AS7620

Datasheet AS7620 5 0 0 m A H y s t e r e t i c H i g h Vo l ta g e St e p - D o w n C o n v e r t e r with Dual Power Monitor 1 General Description The AS7620 is an easy-to-use, high-efficiency, highvoltage, hysteretic step-down DC-DC converter, operating in asynchronous mode. Its low-power architecture extends hold-up time in battery-backed and critical applications where maximum up-time over a wide input supply voltage range is needed, while still providing for high efficiencies of up to 90% during peak current demands. Although the AS7620 is optimized for 24V applications found in industrial and medical systems, its ability to support 100% Duty Cycle makes the AS7620 ideal for applications demanding maximum up-time and soft power fail behavior. In combination with low idle current of only 30µA, on-demand switching reduces operating current at low load currents. By selecting an appropriate inductor value, operating current can be lowered and switching frequencies tuned to certain load conditions. A pin-strapped current limit input minimizes inductor peak current and thus inductor size and cost for any given application. The device further includes output short-circuit protection and thermal shutdown. In shutdown mode, only 1µA (typ) of current is consumed. Figure 1. Block Diagram 2 Key Features ! Low quiescent current for efficient partial load operation Wide Supply Voltage Range, 3.6V to 32V 100% Duty Cycle extends operating range Pin-programmable cycle-by-cycle current limit Integrated PMOS eliminates bootstrap capacitor Resistor-programmable Early Power Fail Warning Input Power-Good Flag Thermal Shutdown Fixed 3.3V and adjustable output (1.2V to VIN) Small 4x4mm 12-Lead MLPQ Enhanced Power Package Specified from -40ºC to +125ºC junction and 85ºC maximum ambient temperatures ! ! ! ! ! ! ! ! ! ! 3 Applications The AS7620 is suitable for Industrial 24VDC applications like PLCs, robotics; Home Security and Building Control applications; Solid-state utility meters; Signage and LED column power; and Sensor interfaces. VIN LDO Temp Level Shifter SHDN Hysteretic Controller Soft-Start ISENSE LX FB + VREF ILIM PG + - PF AS7620 VEPF + - www.austriamicrosystems.com Revision 1.13 1 - 16 AS7620 Datasheet - P i n A s s i g n m e n t s 4 Pin Assignments Figure 2. Pin Assignments (Top View) VEPF 12 PG 11 10 VIN 1 PF AS7620 PGND 9 GND GND 2 8 GND LX 3 7 SHDN 4 GND 5 FB 6 ILIM Pin Descriptions Table 1. Pin Descriptions Pin Name VIN GND LX GND FB ILIM SHDN GND GND PF VEPF PG PGND Pin Number 1 2 3 4 5 6 7 8 9 10 11 12 Pad Description High Voltage Power Supply Input Must be connected to GND Power Output to Inductor Must be connected to GND Feedback input Current Limit input Shutdown input, active low Must be connected to GND Must be connected to GND Early Power Fail output, open drain, active LOW Comparator voltage input for early power fail warning Power Good, open drain, active HIGH output, monitors feedback voltage Exposed pad. Connect to GND plane to help thermal dissipation www.austriamicrosystems.com Revision 1.13 2 - 16 AS7620 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 VIN LX FB, SHDN All other pins except LX, FB and SHDN Latch-Up Package Power Dissipation Operating Temperature Range Electrostatic Discharge Humidity (Non-Condensing) Storage Temperature Junction Temperature -40 -1000 5 -55 Min -0.3 -0.3 -0.3 -0.3 -30 Max 40 VIN+0.3 VIN+0.3 or 5.5 3.6 +30 1 +125 +1000 90 125 150 Units V V V V mA W ºC V %R.H. ºC ºC Norm: IPC/JEDEC J-STD-020D. The reflow peak soldering temperature (body temperature) specified is in accordance with IPC/JEDEC J-STD-020D “Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices”. Norm: JEDEC 78 1 Comments Whichever is lower θJA = 32ºC/W for a 4-layer board, 4 vias, TAMB = +70ºC Junction temperature Norm: HBM MIL-Std. 883E 3015.7 methods Package body temperature 260 ºC 1. Voltage on pin 7 (SHDN) limited to +5.5V www.austriamicrosystems.com Revision 1.13 3 - 16 AS7620 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 TJ = -40 to +125ºC, VOUT=3.3V, LX=10µH, CX=100µF (unless otherwise specified). Typ. values at VIN= +24V and TAMB= +25ºC. Table 3. Electrical Characteristics Symbol VIN VCC VST VOUT Parameter Input Voltage Range Start-up Voltage AS7620-A Output Voltage AS7620-B Initial, at 25ºC amb. Over line, load and temperature Initial, at 25ºC amb. Over line and temperature Conditions Min 3.6 VEPF, ILIM -0.3 3.3 1.19 3.267 3.218 1.178 1.166 3.218 At FB node at VEPF of VFB at FB pin VIN=8V to 24V, RL=200Ω 10% to 90% load change FB pin 91 8 22 3.300 15 42 1.19 93 0.1 0.9 200 3 5 ILIM/2 ILIM=0V ILIM Switch Current Limit 1 2 Typ 24 Max 32 3.6 Units V V V VIN 3.300 3.333 3.383 1.190 1.202 1.214 3.383 30 82 V V V V VFB Feedback voltage AS7620-A AS7620-B VHYS VEPF VPG Controller Hysteresis AS7620-A AS7620-B mV V Early Power Fail Threshold Power Good Threshold Line Regulation Load Regulation 95 % %/V % nA µA mA IFB IOUT Input Bias Current AS7620-A AS7620-B Output Current 192 576 800 240 720 1000 0.4 At VIN=3.6V Current limit is not attained to turn off the switch before the minimum on-time expired 8 0.22 Non-switching IOUT=500µA 10 0.42 30 37 1 SHDN SHDN 150 10 junction ambient -40 -40 288 864 1200 0.8 100 12 0.62 45 Ω % µs µs µA µA 5 1 1 175 µA V µA ºC ºC 125 85 ºC ºC mA ILIM=VOUT ILIM=open P-Channel on resistance Maximum Duty Cycle tON tOFF IQ ISHDN VLO IIBN TSHDN Minimum On-Time Minimum Off-Time Quiescent Current Shutdown Current Shutdown Threshold Logic Input Bias Current Shutdown Temperature TSHDN Hysteresis TJ TAMB Operating Temperature 1. LX=100µH, CX=10µF, Initial accuracy only. For temperature variation, please refer to performance graphs. 2. VOUT from 1.5V to 3.6V www.austriamicrosystems.com Revision 1.13 4 - 16 AS7620 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 Figure 3. Efficiency vs Output Current, VOUT=4.5V 100 VIN=5V Figure 4. PMOS Rdson vs. Temperature 1000 900 800 90 80 70 60 50 40 30 1 10 VIN=24V VIN=12V Rdson (mohm) . Efficiency (%) VIN=32V 700 600 500 400 300 200 100 100 1000 0 -40 -20 0 20 40 60 80 100 120 Iout (mA) Temp (C) Figure 5. GND Current vs. IOUT @ TAMB 10000 VIN=24V Figure 6. GND Current vs. Temperature @ IOUT=0A 42.0 40.0 38.0 VIN=24V 1000 VIN=12V IGND (uA) IGND (uA) 36.0 34.0 32.0 VIN=32V VIN=12V 100 VIN=32V VIN=5V 10 30.0 1 1.0 10.0 100.0 1000.0 28.0 -4 0 -2 0 0 VIN=5V Iout (mA) Temp (C) Figure 8. Average Switching Frequency vs VIN 1000000 IOUT=500mA Figure 7. Current Limit Threshold vs VIN 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 5 ILIM FLOATING 100000 CL (mA) Fsw (Hz) 10000 ILIM VOUT ILIM GND 1000 100 10 15 20 25 30 5 7 9 11 13 15 1719 21 23 25 27 29 31 Vin (V) Vin (V) www.austriamicrosystems.com Revision 1.13 80 10 0 12 0 IOUT=50mA IOUT=5mA IOUT=500µA 60 20 40 5 - 16 AS7620 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. Average Switching Frequency vs IOUT (ILIM=open) 330000 300000 270000 240000 VIN=24V Figure 10. Shutdown Current vs. Temperature 1.8 1.7 1.6 VIN=32V Fsw (Hz) 210000 180000 150000 120000 90000 60000 30000 0 0 100 200 300 VIN=32V VIN=5V VIN=12V ISHDN (uA) 1.5 1.4 1.3 1.2 1.1 1 VIN=5V VIN=12V VIN=24V 0.9 400 500 0.8 -40 -20 0 20 40 60 80 100 120 Iout (mA) Temp (C) Figure 11. Line Regulation @ IOUT=10mA 0.800% 0.600% Figure 12. Line Regulation @ IOUT=500mA 0.400% 0.300% Vout Variation (%) 0.400% 0.200% 0.000% -0.200% -0.400% -0.600% -0.800% -10% 10% Vout Variation (%) 0.200% 0.100% 0.000% -0.100% -0.200% -0.300% -0.400% -10% 10% Vin Variation (%) Vin Variation (%) Figure 13. Load Regulation 1.000% 0.800% 0.600% Figure 14. Line Regulation VOUT=5V @ 10mA VOUT Vout Variation % 0.400% 0.200% 0.000% -0.200% 0.1 -0.400% -0.600% -0.800% -1.000% 1 10 100 1000 VIN Iout (mA) www.austriamicrosystems.com Revision 1.13 6 - 16 AS7620 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. Line Regulation VOUT=5V @ 10mA Figure 16. Load Regulation VOUT=5V 10mA→500mA VOUT VIN Note: All measurements taken at VIN=24V, VOUT=3.3V, and TAMB=25ºC using the typical application circuit specified in Figure 17, unless otherwise specified. www.austriamicrosystems.com Revision 1.13 7 - 16 AS7620 Datasheet - D e t a i l e d D e s c r i p t i o n 8 Detailed Description Figure 17. System Diagram of AS7620-A with Early Power Fail Warning 3.6V to 32V VIN CIN 2.2µF R3 3.3V R6 R7 VHYS VEPF R5 VIN LX FB 10µH VOUT R4 SHDN PF PG ILIM J1 J2 R1 R3 AS7620-A D1 COUT 100µF C1 Table 4. AS7620 Output Voltage Options AS7620 VOUT AS7620A-BQFT ADJ. AS7620B-BQFT 3.3V Shut Down The device can be shut down by providing a voltage lower than 1V at the SHDN pin (7). In this condition, the consumption is only 1µA (typ.). The AS7620 is providing an internally regulated pull-up circuit. No external pull-up resistor shall be used, which could otherwise damage the shutdown input. Connect the SHDN input directly to an open drain port only. Soft Start The device implements a soft start by limiting the inrush current into the output choke. Initially, the internal PMOS is turned on until the current reaches the programmed current limit (see Current Limit on page 9) and then is immediately turned off. It will be turned on again when the current approaches 0A. In this time frame, the FB voltage (VFB) will be lower than the reference and so the duty cycle will be driven by the current limit only. Regulation Both AS7620-A and AS7620-B are based on a hysteretic control method. Moreover, the switch current is monitored to make the converter always work in discontinuous current mode (DCM). The advantages of this type of control system can be summarized as following: ! ! ! ! High efficiency even at light load Intrinsically stable Simplicity Readiness during the load transient The internal PMOS is switched on when the VFB is lower than VREF-VHYST/2 and the current is 0A (DCM). The on time will be terminated if the VFB is over VREF+VHYST/2 or if the current limit (CL) is triggered. In practice, considering the most common application conditions (L=10µH ÷ 100µH; C=10µF - 100µF) and setting the CL threshold according to the load, the on time is normally terminated by the CL intervention and the output voltage ripple will stay within 1.25% of the output voltage (typ.) or VHYST * VOUT / VREF. www.austriamicrosystems.com Revision 1.13 8 - 16 AS7620 Datasheet - D e t a i l e d D e s c r i p t i o n VOUT Selection The AS7620-B features a 3.3V fixed output voltage. The AS7620-A provides an adjustable output from 1.2V (VREF) up to virtually VIN (see 100% Duty Cycle Operation on page 11). To select the desired VOUT, the related resistor divider has to be tuned according to the following formula: Rh V OUT = V REF • ⎛ 1 + ------⎞ ⎝ Rl ⎠ Where: Rh is the high side resistor of the output divider Rl is the resistor of the output divider (EQ 1) Note: It is suggested to select resistors in the range of hundreds of kΩ in order to limit the current consumption. Current Limit The current is sensed during the on time of the internal PMOS. Three different current limit thresholds can be selected by the ILIM pin: 1. 240mA (typ.) ILIM shorted to GND 2. 720mA (typ.) ILIM shorted to VOUT (from 1.5V to 3.6V) 3. 1000mA (typ.) ILIM floating This threshold is intended as peak current limit. If the current reaches the threshold during the on time, the PMOS is turned off and it will be turned on again only when the current approaches 0A and the feedback voltage is equal or lower than VREF. The maximum output current is ILIM/2. Switching Frequency The switching frequency (fsw) changes according to the application conditions and, in particular, to the output current in order to optimize the efficiency in any load condition. Anyway, it is always possible to estimate the fsw during the design process. As described in the Regulation (refer to page 8) – the converter always works in DCM and, normally, the peak current into the inductor is the CL threshold (ILIM). The average of the inductor current must be equal to the output current. The following formula provides the relationship between inductor current and output current: IN -IOUT = --------- • -- • -------------------------------------------------- 1 Tsw 1 2 ILIM • L • V ( V IN – V OUT ) • V OUT 2 (EQ 2) Consequently, the fsw can be expressed as following: 2 • I OUT • ( V IN – V OUT ) • V OUT Fsw = --------------------------------------------------------------------------2 ILIM • L • V IN (EQ 3) Figure 18. Chart Illustrating the Fsw vs. IOUT in a Standard Application (VIN=24V, VOUT=3.3V, L=10µH, ILIM=1A) Fsw vs. Iout 300 250 Fsw (KHz) 200 150 100 50 0 0 0.05 0.1 0.15 0.2 0.25 Iout (A) 0.3 0.35 0.4 0.45 0.5 www.austriamicrosystems.com Revision 1.13 9 - 16 AS7620 Datasheet - D e t a i l e d D e s c r i p t i o n Power Fail / Power Good AS7620A-B monitors input and output voltage by VEPF (pin 11) and VFB (pin 5) respectively. Two dedicated flags PF (pin 10) and PG (pin 12) are provided outside to inform about early input power fail (active low) and output within regulation. Figure 19 illustrates the typical connection for VEPF. During start up, PF is initially low. By selecting R3, R4, R5 and R6, it is possible to set the desired input voltage threshold above which the input power is considered stable. Once VIN (VDDH in Figure 19) reaches Vinth, PF is released and so an additional voltage contribution from VDD is added at the VPF pin, realizing in fact a hysteresis to eliminate PF oscillation due to power supply noise. Figure 19. Open-Drain Output Stage for Comparator VDD 1.2…3.6 VDDH 3.6…32V R6 Power Fail R3 VREF INV + RON R4 R5 Table 5 provides the resistors values covering all the standard input BUS. The resistors values are 1% commercial values. It is mandatory to use the correct resistors values to guarantee the respect of maximum absolute voltages at EPF and PF pin. VDD has been considered 3.3V. Otherwise EPF pin should be shorted to GND and PF left floating. Terminology: VRST: Reset voltage for the EPF. It is 90% of the Input BUS voltage. VTRIP: Trip voltage for the EPF. It is 80% of the Input BUS voltage. Table 5. EPF Network Selection with Different Input BUS VIN (V) 5 6 9 12 15 20 24 28 VRST (V) 4.5 5.4 8.1 10.8 13.5 18 21.6 25.3 VTRIP (V) 4 4.8 7.2 9.6 12 16 19.2 22.5 R3 (KΩ) 365 464 768 1070 1370 1870 2260 2670 R4 (KΩ) 143 143 140 140 140 140 140 140 R5 (KΩ) 1740 1870 2050 2100 2150 2210 2260 2260 R6 (KΩ) 1370 1430 1580 1650 1690 1740 1740 1740 Thermal Protection The internal junction temperature is continuously monitored. If it reaches 150ºC (min), the PMOS is turned off. The device can switch again if the temperature is decreased by at least 10ºC. If the over-temperature persists, the device will be shut down again resulting in a hiccup mode for the output power. www.austriamicrosystems.com Revision 1.13 10 - 16 AS7620 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 Input Capacitors An input capacitor is required to sustain the peak current requested by the turning on of the internal PMOS. When used, the capacitor helps to reduce the noise and saves the input battery life. The input capacitor has to withstand the input RMS current, which can be calculated by the following formula: V OUT • ( V IN – V OUT ) Irms = I OUT • -------------------------------------------------V IN (EQ 4) While designing for wide input/output voltage range, the worst case of Irms=1/2*IOUT must be considered. Suggested capacitors are low ESR OSCON, polymer, aluminum or MLCCs. Tantalum types are not recommended for their weakness in withstanding big inrush currents. Output Inductor The inductor together with the output capacitor represents the output filter. Using the AS7620, the inductor is charged and completely discharged at every switching cycle being that the converter is forced to work in DCM. Values from 10µH to 100µH are suitable to work with AS7620 and its selection should consider the following statements: ! ! Bigger inductor implies lower fsw Bigger inductor implies lower bandwidth The inductor must be rated to withstand the peak current (ILIM) and the RMS current Irms = ΔIL 2 I OUT + ---------3 2 Output Capacitor The output capacitor together with the inductor represents the output filter. The bigger the capacitance is, the lower will be the output ripple. Usually, low ESR MLCCs are preferred as they are inexpensive and small in size. Any value from 10µF is suitable, considering the load transient specifications of the application as well. Free Wheeling Diode The inductor current is forced through the diode during the off-times. The average current flowing through it is 1 ILIM • L -- • fsw • -----------------------2 V OUT The reverse voltage must be higher than the input voltage and safely it is common to consider 30% more. Normally, a schottky diode is preferred because of its low forward voltage. 2 Stability Even though the hysteretic voltage mode is intrinsically stable, an excessive noise at the FB could cause instability. For this reason care must be taken drawing the layout, reducing the noise and shielding the FB path from it. The main noise generator is the switching node, which is commutated from GND to VIN by the internal PMOS and the free wheeling diode and through which a pulse current flows. It is wise to add a MLCC capacitor as close as possible to the VIN pin of the device and provide a wide/short path between the LX pin and the external components (inductor and diode). It is preferable to draw the FB path as far as possible from the LX node and, perhaps, shielding it with a GND track. Another recommendation is to use low ESL output capacitors, thus avoiding electrolytic parts. A big ESL adds a square wave contribution on the FB that can make the device work improperly. 100% Duty Cycle Operation Thanks to the PMOS structure of the internal switch, the device can actually work at 100% duty cycle. This feature is very helpful during the load transient, because the maximum power can be transferred to the output in order to recover as fastest. The device will try to work at 100% duty whenever the FB voltage is lower than the upper window’s threshold. Moreover, in this condition, the safety is always guaranteed by the current limit. www.austriamicrosystems.com Revision 1.13 11 - 16 AS7620 Datasheet - A p p l i c a t i o n I n f o r m a t i o n Demo Board A demonstration board is available to test the device functionalities and performance in a standard application. For further information, please refer to the AS7620EB datasheet. Figure 20. Demo Board Photograph www.austriamicrosystems.com Revision 1.13 12 - 16 AS7620 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 The device is available in a 12-Lead MLPQ package. Figure 21. 4x4mm MLPQ Package Drawings www.austriamicrosystems.com Revision 1.13 13 - 16 AS7620 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 Table 6. 4x4mm MLPQ Package Dimensions www.austriamicrosystems.com Revision 1.13 14 - 16 AS7620 Datasheet - O r d e r i n g I n f o r m a t i o n 11 Ordering Information The devices are available as the standard products shown in Table 7. Table 7. Ordering Information Ordering Code AS7620A-BQFT AS7620B-BQFT* *) on request Marking AS7620 or AS7620A AS7620B Description 500mA hysteretic buck converter, adjustable output 500mA hysteretic buck converter, 3.3V output Delivery Form Tape and Reel Tape and Reel Package 12-Lead MLPQ, 4x4mm 12-Lead MLPQ, 4x4mm Note: All products are RoHS compliant and Pb-free. Buy our products or get free samples online at ICdirect: http://www.austriamicrosystems.com/ICdirect For further information and requests, please contact us mailto:sales@austriamicrosystems.com or find your local distributor at http://www.austriamicrosystems.com/distributor www.austriamicrosystems.com Revision 1.13 15 - 16 AS7620 Datasheet Copyrights Copyright © 1997-2009, austriamicrosystems 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 austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. austriamicrosystems 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. austriamicrosystems 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 austriamicrosystems 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 austriamicrosystems AG for each application. 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