View AE2359_7235894.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter description the AE2359 is a current mode step - down converter with a built - in power mosfet to enable smallest solution size power conversion. with the low series resistance power switch it enables a constant output current of up to 1.2a over a wide input su pply range. the load and line regulation has excellent response time over the operating input voltage and temperature range. the a e2359 is self protected, through a cycle - by - cycle current limiting algorithm and an on chip thermal protection. the a e2359 wil l provide the voltage conversion with a low count of widely available standard external components. features ? vin 4.75v to 24v ? load current of up to 1.2a ? internal power mosfet ? stable with low esr ceramic output capacitors ? up to 90% efficiency ? 0.1a shutdow n mode ? fixed 1.4mhz frequency ? thermal shutdown ? cycle - by - cycle over current protection ? resistor divider adjustable output: 0.81v to 15v ? sot26 package, lead free finish/rohs compliant applications ? distributed power systems ? battery charger ? pre - regulator for linear regulators ? wled drivers baidu micro electrons co., ltd. 1 tel:0755-88856770
pin assignments pin descri pt ion pin name description 1 bs t bootstrap. to form a boost circuit, a capacitor is connected between sw and bst pins to form a floating supply across the power switch driver. this cap acitor is needed to drive the power switch?s gate above the supply voltage. typical values for cbst range from 0.1uf to 1uf. 2 gnd ground. this pin is the voltage reference for the regulated output voltage. all control circuits are referenced to this pin. for this reason care must be taken in its layout. 3 fb feedback. to set the output voltage, connect this pin to the output resistor divider or directly to vout. to prevent current limit run away during a current l imit condition, the frequency f ee dback co mparator lowers the oscillator frequency when the fb voltage is below 400mv. 4 en on/off control input. do not leave this pin floating. to turn the device on, pull en above 1.2v and to turn it off pull below 0.4v. if enable/disable is not used, connect a 100kohm resistor between en to vin. 5 in supply voltage. the a e2359 operates from a +4.75v to +24v unregulated input. a decoupling capacitor c1 is required to prevent large voltage spikes from appearing at the input. place this capacitor near the ic. 6 s w switch output. this is the reference for the floating top gate driver. ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. 2 tel:0755-88856770
typical application circuit absolute maximum ratings recommanded operating range (note 1) ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. 3 tel:0755-88856770
electrical characteristics ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. 4 tel:0755-88856770
typical performance characteristics ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. 5 tel:0755-88856770
typical ap plication example for example 1 : 1.4mhz, 3.3v output at 1a step - down converter for example 2 : white led driver application ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. 6 tel:0755-88856770
application information operation the AE2359 is a current mode control, asynchronous buck regulator. current mode control as sures excellent line and load regulation and a wide loop bandwidth for fast response to load transients. figure. 4 depicts the functional block diagram of a e2359 . the operation of one switching cycle can be explained as follows. at the beginning of each cy cle, hs (high - side) mosfet is off. the ea output voltage is higher than the current sense amplifier output, and the current comparator?s output is low. the rising edge of the 1.4mhz oscillator clock signal sets the rs flip - flop. its output turns on hs mosf et. when the hs mosfet is on, inductor current starts to increase. the current sense amplifier senses and amplifies the inductor current. since the current mode control is subject to sub - harmonic oscillations that peak at half the switching frequency, ramp slope compensation is utilized. this will help to stabilize the power supply. this ramp compensation is summed to the current sense amplifier output and compared to the error amplifier output by the pwm comparator. when the sum of the current sense amplif ier output and the slope compensation signal exceeds the ea output voltage, the rs flip - flop is reset and hs mosfet is turned off. the external schottky rectifier diode (d1) conducts the inductor current. for one whole cycle, if the sum of the current sens e amplifier output and the slope compensation signal does not exceed the ea output, then the falling edge of the oscillator clock resets the flip - flop. the output of the error amplifier increases when feedback voltage (vfb) is lower than the reference volt age of 0.81v. this also increases the inductor current as it is proportional to the ea voltage. setting the output voltage the output voltage can be adjusted from 0.81v to 15v using an external resistor divider. table 1 shows a list of resistor selection for common output voltages. resistor r1 is selected based on a design tradeoff between efficiency and output voltage accuracy. for high values of r1 there is less current consumption in the feedback network. however the trade off is output voltage accuracy due to the bias current in the error amplifier. r2 can be determined by the following equation: ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. 7 tel:0755-88856770
setting the output voltage (continued) choose the inductor ripple current to be 30% of the maximum load current. the maximum inductor peak current i s calculated from: peak current determines the required saturation current rating, which influences the size of the inductor. saturating the inductor decreases the converter efficiency while increasing the temperatures of the inductor, the mosfet and the diode. hence choosing an inductor with appropriate saturation current rating is important. a 1h to 10h inductor with a dc current rating of at least 25% percent higher than the maximum load current is recommended for most applications. for highest effi ciency, the inductor?s dc resistance should be less than 200m . use a larger inductance for improved efficiency under light load conditions. input capacitor the input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. the input capacitor has to sustain the ripple current produced during the on time on the upper mosfet. it must hence have a low esr to minimize the losses. due to large di/dt through the input capacitors, electrolytic or ceramics should be used. if a tantalum must be used, it must be surge protected. otherwise, capacitor failure could occur. for most applications, a 4.7f ceramic capacitor is sufficient. output capacitor the output capacitor keeps the output voltage ripple small, ensures feedback loop stability and reduces the overshoot of the output voltage. the output capacitor is a basic component for the fast response of the power supply. in fact, during load transient, for the first few microseconds it supplies the current to the load. the converter recognizes the load transient and sets the duty cycle to maximum, but the curr ent slope is limited by the inductor value. maximum capacitance required can be calculated from the following equation: where v is the maximum output voltage overshoot. esr of the output capacitor dominates the output voltage ripple. the amount of ripple can be calculated from the equation below: voutcapacitor = iinductor esr an output capacitor with ample capacitance and lo w esr is the best option. for most applications, a 22f ceramic capacitor will be sufficient. ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. 8 tel:0755-88856770
external diode the external diode?s forward current must not exceed the maximum output current. since power dissipation is a critical factor when choosing a diod e, it can be calculated from the equation below: note: 0.3v is the voltage drop across the schottky diode. a diode that can withstand this power dissipation must be chosen. external bootstrap diode it is recommended that an external bootstrap diode be a dded when the input voltage is no greater than 5v or the 5v rail is available in the system. this helps improve the efficiency of the regulator. the bootstrap diode can be a low cost one such as in4148 or bat54. under voltage lockout (uvlo) under voltag e lockout is implemented to prevent the ic from insufficient input voltages. the AE2359 has a uvlo comparator that monitors the internal regulator voltage. if the input voltage falls below the internal regulator voltage, the AE2359 will latch an under volt age fault. in this event the output will be pulled low and power has to be re - cycled to reset the uvlo fault. internal soft start soft start is traditionally implemented to prevent the excess inrush current. this in turn prevents the converter output volt age from overshooting when it reaches regulation. the AE2359 has an internal current source with a soft start capacitor to ramp the reference voltage from 0v to 0.810v. the soft start time is internally fixed at 200us (typ). the soft start sequence is rese t when there is a thermal shutdown, under voltage lockout (uvlo) or when the part is disabled using the en pin. current limit the AE2359 has cycle - by - cycle current limiting implementation. the voltage drop across the internal highside mosfet is sensed and compared with the internally set current limit threshold. this voltage drop is sensed at about 30ns after the hs turns on. when the peak inductor current exceeds the set current limit threshold, current limit protection is activated. during this time the f eedback voltage (vfb) drops down. when the voltage at the fb pin reaches 0.4v, the internal oscillator shifts the frequency from the normal operating frequency of 1.4mhz to a foldback frequency of 480khz. the ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. 9 tel:0755-88856770
current limit is reduced to 70% of nominal current limit when the part is operating at 480khz. this low fold - back frequency prevents runaway current. thermal shutdown the AE2359 has on - chip thermal protection that prevents damage to the ic when the die temperature exceeds safe margin s. it implements a thermal sensing to monitor the operating junction temperature of the ic. once the die temperature rises to approximately 140c, the thermal protection feature gets activated .the internal thermal sense circuitry turns the ic off thus pre venting the power switch from damage. a hysteresis in the thermal sense circuit allows the device to cool down to approximately 120c before the ic is enabled again. this thermal hysteresis feature prevents undesirable oscillations of the thermal protecti on circuit. pc board layout this is a high switching frequency converter. hence attention must be paid to the switching currents interference in the layout. switching current from one power device to another can generate voltage transients across the imped ances of the interconnecting bond wires and circuit traces. these interconnecting impedances should be minimized by using wide, short printed circuit traces. the input capacitor needs to be as close as possible to the in and gnd pins. the external feedback resistors should be placed next to the fb pin. ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. tel:0755-88856770 10 tel:0755-88856770
packae information ae2 3 59 1. 2 a , 24v, 1.4mhz step - down converter baidu micro electrons co., ltd. tel:0755-88856770 11

▲Up To Search▲

Price & Availability of AE2359

	To Download AE2359 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .