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| www..com SEA05 Advanced constant voltage and constant current controller Features Constant voltage and constant current control Wide operating VCC range [3.5 - 36] V Low quiescent consumption: 200 A Voltage reference: 2.5 V Voltage control loop accuracy +/- 0.5% Current sense threshold: 50 mV Open-drain output stage Low external component count SOT23-6L micro package SOT23 - 6L adequately rated in terms of power dissipation; the frequency compensation components (R-C networks) for both loops. The device, housed in one of the smallest available package, is ideal for space-shrunk applications such as adapters and chargers. Figure 1. Internal schematic 2.5 V 1.23 V Vcc 6 Applications Battery chargers AC-DC adapters LED drivers Description The SEA05 is a highly integrated solution for SMPS applications requiring a dual control loop to perform CV (constant voltage) and CC (constant current) regulation. The device integrates a voltage reference, two opamps (with OR-ed open-drain outputs), and a lowside current sensing circuit. The voltage reference, along with one op-amp, is the core of the voltage control loop; the current sensing circuit and the other op-amp make up the current control loop. The external components needed to complete the two control loops are: a resistor divider that senses the output of the power supply and fixes the voltage regulation setpoint at the specified value; a sense resistor that feeds the current sensing circuit with a voltage proportional to the dc output current; this resistor determines the current regulation setpoint and must be Table 1. + + - 5 3 Out Vctrl 2 1 Isense Gnd 4 Ictrl Device summary Package SOT23-6L Packing Tape and reel Order code SEA05TR April 2010 Doc ID 17014 Rev 1 1/10 www.st.com 10 www..com Pin description SEA05 1 Pin description Figure 2. Pin configuration Isense GND Vctrl Note: 1 2 3 6 5 4 Vcc Out Ictrl The adjacent pins have the same AMR to increase the robustness of the IC against accidental short circuit among pins. Table 2. n. 1 Pin description Name Isense Function Inverting input of the current loop op-amp. The pin is tied to the cold end of the current sense resistor through a decoupling resistor. Ground. Return of the bias current of the device. 0 V reference for all voltages. The pin should be tied as close to the ground output terminal of the converter as possible to minimize load current effect on the voltage regulation setpoint. Inverting input of the voltage loop op-amp. The pin is tied to the mid-point of a resistor divider that senses the output voltage. Non-inverting input of the current loop op-amp. It is tied directly to the hot (negative) end of the current sense resistor Common open-drain output of the two internal op-amps. The pin, able to sink current only, is connected to the branch of the optocoupler's photodiode to transmit the error signal to the primary side. Supply Voltage of the device. A small bypass capacitor (0.1 F typ.) to GND, located as close to IC's pins as possible, might be useful to get a clean supply voltage. 2 GND 3 4 Vctrl Ictrl 5 OUT 6 Vcc 2/10 Doc ID 17014 Rev 1 www..com SEA05 Maximum ratings 2 Maximum ratings Table 3. Symbol Vcc Vout Iout Ictrl Isense Vctrl Absolute maximum ratings Pin 6 5 5 4 1 3 Dc supply voltage Open-drain voltage Max sink current Analog input Analog input Analog input Parameter Value -0.3 to 38 -0.3 to Vcc 20 -0.3 to Vcc -0.3 to 3.3 -0.3 to 3.3 Unit V V mA V V V Table 4. Symbol RthJA Tjop TSTG Thermal data Parameter Thermal resistance, junction-to-ambient Junction temperature operating range Storage temperature Value 250 -40 to 150 C -55 to 150 Unit C/W 3 Typical application schematic Figure 3. Typical application schematic 0.1F Vcc 2.5 V 1.23 V 6 R1 5 Out 3 Vctrl Vo + + 1 0V 2 Gnd R2 4 -50 mV Ictrl Vcsth Rsense Io Isense VO = R1 + R2 * 2.5 V R2 IO max = 0 .05 V R sense Doc ID 17014 Rev 1 3/10 www..com Electrical characteristics SEA05 4 Electrical characteristics -25 C Electrical characteristics Parameter Test condition Min. Typ. Max. Unit Voltage control loop op-amp Gmv Vctrl Ibias Transconductance (sink current only) (1) Voltage reference default value (2) Inverting input bias current TJ = 25 C 1 2.488 2.48 25 3.5 2.5 2.512 V 2.52 nA S Current control loop Gmi V Transconductance (sink current only) (3) Current sense threshold Vcsth = V(Isense)-V(Ictrl) (4) @ I(Iout) = 1 mA Non-inverting input source current @ V(Ictrl) = -50 mV 1.5 7 S csth 46 50 54 mV Ibias 6 A Output stage VOUTlow Low output level @ 2 mA sink current 200 400 mV 1. If the voltage on Vctrl (the negative input of the amplifier) is higher than the positive amplifier input, and it is increased by 1 mV, the sinking current at the output OUT is increased by 3.5 mA. 2. The internal voltage reference is set at 2.5 V. The voltage control loop precision takes into account the cumulative effects of the internal voltage reference deviation as well as the input offset voltage of the transconductance operational amplifier. The internal Voltage Reference is fixed by bandgap, and trimmed to 0.48 % accuracy at room temperature. 3. When the positive input at Ictrl is lower than -50 mV, and the voltage is decreased by 1 mV, the sinking current at the output out is increased by 7 mA. 4. Considering Ictrl pin directly connected to the hot (negative) end of the current sense resistor and Isense pin connected to the cold end of the current sense resistor through a decoupling resistor (see fig.3), the internal current sense threshold is triggered when the voltage on pin Ictrl is -50 mV. The current loop reference precision takes into account the cumulative effects of the internal voltage reference deviation as well as the input offset voltage of the transconductance operational amplifier. 4/10 Doc ID 17014 Rev 1 www..com SEA05 Application information 5 Application information Figure 4. Application information Note: A 15 resistor in series to Ictrl pin helps to protect the IC in case of negative voltage that exceed the AMR of Ictrl pin. As example a potential dangerous phenomenon could happen during converter output short-circuit. Consider the steady state operation of the circuit during voltage mode regulation (i.e. the output is at its nominal voltage). The output capacitor is fully charged at Vo. If an abrupt short (i.e. with negligible impedance) is applied at the output, instantly the positive pin of the electrolytic capacitor is connected to the SEA05 ground. Since the capacitor acts like a battery, all its voltage is applied across the Rsense pin and therefore the Ictrl pin is pulled down to -Vo. This could damage the IC in case the Ictrl pin AMR is violated. In reality the short is not so severe because it has a some impedance, the electrolytic capacitor has an ESR and it starts discharging as soon as the short is applied. The Ictrl pin is brought to a negative voltage anyway. The pin internal structure has been design to be robust against negative voltage but, since the severity of this phenomenon is proportional to the output voltage, for some applications an external resistor in series with Ictrl pin helps protect the IC. The resistor added in series with Ictrl pin introduces an error in the current sense threshold voltage. This error can be calculated considering the Ictrl pin current: this current multiplied by the value of the external resistor gives the current sense threshold variation. As example if we add a 15 resistor in series to Ictrl pin, we have Ictrl current = Ibias = 6 A and therefore the error 6 A x 15 = 80 V, the error is 80 V / 50 mV = 0.16% Doc ID 17014 Rev 1 5/10 www..com Voltage and current control SEA05 6 6.1 Voltage and current control Voltage control The voltage loop is controlled via a first transconductance operational amplifier, the voltage divider R1, R2, and the optocoupler which is directly connected to the output. Its possible to choose the values of R1 and R2 resistors using Equation 1-2: Equation 1 Vo = Vctrl (R 1 + R 2 ) R2 Equation 2 R1 = R2 where Vo is the desired output voltage. ( VO - Vctrl ) Vctrl As an example, with R1 = 100 k and R2 = 15 k Vo = 19.17 V 6.2 Current control The current loop is controlled via the second trans-conductance operational amplifier, the sense resistor Rsense, and the optocoupler. The control equation verifies: Equation 3 Rsense Io max = Vcsth Equation 4 Rsense = Vcsth Io max where Iomax is the desired limited current, and Vcsth is the threshold voltage for the current control loop. As an example, with Iomax = 1 A, Vcsth = 50 mV, then Rsense = 50 m . Note that the Rsense resistor should be chosen taking into account the maximum dissipation (Plim) through it during full load operation. Equation 5 P Lim = V csth l omax As an example, with Iomax = 1 A, and Vcsth = 50 mV, Plim = 50 mW. Therefore, for most adaptor and battery charger applications, it is suitable a low power resistor to make the current sensing function. 6/10 Doc ID 17014 Rev 1 www..com SEA05 Compensation Vcsth threshold is achieved internally by a voltage divider tied to an internal voltage reference. Its middle point is tied to the positive input of the current control operational amplifier, and its foot has to be connected to lower potential point of the sense resistor as shown in Figure 4. The resistors of this voltage divider are matched to provide the best possible precision. The current sinking outputs of the two trans-conductance operational amplifiers are common (to the output of the IC). This makes an ORing function which ensures that whenever the current or the voltage reaches too high values, the optocoupler is activated. The relation between the controlled current and the controlled output voltage can be described with a square characteristic as shown in the following V/I output-power graph. (with power supply of the device independent from the output voltage) Figure 5. Output voltage versus output current Vo V Voltage regulation Current regulation (Vcc of the device independent from output voltage) Io 7 Compensation The voltage control trans-conductance operational amplifier can be fully compensated. Both of its output and negative input are directly accessible for external compensation components as shown in Figure 4. Doc ID 17014 Rev 1 7/10 www..com Package mechanical data SEA05 8 Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK(R) packages, depending on their level of environmental compliance. ECOPACK(R) specifications, grade definitions and product status are available at: www.st.com. ECOPACK(R) is an ST trademark. Table 6. Dim. Min. A A1 A2 b c D E e H L (degrees) 0.95 2.6 0.1 0 3 0.6 10 Typ. 0.9 0 0.9 0.35 0.09 2.8 1.5 Max. 1.45 0.1 1.3 0.5 0.2 3.05 1.75 0.037 0.102 0.004 0 0.118 0.024 10 Min. Typ. 0.035 0 0.035 0.014 0.004 0.11 0.059 Max. 0.057 0.0039 0.0512 0.02 0.008 0.120 0.0689 SOT23-6L mechanical data mm. inch Note: Dimensions per JEDEC MO178AB Figure 6. SOT23-6L package dimensions 8/10 Doc ID 17014 Rev 1 www..com SEA05 Revision history 9 Revision history Table 7. Date 26-Apr-2010 Document revision history Revision 1 Initial release. Changes Doc ID 17014 Rev 1 9/10 www..com SEA05 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries ("ST") reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST's terms and conditions of sale. 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Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any liability of ST. ST and the ST logo are trademarks or registered trademarks of ST in various countries. Information in this document supersedes and replaces all information previously supplied. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners. (c) 2010 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Philippines - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com 10/10 Doc ID 17014 Rev 1 |
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