www. belling .com .cn 1 1 .2 a 1.5mhz synchronous buck converter BL8021 description the BL8021 is a high - efficiency, dc - to - dc step - down switching regulators, capable of delivering up to 1 .2 a of output current. the device operates from an input voltage range of 2.6v to 5 .5 v and provide s an output voltage from 0. 6 v to vin, m aking the BL8021 ideal for low voltage power conversions. running at a fixed frequency of 1.5mhz allows the use of small external components, such as ceramic input and output caps, as well as small inductors, while still providing low output ripples. this low noise output along with its excellent efficiency achieved by the internal synchronous rectifier, making BL8021 an ideal green replacement for large power consuming linear regulators. internal soft - start control circuitry reduces inrush current. short - c ircuit and thermal - overload protection improve s design reliability. BL8021 is housed in a sot23 - 5 package features ? high efficiency : up to 96% ? capable of d elivering 1 .2 a ? 1.5 mhz switching frequency ? no external schottky diode needed ? low dropout 100% duty operation ? internal compensation and soft - start ? current mode control ? 0.6v reference for low output voltages ? logic control shutdown (iq<1ua) ? thermal shutdown and uvlo ? available in sot23 - 5 applications ? cellular phones ? digital cameras ? mp3 and mp4 players ? set top boxes ? wireless and dsl modems ? usb supplied devices in notebooks ? portable devices typical application pin out & marking gg: product code yw : date code ( year & week ) BL8021 5 .5v g n d f b i n s w 2 4 0 k 1 2 0 k 1 0 u f l c 3 4 0 6 1 0 u f v o u t 1 . 8 v / 1 a v i n 2 . 6 v t o 7 v 1 . 8 v / 1 a s t e p - d o w n c o n v e r t e r 2 . 2 u h e n
www. belling .com .cn 2 BL8021 ordering information part no. packa ge tape&reel BL8021 c b5 tr sot23 - 5 3000/reel absolute maximum rating parameter value max input voltage 7 v max operating junction temperature(tj) 1 25 ? c ambient temperature(ta) - 4 0 ? c C 85 ? c maximum power dissipation sot23 - 5 400m w storage temperature( ts) - 40 ? c - 150 ? c lead temperature & time 260 ? c , 10s esd (hbm) >2000v note: exceed these limits to damage to the device. exposure to absolute maximum rating conditions may affect device reliability. r ecommended work conditions parameter value input v oltage range max. 5.5 v operating junction t emperature(tj) - 20 ? c C 125 ? c electrical characteristics ( vdd=5v, t a =25 ? c ) symbol parameter conditions min typ max unit vdd input voltage range 2.6 5 .5 v vref feedback voltage vin=5v 0. 585 0. 6 0.615 v ifb fee dback leakage current 0.1 0.4 ua iq quiescent current active, vfb=0 .65 , no switching 3 5 ua shutdown 1 ua lnreg line regulation vin=2.7 v to 5.5v 0. 04 0.2 %/v ldreg load regulation iout= 0.01 to 1 a 0. 1 0.2 %/a fsoc switching frequency 1. 5 mh z rdsonp pmos rdson 300 400 mohm rdsonn nmos rdson 220 300 mohm ilimit peak current limit 1.2 1 . 5 2 a iswlk sw leakage c urrent vout=5.5v, vsw=0 or 5.5v, en=0v 10 ua ienlk en leakage current 1 ua vh_en en input high voltage 1.5 v vl_en e n input low voltage 0.4 v
www. belling .com .cn 3 BL8021 pin description pin # name description 1 en enable pin for the ic. drive the pin to high to enable the part, and low to disable 2 gnd ground 3 sw inductor connection. connect an inductor between sw and the regulator out put. 4 in supply voltage. 5 fb feedback input. connect an external resistor divider from the output to fb and gnd to set the output to a voltage between 0.6v and vin electrical performance tested under ta=25 ? c , unless otherwise specified 35 40 45 50 55 60 65 70 75 80 85 90 95 100 0 100 200 300 400 500 600 700 800 900 1000 efficiency (%) load current (ma) efficiency vs load current, vout=1.8v vin=4.2v vin=3.6v vin=2.7v 35 40 45 50 55 60 65 70 75 80 85 90 95 100 0 100 200 300 400 500 600 700 800 900 1000 efficiency (%) load current (ma) efficiency vs load current, vout=2.5v vin=4.2v vin=3.6v vin=2.7v 35 40 45 50 55 60 65 70 75 80 85 90 95 100 0 100 200 300 400 500 600 700 800 900 1000 efficiency (%) load current (ma) efficiency vs load current, vout=1.2v vin=4.2v vin=3.6v vin=2.7v
www. belling .com .cn 4 BL8021 output ripple and sw at no load vin=5v / vout=2.5v output ripple and sw at 1a load vin=5v / vout=2.5v block diagram + - 0 . 6 v r e f p w m l o g i c a n t i - s h o o t t h r o u g h d r i v e r + - e a + - + - s l o p e c o m p o s c s w g n d u v l o & t h e r m a l s h u t d o w n v c o m p i s e n s e c o m p n e t w o r k f b e n i n
www. belling .com .cn 5 BL8021 detailed description the BL8021 high - efficiency switching regulator is a small, simple, dc - to - dc step - down converter capable of delivering up to 1a of output current. the device operates in pulse - width modulation (pwm) at 1.5mhz from a 2.6v to 5.5v input voltage and provides an output voltage from 0.6v to vin, making the BL8021 ideal for on - board post - regulation applications. an internal synchronous rectifier improves efficiency and eliminates the typical schottky free - wheeling diode. using the on resistance of the internal high - side mosfet to sense switching currents eliminates current - sense resis tors, further improving efficiency and cost. loop operation BL8021 uses a pwm current - mode control scheme. an open - loop comparator compares the integrated voltage - feedback signal against the sum of the amplified current - sense signal and the slope compens ation ramp. at each rising edge of the internal clock, the internal high - side mosfet turns on until the pwm comparator terminates the on cycle. during this on - time, current ramps up through the inductor, sourcing current to the output and storing energy in the inductor. the current mode feedback system regulates the peak inductor current as a function of the output voltage error signal. during the off cycle, the internal high - side p - channel mosfet turns off, and the internal low - side n - channel mosfet turns on. the inductor releases the stored energy as its current ramps down while still providing current to the output. current sense an internal current - sense amplifier senses the current through the high - side mosfet during on time and produces a proportional current signal, which is used to sum with the slope compensation signal. the summed signal then is compared with the error amplifier output by the pwm comparator to terminate the on cycle. current limit there is a cycle - by - cycle current limit on the high - side mosfet of 1.5a(typ). when the current flowing out of sw exceeds this limit, the high - side mosfet turns off and the synchronous rectifier turns on. BL8021 utilizes a frequency fold - back mode to prevent overheating during short - circuit output condition s. the device enters frequency fold - back mode when the fb voltage drops below 200mv, limiting the current to 1.5a (typ) and reducing power dissipation. normal operation resumes upon removal of the short - circuit condition. soft - start BL8021 has a interna l soft - start circuitry to reduce supply inrush current during startup conditions. when the device exits under - voltage lockout (uvlo), shutdown mode, or restarts following a thermal - overload event, the l soft - start circuitry slowly ramps up current availabl e at sw. uvlo and thermal shutdown if in drops below 2.5v, the uvlo circuit inhibits switching. once in rises above 2.6v, the uvlo clears, and the soft - start sequence activates. thermal - overload protection limits total power dissipation in the device. whe n the junction temperature exceeds tj= +160c, a thermal sensor forces the device into shutdown, allowing the die to cool. the thermal sensor turns the device on again after the junction temperature cools by 15c, resulting in a pulsed output during contin uous overload conditions. following a thermal - shutdown condition, the soft - start sequence begins. design procedure setting output voltages output voltages are set by external resistors. the fb_ threshold is 0.6v. rtop = rbottom[(vout / 0.6) - 1] input c apacitor selection the input capacitor in a dc - to - dc converter reduces current peaks drawn from the battery or other input power source and reduces switching noise in the controller. the impedance of the input capacitor at the switching frequency should be less than that of the input source so high - frequency
www. belling .com .cn 6 BL8021 switching currents do not pass through the input source. the output capacitor keeps output ripple small and ensures control - loop stability. the output capacitor must also have low impedance at the swit ching frequency. ceramic, polymer, and tantalum capacitors are suitable, with ceramic exhibiting the lowest esr and high - frequency impedance. output ripple with a ceramic output capacitor is approximately as follows: vripple = il(peak)[1 / (2 x fosc x c out)] if the capacitor has significant esr, the output ripple component due to capacitor esr is as follows: vripple(esr) = il(peak) x esr a pplication information layout is critical to achieve clean and stable operation. the switching power stage requires particular attention. follow these guidelines for good pc board layout: 1) place decoupling capacitors as close to the ic as possibl e 2) connect input and output capacitors to the same power ground node with a star ground configuration then to ic ground. 3) keep the high - current paths as short and wide as possible. keep the path of switching current (c1 to in and c1 to gnd) short. avoid vias in the switching paths. 4) if possible, connect in, sw, and gnd separately to a large copper area to help cool the ic to furthe r improve efficiency and long - term reliability. 5) ensure all feedback connections are short and direct. place the feedback resistors as close to the ic as possible . 6) route high - speed switching nodes away from sensitive analog areas
www. belling .com .cn 7 BL8021 package out line pa ckage sot23 - 5 devices per reel 3000 unit mm package specification
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