AS1341_13 AMSCO
Document overview
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Technical content
1 General Description
range of the output voltage. surface-mount inductors and output capacitors. The device is available in a TDFN-8 3x3mm pin package. Figure 1. AS1341 - Typical Application
2 Key Features
3 Applications
4 Pin Assignments
Figure 2. Pin Assignments (Top View)
4.1 Pin Descriptions
resistive divider between VOUT and GND to set the output voltage between 1.25V and VIN .
2 GND Ground
3 POK Power OK . Active-low open-drain reset output. Note: Connect pin POK to GND when the Power-Ok feature is not used. 4 LX Inductor Connection . Connect this pin to an external inductor. 0.8µA and LX goes high-impedance. VOUT . For adjustable output connect this pin to GND. 9 NC Exposed Pad. This pad is not connected internally. Connect to GND or do not connect.
7 SHDNN
6 ILIMIT
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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. T able 2. Absolute Maximum Ratings Parameter Min Max Units Comments Electrical Parameters 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 Peak Input Current 2 A Temperature Ranges and Storage Conditions Thermal Resistance Θ JA 36.3 ºC/W on PCB Storage Temperature Range -55 +150 ºC Junction Temperature +150 ºC Package Body Temperature +260 ºC 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). Humidity non-condensing 5 85 % Moisture Sensitive Level 1 Represents a max. floor life time of unlimited
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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 . Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality Control) methods. T able 3. Electrical Characteristics Symbol Parameter Conditions Min Typ Max Units TAMB Operating Temperature Range -45 85 °C VIN Input Voltage Range 4.5 20 V VOUT Output Voltage (Preset Output) FB = GND 4.85 5.00 5. 15 V Output Voltage (Adjustable) 1.25 V IN VDROPOUT Dropout Voltage I OUT = 600mA, ILIMIT = VIN 250 mV Line Regulation V IN = 6V to 20V, 200 Ω load 0.1 %/V Load Regulation ILIMIT = V IN , IOUT = 0 to 500mA 1 % VFB Feedback Set Voltage (Adjustable Output) 1.212 1.25 1.288 V IIN Input Supply Current No load 12 18 µA IINDROP Input Supply Current in Dropout No load 45 60 µA Input Shutdown Current SHDNN = GND 0.8 3 µA VUVLO Input Undervoltage Lockout Threshold VIN rising 3.6 4.0 4.4 V VIN falling 3.5 3.9 4.3 OUT Bias Current V OUT = 5.5V 2 3.5 5 µA IFB FB Bias Current V FB = 1.3V -25 +25 nA FB Threshold Low 50 100 150 mV Thermal Shutdown 10ºC hysteresis 145 ºC DC-DC Switches tOFFMIN LX Switch Minimum Off-Time 0.2 0.4 0.6 µs tONMAX LX Switch Maximum On-Time V FB = 1.3V 8 10 12 µs RLX LX Switch On-Resistance VIN = 6V 0.4 Ω VIN = 4.5V 0.5 ILXPEAK LX Current Limit ILIMIT = GND, L = 39µH 500 700 900 mA ILIMIT = IN, L = 10µH 1000 1400 1800 LX Zero-Crossing Threshold -75 +75 mV Zero-Crossing Timeout LX does not rise above the th reshold 30 µs LX Switch Leakage Current VIN = 20V, LX = GND, TAMB = +25ºC 0.1 µA VIN = 20V, LX = GND 1 Control Inputs Digital Input Level SHDNN, ILIMIT = GND 0.8 V SHDNN, ILIMIT = IN 2.4 Digital Input Leakage Current V SHDNN , VILIMIT = 0 to 20V, VIN = 20V -100 +100 nA Power-OK Power-OK Threshold Falling edge, relative to V OUT 90 92.5 95 % POK Output Voltage Low I POK = 1mA 0.4 V POK Output Leakage Current VIN , V POK = 16V, TAMB = 25°C 0.1 µA VIN , V POK = 16V 1
7 Typical Operating Characteristics
VOUT = 5V, TAMB = +25ºC (unless otherwise specified). Figure 3. Efficiency vs. IOUT Figure 4. Efficiency vs. I OUT Figure 7. Efficiency vs. IOUT ; VIN = 12V Figure 8. Efficiency vs. I OUT ; VIN = 12V
8 Detailed Description
AS1341 draws only 12µA; in shutdown mode it draws only 0.8µA to further reduce power consumption and extend battery life. and external component requirements. Figure 21. AS1341 - Block Diagram - 5V fixed Output Voltage
8.1 Current-Limit Control
with conventional constant-frequency pulse-width-modulation (PWM) controllers that unnecessarily switch the MOSFET. 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. expires, and the output voltage goes out of regulation.
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8.2 Dropout Voltage
A buck converter’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In battery- powered 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 (R DSON ) and inductor series resistance (R INDUCTOR ), 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 12k Ω to 1M Ω 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.
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 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
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9.3 Setting Current Limit
The AS1341 adjustable peak current limit is set by connecting ILIMIT as shown in Table 4 . 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 = ((V INMAX - VOUTPUT ) x t ONMIN /I LXPEAK (EQ 3) Where: t ONMIN = 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 = (I LXPEAK + (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. T able 4. Setting Peak Current Limit Current Limit ILIMIT Connected To 700mA GND 1400mA IN T able 5. Recommended Inductors Part Number L DCR Current Rating Manufacturer MSS6132-103ML 10µH 85m Ω 1.4A Coilcraft www.coilcraft.com LPS4018-472ML 4.7µH 125m Ω 1.8A MSS6132-393ML 39µH 345m Ω 0.8A LPS4018-223ML 22µH 360m Ω 0.7A CDRH6D28NP-150 15µH 62m Ω 1.4A Sumida www.sumida.com CDRH5D18NP-4R1 4.1µH 57m Ω 1.95A CDRH6D28NP-470 47µH 176m Ω 0.8A CDRH5D18NP-220 22µH 215m Ω 0.8A LQH66SN-100M03 10µH 36m Ω 1.6A Murata www.murata.com LQH55DN-150M03 15µH 150m Ω 1.4A LQH66SN-470M03 47µH 170m Ω 0.8A LQH55DN-470M03 47µH 400m Ω 0.8A
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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 I LXPEAKMIN (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 ≅ V RIPPLEESR + V RIPPLEC (EQ 7) The output voltage ripple as a consequence of the ESR and output capacitance is: VRIPPLEESR = ESR x I PEAK (EQ 8) VRIPPLEC = (L x (I PEAK - I OUTPUT )2)/(2 x (C OUT x V OUTPUT )) x V IN /(V IN - V OUTPUT ) (EQ 9) Where: I PEAK 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. T able 6. Recommended Output Capacitor Part Number C ESR Rated Voltage Manufacturer T520V107M010ATE018 100µF 18m Ω 10V Kemet www.kemet.com A700V826M006ATE018 82µF 18m Ω 6.3V T520B107M006ATE040 100µF 40m Ω 6V T520A336M006ATE070 33µF 70m Ω 6.3V A700V226M006ATE028 22µF 28m Ω 6.3V 510X107M020ATE040 10µF 40m Ω 20V EEFUD0J101R 100µF 15m Ω 6.3V Panasonic www.panasonic.com EEFCD0K330R 33µF 18m Ω 8V 10TPB100ML 100µF 55m Ω 10V Sanyo www.edc.sanyo.com 6TPB47M 47µF 70m Ω 6.3V
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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 (I RMS ) imposed by the switching current defined as: IRMS = (I LOAD x V OUTPUT )/V IN x √((4/3) x (V IN - V OUTPUT ) - 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.
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
T able 7. Recommended Input Capacitor C TC Code Rated Voltage Manufacturer 10µF X7R 25V Murata www.murata.com Taiyo Yuden www.t-yuden.com Kemet www.kemet.com Panasonic www.panasonic.com Sanyo www.edc.sanyo.com T able 8. Recommended Components Input Voltage Output Voltage ILIMIT Inductor Output Capacitor 4.5V to 20V 1.25V to 5V High MSS6132-103ML LQH66SN-100M03 LQH55DN-150M03 CDRH6D28NP-150 T520V107M010ATE018 A700V826M006ATE018 T520B107M006ATE040 EEFUD0J101R 10TPB100ML 4.5v to 12V CDRH5D18NP-4R1 LPS4018-472ML 4.5V to 20V 1.25V to 5V Low MSS6132-393ML CDRH6D28NP-470 LQH66SN-470M03 LQH55DN-470M03 EEFCD0K330R 6TPB47M T520A336M006ATE070 A700V226M006ATE028 4.5V to 12V MSS6132-103ML LPS4018-223ML CDRH5D18NP-220 6V to 20V 5V to V IN High or Low See Inductors above 510X107M020ATE040
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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 (C IN , C OUT , 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.
Figure 24. TDFN-8 3x3mm Marking
Figure 25. TDFN-8 3x3mm Package
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 17 - 18 AS1341 Datasheet - O r d e r i n g I n f o r m a t i o n The device is available as the standard products shown in Table 9 . 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:sales@ams.com or find your local distributor at http://www.ams.com/distributor T able 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
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