april 2010 doc id 17014 rev 1 1/10 10 sea05 advanced constant voltage and constant current controller features constant voltage and constant current control wide operating v cc 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 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 op- amps (with or-ed open-drain outputs), and a low- side 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 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 table 1. device summary order code package packing SEA05TR sot23-6l tape and reel ? sot23 - 6l + - + - 1.23 v 2.5 v 1 4 5 3 2 6 ictrl isense gnd v ctrl out v cc www.st.com
pin description sea05 2/10 doc id 17014 rev 1 1 pin description figure 2. pin configuration note: the adjacent pins have the same amr to increase the robustness of the ic against accidental short circuit among pins. ? vcc ou t ictrl isense vctrl gnd 1 2 3 6 5 4 1 2 3 6 5 4 1 2 3 6 5 4 1 2 3 6 5 4 table 2. 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. 2gnd 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. 3vctrl 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. 4ictrl non-inverting input of the current loop op-amp. it is tied directly to the hot (negative) end of the current sense resistor 5out common open-drain output of the two inte rnal op-amps. the pin, able to sink current only, is connected to the br anch of the optocoupler?s photodiode to transmit the error signal to the primary side. 6vcc supply voltage of the device. a small by pass 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.
sea05 maximum ratings doc id 17014 rev 1 3/10 2 maximum ratings 3 typical application schematic figure 3. typical application schematic table 3. absolute maximum ratings symbol pin parameter value unit vcc 6 dc supply voltage -0.3 to 38 v vout 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 table 4. thermal data symbol parameter value unit r thja thermal resistance, junction-to-ambient 250 c/w tj op junction temperature operating range -40 to 150 c t stg storage temperature -55 to 150 v csth vo + - + - 1.23 v 2.5 v 0 v 1 4 5 3 2 6 ictrl isense gnd vctrl out v cc -50 mv i o r1 r2 0.1 f rsense v r r r v o 5 . 2 * 2 2 1 + = sense o r v i 05 . 0 max =
electrical characteristics sea05 4/10 doc id 17014 rev 1 4 electrical characteristics -25 c sea05 application information doc id 17014 rev 1 5/10 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 v o . if an abrupt short (i.e. with negligible impedance) is applied at the output, instantly the positive pin of the electrolytic capacitor is co nnected to the sea05 ground. si nce the capacitor acts like a battery, all its voltage is applied across the r sense 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 i ctrl current = ibias = 6 a and therefore the error 6 a x 15 = 80 v, the error is 80 v / 50 mv = 0.16% 9 f v w k 9 r , f w u o , v h q v h 9 9 9 * q g 9 f w u o 2 x w 9 f f p 9 , 5 5 ) 5 v h q v h 9 5 5 5 9 2
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voltage and current control sea05 6/10 doc id 17014 rev 1 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 equation 2 where vo is the desired output voltage. 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 r sense , and the optocoupler. the control equation verifies: equation 3 equation 4 where i omax is the desired limited current, and v csth is the threshold voltage for the current control loop. as an example, with i omax = 1 a, v csth = 50 mv, then r sense = 50 m . note that the r sense resistor should be chosen taking into account the maximum dissipation (plim) through it during full load operation. equation 5 as an example, with i omax = 1 a, and v csth = 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. 2 2 1 o r ) r r ( vctrl v + ? = vctrl ) vctrl v ( r r o 2 1 ? ? = vcst h i r max o sense = ? = p lim v csth l omax ? =
sea05 compensation doc id 17014 rev 1 7/10 v csth 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 curren t and the controlled out put voltage can be described with a square characteristic as sh own 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 7 compensation the voltage control trans-conductance operational amplifier can be fully compensated. both of its output and negative input are direct ly accessible for ex ternal compensation components as shown in figure 4 . v io vo ltag e r eg ulatio n current regulation ( vcc of the device inde p e nde nt fr om out p ut volta g e ) vo io vo ltag e r eg ulatio n current regulation ( vcc of the device inde p e nde nt fr om out p ut volta g e )
package mechanical data sea05 8/10 doc id 17014 rev 1 8 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 an d product status are available at: www.st.com . ecopack ? is an st trademark. note: dimensions per jedec mo178ab figure 6. sot23-6l package dimensions table 6. sot23-6l mechanical data dim. mm. inch min. typ. max. min. typ. max. a 0.9 1.45 0.035 0.057 a1 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 0.95 0.037 h 2.6 3 0.102 0.118 l 0.1 0.6 0.004 0.024 (degrees) 0 10 0 10
sea05 revision history doc id 17014 rev 1 9/10 9 revision history table 7. document revision history date revision changes 26-apr-2010 1 initial release.
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