AS1335-BTDT-100

Da t as heet AS1335 1 . 5 A , 1 . 5 M H z , S y n c h r o n o u s D C / D C St e p - D o w n C o n v e r t e r 1 General Description The AS1335 is a high-efficiency, constant-frequency synchronous buck converter available in a fixed or an adjustable output voltage version. The wide input voltage range (2.6V to 5.25V), the high output current (up to 1.5A) and minimal external component requirements make the AS1335 perfect for any single Li-Ion batterypowered application. Typical supply current with no load is 400µA and decreases to ≤1µA in shutdown mode. The highly efficient duty cycle (100%) provides low dropout operation, prolonging battery life in portable systems. The device also offers a power-ok signal with a 215ms delay, which can be reseted or delayed further via the RSI pin. An internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. The internally fixed switching frequency (1.5MHz) allows for the use of small surface mount external components. The AS1335 is available in a 10-pin TDFN 3x3mm package. 2 Key Features ! ! ! ! ! ! ! ! ! ! ! High Efficiency: Up to 96% Output Current: 1.5A Input Voltage Range: 2.6V to 5.25V Output Voltage Range: 0.6V to VIN Constant Frequency Operation: 1.5MHz No Schottky Diode Required Power OK with 215ms delay Low Dropout Operation: 100% Duty Cycle Low Quiescent Supply Current: 400µA Shutdown Mode Supply Current: ≤1µA Current Mode Operation for Excellent Line/Load Transient Response Thermal Protection 10-pin TDFN 3x3mm Package ! ! 3 Applications The device is ideal for mobile communication devices, laptops and PDAs, ultra-low-power systems, threshold detectors/discriminators, telemetry and remote systems, medical instruments, or any other space-limited application with low power-consumption requirements. Figure 1. AS1335 - Typical Application Diagram VIN 2.6V to 5.25V CIN 22µF VIN NC SW 2.2µH COUT 22µF VOUT 1.0V, 1.5A PGND AS1335 EN POK GND GND FB RSI www.austriamicrosystems.com Revision 1.02 1 - 18 AS1335 Datasheet - P i n o u t 4 Pinout Pin Assignments Figure 2. Pin Assignments (Top View) VIN 1 NC 2 EN 3 POK 4 GND 5 11 10 SW 9 PGND AS1335 8 GND 7 FB 6 RSI Pin Descriptions Table 1. Pin Descriptions Pin Number 1 2 Pin Name VIN NC Description Positive Supply Voltage. This pin must be closely decoupled to PGND with a ≥ 22µF ceramic capacitor. Not Connected. Enable Input. Driving this pin above 1.4V enables the device. Driving this pin below 0.3V puts the device in shutdown mode. In shutdown mode all functions are disabled, drawing ≤1µA supply current. Note: This pin should not be left floating. Power-OK Output. Open-drain output with 215ms delay. Connect a 100kΩ pull-up resistor to VOUT or pin VIN for logic levels. Leave this pin unconnected if the Power-OK feature is not used. LOW Signal: Out of regulation HIGH signal: Within Regulation (after 215ms delay) Analog Ground. Reset Input for POK. This input resets the 215ms timer of the POK signal. As long as RSI is low the POK signal will work as described above. A high input to RSI will reset the 215ms POK timer and delay the signal as long as RSI stays high. A RSI low-to-high transition restarts the 215ms counter as long as the output voltage is within regulation. Note: Do not leave this pin floating. 7 8 9 10 11 FB GND PGND SW Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor divider tap to this pin. The output can be adjusted from 0.6V to 5.25V by VOUT = 0.6V[1+(R1/R2)]. If the fixed output voltage version is used, connect this pin to VOUT. Analog Ground. GND and PGND should only have one point connection. Power-Ground. Connect all power grounds to this pin. Switch Node Connection to Inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches. Exposed Pad. The exposed pad must be connected to PGND. Ensure a good connection to the PCB to achieve optimal thermal performance. 3 EN 4 POK 5 GND 6 RSI www.austriamicrosystems.com Revision 1.02 2 - 18 AS1335 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 to GND SW to GND EN, FB to GND P-Channel Switch Source Current (DC) N-Channel Switch Source Current (DC) Peak SW Sink and Source Current Thermal Resistance ΘJA Latch-Up Electrostatic Discharge Operating Temperature Range Storage Temperature Range Junction Temperature -40 -65 -100 2 +85 +150 125 Min -0.3 -0.3 -0.3 Max 6 VIN + 0.3 VIN 1.5 1.5 3 36.7 100 Units V V V A A A ºC/W mA kV ºC ºC ºC 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”. The lead finish for Pb-free leaded packages is matte tin (100% Sn). on PCB @85°C, JEDEC 78 HBM MIL-Std. 883E 3015.7 methods Comments Package Body Temperature +260 ºC www.austriamicrosystems.com Revision 1.02 3 - 18 AS1335 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 = EN = 3.6V, VOUT = VIN-0.5V, TAMB = -40°C to +85°C, typ. values @ TAMB = +25ºC (unless otherwise specified). Table 3. Electrical Characteristics Symbol VIN IQ IOUT ISHDN Regulation VOUT Regulated Output Voltage Regulated Feedback 2,3 Voltage Feedback Current Line Regulation Output Voltage Load Regulation 3 Parameter Input Voltage Range Quiescent Supply 1 Current Output Current RMS Shutdown Current Conditions Min 2.6 Typ Max 5.25 Units V µA A Normal Operation; VFB = 0.5V or VOUT = 90% of regulated output voltage, ILOAD = 0 A 300 1.5 400 Shutdown Mode; VEN = 0V, VIN = 4.2V 0.1 1 µA fixed VOUT adjustable VOUT TAMB = +25°C TAMB = -40°C to +85°C 0.975 0.6 0.5880 0.5850 -30 1.0 1.025 VIN 0.5V V V V nA mV mA VFB IFB ΔVLNR ΔVLOADREG 0.6 0.6 0.6120 0.6150 +30 Reference Voltage VIN = 2.6V to 5.25V ILOAD = 0A to 1.5A 100 100 DC-DC Switches IPK RPFET RNFET ILSW Enable VIH VIL IEN Logic Input Threshold EN Leakage Current Input High Input Low VIN = 3.6V, VEN = 0V to 3.6V -1 0.01 1.4 0.4 +1 V µA Peak Inductor Current P-Channel FET RDS(ON) N-Channel FET RDS(ON) SW Leakage VIN = 3V, VFB = 0.5V or VOUT = 90% of regulated output voltage, Duty Cycle < 35% ILSW = 100mA ILSW = -100mA VEN = 0V, VSW = 0V or 5V, VIN = 5V -1 2.4 0.4 0.35 0.01 +1 A Ω Ω µA Power-OK Output Power Good Low Voltage Threshold VPOK Power Good High Voltage Threshold tDELAY VOL POK Delay Time POK Output Voltage Low ISINK = 1mA, VFB = 0.7V Rising Falling Rising Falling 89.5 85 108.2 104 150 92 88 110.7 107 215 94.5 91 113.2 110 275 0.3 % VOUT % VOUT ms V www.austriamicrosystems.com Revision 1.02 4 - 18 AS1335 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 Table 3. Electrical Characteristics Symbol IPOK Oscillator fOSC Oscillator Frequency VFB = 0.6V or VOUT = 100% of regulated output voltage 1.2 1.5 1.8 MHz Parameter POK Output Leakage Current Conditions VPOK = VIN = 3.6V Min Typ 0.01 Max 1 Units µA Thermal Shutdown Thermal Shutdown Thermal Shutdown Hysteresis 150 25 °C °C 1. The dynamic supply current is higher due to the gate charge delivered at the switching frequency. The Quiescent Current is measured while the DC-DC Converter is not switching. 2. The device is tested in a proprietary test mode where VFB is connected to the output of the DC/DC converter. 3. Only valid for the adjustable version; www.austriamicrosystems.com Revision 1.02 5 - 18 AS1335 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 = 1.0V, IOUT = 100mA, TAMB = +25°C (unless otherwise specified). Figure 3. Efficiency vs. Output Current, VOUT = 1.0V 100 90 80 Figure 4. Efficiency vs. Output Current, VOUT = 1.5V 100 90 80 Efficiency (%) 60 50 40 30 20 10 0 10 100 1000 10000 Vin = 5.5V Vin = 4.0V Vin = 3.5V Vin = 3.0V Vin = 2.5V Efficiency (%) 70 70 60 50 40 30 20 10 0 10 100 1000 10000 Vi n = 5.5V Vi n = 5.0V Vi n = 4.0V Vi n = 3.6V Vi n = 2.6V Output Current (mA) Figure 5. Efficiency vs. Output Current, VOUT = 2.5V 100 90 80 Output Current (mA) Figure 6. Efficiency vs. Output Current, VOUT = 3.0V 100 90 80 Efficiency (%) 60 50 40 30 20 10 0 10 100 1000 10000 Vi n = 5.5V Vi n = 5.0V Vi n = 4.0V Vi n = 3.6V Efficiency (%) 70 70 60 50 40 30 20 10 0 10 100 1000 10000 Vi n = 5.5V Vi n = 5.0V Vi n = 4.0V Vi n = 3.6V Output Current (mA) Figure 7. Efficiency vs. Output Current, VOUT = 3.5V 100 90 80 90 Output Current (mA) Figure 8. Efficiency vs. Input Voltage, VOUT = 1.0V 100 Efficiency (%) Efficiency (%) 70 60 50 40 30 20 10 0 10 100 1000 10000 Vi n = 5.5V Vi n = 5.0V Vi n = 4.5V Vi n = 4.0V 80 70 60 50 40 2.5 3.5 4.5 5.5 Iout = 100mA Iout = 300mA Iout = 700mA Iout = 1000mA Iout = 1500mA Output Current (mA) www.austriamicrosystems.com Revision 1.02 Input Voltage (V) 6 - 18 AS1335 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, VOUT = 3.5V 100 Figure 10. Load Regulation, VOUT = 1.0V 1.05 90 1.03 80 Output Voltage (V) Efficiency (%) 1.01 70 Iout = 400mA 0.99 Vin = 5.5V Vin = 5.0V Vin = 4.5V Vin = 3.5V Vin = 2.5V 60 Iout = 600mA Iout = 800mA Iout = 950mA 0.97 50 2.6 3 3.4 3.8 4.2 4.6 5 0.95 10 100 1000 10000 Input Voltage (V) Output Current (mA) Figure 11. Load Regulation, VOUT = 1.5V 1.7 1.65 Figure 12. Line Regulation, VOUT vs. VIN; 1.02 1 Output Voltage (V) Output Voltage (V) 1.6 1.55 1.5 1.45 1.4 Vi n = 5.5V 0.98 0.96 0.94 0.92 0.9 Iout Iout Iout Iout Iout = 100mA = 300mA = 700mA = 1000mA = 1500mA 1.35 1.3 10 Vi n = 5.0V Vi n = 3.6V 100 1000 10000 2.5 3 3.5 4 4.5 5 5.5 Output Current (mA) Input Voltage (V) Figure 13. Load Step 40mA to 500mA; VIN = 4V Figure 14. Load Step 40mA to 1A; VIN = 4V 200mA/Div 100mV/Div 100µs/Div 100µs/Div www.austriamicrosystems.com Revision 1.02 50mV/Div VOUT VOUT 500mA/Div IOUT IOUT 7 - 18 AS1335 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. Shutdown Response; VIN = 3.4V Figure 16. Startup Response; VIN = 3.4V 2V/Div VOUT 1V/Div VOUT 200µs/Div 20µs/Div Figure 17. Line Transient Response; VIN = 3.5V to 4.5V, IOUT = 500mA 100µs/Div www.austriamicrosystems.com 100mV/Div VOUT 500mV/Div VIN Revision 1.02 1V/Div 500mA/Div 20mA/Div IIN IIN 2V/Div EN EN 8 - 18 AS1335 Datasheet - D e t a i l e d D e s c r i p t i o n 8 Detailed Description The AS1335 is a high-efficiency buck converter that uses a constant-frequency current-mode architecture. The device contains two internal MOSFET switches and is available with a user-adjustable output voltage. Figure 18. AS1335 - Block Diagram Ramp Compensator OSC OSCN – ICOMP + VIN Frequency Shift FB 0.6V + Error Amp – – OVDET AS1335 Main 0.6V + ΔVOVL + – Digital Logic AntiShoot Through SW EN 0.6V Reference 0.6V ΔVOVL + + IRCMP Power-OK Compare Logic – GND Shutdown RSI POK Main Control Loop During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch. This switch is turned off when the current comparator (ICOMP) resets the RS latch. The peak inductor current (IPK) at which ICOMP resets the RS latch, is controlled by the error amplifier. When ILOAD increases, VFB decreases slightly relative to the internal 0.6V reference, causing the error amplifier’s output voltage to increase until the average inductor current matches the new load current. When the top MOSFET is off, the bottom MOSFET is turned on until the inductor current starts to reverse as indicated by the current reversal comparator (IRCMP), or the next clock cycle begins. The over-voltage detection comparator (OVDET) guards against transient overshoots >7.8% by turning the main switch off and keeping it off until the transient is removed. www.austriamicrosystems.com Revision 1.02 9 - 18 AS1335 Datasheet - D e t a i l e d D e s c r i p t i o n Short-Circuit Protection This frequency reduction ensures that the inductor current has more time to decay, thus preventing runaway conditions. fOSC will progressively increase to 1.5MHz when VOUT > 0V or VFB > 0V. Dropout Operation The AS1335 is working with a low input-to-output voltage difference by operating at 100% duty cycle. In this state, the PMOS is always on. This is particularly useful in battery-powered applications with a 3.3V output. The AS1335 allows the output to follow the input battery voltage as it drops below the regulation voltage. The quiescent current in this state rises minimally to only 400µA (max), which aids in extending battery life. This dropout (100% duty-cycle) operation achieves long battery life by taking full advantage of the entire battery range. The input voltage requires maintaining regulation and is a function of the output voltage and the load. The difference between the minimum input voltage and the output voltage is called the dropout voltage. The dropout voltage is therefore a function of the on-resistance of the internal PMOS (RDS(ON)PMOS) and the inductor resistance (DCR) and this is proportional to the load current. Note: At low VIN values, the RDS(ON) of the P-channel switch increases (see Electrical Characteristics on page 4). Therefore, power dissipation should be taken in consideration. Shutdown Connecting EN to GND or logic low places the AS1335 in shutdown mode and reduces the supply current to 0.1µA. In shutdown the control circuitry and the internal NMOS and PMOS turn off and SW becomes high impedance disconnecting the input from the output. The output capacitance and load current determine the voltage decay rate. For normal operation connect EN to VIN or logic high. Note: Pin EN should not be left floating. Power-OK Functionality The AS1335’s power-ok circuitry offers a 215ms delayed power-ok signal. As long as the output voltage is outside of the power-ok regulation window the POK pin drives an open-drain low signal. As soon as the output voltage is within the regulation window, the internal open-drain MOSFET is turned off and the POK pin can be externally pulled to high. The output of the power-ok signal is delayed by 215ms. RSI Signal With the RSI signal the internal power-ok timer can be reseted or delayed. As long as the input to RSI is high the POK signal remains low, regardless of the output voltage condition. Thermal Shutdown Due to its high-efficiency design, the AS1335 will not dissipate much heat in most applications. However, in applications where the AS1335 is running at high ambient temperature, uses a low supply voltage, and runs with high duty cycles (such as in dropout) the heat dissipated may exceed the maximum junction temperature of the device. As soon as the junction temperature reaches approximately 150ºC the AS1335 goes in thermal shutdown. In this mode the internal PMOS & NMOS switch are turned off. The device will power up again, as soon as the temperature falls below +125°C again. www.austriamicrosystems.com Revision 1.02 10 - 18 AS1335 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 The AS1335 is perfect for mobile communications equipment, LED matrix displays, bar-graph displays, instrumentpanel meters, dot matrix displays, set-top boxes, white goods, professional audio equipment, medical equipment, industrial controllers to name a few applications. Figure 19. AS1335 - Step-Down Converter, Single Li-Ion to 1.0V / 1.5A fixed Output VIN 2.7V to 4.2V 2.2µH VIN NC 100kΩ EN POK GND SW PGND VOUT 1.0V, 1.5A CIN 22µF COUT 100µF AS1335-100 GND FB RSI Figure 20. AS1335 - Step-Down Converter, Single Li-Ion to 3.3V adjustable Output VIN 3.35V to 5.25V 2.2µH VIN NC 100kΩ EN POK GND SW PGND VOUT 3.3V CIN 22µF COUT 100µF 470kΩ AS1335-AD GND FB 100kΩ RSI www.austriamicrosystems.com Revision 1.02 11 - 18 AS1335 Datasheet - A p p l i c a t i o n I n f o r m a t i o n External Component Selection Inductor Selection For most applications the value of the external inductor should be in the range of 2.2µH to 4.7µH as the inductor value has a direct effect on the ripple current. The selected inductor must be rated for its DC resistance and saturation current. The inductor ripple current (ΔIL) decreases with higher inductance and increases with higher VIN or VOUT. In Equation (EQ 1) the maximum inductor current in PWM mode under static load conditions is calculated. The saturation current of the inductor should be rated higher than the maximum inductor current as calculated with Equation (EQ 2). This is recommended because the inductor current will rise above the calculated value during heavy load transients. V OUT 1 – ------------V IN Δ I L = V OUT × ---------------------L×f Δ IL I LMAX = I OUTMAX + -------2 f = Switching Frequency (1.5 MHz typical) L = Inductor Value ILmax = Maximum Inductor current ΔIL = Peak to Peak inductor ripple current The recommended starting point for setting ripple current is ΔIL = 600mA (40% of 1.5A). The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 1.8A rated inductor should be sufficient for most applications (1.5A + 300mA). Note: For highest efficiency, a low DC-resistance inductor is recommended. (EQ 1) (EQ 2) Accepting larger values of ripple current allows the use of low inductance values, but results in higher output voltage ripple, greater core losses, and lower output current capability. The total losses of the coil have a strong impact on the efficiency of the DC/DC conversion and consist of both the losses in the DC resistance and the following frequency-dependent components: 1. The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies). 2. Additional losses in the conductor from the skin effect (current displacement at high frequencies). 3. Magnetic field losses of the neighboring windings (proximity effect). 4. Radiation losses. Output Capacitor Selection The advanced fast-response voltage mode control scheme of the AS1335 allows the use of tiny ceramic capacitors. Because of their lowest output voltage ripple low ESR ceramic capacitors are recommended. X7R or X5R dielectric output capacitor are recommended. At high load currents, the device operates in PWM mode and the RMS ripple current is calculated as: V OUT 1 – ------------V IN 1= V OUT × ---------------------- × --------------L×f 2× 3 (EQ 3) I RMSC OUT While operating in PWM mode the overall output voltage ripple is the sum of the voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and discharging the output capacitor: www.austriamicrosystems.com Revision 1.02 12 - 18 AS1335 Datasheet - A p p l i c a t i o n I n f o r m a t i o n Δ V OUT V OUT 1 – ------------V IN 1 = V OUT × ---------------------- × ⎛ ------------------------------ + ESR⎞ ⎝ 8 × C OUT × f ⎠ L×f (EQ 4) Higher value, low cost ceramic capacitors are available in very small case sizes, and their high ripple current, high voltage rating, and low ESR make them ideal for switching regulator applications. Because the AS1335 control loop is not dependant on the output capacitor ESR for stable operation, ceramic capacitors can be used to achieve very low output ripple and accommodate small circuit size. At light loads, the converter operates in powersave mode and the output voltage ripple is in direct relation to the output capacitor and inductor value used. Larger output capacitor and inductor values minimize the voltage ripple in powersave mode and tighten DC output accuracy in powersave mode. Input Capacitor Selection In continuous mode, the source current of the PMOS is a square wave of the duty cycle VOUT/VIN. To prevent large voltage transients while minimizing the interference with other circuits caused by high input voltage spikes, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given as: V OUT × ( V IN – V OUT ) I RMS = I MAX × --------------------------------------------------------V IN (EQ 5) where the maximum average output current IMAX equals the peak current minus half the peak-to-peak ripple current, IMAX = ILIM - ΔIL/2 This formula has a maximum at VIN = 2VOUT where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations only provide negligible affects. The input capacitor can be increased without any limit for better input voltage filtering. Take care when using small ceramic input capacitors. When a small ceramic capacitor is used at the input, and the power is being supplied through long wires, such as from a wall adapter, a load step at the output, or VIN step on the input, can induce ringing at the VIN pin. This ringing can then couple to the output and be mistaken as loop instability, or could even damage the part by exceeding the maximum ratings. Ceramic Input and Output Capacitors When choosing ceramic capacitors for CIN and COUT, the X5R or X7R dielectric formulations are recommended. These dielectrics have the best temperature and voltage characteristics for a given value and size. Y5V and Z5U dielectric capacitors, aside from their wide variation in capacitance over temperature, become resistive at high frequencies and therefore should not be used. Table 4. Recommended External Components Name COUT CIN, COUT L Part Number T520B107M006ATE040 GRM21BR60J226ME39 MOS6020-222ML MOS6020-472ML Value 100µF 22µF 2.2µH 4.7µH Rating 6.3V 6.3V 3.26A 1.82A Type Tantal X5R 35mΩ 50mΩ Manufacturer Kemet B (3.5x2.8x1.9mm) www.kemet.com Murata 0805 www.murata.com Coilcraft 6.8x6.0x2.4mm www.coilcraft.com 6.8x6.0x2.4mm Size Because ceramic capacitors lose a lot of their initial capacitance at their maximum rated voltage, it is recommended that either a higher input capacity or a capacitance with a higher rated voltage is used. www.austriamicrosystems.com Revision 1.02 13 - 18 AS1335 Datasheet - A p p l i c a t i o n I n f o r m a t i o n Efficiency The efficiency of a switching regulator is equivalent to: Efficiency = (POUT/PIN)x100% (EQ 6) For optimum design, an analysis of the AS1335 is needed to determine efficiency limitations and to determine design changes for improved efficiency. Efficiency can be expressed as: Efficiency = 100% – (L1 + L2 + L3 + ...) Where: L1, L2, L3, etc. are the individual losses as a percentage of input power. Althought all dissipative elements in the circuit produce losses, those four main sources should be considered for efficiency calculation: (EQ 7) Input Voltage Quiescent Current Losses The VIN current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and control currents. VIN current results in a small (