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july 2007 rev 1 1/21 an2448 application note EVALTSM1052: ultra small battery charger using tsm1052 introduction this document describes a low power adapter that can be used in travel battery charger applications. it uses the new constant voltage constant current (cvcc) controller tsm1052, which is housed in one of the smallest packages available (sot23-6l). thanks to its low consumption and low operating voltage, good electrical performance is achieved. another important feature of this smps is the absence of the y1 safety capacitor between primary and secondary grounds. figure 1. EVALTSM1052 demo board www.st.com
contents an2448 2/21 contents 1 adapter features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 main characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 electrical behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 electrical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1 efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2 output characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.3 hold-up time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4 conducted noise measur ements (pre-compliance test) . . . . . . . . . . . 16 5 thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6 bom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 7 pcb layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
an2448 list of figures 3/21 list of figures figure 1. EVALTSM1052 demo board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 figure 2. electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 figure 3. v in = 115 vrms - 60 hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 figure 4. v in = 230 vrms - 50 hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 figure 5. maximum supply voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 figure 6. minimum supply voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 figure 7. v in = 115 v ac - no-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 figure 8. v in = 230 v ac - no-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 figure 9. v in = 115 v ac - short circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 figure 10. v in = 230 v ac - short circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 figure 11. efficiency vs. output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 figure 12. output characteristics at 115 v ac with cdc (cable drop compensation) . . . . . . . . . . . . . . 13 figure 13. power down at 115 v ac - 60 hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 figure 14. power down at 230 v ac - 50 hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 figure 15. ce peak measure at 115 v ac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 figure 16. ce peak measure at 230 v ac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 figure 17. v in = 115 v ac - full load - bottom and top sides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 figure 18. v in = 230 v ac - full load - bottom and top sides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 figure 19. tht components placing (top side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 figure 20. smt components placing (bottom side) and copper tracks. . . . . . . . . . . . . . . . . . . . . . . . 20
adapter features an2448 4/21 1 adapter features 1.1 main characteristics input: ?v in : 90 ~ 264 vrms ? f: 45 ~ 66 hz output: ?5.1vdc 2% ? 600 ma ? cable drop compensation (0.33 mv/ma) no-load: ? pin below 0.3 w short circuit: protected with nominal current regulation pcb type & size: ?cem-1 ? single side 35 m ? 48 x 18 mm safety: according to en60065 emi: according to en55022 - class b
an2448 adapter features 5/21 figure 2. electrical diagram 3 4 ic1a sfh617-a3 x007 c5 330nf i1 1mh f1 10 ohm 2w r13 220k r14 22k c1 2.2f 400v r3 1k r4 2.2 ohm 2 3 1 4 -+ d1 s1zb60 vdd 4 s 1 d 5 d 7 d 6 d 8 fb 3 s 2 ic2 viper12as-e c6 470f 16v r7 22k 1% c9 1uf vctrl 1 gnd 2 out 3 ictrl 4 vs 5 vcc 6 ic3 tsm1052 d5 1n4148ws r5 100 ohm c8 4.7nf ac2 vout gnd r9 22k 1% r12 2.2k 2 1 tr 1a ef12.6lp c11 1.8nf 5 4 tr 1b ef12.6lp r15 0 ohm 8 6 tr 1c ef12.6lp 9 7 tr 1d ef12.6lp r10 10k 1% r8 4.7k c10 10nf d4 stps3l40s ac1 r11 0.33 ohm c7 22nf r6 330 ohm 5.1v - 600ma c4 1.5nf 250v r1 330k r2 680 ohm d2 uf108g c3 33f 50v d3 1n4148ws c2 4.7f 400v 1 2 ic1b sfh617-a3 x007 90264vac
adapter features an2448 6/21 1.2 circuit description the circuit used implements a flyback topology , which is ideal for a low power, low cost isolated converter. at primary side a viper12a-e has been used. this ic includes a current mode pwm controller and a power mosfet in a small so-8 package. the converter works in both continuous and discontinuous conduction mode depending on the input voltage (the circuit has a wide range input) and the output load. the switching frequency is internally fixed at 60 khz. the design has been developed to reduce overall component count and adapter cost. the input section includes a resistor for in rush current limiting, a diode bridge, two electrolytic bulk capacitors and an inductor as front-end ac-dc converter and emc filter. the transformer is a layer type, uses a standard ef12.6 ferrite core and is designed to have a reflected voltage of about 90 v. the peculiarity of this transformer is the winding technique which allows the elimination of the usual y1 safety capacitor between the primary and the secondary. a rcd clamp network is used for leakage inductance de magnetization. the power supply for the viper12a-e is obtained with a self supply winding from the transformer connected in forward configuration. this circuit provides a voltage that is directly proportional to the input rectified voltage and independent from the load voltage. in this way even in short circuit condition (v out = 0), the ic is correctly supplied. the wide v dd operating range (9 v to 38 v) of the viper12a-e allows a wide range mains input voltage. at secondary side, the tsm1052 constant volt age constant current (cvcc) controller is used. like the viper12a-e, the tsm1052 is also supplied with a forward configuration, in order to obtain the same benefit. the voltage is taken on one half of the secondary winding (between pins 8 and 6), rectified with diode d5 and added to the output voltage. under all working conditions, the voltage supply for the tsm1052 and the photodiode ic1b is equal to the output voltage plus forward rectified voltage on half secondary. with this configuration a correct supply is provided over the whole input range, even with the output short circuited. with this configuration a small ripple at twice line frequency is present at the output. this is due to the supply of the photodiode ic1b, whic h is a replica of the voltage on c2. usually this is not a problem in battery chargers. there are two ways to eliminate this phenomenon if necessary: c9 can be substituted by an electrolytic capacitor (at least 47 f) the tsm1052 and ic1b can be attached directly to the output voltage. in this case the current regulation is guaranteed only for output voltages down to 1.7 v resistor r7 has been added for cable drop compensation (the higher the output current the higher the output voltage). r7 has been chosen according to the cable characteristics (it has about 0.3 ? of resistance).
an2448 electrical behavior 7/21 2 electrical behavior figure 3 and figure 4 show all the viper12a-e waveforms during normal operation at full load. the converter operates in dcm at both 115 vrms and 230 vrms: figure 3. v in = 115 vrms - 60 hz ch1: viper12a-e supp ly voltage (yellow) ch2: viper12a-e feedback pin (red) ch3: viper12a-e drain voltage (green)
electrical behavior an2448 8/21 figure 4. v in = 230 vrms - 50 hz due to the forward supply, the v dd voltage is directly proportional to the input voltage, so it is nearly double at 230 v ac with respect to 115 v ac . the worst case (maximum / minimum) supply voltages for both primary and secondary sides are shown in figure 5 and figure 6 . for the maximum voltages, the converter operates with the maximum load in cv mode (that is, the maximum output voltage is present, thanks to the cable drop compensation) and with the maximum input voltage (264 v ac ). in this condition the viper12a-e has a maximum supply voltage of 35.2 v and the tsm1052 16.16 v. minimum voltages are taken with short circuit on the output (cc regulation) and minimum input voltage (90 v ac ). given this condition the viper12a-e has a minimum supply voltage of 10.48 v and the tsm1052 2.12 v. ch1: viper12a-e supply voltage (yellow) ch2: viper12a-e feedback pin (light blue) ch3: viper12a-e drain voltage (purple)
an2448 electrical behavior 9/21 figure 5. maximum supply voltages figure 6. minimum supply voltages ch1: output voltage (yellow) ch2: viper12a-e supply voltage (light blue) ch3: tsm1052 supply voltage (green) ch1: output voltage (yellow) ch2: viper12a-e supply voltage (light blue) ch3: tsm1052 supply voltage (green)
electrical behavior an2448 10/21 let's see what happens at the extreme conditions: no load and short circuit. during no load conditions, the circuit operates in burst mode allowing an input power of less than 300 mw over the whole input voltage range. figure 7. v in = 115 v ac - no-load figure 8. v in = 230 v ac - no-load ch1: output voltage (yellow) ch2: viper12a-e drain pin (purple) ch3: tsm1052 supply voltage (green) ch1: output voltage (yellow) ch2: viper12a-e drain pin (purple) ch3: tsm1052 supply voltage (green)
an2448 electrical behavior 11/21 figure 9. v in = 115 v ac - short circuit figure 10. v in = 230 v ac - short circuit ch1: output voltage (yellow) ch2: viper12a-e drain pin (purple) ch3: tsm1052 supply voltage (green) ch1: output voltage (yellow) ch2: viper12a-e drain pin (purple) ch3: output current (green)
electrical performance an2448 12/21 with the circuit used in this evaluation boar d, when the output current has rapid variation from maximum to zero and the input voltage is low ( < 105 v ac ), the viper12a-e loses the supply for about 400-500 ms. the output voltage thereby decreases. after that time the ic turns on again and the output returns to the nominal value. this behavior is not problematic in this kind of application and has not been modified, in order to have a smaller and cheaper solution. if this phenomenon must be avoided, however, it is enough to increase c3 to 100 f. 3 electrical performance 3.1 efficiency ta bl e 1 and ta bl e 2 show the board efficiency at the two nominal voltages. table 1. efficiency at 115 vrms io [a] vo [v] po [w] iin [ma] pin [w] efficiency 0.1 5.153 0.520 16.9 0.832 62.5% 0.2 5.185 1.036 27.4 1.483 69.9% 0.3 5.217 1.566 38.2 2.235 70.1% 0.4 5.248 2.096 47.6 2.928 71.6% 0.5 5.280 2.638 58.7 3.769 70.0% 0.6 5.310 3.187 68.5 4.530 70.3% table 2. efficiency at 230 vrms io [a] vo [v] po [w] iin [ma] pin [w] efficiency 0.1 5.158 0.520 12.8 1.033 50.4% 0.2 5.190 1.037 20.1 1.740 59.6% 0.3 5.222 1.568 25.5 2.364 66.3% 0.4 5.254 2.098 32.6 3.193 65.7% 0.5 5.286 2.641 38.4 3.908 67.6% 0.6 5.319 3.192 43.6 4.572 69.8%
an2448 electrical performance 13/21 figure 11. efficiency vs. output current as indicated in ta bl e 3 , the no-load consumption is always below 300 mw, and therefore complies with the more restrictive standards (european code of conduct). 3.2 output characteristics figure 12 shows the output characteristics (taken with 115 v ac mains input) on pcb pads and at the end of the output cable. values are very close also at 230 v ac . it is interesting to note that, while in the constant current region, the output voltage can reach zero. figure 12. output characteristics at 115 v ac with cdc (cable drop compensation) table 3. no-load consumption value 90v ac 115v ac 230v ac 264v ac pin [w] 0.106 0.131 0.239 0.273 v out [v] 5.12 5.12 5.12 5.12 efficiency 40.0% 45.0% 50.0% 55.0% 60.0% 65.0% 70.0% 75.0% 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 output current [a] efficiency 115vac 230vac v-i characteristics 0 1 2 3 4 5 6 0 200 400 600 800 output current [ma] output voltage [v] pcb output end of cable
electrical performance an2448 14/21 the effect of the cable drop compensation is also worthy of note. ta b l e 4 shows the output voltage at various load amounts measured at the output connector, after the output cable. 115 v ac and 230 v ac mains input give very similar results. with the cable drop compensation the output voltage is nearly constant while, without this feature, at maximum load the output voltage goes down to 4.96 v (about -3.1%). the effect of this feature is also clearly visible in the output characteristic ( figure 12 ), with a flat line while in the constant voltage regulation region. 3.3 hold-up time during power down phase the output voltage undergoes a clean transition without restart trials or glitches. by observing the waveforms it is possible to measure the hold-up time. in figure 13 and figure 14 this condition is shown for the two nominal voltages of 115 v ac and 230 v ac . in the worst case, 115 v ac , a hold-up time of about 17.1 ms is measured. figure 13. power down at 115 v ac - 60 hz table 4. output voltage at output connector iout [a] 0 0.1 0.2 0.3 0.4 0.5 0.6 vout [v] with cdc 5.12 5.13 5.13 5.14 5.14 5.15 5.15 vout [v] without cdc 5.12 5.09 5.07 5.04 5.01 4.98 4.96 ch1: output voltage (yellow) ch3: rectified input voltage (purple)
an2448 electrical performance 15/21 figure 14. power down at 230 v ac - 50 hz ch1: output voltage (yellow) ch3: rectified input voltage (purple)
conducted noise measurements (pre-compliance test) an2448 16/21 4 conducted noise measurements (pre-compliance test) figure 15 and figure 16 show the conducted noise measurements performed at the two nominal voltages with peak detection and considering only the worst phase. the measurements have a good margin with resp ect to the limits (sta ted in en55022 class b specifications). figure 15. ce peak measure at 115 v ac and full load figure 16. ce peak measure at 230 v ac and full load
an2448 thermal measurements 17/21 5 thermal measurements a thermal analysis of the board was performed using an ir camera. the results are shown in figure 17 and figure 18 for 115 v ac and 230 v ac mains input. both images refer to full load condition (iout = 600 ma). t amb = 25 c for both figures emissivity = 0.9 for all points figure 17. v in = 115 v ac - full load - bottom and top sides table 5. key component temperatures at 115 v ac - 600 ma point temperature [ o c] reference a 69.2 r2 (clamp) b 72.3 r1 (clamp) c 63.0 ic2 (viper12a-e) d 66.3 d4 (output diode) e 68.3 tr1 (windings) f 64.0 tr1 (ferrite) g 66.2 hot spot on pcb due to bottom side components
thermal measurements an2448 18/21 figure 18. v in = 230 v ac - full load - bottom and top sides table 6. key component temperatures at 230 v ac - 600 ma point temperature [ o c] reference a 70.4 r2 (clamp) b 72.7 r1 (clamp) c 67.9 ic2 (viper12a-e) d 66.1 d4 (output diode) e 70.4 tr1 (windings) f 66.0 tr1 (ferrite) g 68.5 hot spot on pcb due to bottom side components
an2448 bom 19/21 6 bom table 7. EVALTSM1052 bill of material ref description size manufacturer c1 electr.cap. 2.2 f 400 v 105oc sek ?6x11 p2.5 teapo/yageo c2 electr.cap. 4.7 f 400 v 105oc sek ?8x11 p3.5 teapo/yageo c3 electr.cap. 33 f 50 v 105oc ?5x11 p2.5 c6 electr.cap. 470 f 16 v 105oc sek ?8x11 p3.5 teapo/yageo c4 chip capacitor 1.5 nf/250 v x7r 0805 c5 chip capacitor 330 nf/16 v x7r 0603 c7 chip capacitor 22 nf/25 v x7r 0603 c8 chip capacitor 4.7 nf/25 v x7r 0603 c9 chip capacitor 1 uf/16 v x7r 0603 c10 chip capacitor 10 nf/50 v x7r 0603 c11 chip capacitor 1.8 nf/50 v x7r 0603 d1 single phase bridge s1zb60 mbs d2 diode uf108g d041 panjit d3 d5 diode 1n4148ws sod323 d4 diode stps3l40s smc stmicroelectronics f1 fuse res. 10 ohm 5% 2 w i1 inductor 1 mh cecl-102k coils electr. ic1 opto sfh617-a3 x007 smt siemens ic2 i.c. viper12as-e so8 stmicroelectronics ic3 i.c. tsm1052clt sot23-6l stmicroelectronics r1 chip resistor 330 k 5% 0805 r2 chip resistor 680 ohm 5% 0805 r3 chip resistor 1 k 5% 0603 r4 chip resistor 2.2 ohm 5% 0603 r5 chip resistor 100 ohm 5% 0603 r6 chip resistor 330 ohm 5% 0603 r7 r9 chip resistor 22 k 1% 0603 r8 chip resistor 4.7 k 5% 0603 r10 chip resistor 10 k 1% 0603 r11 chip resistor 0.33 ohm 1% 200 ppm 1206 r12 chip resistor 2.2 k 5% 0805 r13 chip resistor 220 k 5% 0603
pcb layout an2448 20/21 7 pcb layout figure 19. tht components placing (top side) figure 20. smt components placing (bottom side) and copper tracks 8 revision history r14 chip resistor 22 k 5% 0603 r15 chip resistor 0 ohm 0603 tr1 transformer ef12.6 lp table 7. EVALTSM1052 bill of material (continued) ref description size manufacturer table 8. revision history date revision changes 04-jul-2007 1 first issue
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