1 description lt c4121eud/lt c4121eud-4.2 400ma synchronous buck battery charger dc1977a-a ltc4120eud-4.2 (fixed output) dc1977a-b LTC4121EUD (adjustable output) demonstration board dc1977 a showcases the ltc4121-4.2 and ltc4121 40v, 400ma synchronous- buck battery charger integrated circuit. the dc1977 a supports the maximum-power-point tracking (mppt) feature of the ltc4121 eud to optimize power delivery from photovotalic cells or highly resistive sources. l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of analog devices, inc. all other trademarks are the property of their respective owners. p erformance s ummary demo boar d a pplication the ltc4121 and ltc4121-4.2 feature constant-currentC constant-voltage charging capability suitable for lithium- ion or lead-acid cells. the ltc4121 -4.2 supports charging a single lithium-ion cell with a cell voltage of 4.2v. the ltc4121 may be programmed to charge battery voltages up to 18v with a resistive divider. design files for this circuit board are available at http://www.linear.com/demo/dc1977 specifications are at t a = 25c high efficiency, wide input voltage range charging with ltc4121 ltc4121 efficiency vs v in symbol parameter conditions note: reference designators refer to schematic on p. 7. min ty p max units in dc1977a input voltage i(in) < 800ma 4.4 40 v pv in dc1977a pv cell input i(in) < 800ma 5 40.5 v v(bat) dc1977a bat pin voltage r11 = 1.40m, r12 = 1.05m 2.5 4.25 v i(bat) dc1977a bat pin current v(bat) = 3.7v; dc1977a; (r7) = 3.01k; jp1 (mppt) = off 383 402 421 ma intv cc boost in run mppt ltc4121 dc1977a f01 gnd r mppt1 787k r mppt2 121k r run1 261k r run2 324k c in 10f r prog 3.01k v in v bat + 200mv to 40v c boost 22nf lps4018-333ml c intvcc 2.2f freq + c bat 47f r fb1 1.05m r fb2 1.40m li-ion + ? sw chgsns bat fb fbg prog v in (v) 5 70 efficiency (%) 75 85 80 90 95 100 10 15 20 25 30 35 40 r prog = 6.04k r prog = 3.01k v bat = 4.1v dc1977a f02 dc1977afb demo manual dc1977a-a/dc1977a-b
2 assem b ly test p roce d ure refer to figure 1 for the proper measurement equipment setup and jumper settings and follow the procedure below. 1. set jp1 ( mppt ) to on, set ps1 to 3.6v and turn on. 2. connect ps2 to point a, set to 15v and turn on. 3. verify that v m1 indicates 3.3v to 3.9v , and then verify that am1 indicates 387ma to 417ma . verify that vm2 shows 14.5v to 15.1v. there is only a series diode between pv + and the v in pin of the ltc4121 . the purpose of this diode is prevent backfeeding a pv cell, if connected. a single diode v f is insufficient to activate the mppt feature, and the ltc4121 delivers full charge current to the battery. 4. turn p s2 off, move connection to point b, and turn ps2 on. 5. verify that v m1 indicates 3.3v to 3.9v , and then verify that am1 indicates 387ma to 417ma . verify that vm2 shows 12.6v to 13.2. the source impedance of the power supply is now 16. but this impedance still allows delivering full charge current without engaging the mppt feature. 6. turn p s2 off, move connection to point c, and turn ps2 on. 7. verify that v m1 indicates 3.3v to 3.9v , and then verify that am1 indicates 105ma to 115ma . verify that vm2 shows 10.6v to 11.3v . the source impedance of the power supply is now 98 . the mppt feature has engaged and the charge delivered to the battery has been reduced to allow v in to stay at the programmed mppt point. 8. set jp1 (mpp t) to off, test is finished. + ? + ? b c ps2 15v power supply 0.25a + ? ps1 3.6v bipolar supply 1a + ? ? + ? +? ? am1 3.6 vm1 vm2 15.8 2w 82.4 2w am2 a dc1977a f03 figure?1. dc1977a equipment setup note: all connections from equipment should be kelvin-connected directly to the board pins which they are connected on this diagram. all input or output leads should be twisted pair. dc1977afb demo manual dc1977a-a/dc1977a-b
3 theory of operation the LTC4121EUD-4.2/ltc4121 eud is a 4.4v ~ 40v input buck topology battery charger with maximum power point tracking (mppt) for use with pv cells or highly resistive power supplies. the buck-topology charger uses current mode control for stable operation. LTC4121EUD enable the ltc4121 can be enabled or disabled via the run pin, and this functionality can be accessed via jp2, the run jumper. when jp2 is in the enable position, r3 and r4 ensure that the ltc4121 is not enabled until vin is greater than 4.4v. note: do not float the ltc4121 run pin. operate the demo board with jp2 in either the disabled or enabled position. buck charger the heart of the ltc4121 eud is the buck-topology bat - tery charger. the buck-topology charger is a synchronous, current-mode-control regulator with n-channel fets. the use of n-channel fets minimizes conduction losses, and requires only a single external 0.022f capacitor to gener - ate the high-side gate drive. the ltc4121 eud can charge up to four li-ion cells in series, and supports a maximum battery voltage of 18v. the ltc4121 eud-4.2 is optimized for charging a single li-ion cell to a fixed cell voltage of 4.2v. the current in the buck inductor passes through a small on-die resistor for current measurement, and then goes back out to the bat pin. the battery is connected to the bat pin ; this allows the ltc4121 eud to measure not only the cycle-by-cycle current, but also the average current. the cycle-by-cycle current is used by the current-mode buck regulator, and the average current is the battery charge current as programmed by r prog . on dc1977a, r prog = 3.01k , so i(bat) = 402ma provided that the mppt function does not reduce the current. the buck regulator acts as a current source when the battery is in the constant-current charging region and as a classic voltage output buck regulator when the battery is in the constant-voltage charging region. the battery charge current is programmed by r prog ?=? 3.01k. the equation for r prog is: r prog = h prog ? v prog i chg = 986 ? 1.227v 0.4 = 3.01k the ltc4121 eud provides a switching frequency select pin, freq, to select between 750khz and 1.5mhz; this function is accessed by jp4, the freq jumper. note: do not float the ltc4121 freq pin. operate the demo board with jp3 in either the 750khz or 1.5mhz position. figure?2 shows various nodes of interest with v in = 5v, and the switching frequency at 750khz (t = 1.333s ), the duty cycle is 86% for v(bat) = 3.6v , not the 72% duty expected from a buck regulator. when the battery voltage is 3.6v , the charger is in constant-current mode, so the control loop is forcing the output of the buck regulator to the voltage necessary to push 400ma into the battery. this effective voltage, 5 ? 0.86 = 4.3v , is the voltage necessary to ensure that a 400ma average current is flow - ing through the on-die sense resistor. figure?3 shows the same nodes as figure?2, but with v in = 40v . the switching frequency is still 750khz. the duty cycle is 200ns/1.333s, or 15%, but the period is 2.7s. this is because the ltc4121 minimum on time was greater than that needed to achieve 4.3v , and the ltc4121 starts to pulse skip to get the necessary average duty cycle. the average duty cycle is 300ns/2.667s?=?11%. this produces an output voltage of 4.3v , so the battery still charges at 400ma. maximum power point tracking (mppt) the ltc4121 eud provides a maximum-power-point tracking (mppt) function for use with pv cells or highly dc1977afb demo manual dc1977a-a/dc1977a-b
4 theory of operation resistive power supplies. the mppt pin allows program - ming of the mppt point as a percentage of the open- circuit v in (v oc ). to access this functionality the demo board provides jp1, the mppt jumper, and r1 and r2. it is important to note that the disabled position for mppt is the mppt pin at v in . to enable mppt, set the mppt point as a fraction of v oc . see the discussion in maximum power point tracking section of the ltc4121 data sheet. when mppt is enabled (not equal to v in ), the LTC4121EUD periodically disconnects the load from the power source, and measures v in with no load = v oc . it then increases the load on v in to meet charger demand until the v mppt threshold is reached, after which it no longer increases the load. this allows the mppt voltage divider to set the desired mppt point as a percentage of v in with no load. figure?4 shows the ltc4121 eud operating from a source impedance of 98 . the mppt pin of the LTC4121EUD sets the mppt point to 0.75 of the open-circuit voltage. first, v oc is determined by removing all load and letting v in rise to v oc . the power drawn from v in is increased until the voltage at v in falls to the mppt point, 0.75 ? v oc = 0.75? ? ?15v = 11.25v . the resolution of the mppt dac is 330mv , thus this example has the mppt point at 11v . the ltc4121 stops drawing power at this point, and the charge current (green) never exceeds 200ma, even though the rprog value was chosen for 400ma. figure?5 shows the same system, but the source imped - ance was lowered to 16 . consequently, the full power needed to meet the requirements of the programmed charge current is available before v in falls to the mppt voltage. figure?2. normal operation, zoom, v in = 5.1v, dk. blue = v in , grn = i charge , lt. blue = v sw , pk. = intv cc , 750khz figure?3. normal operation, zoom, v in = 40v, dk. blue = v in , grn = i charge , lt. blue = v sw , pk. = v boost , 750khz dc1977afb demo manual dc1977a-a/dc1977a-b
5 theory of operation battery capacitors c1 and c2 the maximum battery voltage for the ltc4121 eud is 18v, and for the LTC4121EUD-4.2, it is 4.2v . analog devices recommends 47f of capacitance on the bat pin, if the battery is not present. for the LTC4121EUD the voltage rating of the capacitor will need to be 25v, so two 22f, 25v , mlcc capacitors are used. in the case of the ltc4121 eud-4.2, a 6.3v capacitor will suffice, and a single 47f, 6.3v, mlcc capacitor is used for c1, with c2 not placed. reverse-blocking circuit components q1, r16 and c6 comprise a reverse-blocking circuit. the circuit performs two functions. first, the cir - cuit prevents the battery from back-charging the power sour ce when the power sour ce is dormant (e.g., a solar cell in the absence of illumination). note that this func - tionality can also be provided through d1 . second, when a charged battery is connected to the circuit in the absence of input voltage, current will flow from the battery into the bat pin and out the in pin, charging c4 . with battery volt - ages in excess of ~ 10v , this current surge can destroy the device. note that this is not a problem when only one or two series li-ion cells are employed. thus, this reverse- blocking circuit may not be necessary depending on the application. if reverse-blocking is not required, c6 and r16 also become unnecessary. these two components provide a path to the bat pin from which the ltc4121 derives bias for internal circuits which would be provided by the battery directly in the absence of q1. see, for exam - ple, the application on the first page of this manual. figure?4. mppt test, dk. blue = v in (through 98), green = i l , lt. blue = v(sw), k = 0.15, v mppt /v oc = 0.75 figure?5. mppt test, dk. blue = v in (through 16), green = i l , lt. blue = v(sw), k = 0.15, v mppt /v oc = 0.75 dc1977afb demo manual dc1977a-a/dc1977a-b
6 p arts l ist item qty reference part description manufacturer/part number dc1977a general bill of materials required circuit components 1 1 c3 cap, chip, x7r, 0.022f, 10%, 50v, 0402 tdk, c1005x7r1e223k 2 1 c4 cap, chip, x5r, 10f, 10%, 50v, 1210 taiyo-yuden, umk325bj106km-t 3 1 c5 cap, chip, x5r, 2.2f, 20%, 6.3v, 0402 murata, grm155r60j225me15d 4 1 l1 ind, smt, 33h, 420m, 20%, 0.80a, 4mm 4mm coilcraft, lps4018-333ml 5 1 r1 res, chip, 787k, 1%, 1/16w, 0402 vishay, crcw0402787kfked 6 1 r2 res, chip, 121k, 1%, 1/16w, 0402 vishay, crcw0402121kfked 7 1 r3 res, chip, 261k, 1%, 1/16w, 0402 vishay, crcw0402261kfked 8 1 r4 res, chip, 324k, 1%, 1/16w, 0402 vishay, crcw0402324kfked 9 1 r7 res, chip, 3.01k, 1, 1/16w, 0402 vishay, crcw04023k01fked additional demo board circuit components 1 1 c6 cap, chip, x5r, 4.7f, 20%, 6.3v, 0603 murata, grm188r60j475ke19d 2 1 d1 diode, schottky, 40v, 2a, powerdi123 diodes, dfls240l 3 1 m1 mosfet, p-channel, C30v, C5.9a, 45m, sot-23 vishay, si2343cds 4 2 r5, r9 res, chip, 10k, 1%, 1/16w, 0402 vishay, crcw040210k0fked 5 1 r6 res, chip, 2k, 5%, 1/16w, 0402 vishay, crcw04022k00jned 6 2 r8, r10 res, chip, 0 jumper, 1/16w, 0402 vishay, crcw04020000z0ed 7 1 r13 res, chip, 47k, 5%, 1/16w, 0402 vishay, crcw040247k0jned 8 1 r14 res, chip, 5.1k, 1%, 1/16w, 0402 vishay, crcw04025k10jned 9 1 r15 res, chip, 100k, 5%, 1/16w, 0402 vishay, crcw0402100kjned 10 1 r16 res, chip, 464k, 1%, 1/10w, 0603 yageo, rc0603fr-07464kl hardware: for demo board only 1 7 e1, e2, e3, e6, e7, e10, e11 turret, 0.09 dia mill-max, 2501-2-00-80-00-00-07-0 2 4 e4, e5, e8, e9 turret, 0.061" mill-max, 2308-2-00-80-00-00-07-0 3 0 j1-opt conn, 3 pin polarized hirose, df3-3p-2dsa 4 4 jp1-jp4 header, 3 pin, smt, 2mm sullin, nrpn031paen-rc 5 4 jp1-jp4 shunt, 2mm samtec, 2sn-bk-g item qty reference part description manufacturer/part number dc1977a-a bill of materials required circuit components 1 0 r11 do not install 2 1 r12 res, chip, 0 jumper, 1/16w, 0402 vishay, crcw04020000z0e 3 1 u1 40v 400ma synchronous step-down battery charger, 3mm 3mmqfn16 linear tech., LTC4121EUD-4.2#pbf 1 1 c1 cap, chip, x5r, 47f, 10%, 16v, 1210 murata, grm32er61c476ke15l 2 0 c2 cap, chip, x5r, 47f, 10%, 16v, 1210 murata, grm32er61c476ke15l item qty reference part description manufacturer/part number dc1977a-b bill of materials required circuit components 1 1 r11 res, chip, 1.40m, 1%, 1/16w, 0402 vishay, crcw04021m40fke 2 1 r12 res, chip, 1.05m, 1%, 1/16w, 0402 vishay, crcw04021m05fked 3 1 u1 40v, 400ma synchronous step-down battery charger, 3mm 3mmqfn16 linear tech., LTC4121EUD#pb 1 2 c1, c2 cap, chip, x5r, 47f, 10%, 16v, 1210 murata, grm32er61c476ke15l dc1977afb demo manual dc1977a-a/dc1977a-b
7 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa - tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. s chematic diagram 4 4 3 3 2 2 1 1 4 4 3 3 2 2 1 1 unless noted: resistors: ohms, 0402, 1%, 1/16w capacitors: uf, 0402, 10%, 50v opt freq ext 1.5 mhz ntc int 400ma disabled run enabled 2.7v - 18v 750 khz * r12 assy 1.40m 1.05m 0 ohm open r11 -b -a LTC4121EUD LTC4121EUD - 4.2 u1 4.4v - 40v 0.4a off mppt on r12 to be connected to c2 & c3 battery charger c1 c2 22f/25v 22f/25v open 47f/16v * * intvcc intvcc revision history description date approved eco rev - revision history description date approved eco rev - revision history description date approved eco rev - size date: ic no. rev. sheet of title: approvals pcb des. app eng. technology fax: (408)434-0507 milpitas, ca 95035 phone: (408)432-1900 1630 mccarthy blvd. ltc confidential-for customer use only customer notice linear technology has made a best effort to design a circuit that meets customer-supplied specifications; however, it remains the customer's responsibility to verify proper and reliable operation in the actual application. component substitution and printed circuit board layout may significantly affect circuit performance or reliability. contact linear technology applications engineering for assistance. this circuit is proprietary to linear technology and schematic supplied for use with linear technology parts. scale = none www.linear.com 1 demo circuit 1977a - a / b 1 1 40v 400ma synchronous step-down n/a LTC4121EUD - 4.2 / LTC4121EUD nc wat 2017-02-22 size date: ic no. rev. sheet of title: approvals pcb des. app eng. technology fax: (408)434-0507 milpitas, ca 95035 phone: (408)432-1900 1630 mccarthy blvd. ltc confidential-for customer use only customer notice linear technology has made a best effort to design a circuit that meets customer-supplied specifications; however, it remains the customer's responsibility to verify proper and reliable operation in the actual application. component substitution and printed circuit board layout may significantly affect circuit performance or reliability. contact linear technology applications engineering for assistance. this circuit is proprietary to linear technology and schematic supplied for use with linear technology parts. scale = none www.linear.com 1 demo circuit 1977a - a / b 1 1 40v 400ma synchronous step-down n/a LTC4121EUD - 4.2 / LTC4121EUD nc wat 2017-02-22 size date: ic no. rev. sheet of title: approvals pcb des. app eng. technology fax: (408)434-0507 milpitas, ca 95035 phone: (408)432-1900 1630 mccarthy blvd. ltc confidential-for customer use only customer notice linear technology has made a best effort to design a circuit that meets customer-supplied specifications; however, it remains the customer's responsibility to verify proper and reliable operation in the actual application. component substitution and printed circuit board layout may significantly affect circuit performance or reliability. contact linear technology applications engineering for assistance. this circuit is proprietary to linear technology and schematic supplied for use with linear technology parts. scale = none www.linear.com 1 demo circuit 1977a - a / b 1 1 40v 400ma synchronous step-down n/a LTC4121EUD - 4.2 / LTC4121EUD nc wat 2017-02-22 jp2 jp4 e4 ntc d1 dfls240l c2 c6 4.7uf 6.3v 0603 e6 gnd r13 47k 5% r16 464k 0603 0 ohm jumper r8 r11 * 0 ohm jumper r10 jp3 e1 pv+ e8 chrg r1 787k r5 10.0k r15 100k 5% q1 si2343ds r4 324k e10 gnd e2 vin + j1 df3-3p-2dsa bat 1 gnd 2 entc 3 e9 fault r7 3.01k c1 u1 LTC4121EUD-4.2 / LTC4121EUD intvcc 1 boost 2 in 3 sw 4 gnd 5 mppt 6 freq 7 chgsns 8 bat 9 batsns/fb 10 nc/fbg 11 ntc 12 prog 13 chrg 14 fault 15 run 16 epad 17 r9 10.0k r12 * r2 121k r6 2.0k 5% c4 10uf 50v 1210 c3 0.022f 25v e3 pv- or vin- r14 5.1k 5% e11 4.4v - 40v vin l1 33.0uh e5 prog c5 2.2uf 6.3v 20% r3 261k jp1 e7 bat dc1977afb demo manual dc1977a-a/dc1977a-b
8 ? linear technology corporation 2014 lt 0817 rev b ? printed in usa demonstration board important notice linear technology corporation (ltc) provides the enclosed product(s) under the following as is conditions: this demonstration board (demo board) kit being sold or provided by linear technology is intended for use for engineering development or evaluation purposes only and is not provided by ltc for commercial use. as such, the demo board herein may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety measures typically found in finished commercial goods. as a prototype, this product does not fall within the scope of the european union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations. if this evaluation kit does not meet the specifications recited in the demo board manual the kit may be returned within 30 days from the date of delivery for a full refund. the foregoing warranty is the exclusive warranty made by the seller to buyer and is in lieu of all other warranties, expressed, implied, or statutory, including any warranty of merchantability or fitness for any particular purpose. except to the extent of this indemnity, neither party shall be liable to the other for any indirect, special, incidental, or consequential damages. the user assumes all responsibility and liability for proper and safe handling of the goods. further, the user releases ltc from all claims arising from the handling or use of the goods. due to the open construction of the product, it is the users responsibility to take any and all appropriate precautions with regard to electrostatic discharge. also be aware that the products herein may not be regulatory compliant or agency certified (fcc, ul, ce, etc.). no license is granted under any patent right or other intellectual property whatsoeve r. ltc assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. ltc currently services a variety of customers for products around the world, and therefore this transaction is not exclusive. please read the demo board manual prior to handling the product. persons handling this product must have electronics training and observe good laboratory practice standards. common sense is encouraged. this notice contains important safety information about temperatures and voltages. for further safety concerns, please contact a ltc application engineer. mailing address: linear technology 1630 mccarthy blvd. milpitas, ca 95035 copyright ? 2004, linear technology corporation dc1977afb demo manual dc1977a-a/dc1977a-b
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