3/97 description transformerless off-line operation low voltage operation to 0.8v ideal for battery trickle charger applications current mode operation with 100mv shunt voltage mode operation with fixed 1.25v output or resistor adjustable output efficient bicmos design inherent short circuit protection the ucc3890 controller is optimized for use as an off-line, low power, low voltage, regulated current supply, ideally suited for battery trickle charger applications. the unique circuit topology used in this device can be visual- ized as two cascaded flyback converters; each operating in the discon- tinuous mode, and both driven from a single external power switch. the significant benefit of this approach is the ability to charge low voltage bat- teries in off-line applications with no transformer, and low internal losses. the control algorithm used by the ucc3890 forces a switch on time in- versely proportional to the input line voltage, while the switch off time is inversely proportional to the output voltage. this action is automatically controlled by an internal feedback loop and reference. the cascaded con- figuration allows a large voltage conversion ratio with reasonable switch duty cycle. while the ucc3890 is ideally suited for control of constant current battery chargers, provision is also made to operate as a fixed 1.25v regulated supply, or to use a resistor voltage divider to obtain output voltages higher than 1.25v. ucc1890 UCC2890 ucc3890 off-line battery charger circuit features block diagram udg-96052 note: this device incorporates patented technology used under license from lambda electronics, inc.
ucc1890 UCC2890 ucc3890 i dd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5ma current into ton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5ma voltage on v out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20v current into toff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 m a storage temperature . . . . . . . . . . . . . . . . . . . C65c to +150c junction temperature . . . . . . . . . . . . . . . . . . C55c to +150c lead temperature (soldering, 10 sec.) . . . . . . . . . . . . . +300c connection diagrams currents are positive into, negative out of the specified terminal. consult packaging section of databook for thermal limitations and considerations of packages. absolute maximum ratings parameter test conditions min typ max units general vdd zener voltage i dd = 4.75ma,i ton = 0ma 8.3 9.0 9.4 v minimum operating current i ton i dd = C1ma, f = 150khz 1.65 2.0 ma undervoltage lockout minimum voltage to start fb = 0 7.8 8.6 9.2 v minimum voltage after start fb = 0 5.75 6.3 6.65 v hysteresis fb = 0 1.8 2.3 2.6 v vdd C v start fb = 0 0.2 0.4 0.7 v oscillator amplitude i ton = 3ma; i toff = 50 m a; v fb = 0v ct = 100pf 3.1 3.4 3.7 v ct to drive high delay overdrive = 200mv 80 200 ns ct to drive low delay overdrive = 200mv 50 100 ns charge coefficient i ct /i ton i ton = 3ma; v ct = 3.0v 0.135 0.15 0.165 m a/ m a discharge coefficent i ct /i toff i toff = 50 m a; v ct = 3.0v 0.95 1.00 1.05 m a/ m a driver v ol i = 100ma (note 1) 0.7 1.8 v v oh i = C100ma referred to vdd (note 1) C2.9 C1.5 v rise time c l = 1nf 35 70 ns fall time c l = 1nf 30 60 ns line voltage detection minimum i ton for fault 1.0 1.5 2.0 ma i ton detector hysteresis 110 m a on time during fault 0.5 m s v out error amplifier reference level i toff = 50 m a, i ct = 25 m a, t j = 25c 1.20 1.25 1.30 v i toff = 50 m a, i ct = 25 m a, over temperature 1.15 1.25 1.35 v voltage at toff i toff = 50 m a 0.3 0.4 0.5 v regulation gm i toff = 50 m a (note 2) 2.0 4.0 7.7 ma/v current sense amplifier gain v cs = 90 C 110mv 11.8 12.5 13.0 v/v input offset voltage v cs = 90 C 110mv C5 0 5 mv input voltage for cs amplifier enabled i ton = 3ma, referred to vdd C1.5 C0.8 v input voltage for cs amplifier disabled i ton = 3ma, referred to vdd C0.8 C0.3 v electrical characteristics: unless otherwise stated, these specifications apply for t a = C55 c to 125 c for ucc1890, C40c to 85c for the UCC2890, and 0c to 70c for the ucc3890. no load at drive pin (c load = 0), t a = t j . dil-8, soic-8 (top view) j, n, or d packages note 1: vdd forced to 100mv below vdd zener voltage note 2: gm is defined as d i ct d v fb for the values of v fb where the error amp is in regulation. the two points used to calculate gm are for i ct at 65% amd 35% of its maximum value. 2
ucc1890 UCC2890 ucc3890 pin descriptions cs: the high side of the current sense shunt is con- nected to this pin. short cs to vdd for voltage feedback operation. ct: oscillator timing capacitor is connected to this pin. drive: gate drive to external power switch. fb: output of current sense amplifier. this pin can be used for direct output voltage feedback if the current sense amp input pin cs is shorted to the vdd pin. gnd: ground pin. toff: resistor r off connects from voltage output to this pin to provide a maximum capacitor discharge cur- rent proportional to output voltage. ton: resistor r on connects from line input to this pin to provide capacitor charge current proportional to line volt- age. the current in r on also provides power for the 9v shunt regulator at vdd. vdd: output of 9v shunt regulator. application information operation (voltage output) figure 1 shows a typical voltage mode application. when input voltage is first applied, all of the current through r dd and 80% of the current through r on, charge the external capacitor c3 connected to vdd. as the voltage builds on vdd, undervoltage lockout holds the circuit off and the output drive low until vdd reaches 8.4v. at this time, drive goes high, turning on the external power switch q1, and 15% of the current into ton is directed to the timing capacitor c t . the volt- age at ton is fixed at approximately 11v, so c t charges to a fixed threshold with current i = 0.2 v in C 11v r on since the input line is much greater than 11v, the charge current is approximately proportional to the input line voltage. drive is only high while c t is charging, so the power switch on time is inversely proportional to line voltage. this provides a constant line voltage-switch on time product. at the end of the switch on time, q1 is turned off, and the 15% of the r on current which was charging c t is diverted to ground. the power switch off time is control- led by discharge of c t , which is determined by the outut voltage as described here: figure 1. typical voltage mode application udg-96053 udg-96054 3
ucc1890 UCC2890 ucc3890 1. when v out = 0, the off time is infinite. this feature provides inherent short circuit protection. however, to ensure output voltage startup when the output is not a short, a high value resistor, r s, is placed in parallel with c t to establish a minimum switching frequency. 2. as v out rises above approximately 0.4v, i dchg is set by r off , and is defined by i dchg = v out C 0.4v r off as v out increases, i dchg increases resulting in the reduction of off time. the frequency of operation in- creases and v out rises quickly to its regulated value. 3. in this region, a transconductance amplifier reduces i dchg in order to maintain v out in regulation. the input to the transconductance amplifier is the pin fb. (in this mode the pin cs should be shorted to vdd.) fb can either be connected directly to v out to regu- late at nominal v out = 1.25v or to be connected to v out through a resistor divider r vs1 /r vs2 to regu- late at nominal v out = 1.25v ( r vs1 + r vs2 ) r vs2 4. if v out should rise above its regulation range, i dchg falls to zero and the circuit returns to the minimum frequency established by r s and c t . the range of switching frequencies is established by r on , r off , r s , and c t as follows: frequency = 1 ton + toff ton = ct 3.4v 0.15 r on v in C 11v toff ( max ) = 1.5 r s c t ( regions 1 and 4 ) toff = c t 3.4v r off v out - 0.4v ( region 2 ) the above equations assume vdd = 9, the voltage at ton = 11v, the voltage at toff = 0.4v. operation (current output) figure 2 shows a typical current mode application. in current mode, operation is the same as in voltage mode, except that in region 3 the transconductance am- plifier is controlled by the current sense amplifier which senses the voltage across a shunt resistor r sh . the cir- cuit then regulates the current in the shunt to the nomi- nal value i sh = 100mv r sh the circuit shown in this schematic would be suitable for an application which trickle charges a battery at a low current, (e.g. c/10), and has a battery load which draws a high current, (e.g. c), when turned on. in that case, r sh1 value is chosen so that 100mv r sh1 = c 10 figure 2. typical current mode application udg-96055 application information (cont.) 4
ucc1890 UCC2890 ucc3890 if r sh2 is chosen so that 100mv r sh2 = c then the regulator output will assist the battery, minimiz- ing or eliminating battery output current. design example a typical design has the following requirements: v in = 80 to 132 vac or 100 to 180 vdc v out = 1.25v v out = 2.0v (assumes 1.25 v out with 750mv forward drop in d3) i load = 500madc max f switching = 100khz h (eff.) = 50% (excluding efficiency losses in d3 which will be very large due to the low output voltage. losses in d3 are accounted for by using v out in the calculations). component values are indicated in figure 3. the expla- nation for the choices in component values follows. first calculate the maximum duty cycle, d(max). to cal- culate this assume that at maximum load/minimum line conditions, the converter will be at the continuous con- duction boundary and there will be no idle time after the inductors are discharged. for all other load/line condi- tions, the ucc3890 will stretch the off time, to create an idle time after the inductors are discharged, in order to maintain a constant output voltage. for a single flyback stage at continuous conduction boundary d = 1 1 + v in v out for the cascaded flyback stages of the ucc3890 topol- ogy, the corresponding equation is d ( max ) = 1 1 + ? ``` v in v out in this case d ( max ) = 1 1 + ? ``` 100v 2v = 0.125 next using the operating frequency and the maximum duty cycle to calculate the maximum on time ton ( max ) = d ( max ) f switching in this case ton ( max ) = 0.125 100khz = 1.25 m s correspondingly toff ( min ) = 1 - 0.125 100khz = 8.75 m s figure 3. example application udg-96056 application information (cont.) 5
the average input current at minimum line and maxi- mum load will be i in = i out h v out v in in this case i in = 500ma 0.5 2v 100v = 20ma knowing that input current is drawn from the line only during ton, calculate the peak current in l1 to be i l1 ( pk ) = 2 i in ton + toff ton in this case i l1 ( pk ) = 2 20ma 1.25 m s + 8.75 m s 1.25 m s = 320ma now calculate the value for l1 l 1 = v in ton i l1 ( pk ) in this case l 1 = 100v 1.25 m s 320ma = 390 m h the output voltage of the first flyback stage is v c1 = v in ton toff in this case v c1 = 100v 1.25 m s 8.75 m s = 14.3v knowing that output current is provided to the load only during toff, calculate the peak current in l2 to be i l2 ( pk ) = 2 i out ton + toff toff in this case i l2 ( pk ) = 2 0.5a 1.25 m s + 8.75 m s 8.75 m s = 1.14a now calculate the value of l 2 l 2 = v out toff i l2 ( pk ) in this case l 2 = 2v 8.75 m s 1.14a = 15 m h for all of the calculations so far only the maximum load/minimum line condition have been considered. the entire range of operation must be considered to choose values for the rest of the components. under all normal operating conditions the current i ton, (which is the current in r on ), should be greater than 2ma and less than 7.5ma. in this case set r on to give i ton = 2.8ma at low line. the voltage at ton will be about 11v so r on = 100v - 11v 2.8ma = 33k w with r on = 33k, i ton at high line will be i ton = 180v - 11v 33k = 5.1ma at high line, the power dissipation in r on will be p ( r on ) = ( 180v - 11v ) 5.1ma = 860mw r on will need to be at least a 1w resistor. alternately it could be four 1/4w 8.2k w resistors in series. once r on is set, c t can be chosen. the charge current for c t is nominally 15% of i ton , and the nominal oscilla- tor amplitude is 3.4v, so ton = ct 3.4v 0.15 i ton solving for ct ct = ton 0.15 i ton 3.4v i ton at low line is 2.8ma, and the target ton at low line is 1.25 m s, so in this case ct = 1.25 m s 0.15 2.8ma 3.4v = 150pf the final component to be chosen is r off , which deter- mines the minimum value of toff. when the output voltage is below the regulation point, the discharge cur- rent for ct is equal to i toff (the current in r off ). un- der that condition toff = ct 3.4v i toff since the voltage at the toff pin = 0.4v i toff = v out - 0.4v r off substituting and solving for r off r off = t off ( v out - 0.4v ) ct 3.4v the largest discharge current, and hence the minimum off time, will occur when the output is about 10mv be- ucc1890 UCC2890 ucc3890 application information (cont.) 6
ucc1890 UCC2890 ucc3890 low the regulation point of 1.25v. the minimum value for toff is 8.75 m s. so in this case r off = 8.75 m s ( 1.24v - 0.4v ) 150pf 3.4v = 15k other application considerations output capacitor: for best regulation of the output voltage or current, the output capacitor should be a low esr type. this is especially true when operating in cur- rent sense mode with a non-linear load such as a bat- tery. if a low esr capacitor cannot be used, excellent regulation can also be achieved by placing a low pass r/c filter between the current shunt and the cs input. no load operation: the ucc3890 is inherently pro- tected for short circuits, but not for open circuits. if the load is removed, the output voltage will quickly rise up to the regulation point. once the output is above the regulation voltage, the oscillator will drop to the mini- mum frequency set by r s /c t . with no load on the out- put, even at this low frequency the output voltage can quickly rise to a dangerous level. to protect against this, it is recommended that a zener or other voltage clamp always be connected across the output. the clamp should be chosen to be above the normal range of out- put voltage, but low enough to protect the output ca- pacitor. in current sense operation, removal of the load will also break the regulation loop, in which case a sim- ple clamp on the output may not be adequate. in current sense mode it is recommended that a second zener be connected from the output to the fb pin, the breakdown voltage of this clamp chosen to be high enough so that it will not conduct during normal operation, but will con- duct at least 2v lower than the breakdown voltage of the other clamp. gate drive for the external fet: the ucc3890 is guaranteed to be able to deliver at least 1ma of steady state current to the gate of the external fet at i ton = 2ma. if i ton is higher than 2ma, 80% of the additional current is available to drive the fet gate. if, as in the design example above, a moderate sized fet such as the irf820 is used, the operating frequency is 100khz, and the minimum i ton at low line is 2.8ma, then the available gate drive current may be adequate. the irf820 needs about 13nc to charge the gate on each cycle. at 100khz, this is equivalent to 1.3ma steady state; below the minimum 1.64ma available. in some combinations of a larger fet, and/or higher frequency operation, the current available for driving the gate may not be adequate. in that case extra current may be pro- vided by connecting a resistor r dd from the line input to the vdd pin. this resistor should be sized so that under all conditions the current input to vdd is below the 7.5ma absolute maximum limit. r dd will likely need to be a power resistor. unitrode corporation 7 continental blvd. merrimack, nh 03054 tel. (603) 424-2410 fax (603) 424-3460 application information (cont.) 7
packaging information orderable device status (1) package type package drawing pins package qty eco plan (2) lead/ball finish msl peak temp (3) ucc3890d obsolete soic d 8 tbd call ti call ti ucc3890dtr obsolete soic d 8 tbd call ti call ti ucc3890n obsolete pdip p 8 tbd call ti call ti (1) the marketing status values are defined as follows: active: product device recommended for new designs. lifebuy: ti has announced that the device will be discontinued, and a lifetime-buy period is in effect. nrnd: not recommended for new designs. device is in production to support existing customers, but ti does not recommend using this part in a new design. preview: device has been announced but is not in production. samples may or may not be available. obsolete: ti has discontinued the production of the device. (2) eco plan - the planned eco-friendly classification: pb-free (rohs), pb-free (rohs exempt), or green (rohs & no sb/br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. tbd: the pb-free/green conversion plan has not been defined. pb-free (rohs): ti's terms "lead-free" or "pb-free" mean semiconductor products that are compatible with the current rohs requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. where designed to be soldered at high temperatures, ti pb-free products are suitable for use in specified lead-free processes. pb-free (rohs exempt): this component has a rohs exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. the component is otherwise considered pb-free (rohs compatible) as defined above. green (rohs & no sb/br): ti defines "green" to mean pb-free (rohs compatible), and free of bromine (br) and antimony (sb) based flame retardants (br or sb do not exceed 0.1% by weight in homogeneous material) (3) msl, peak temp. -- the moisture sensitivity level rating according to the jedec industry standard classifications, and peak solder temperature. important information and disclaimer: the information provided on this page represents ti's knowledge and belief as of the date that it is provided. ti bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. efforts are underway to better integrate information from third parties. ti has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. ti and ti suppliers consider certain information to be proprietary, and thus cas numbers and other limited information may not be available for release. in no event shall ti's liability arising out of such information exceed the total purchase price of the ti part(s) at issue in this document sold by ti to customer on an annual basis. package option addendum www.ti.com 18-sep-2008 addendum-page 1
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