (see Inductor Selection on page 11). The worst-case ripple occurs at no-load. Equations EQ 7, EQ 8, and EQ 9 are suitable for initial capacitor selection, but actual values should be set by testing a prototype or evaluation circuit. As a general rule, a smaller amount of charge delivered in each pulse results in less output ripple. Since the amount of charge delivered in each oscillator pulse is determined by the inductor value and input voltage, the voltage ripple increases with larger inductance, and as the input voltage decreases. Table 6. Recommended Output Capacitor Part Number C ESR Rated Voltage T520V107M010ATE018 100µF 18mΩ 10V A700V826M006ATE018 82µF 18mΩ 6.3V T520B107M006ATE040 100µF 40mΩ 6V T520A336M006ATE070 33µF 70mΩ 6.3V A700V226M006ATE028 22µF 28mΩ 6.3V 510X107M020ATE040 10µF 40mΩ 20V EEFUD0J101R 100µF 15mΩ 6.3V EEFCD0K330R 33µF 18mΩ 8V 10TPB100ML 100µF 55mΩ 10V 6TPB47M 47µF 70mΩ 6.3V www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 Manufacturer Kemet www.kemet.com Panasonic www.panasonic.com Sanyo www.edc.sanyo.com 12 - 18 AS1341 Datasheet - A p p l i c a t i o n I n f o r m a t i o n 9.7 Input Capacitor The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on the input caused by the circuit’s switching. The input capacitor must meet the ripple-current requirement (IRMS) imposed by the switching current defined as: IRMS = (ILOAD x VOUTPUT)/VIN x √((4/3) x (VIN - VOUTPUT) - 1) (EQ 10) For most applications, non-tantalum type (ceramic, aluminum, polymer, or OS-CON) are preferred due to their robustness to high in-rush currents typical of systems with low-impedance battery inputs. Alternatively, connect two (or more) smaller value low-ESR capacitors in parallel to reduce cost. Choose an input capacitor that exhibits less than +10ºC temperature rise at the RMS input current for optimal circuit life. Table 7. Recommended Input Capacitor C TC Code 10µF X7R Rated Voltage 25V Manufacturer Murata www.murata.com Taiyo Yuden www.t-yuden.com Kemet www.kemet.com Panasonic www.panasonic.com Sanyo www.edc.sanyo.com 9.8 Diode Selection The current in the D1 (see Figure 22 on page 10) changes abruptly from zero to its peak value each time the LX switch turns off. To avoid excessive losses, the diode must have a fast turn-on time and a low forward voltage. Note: Ensure that the diode peak current rating exceeds the peak current limit set by the current limit (see Setting Current Limit on page 11), and that its breakdown voltage exceeds VIN. Schottky diodes are recommended. 9.9 Stable Operation A well-designed system and selection of high-quality external components can eliminate excessive noise on pins OUT, FB, or GND, which can lead to unstable device operation. Instability typically manifests itself as grouped switching pulses with large gaps and excessive low-frequency output ripple (motorboating) during no-load or light-load conditions. 9.10 Recommended Components Table 8. Recommended Components Input Voltage Output Voltage ILIMIT Inductor High MSS6132-103ML LQH66SN-100M03 LQH55DN-150M03 CDRH6D28NP-150 4.5V to 20V 1.25V to 5V 4.5v to 12V CDRH5D18NP-4R1 LPS4018-472ML 4.5V to 20V MSS6132-393ML CDRH6D28NP-470 LQH66SN-470M03 LQH55DN-470M03 1.25V to 5V Low MSS6132-103ML LPS4018-223ML CDRH5D18NP-220 4.5V to 12V 6V to 20V 5V to VIN www.ams.com/DC-DC_Step-Up/AS1341 High or Low See Inductors above Revision 1.09 Output Capacitor T520V107M010ATE018 A700V826M006ATE018 T520B107M006ATE040 EEFUD0J101R 10TPB100ML EEFCD0K330R 6TPB47M T520A336M006ATE070 A700V226M006ATE028 510X107M020ATE040 13 - 18 AS1341 Datasheet - A p p l i c a t i o n I n f o r m a t i o n 9.11 PC Board Layout and Grounding High switching frequencies and large peak currents make PC board layout an important part of AS1341-based designs. Good PCB layout can avoid switching noise being introduced into the feedback path, resulting in jitter, instability, or degraded performance. - High-power traces (see Figure 22 on page 10) should be as short and wide as possible. - The current loops formed by the external components (CIN, COUT, L1, and D1 see Figure 22 on page 10) should be as short as possible to avoid radiated noise. Connect the ground pins of these power components at a common node in a star-ground configuration. - Separate noisy traces, such as the LX node, from the feedback network with grounded copper. - Keep the extra copper on the PCB and integrate it into a pseudo-ground plane. - When using external feedback, place the resistors as close to pin FB as possible to minimize noise coupling. www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 14 - 18 AS1341 Datasheet - P a c k a g e D r a w i n g s a n d M a r k i n g s 10 Package Drawings and Markings Figure 24. TDFN-8 3x3mm Marking AS1341 XXXX xxx - encoded Datecode www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 15 - 18 AS1341 Datasheet - P a c k a g e D r a w i n g s a n d M a r k i n g s Figure 25. TDFN-8 3x3mm Package www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 16 - 18 AS1341 Datasheet - O r d e r i n g I n f o r m a t i o n 11 Ordering Information The device is available as the standard products shown in Table 9. Table 9. Ordering Information Ordering Code Marking Description Delivery Form Package AS1341-BTDT-1k 1341 20V, 600mA, 100% Duty Cycle, Step-Down Converter Tape and Reel 1000 pcs TDFN-8 3x3mm AS1341-BTDT-6k 1341 20V, 600mA, 100% Duty Cycle, Step-Down Converter Tape and Reel 6000 pcs TDFN-8 3x3mm Note: All products are RoHS compliant and ams green. Buy our products or get free samples online at ICdirect: http://www.ams.com/ICdirect Technical Support is found at http://www.ams.com/Technical-Support For further information and requests, please contact us mailto:[email protected] or find your local distributor at http://www.ams.com/distributor www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 17 - 18 AS1341 Datasheet Copyrights Copyright © 1997-2010, ams AG, Tobelbaderstrasse 30, 8141 Unterpremstaetten, Austria-Europe. Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. All products and companies mentioned are trademarks or registered trademarks of their respective companies. Disclaimer Devices sold by ams AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. ams AG makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement. ams AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior to designing this product into a system, it is necessary to check with ams AG for current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or life-sustaining equipment are specifically not recommended without additional processing by ams AG for each application. For shipments of less than 100 parts the manufacturing flow might show deviations from the standard production flow, such as test flow or test location. The information furnished here by ams AG is believed to be correct and accurate. However, ams AG shall not be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of ams AG rendering of technical or other services. Contact Information Headquarters ams AG Tobelbaderstrasse 30 A-8141 Unterpremstaetten, Austria Tel: +43 (0) 3136 500 0 Fax: +43 (0) 3136 525 01 For Sales Offices, Distributors and Representatives, please visit: http://www.ams.com/contact www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 18 - 18