www. belling .com .cn 1 60 0 khz , 1 6 v, 2a synchronous step - down converter BL8031 description the BL8031 is a fully integrated, high C efficiency 2a synchronous rectified step - down converter. the BL8031 operates at high efficiency over a wide output current load range. this device offers two operation modes, pwm control and pfm mode switching control, which allows a high efficiency over the wider range of the load. the BL8031 requires a minimum number of readily available standard external components and is available in a 6 - pin sot23 rohs compliant package. features ? high efficiency : up to 9 6 % ? 60 0 khz frequency operation ? 2a output current ? no schottky diode required ? 3 .5v to 1 6 v input voltage range ? 0.6v reference ? slope compensated current mode control for excellent line and load transient response ? integrated internal compensation ? stable with low esr ceramic output capacitors ? over current protection with hiccup - mode ? thermal shutdown ? inrush current limit and soft start ? available in sot23 - 6 ? - 40c to +85c temperature range applications ? distributed power systems ? digital set top boxes ? flat panel television and monitors ? wireless and dsl modems ? notebook computer typical application pin out & marking ka : product code yw: date code ( year & week ) v i n e n b s s w f b g n d v i n v o u t c 1 2 2 u f c 3 1 0 0 n f l 1 4 . 7 u h r 1 7 3 k r 2 1 0 k c 2 2 2 u f / 6 v s o t 2 3 - 6 s w f b e n g n d v i n k a y w b s 2 3 6 5 4 1
www. belling .com .cn 2 BL8031 ordering information part no. package tape&reel BL8031 c b 6 tr sot23 - 6 3000/reel absolute maximum rating parameter value supply voltage v in - 0.3v to 25 v switch node voltage v sw - 0.3v to (v in +0.5v) boost voltage v bs v sw - 0.3v to v sw +5v all other pins - 0.3v to 6v operating temperature range - 40 ? c to 85 ? c storage temperature range - 65 ? c to 150 ? c lead temperature (soldering, 10s) 300 ? c electrical characteristics ( v in = 12v, v out =5v, t a =25 ? c , unless otherwise stated ) parameter conditions min typ max unit input voltage range 3 .5 1 6 v uvlo threshold 2 v supply current in operation v en = 2.0v, v fb = 1.1v 0.4 0.6 m a supply current in shutdown v en = 0v or v en = gnd 1 ua regulated feedback voltage 4.5vv in m m en = 0v, v sw = 0v 0 10 ua upper switch current limit minimum duty cycle 4.2 a oscillation frequency 600 khz maximum duty cycle v fb = 0.6v 92 % minimum on time 60 ns thermal shutdown 170 c pin description pin # name description 1 bs boostrap. a capacitor connected between sw and bs pins is required to form a floating supply across the high - side switch driver. 2 gnd ground 3 fb adjustable version feedback input. connect fb to the center point of the external resistor divider. 4 en drive this pin to a logic - high to enable the ic. drive to a logic - low to disable the ic and enter micro - power shutdown mode. 5 vin power supply pin 6 sw switching pin
www. belling .com .cn 3 BL8031 electrical performance tested under , l= 4.7 uh, t a =25 ? c , unless otherwise specified 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 0.5 1.0 1.5 2.0 efficiency(%) iout (a) efficiency vs. iout (vout=1.2v) vin=12v vin=5v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 0.5 1.0 1.5 2.0 efficiency(%) iout (a) efficiency vs. iout (vout=5.0v) vin=6v vin=12v vin=16v 3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40 3.45 3.50 0.0 0.5 1.0 1.5 2.0 vout (v) iout (a) vout vs. iout (vout=3.3v) vin=5v vin=6v vin=12v vin=16v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 0.5 1.0 1.5 2.0 efficiency(%) iout (a) efficiency vs. iout (vout=3.3v) vin=5v vin=6v vin=12v vin=16v 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 0.0 0.5 1.0 1.5 2.0 vout (v) iout (a) vout vs. iout (vout=1.2v) vin=12v vin=5v 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 0.0 0.5 1.0 1.5 2.0 vout (v) iout (a) vout vs. iout (vout=5.0v) vin=6v vin=12v vin=16v
www. belling .com .cn 4 BL8031 block diagram 90.0% 91.0% 92.0% 93.0% 94.0% 95.0% 96.0% 97.0% 98.0% 99.0% 100.0% 6 8 10 12 14 16 efficiency(%) vin (v) efficiency vs. vin iout=1a vout=3.3v 3.10 3.15 3.20 3.25 3.30 3.35 3.40 6 8 10 12 14 16 vout (v) vin(v) vout vs. vin iout=1a v c c r e g u l a t o r r e f e r e n c e o s c i l l a t o r c u r r e n t s e n s e a m p l i f i e r c u r r e n t l i m i t c o m p a r a t o r b o o s t r e g u l a t o r h s d r i v e r l s d r i v e r c o m p a r a t o r o n t i m e c o n t r o l l o g i c c o n t r o l e r r o r a m p l i f i e r + - + - + + - 1 m r s e n v c c b s s w g n d f b e n v i n v c c
www. belling .com .cn 5 BL8031 detailed description internal regulator the BL8031 is a current mode step down dc/dc converter that provides excellent transient response with no extra external compensation components. this device contains an internal, low resistance, high voltage power mosfet, and operates at a high 600k operating frequ ency to ensure a compact, high efficiency design with excellent ac and dc performance. error amplifier the error amplifier compares the fb pin voltage with the internal fb reference (vfb) and outputs a current proportional to the difference between the two. this output current is then used to charge or discharge the internal compensation network to form the comp voltage, which is used to control the power mosfet current. the optimized internal compensation network minimizes the external component counts and simplifies the control loop design. internal soft - start the soft - start is implemented to prevent the converter output voltage from overshooting during startup. when the chip starts, the internal circuitry generates a soft - start voltage (ss) ramping up from 0v to 0.6v. when it is lower than the internal reference (ref), ss overrides ref so the error amplifier uses ss as the reference. when ss is higher than ref, ref regains control. the s s time is internally fixed to 1 ms. over - current - protection and hi ccup the BL8031 has cycle - by - cycle over current limit when the inductor current peak value exceeds the set current limit threshold. meanwhile, output voltage starts to drop until fb is below the under - voltage (uv) threshold, typically 30% below the referen ce. once a uv is triggered, the BL8031 enters hiccup mode to periodically restart the part. this protection mode is especially useful when the output is dead - short to ground. the average short circuit current is greatly reduced to alleviate the thermal iss ue and to protect the regulator. the BL8031 exits the hiccup mode once the over current condition is removed. startup and shutdown if both vin and en are higher than their appropriate thresholds, the chip starts. the reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. the regulator provides stable supply for the remaining circuitries. three events can shut down the chip: en low, vin low and thermal shutdown. in the shutdown pro cedure, the signaling path is first blocked to avoid any fault triggering. the comp voltage and the internal supply rail are then pulled down. the floating driver is not subject to this shutdown command. a pplications information setting output voltages the external resistor divider is used to set the output voltage (see typical application on page 1). the feedback resistor r1 also sets the feedback loop bandwidth with the internal compensation capacitor. choose r1 to be around 100k for optimal transient response. r2 is then given by: selecting the inductor a 4.7h to 22h inductor with a dc current rating of at least 25% percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductor dc resistance should be less than 15m. for most designs, the inductance value can be derived from the following equation. where il is the inductor ripple current. choose inductor ripple curr ent to be approximately 30% if the maximum load current, 2a. the maximum inductor peak current is:
www. belling .com .cn 6 BL8031 under light load conditions below 100ma, larger inductance is recommended for improved efficiency. selecting the output capacitor the output capacitor (c2) 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 l is the inductor value and resr is the equivalent series resistance (esr) value of the output capacitor. in the case of ceramic capacitors, the impedance at the switchi ng frequency is dominated by the capacitance. the output voltage ripple is mainly caused by the capacitance. for simplification, the output voltage ripple can be estimated by: in the case of tantalum or electrolytic capacitors, the esr dominates the impedance at the switching frequency. for simplification, the output ripple can be approximated to: the characteristics of the output capacitor also affect t he stability of the regulation system. the BL8031 can be optimized for a wide range of capacitance and esr values. package out line package sot23 - 6 devices per reel 3000 unit mm package specification
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