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 µA ■ 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. Applications ■ Battery chargers ■ AC-DC adapters ■ LED drivers Figure 1. Internal schematic Description 1.23 V 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 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 + + - The device integrates a voltage reference, two opamps (with OR-ed open-drain outputs), and a lowside current sensing circuit. April 2010 Vcc 6 2.5 V Table 1. 5 Out 3 Vctrl 2 Gnd 4 1 Ictrl Isense Device summary Order code Package Packing SEA05TR SOT23-6L Tape and reel Doc ID 17014 Rev 1 1/10 www.st.com 10 Pin description 1 SEA05 Pin description Figure 2. Pin configuration Note: 1 6 Vcc GND 2 5 Out Vctrl 3 4 Ictrl The adjacent pins have the same AMR to increase the robustness of the IC against accidental short circuit among pins. Table 2. 2/10 Isense Pin description n. Name Function 1 Isense 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. 2 GND 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. 3 Vctrl 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. 4 Ictrl Non-inverting input of the current loop op-amp. It is tied directly to the hot (negative) end of the current sense resistor 5 OUT 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. 6 Vcc Supply Voltage of the device. A small bypass capacitor (0.1 µF typ.) to GND, located as close to IC’s pins as possible, might be useful to get a clean supply voltage. Doc ID 17014 Rev 1 SEA05 2 Maximum ratings Maximum ratings Table 3. Absolute maximum ratings Symbol Pin Vcc 6 Vout Value Unit Dc supply voltage -0.3 to 38 V 5 Open-drain voltage -0.3 to Vcc V Iout 5 Max sink current 20 mA Ictrl 4 Analog input -0.3 to Vcc V Isense 1 Analog input -0.3 to 3.3 V Vctrl 3 Analog input -0.3 to 3.3 V Value Unit 250 °C/W Table 4. Parameter Thermal data Symbol 3 Parameter RthJA Thermal resistance, junction-to-ambient Tjop Junction temperature operating range -40 to 150 TSTG Storage temperature -55 to 150 °C Typical application schematic Figure 3. Typical application schematic 0.1μF Vcc 1.23 V + - 0V 5 Out 3 Vctrl + - 4 -50 mV R1 6 2.5 V 2 Gnd R2 1 Ictrl Vo Isense Vcsth Rsense Io VO = Doc ID 17014 Rev 1 R1 + R2 * 2.5 V R2 IO max = 0 .05 V R sense 3/10 Electrical characteristics 4 SEA05 Electrical characteristics -25 °C <TJ < 125 °C, VCC = 20 V; unless otherwise specified Table 5. Electrical characteristics Symbol Parameter Test condition Min. Typ. Max. Unit 36 V 300 µA Device supply Vcc Voltage operating range Icc Quiescent current (Ictrl =I sense = 0 V, OUT = open) 3.5 200 Voltage control loop op-amp Gmv Transconductance (sink current only) (1) Vctrl Voltage reference default value (2) Ibias Inverting input bias current TJ = 25 °C 1 3.5 2.488 2.5 S 2.512 V 2.48 2.52 25 nA S Current control loop Gmi V csth Ibias Transconductance (sink current only) (3) 1.5 7 Current sense threshold Vcsth = V(Isense)-V(Ictrl) (4) @ I(Iout) = 1 mA 46 50 Non-inverting input source current @ V(Ictrl) = -50 mV 54 6 mV µA 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 SEA05 5 Application information Application information Figure 4. Application information ȝ) 9FF 9 9 2XW 9FWUO P9 5 9 *QG 5 ,FWUO 9R ,VHQVH 9FVWK 5VHQVH , Note: 92 5 5 9 5 ,2 PD[ # 9 5VHQVH A 15 Ω 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 Ω resistor in series to Ictrl pin, we have Ictrl current = Ibias = 6 µA and therefore the error 6 µA x 15 Ω = 80 µV, the error is 80 µV / 50 mV = 0.16% Doc ID 17014 Rev 1 5/10 Voltage and current control SEA05 6 Voltage and current control 6.1 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 ∗ ( VO − Vctrl ) Vctrl where Vo is the desired output voltage. As an example, with R1 = 100 kΩ and R2 = 15 kΩ 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 Ω. 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 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 V Vo Voltage regulation Current regulation (Vcc of the device independent from output voltage) 7 Io 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 Package mechanical data 8 SEA05 Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK® specifications, grade definitions and product status are available at: www.st.com. ECOPACK® is an ST trademark. Table 6. SOT23-6L mechanical data mm. inch Dim. Min. Typ. Max. A 0.9 A1 Typ. Max. 1.45 0.035 0.057 0 0.1 0 0.0039 A2 0.9 1.3 0.035 0.0512 b 0.35 0.5 0.014 0.02 c 0.09 0.2 0.004 0.008 D 2.8 3.05 0.11 0.120 E 1.5 1.75 0.059 0.0689 e Note: 0.037 H 2.6 3 0.102 0.118 L 0.1 0.6 0.004 0.024 θ (degrees) 0° 10° 0° 10° Dimensions per JEDEC MO178AB Figure 6. 8/10 0.95 Min. SOT23-6L package dimensions Doc ID 17014 Rev 1 SEA05 9 Revision history Revision history Table 7. Document revision history Date Revision 26-Apr-2010 1 Changes Initial release. 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