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CAT7105 2.0a high efficiency step-down dc/dc converter free datasheet http:///
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 2/12 2.0a high efficiency step-down dc/dc converter features high efficiency up to 95% 4.75v to 23v wide input voltage range output adjustable from 1.23 to 21v 2.0a output current 380khz constant frequency operation current mode operation over-temperature protected over current protection under voltage lockout 25a shutdown current sop8 package rohs compliant (100% green available) general description the CAT7105 is a high efficiency and high output current step-down dc/dc converter that integrates a low resistance high side nmos. including on the substrate with the listed features are a high performance voltage error amplifier that provides tight voltage regulation accuracy under transient conditions; an under voltage lockout circuit to prevent start up until the input voltage reaches 4.75v; an internally set soft start circuit to limit inrush currents; and other feature s include an over current protection and thermal shutdown. the CAT7105 is available in a 8 pin soic package. application set-top-box, dvd, lcd displays battery charger and high power led power supply distributed power system data comm. xdsl cpe pin configuration ordering information part number package ship CAT7105ca 8l sop (green) 2500/ tape & reel
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 3/12 pin description pin symbol description 1 bs high side gate drive boos t input. a capacitor must be connected from sw to b s. this capacitor boosts the gate drive to the internal nmos above vi n to fully turn it on. 2 vin power supply pin. the input voltage for the p ower supply is connected to pin2. 3 sw power switch output. this is the output of a power mosfet switch connected directly to the input voltage. 4 gnd ground pin. this is the ground reference conn ection for all components in the power supply. 5 fb voltage feedback pin. this is the input to an error amplifier, which drives the pwm controller. its necessary to connect this pin to the actual output of power supply to set the dc output voltage. 6 comp compensation pin. this pin is used to compensate th e regulation control loop. connect a series rc network from comp pin to gnd pin to compensate t he regulation control loop. 7 en enable pin. this input provides an electrical on/off control of the power supply. 8 nc no connection function block diagram
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 4/12 typical application sw en c9 nc c7 nc c6 22uf c8 u1 CAT7105 7 6 5 4 8 3 2 1 en comp fb gnd nc sw vcc bst en fb r3 l1 1 2 c1 10uf r2 c12 10nf c4 100uf c3 nc c2 10uf c10 0.1uf d1 b320a vin r4 100k c5 0.1uf jp1 1 2 3 c11 0.1uf vin off ss on vout=1.23v*(1+r1/r2) comp vin=4.75v~23v bst r1 vout *note: the recommended applications shall be custom er design-in orientation to fit each customers dema nd. based on the nature of customers demand-oriented, please contact cat or agent for de sign support service. r 1 r 2 r 3 c 8 l 1 v out=5v 68k 22k 15k 2nf 15uh v out=3.3v 16.8k 10k 10k 2nf 6uh v out=1.8v 4.7k 10k 5.6k 1nf 4.7uh
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 5/12 absolute maximum ratings input supply voltage . gnd - 0.3v to +23v sw voltage - 0.3 to vin+0.3v other pins . ..- 0.3v to +6v boost voltage .. vsw-0.3v to vsw+6v sw peak current .3.0 a esd classification ...class 2 junction temperature range 150c operating temperature .. .. -20 o c to 85c storage temperature range ..-65 o c to 150c lead temperature (soldering 10s) ... 260c *note: the ic has a protection circuit against stat ic electricity. do not apply high static electricit y or high voltage that exceeds the performance of t he protection circuit to the ic. electrical characteristic (recommended operating conditions, unless otherwise noted; vin = 12v; ta = 25 o c) ) parameter test conditions min typ. max unit supply voltage 4.75 23 v shutdown supply current ven = 0v 25 50 a regulated feedback voltage 4.75v Q v in Q 23v 1.19 1.23 1.26 v error amplifier trans conductance icomp = 10 a 500 800 1120 a/v current sense to comp trans conductance 3.8 a/v current limit 3.0 a sw leakage current v en = 0v, v sw = 0v 10 a high side on resistance 0.25 low side on resistance i 10 oscillation frequency 320 380 440 khz short circuit oscillation frequency vfb=0v 40 khz maximum duty cycle vfb=1.0v 90 % minimum duty cycle vfb=1.5v 0 % under voltage lockout threshold vin rising 3.9 4.1 4.3 v under voltage lockout threshold hysteresis 200 mv thermal shutdown threshold 160 en high level 2.6 v en low level 0.9 v en input current v en = 0v 1.1 1.8 2.5 a
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 6/12 function description the CAT7105 is a constant frequency current mode pwm step-down converter. it regulates input voltages from 4.75v to 23v down to an output voltage as low as 1.23v, and is able to supply up to 2a of load current. oscillator frequency slope compensated current mode pwm control provides stable switching and cycle-by-cycle current limit for superior load and line response and protection of the internal main switch and synchronous rectifier. the CAT7105 switches at a constant frequency (380 khz) and regulates the output voltage. during each cycle the pwm comparator modulates the power transferred to the load by changing the inductor peak current based on the feedback error voltage. during normal operation, the main switch is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. when the main switch is off, the low side mos will be turned on immediately and stay on until either the next cycle starts. short circuit protection the CAT7105 has short circuit protection. when the output is shorted to ground, the oscillator frequency is reduced to prevent the inductor current from increasing beyond the n mos current limit. the nmos current limit is also reduced to lower the short circuit current. the frequency and current limit will return to the normal values once the short circuit condition is removed and the feedback voltage reaches 1.23v. maximum load current the CAT7105 can operate down to 4.75v input voltage; however the maximum load current decreases at lower input due to large ir drop on the main switch and low side switch. the slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. enable the en pin provides electrical on/off control of the regulator. once the en pin voltage exceeds the threshold voltage, the regulator starts operation and the internal slow start begins to ramp. if the en pin voltage is pulled below the threshold, the regulator stops switching and the internal slow start resets. connecting the pin to ground or to any voltage less than 0.9v will disable the regulator and activate the shutdown mode. under voltage lockout the CAT7105 incorporates an under voltage lockout circuit to keep the device disable when vin is below the uvlo start threshold. during power up, internal circuit are held inactive until vin exceeds the uvlo start threshold voltage. once the vulo start threshold voltage is reached, device start-up begins. the device operates until vin fall below the uvlo stop threshold voltage. the typical hysteretic in the uvlo comparator is 200mv. boost capacitor connect a 0.01f low esr ceramic capacitor between the bs pin and sw pin. this capacitor
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 7/12 provides the gate drive voltage for the high side mosfet. thermal shutdown the CAT7105 protects itself from overheating with an internal thermal shutdown circuit. if the junction temperature exceeds the thermal shutdown threshold, the voltage reference is grounded and high side mosfet is turned off. compensation the system stability is controlled through comp pin. it will present a general design procedure to help insure a stable and operational circuit. the design in this data sheet is optimized for particular requirements. if different conversions are requires, some of the components may need to be changed to ensure stability. the power components and their effects will be determined first, and then the compensation components will be chosen to produce stability. output voltage the output voltage is set using the fb pin and a resistor divider connected to the output as shown in figure1. the fb pin voltage is 1.23v, so the ratio of the feedback resistors sets the output voltage according to the following equation: v fb = v out * r2 / (r1 + r2) thus the output voltage is: v out = 1.23 * (r1 + r2) / r2
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 8/12 package dimensions
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 9/12 classification reflow profiles reflow profile green assembly average ramp-up rate (ts max to tp) 3 /second max. preheat -temperature min(ts min ) -temperature max(ts max ) -time(ts min to ts ts max ) 150 200 60-180 seconds time maintained above: -temperature(t l ) -time(t l ) 217 60-150 seconds peak temperature(tp) 260 +0/-5 time within 5 of actual peak temperature(tp) 20-40 seconds ramp-down rate 6 /second max. time 25 to peak temperature 8 minutes max. note: all temperature refer to topside of the package, measur ed on the package body surface.
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 10/12 carrier tape & reel dimensions carrier tape width c nominal t w total length 12mm 76.2mm 0.060.01mm 9.30.1mm 300m
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 11/12
CAT7105 the cat logo is a registered trademark of chip adva nced technology 2007 chip advanced technology inc. C all right rese rved. may-2007 rev:0.94 12/12 headquarters: 3f, no.1, jin-shan 8 th st., hsin-chu city 300, taiwan (r.o.c.) tel: +886-3-666-8301 fax: +886-3-666-8630 website: http://www.chipadvanced.com taipei office: 4f, no.112, jhouzih st., neihu district, taipei cit y 114, taiwan (r.o.c.) tel: +886-2-87516119 fax: +886-2-87516359 information furnished is believed to be accurate an d reliable. however, cat inc. assumes no responsibility for the consequences for use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of cat inc. specifications mentioned in this publication a re subject to change without notice. this publication supersedes and replaces all information if previously supplied. cat inc. products are not auth orized for use as critical components in life suppo rt devices or systems without the express written appr oval of cat inc.

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