AN1623 APPLICATION NOTE

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1 PNCPLE OF OPEATON This technical note shows how it is possible to calculate the current and voltage precisn in the regulatn loop of the TSM0. The TSM0 is a highly integrated solutn for SMPS applicatns requiring C (Constant oltage) and CC (Constant Current) ode. The TSM0 integrates one voltage erence and two operatnal aplifiers (with Oed puts - coon collector). Figure : Typical applicatn using TSM0 inssmps AN63 APPLCATON NOTE TSM0: EULATON LOOPS PECSON CALCULATON by iuseppe SCUDE The voltage erence cobined with one operatnal aplifier akes it an ideal voltage controller. The other operatnal aplifier, cobined with few external resistors and the voltage erence, can be used as a current iter. This circuit is designed for use in battery chargers with a constant voltage and a ited put current and in adapters. t can be used in every type of applicatn requiring 0.% and % voltage erence precisn fixed at. olts. D it optocoupler secondary side PWM controller C C TSM0 8 cc 3, 8 C C Out vc 7 CC CC 3 C- Cvc C3 OUT optocoupler priary side D CC- ic nd 6 ic Cic OUT-. oltage Control The oltage Control loop is controlled via a first transconductance operatnal aplifier, the optocoupler which is directly connected to the put and an external resistor bridge connected between the put positive line and the round erence. The iddle point is to be connected to the C- pin of TSM0, and, if is the upper resistor, and, the lower resistor of the bridge, the relatnship between and value should be chosen as written in Equatn : f (,, ) Equatn where is the desired axiu put voltage. When under constant voltage control ode, the put voltage is fixed thanks to the / resistor bridge. To avoid the discharge of the load, the resistor bridge,, should be highly resistive. Noveber 00 /6

2 AN63 - APPLCATON NOTE For this type of applicatn a al value of 00kΩ (or ore) would be appropriate for the resistors and. Note that if the low drop dde should be inserted between the load and the voltage regulatn resistor bridge to avoid current flowing fro the load through the resistor bridge, this loop should be taken into account in the above calculatns by replacing by ( drop ).. Current Control The Current Control loop is controlled via the second transconductance operatnal aplifier, the optocoupler and the resistor that is to be placed in series on the put negative line. threshold is achieved externally by a resistor bridge tied to the voltage erence. ts iddle point is tied to the positive input of the current control operatnal aplifier and its foot is to be connected to lower potential point of the resistor. The resistors of the bridge are atched to provide the best precisn possible. Equatn f (,,, ) Equatn 3 Equatn where is the desired axiu put current, and is the threshold voltage for the current control loop. Note that resistor should be chosen taking into account the axiu dissipatn (P ) through it during full load operatn: Equatn P For ost adapter and battery charger applicatns, a quarter-watt, or half-watt resistor to ake the current sensing functn is sufficient. The current sinking puts of the two transconductance operatnal aplifiers are coon (to the put of the C), this akes an Oing functn that ensures that whenever the current or the voltage reaches too high values, the optocoupler is activated. The relatn between the controlled current and the controlled put voltage can be described with a square characteristic as shown in the following / put power graph Figure. Figure : Output voltage versus put current oltage regulatn < %.3 Start Up and Circuit Conditns f the TSM0 cc is connected to the converter put voltage, then under start-up or short-circuit conditns, the TSM0 was not provided with a high enough supply voltage. This is due to the fact that the chip has its power supply line in coon with the power supply line of the syste. Theore, the current itatn can only be ensured by the priary PWM odule, that should be chosen accordingly. f the priary current itatn is considered not to be precise enough for the applicatn, then a sufficient supply for the TSM0 has to be ensured under any conditn. t would then be necessary to add soe circuitry to supply the chip with a separate power line. The scheatic in Figure shows how to realize a low-cost power supply for the TSM0 (with no additnal winding). Please pay attentn to the fact that in the particular case presented here, this low-cost power supply can reach voltages as high as twice the voltage of the regulated line. The Absolute Maxiu ating of the TSM0 supply voltages is 8 olts. t is possible to insert it resistors in order to it TSM0 cc current in high voltage conditn.the current sunk by internal zener dde can be calculated by following forula: Equatn 6 vz ( cc z ) it current regulatn < 0% /6

3 AN63 - APPLCATON NOTE PECSON CALCULATON n order to calculate the precisn of and in the regulatn loop, it is possible to write one relatnship that point soe paraeters for current and voltage put variatn. As shown in Figure 3 and Figure it is possible to ake a odel of the current and voltage control transconductance operatnal aplifiers using a voltage source for input offset and an ipedence Z with voltage drop. Typical precisn requireents for battery charging are less than 0% for and less then % for see Figure. Now, let s go on to the voltage and current loop precisn calculatn.. Current Loop Precisn Calculatn.. Theoretical Calculatn Let s show soe different steps in order to calculate the current precisn loop According to the Figure 3 it is siple to verify that: Equatn 7 ( ) For the virtual ground at the input of the current aplifier: Equatn 8 e e 0 Equatn 9 Equatn 0 Substituting Equatn 9 in Equatn 7 Equatn where ( )( ) Equatn Equatn 3 Substituting Equatn in Equatn 3 Equatn ( ) is the su of the following: Equatn where ( ) Equatn 6 Equatn 7 Equatn 8 Equatn 9 Equatn Substituting Equatn 6 and Equatn in Equatn and considering the absolute value of these ters: Equatn Equatn is iportant in order to calculate and shows the any paraeters that characterize current variatn. t can be observed that,. and <, so the ter can be neglected with respect to. [ ( )] Equatn 0 [ ( )( ) ] ( ) [ ( )] ( )( ) 3/6

4 AN63 - APPLCATON NOTE Figure 3 : Siplified odel for current precisn calculatn TSM0 3 e Out 3 e- 7 ic nd 6.. Practical Exaple n order to siplify the coprehensn of forula, let s take a practical exaple that uses absolute and relative tolerances typical for TSM0 applicatns. Consider for exaple: see Footnote) ± 0.% ± % ± % ± % see Footnote ± Let s assue that will vary between 0 and A, theore: ±.A 3A 3.A/ - 7kΩ 0kΩ Ω ewriting Equatn Equatn 3 it is possible to obtain a good current variatn ±.3% Footnote using TSM0 A versn /6

5 AN63 - APPLCATON NOTE. oltage Loop Precisn Calculatn.. Theoretical Calculatn Let s show soe different steps in order to calculate the voltage precisn loop. According to Figure it is siple to verify that: Equatn ( ) where Equatn is the su of: Equatn 6 where Equatn 7 Equatn 8 Equatn 9 Equatn 30 Equatn 3 Substituting Equatn 7 and Equatn 3 in Equatn 6 and considering the absolute value of ters: Equatn 3 ( ) ( ) ( ) ( ) Equatn 3 is ore iportant in order to calculate and shows any paraeters that characterize voltage variatn. t can be observed that,. and <, so the ter can be neglected with respect to... Practical Exaple n order to better understand the forula, let s take a practical exaple that uses absolute and relative tolerances typical for TSM0 applicatns. Let s consider for exaple: see Footnote ± 0.% ± % ± % ± Assue that will vary between 0 and A, theore: ±.A 8 3.A/ 30kΩ - 86kΩ rewriting Equatn 3 Equatn 33 it is possible to obtain a good current variatn ±.3% /6

6 AN63 - APPLCATON NOTE Figure : Siplify odel for voltage precisn calculatn cc TSM0 8 3 e Out 7 e- nd 6 3 CONCLUSON This applicatn note relative to the TSM0 shows how very siple it is to calculate a current and voltage variatn in order to discern how any paraeters characterize the precisn of regulatn loop. n accordance with arket needs, current and voltage precisn in the TSM0 is extreely accurate. This allows a broaden applicatn range for our products as copared with those of copetitors. At this oent the current and voltage variatn precisn requested by arket is: ± 0% ± % The TSM0 ("A" versn) shows excellent perforance in typical adapter and battery charger applicatns. The results achieved in the above two practical exaples for current and voltage precisn are: ±.% ±.3% These results confir the optiu perforances and give clear explanatn of the external paraeters that affect accuracy and precisn for the TSM0 Attached to this applicatn note is an Excel file showing the general scheatic of the TSM0 and which allows the possibility of varying values and according to the paraeter variatns that characterize the applicatn. t is possible, oreover, to change the resistor accuracy in order to avoid high-cost coponents when the applicatn requires a lower precisn. nforatn furnished is believed to be accurate and reliable. However, STMicroelectronics assues no responsibility for the consequences of use of such inforatn nor for any infringeent of patents or other rights of third parties which ay result fro its use. No license is granted by iplicatn or otherwise under any patent or patent rights of STMicroelectronics. Specificatns entned in this publicatn are subject to change with notice. This publicatn supersedes and replaces all inforatn prevusly supplied. STMicroelectronics products are not authorized for use as critical coponents in life support devices or systes with express written approval of STMicroelectronics. The ST logo is a registered tradeark of STMicroelectronics 6/6 00 STMicroelectronics - All ights eserved STMicroelectronics OUP OF COMPANES Australia - Brazil - China - Finland - France - erany - Hong Kong - ndia - taly - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdo

TSM1011. Constant Voltage and Constant Current Controller for Battery Chargers and Adapters. PIN CONNECTIONS (top view) DESCRIPTION APPLICATIONS

TSM1011. Constant Voltage and Constant Current Controller for Battery Chargers and Adapters. PIN CONNECTIONS (top view) DESCRIPTION APPLICATIONS Constant Voltage and Constant Current Controller for Battery Chargers and Adapters Constant voltage and constant current control Low voltage operation Low external component count Current sink output stage