1/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 package outline of the ADT7350 the ADT7350 is a step-down converter with integrated switching mosfet. it operates wide input supply voltage range from 4.5v to 24v with 1.2a peak output current. it includes current limiting protection and thermal shutdown. it reduces design complexity and external component count. the ADT7350 is available in small outline sot23-6l package. general description features typical application circuit applications ? distributed power systems ? surveillance camera module ? navigation ? infra-red led drivers ? current mode buck regulator with 1.4mhz fixed frequency ? input voltage range : 4.5v to 24v ? adjustable output range : 0.81v to 15v ? max. output current : 1.2a ? up to 92% efficiency ? internal soft-start function ? integrated power mosfet switch : 400m ? ? thermal shutdown & current limit protection ? sot23-6l package vin c1 en l1 c2 r2 r1 vout cb d1 u1 gnd fb en vin sw bst 1 2 3 6 5 4
2/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 part list component type value (model) manufacturer u1 ic ADT7350 adtech d1 schottky barrier diode rsx101m-30 rohm l1 chip inductor 4.7uh / 1.6a tdk c2 mlcc 22 ? / 16v - c1 mlcc 10 ? / 50v - cb mlcc 10 ? - r1 chip resistor 49.9 ? / 1% - r2 chip resistor 16.2 ? / 1% - gnd fb en vin sw bst 6 4 pin description pin no. name pin description 1bst bootstrap. this pin acts as the power suppl y for internal power transistor driver. connect a 10nf capacitor between this pin and sw pin. 2 gnd ground and heat sink. connect this pin to a large copper pcb area. 3fb feedback voltage input. the voltage of this pin is regulated to 0.81v. the shielding in the pcb layout is option and connect resistor divider as close as possible. 4en chip enable input. the enable voltage range is higher than 1.2v and disable voltage is lower than 0.4v. 5 vin power supply input. the input bypass capacitor should be as close as gnd pin. 6 sw switching node. the free-wheeling diode is connected between this pin and gnd. ? r1,r2 : vout 3.3v typical case 5 4 1 4 2 3 350a
3/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 functional block diagram en fb voltage reference internal regulator error amp z fb 4 3 comparator control logic + - + - driver gnd 2 shutdown sw 6 bst 1 vin 5 osc regulator - + r s current sense current limit absolute maximum ratings (note1) note1. stresses beyond those listed under ?absolute maxi mum ratings? may cause permanent damage to the device. note2. derate 4.0mw/ above +25 . this is recommended to operate under this power dissipation specification. note3. measured on jesd51-7, 4-layer pcb parameter symbol min. typ. max. unit power supply voltage v in --26v sw pin voltage v sw --27v bst pin voltage v bst --v sw + 6v v all other pins - -0.3 - +6 v max. power dissipation (ta=25 ) (note2) p d --400mw thermal resistance (note3) ja -250- /w storage temperature t stg -65 - +150 junction temperature t jmax --+150 operating ratings parameter symbol min. typ. max. unit power supply voltage v in 4.5 12.0 24.0 v output voltage v out 0.81 - 15 v operating temperature t opr -40 - +85 junction temperature t j --+125
4/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 electrical characteristics (ta=25 , v in =12v, unless otherwise noted) parameters condition min. typ. max. unit note supply current (shutdown) v en = 0v - 0.2 - ? supply current (quiescent) v en = 2v, v fb = 1v - - 1 ? feedback voltage (v fb ) 4.5v vin 24v 0.79 0.81 0.83 v feedback current (i fb ) v fb = 0.81v - 0.1 - ? switch on resistance (r ds.on ), (note5) --0.4- ? switch leakage v en = 0v , v sw = 0v - - 30 ? current limit (note5) --1.8- a oscillator frequency (f sw ) v fb = 0.81v 1.2 1.4 1.7 ? fold-back frequency v fb = 0v - 460 - ? maximum duty cycle v fb = 0.81v - 85 - % uvlo rising threshold - 3.8 4 4.2 v uvlo threshold hysteresis - - 250 - ? en input low voltage ---0.4 v en input high voltage -1.2-- v en input current v en = 2v - 5 - ? v en = 0v - 0.1 - ? thermal shutdown (note5) - - 140 - note5. guaranteed by design.
5/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 typical performance characteristics v in =12v, v out =5v, l1=4.7 h, c1=10 f, c2=22 f, t a =25 c, unless otherwise mentioned efficiency vs. load current efficiency [%] efficiency [%] load current [a] load current [a] efficiency vs. load current switching frequency versus temperature feedback voltage versus temperature frequency [mhz] voltage [v] ambient temperature[ c] ambient temperature[ c] v in =12v v out =5v v in =24v v out =5v
6/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 typical performance characteristics v in =12v, v out =3.3v, l1=4.7 h, c1=10 f, c2=22 f, t a =25 c, unless otherwise noted transient load response iout=0.2a to 0.8a step at 0.8a/us v out (ac coupled) i l v sw no load en v out v sw i l iout=1a resistive load no load en iout=1a resistive load en[1khz] start-up through enable shut down through enable start-up through enable shut down through enable dimming control v sw i l en v out v sw i l v out v sw i l v out en v sw i l v out
7/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 architecture and operation the ADT7350 is a current mode step-down converter uses a pwm control and integrated power switch. an internal error amplifier establishes an integrated error voltage which is compared with slope compensated ramp signal in orde r to make internal power switch control signal. the ADT7350 has not only voltage feedback loop but also current feed-forward loop. the peak current detector limit the over current in cycle by cycle basis and gives the information of load current to the pwm controller. at the starting of a cycle, power switch is off , the input and output is isolated. the fixed frequency generator start to operate. after os cillator working , every cycle of beginning, the power switch is turned on. the current flows into i nductor thus input is shor ted to output via to inductor. the power switch is turned off when ; 1) the ramp signal which is the sum of the curre nt sensing amplifier output and artificial compensated signal to prevent from sub- harmonic oscillation crosses the output of integrator . 2) the inductor current reaches th e maximum allowed level (1.8a) 3) the protection signals are trigged. when the power switch is off , the inductor cu rrent can not change abruptly. the external schottky diode conducts the inductor current. enable(en) the ADT7350 features a low-power shut down mode to decrease total current consumption. a logic low at en shuts down the controller and internal power switch. the typical value of vih is 1.2v , vil is 0.4. soft-start the internal soft-start circuitry make a referenc e voltage of error amplifier gradually ramps up to reduce input surge current during start-up . bootstrap in order to generate enough large control voltage of power switch. the purpose of this block is to decrease power switch turn on resistance. protection (ovp/otp/ocp) the ADT7350 monitors the output voltage of controller and limit t he maximum allowed feedback voltage in order not to abruptly ch ange output voltage. the output feed-back voltage over 0.95v, this function is trigged. the adt73 50 monitors the temperature variation using ptat(proportional to absolute temperature) current . when the die temperature exceeds typical +140 c , the over temperature function is trigged. the maximum allowed inductor current is well controlled to prevent fr om falling into over-load or shorted output conditions. the maximum allowed load current is typically 1.8a. detailed description
8/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 detailed description uvlo (under voltage lock out) ADT7350 can monitor the battery output voltage. if the battery output voltage is under 3.8v . the ADT7350 goes to the uvlo status to save the power consumption of applications. oscillator the ADT7350 has a fixed frequency generator (typical 1.4mhz) and also automatically changes the operating frequency in accordance with feedback voltage (0.81v) for protecting the load. if the feedback voltage is under 0.4v, the operating frequency changes to one third of fixed operating frequency. (typical 460khz) error amplifier the high gain error amplifier integrate the error sign al from which the differen ce of reference voltage and feedback voltage. the summed output error signal compares with pwm ramp signal. it provides accuracy of the voltage feedback loop regulation. the feedback voltage of ADT7350 is typical 0.81v. current sense amplifier the current sense amplifier output is proportional to th e current flowing into the in ductor. this output goes to the comparator to make a proper control signal. the ADT7350 has well compensated current slope which is added into ramp generator circuit. compensation network the fixed frequency peak current m ode control scheme to provide easy compensation for stability and fast transient response. the cycle-by-cycle basis monitored peak current of inductor is compared with error amplifier output voltage. the duty cycle is modulat ed based on the inductor?s peak current. the inductor can be emulated to current source. so the inductor?s pole frequency goes to high frequency . it seems to be one-pole system. the ADT7350 has a inner compensation network in error amplifier block.
9/9 * this specifications are subject to be changed without notice http://www.ad-tech.co.kr ADT7350 sep. 9. 2010 / rev. 0.0 symbol dimensions in millimeters dimensions in inches min max min max a 1.050 1.250 0.041 0.049 a1 0.000 0.100 0.000 0.004 a2 1.050 1.150 0.041 0.045 b 0.300 0.500 0.012 0.020 c 0.100 0.200 0.004 0.008 d 2.820 3.020 0.111 0.119 e 1.500 1.700 0.059 0.067 e1 2.650 2.950 0.104 0.116 e 0.950(bsc) 0.037(bsc) e1 1.800 2.000 0.071 0.079 l 0.300 0.600 0.012 0.024 0o 8o 0o 8o package ; sot23-6l
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