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preliminary data this is preliminary information on a new product now in deve lopment or undergoing evaluation. details are subject to change without notice. february 2011 doc id 18462 rev 1 1/12 1 sea05l advanced constant voltage and constant current controller with very efficient led pilot-lamp driver features constant voltage and constant current control very efficient led pilot-lamp driver wide operating v cc range (3.5 v - 36 v) low quiescent consumption: 250 a voltage reference: 2.5 v voltage control loop accuracy 0.5% current sense threshold: 50 mv current control lo op accuracy 4% low external component count open-drain output stage sot23-6l package applications ac-dc adapter with led pilot-lamp battery chargers with led pilot-lamp smps with led pilot-lamp description the device is a highly integrated solution for smps applications, with an led pilot-lamp requiring a dual control loop to perform cv (constant voltage) and cc (constant current) regulation. the ic allows very effici ent led pilot-lamp driving which helps to reduce the standby consumption of the smps. it integrates a voltage reference, two op-amps (with or-ed open-drain outputs), a low- side current sensing circuit and an led pilot-lamp driver pin implemented with an open-drain mosfet driven by square waveform with 12.5% duty cycle at 1 khz that allows reducing led consumption. figure 1. block diagram 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 is ideal for space-critical applications. table 1. device summary order code package packing SEA05LTR sot23-6l tape & reel sot23-6l (plastic package) out ld v ctrl isense + - + - 1.23 v 2.5 v 1 2 5 3 4 6 v cc 50mv osc gnd www.st.com
contents sea05l 2/12 doc id 18462 rev 1 contents 1 operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1 voltage and current control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3 ld pin function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
sea05l operation doc id 18462 rev 1 3/12 1 operation figure 2. pin configuration table 2. absolute maximum ratings symbol pin parameter value unit v cc 6 dc supply voltage ?0.3 to 38 v vout 5 open-drain voltage ?0.3 to v cc v iout 5 max. sink current 20 ma v ld 4 open-drain voltage ?0.3 to v cc v i ld 4 max. sink current 15 ma isense 1 analog input ?0.3 to v cc v vctrl 3 analog input ?0.3 to v cc < 12 (1) 1. vctrl cannot exceed v cc and cannot exceed 12 v. v table 3. thermal data symbol parameter value unit r th j-amb thermal resistance, junction-to-ambient 250 c/w tj op junction temperature operating range ?40 to 150 c tstg storage temperature ?55 to 150 table 4. pin functions pin number name function 1 isense inverting input of the current loop op-amp. the pin is typically used for the current control loop, connecting it to the positive 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 has to be tied as close as possible to the ground output terminal of the converter to minimize load current effect on the voltage regulation setpoint. vcc out ld 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 am049 8 5v1
operation sea05l 4/12 doc id 18462 rev 1 3vctrl inverting input of the voltage loop op-amp. the pin is typically used for the voltage control loop and is connected to the midpoint of a resistor divider that senses the output voltage. 4ld open-drain output able to sink 5 ma (pea k), driven by the internal oscillator at 1 khz square waveform wi th 12.5% duty cycle. the internal mosfet starts to switch when v cc is above the turn-on threshold (typ. 3 v) and it is off (ld high impedance) when v cc is below the uvlo of the ic. the pin can be connected to an external led pilot-lamp with a resistor in series in order to limit the led current 5out common open-drain output of the two internal op-amps. the pin, only able to sink current, is typically connected to the branch of the optocoupler's photodiode to transmit the error signal to the primary side. 6v cc supply voltage of the device. a small bypass capacitor (0.1 f typ.) to gnd, located as close to the ic pins as possible, might be useful to get a clean supply voltage. table 4. pin functions (continued) pin number name function
sea05l operation doc id 18462 rev 1 5/12 table 5. electrical characteristics (?25 c < t j < 125 c, v cc = 20 v; unless otherwise specified) symbol parameter test co ndition min. typ. max. unit device supply v cc voltage operating range 3.5 36 v i cc quiescent current (ictrl = vsense = 0, out = open) 250 500 a voltage control loop op-amp gm v transconductance (sink current only) (1) 13.5 s vctrl voltage reference default value (2) t j = 25 c 2.488 2.5 2.512 v ibias inverting input bias current 25 na current control loop gm i transconductance (sink current only) (3) 1.5 7 s v csth current sense threshold at i(iout) = 1 ma (4) 48 50 52 mv ibias non-inverting input source current 6 a output stage v outlow low output level at 2 ma sink current 200 400 mv led driver i ld led driver sink current capability (peak) 10 ma f ld led driver current modulation frequency 0.6 1 1.4 khz v ldlow low output level at 5 ma sink current (internal mosfet on) 450 900 mv i ld_lkg led driver leakage current (internal mosfet off) 0.5 a 1. if the voltage on vctrl (the negative input of the amplifier) is higher than the positive ampl ifier input, and it is increase d by 1mv, the sinking current at the output out will be increased by 3.5 ma. 2. the internal voltage reference is set at 2.5 v. the voltage co ntrol loop precision takes into account the cumulative effects of the internal voltage reference deviation as well as the inpu t 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 inverting input at isense is gr eater than 50 mv, and the voltage is increased by 1 mv, the sinking current at the output out will be increased by 7 ma. 4. the internal current sense threshold is triggered when t he voltage on pin isense is 50 mv. the current control loop precision takes into account the cumulative effects of the in ternal voltage reference deviation as well as the input offset voltage of the transconduct ance operational amplifier.
application information sea05l 6/12 doc id 18462 rev 1 2 application information figure 3. typical application schematic 2.1 voltage and current control voltage control the voltage loop is controlled via a transconductance operational amplifier, the voltage divider r 1 , r 2 , and the optocoupler which is directly co nnected to the output. it is possible to choose the values of r 1 and r 2 resistors using equation 1 and equation 2 : equation 1 equation 2 where v o is the desired output voltage. as an example, with r 1 = 100 k and r 2 = 15 k v o = 19.17 v. vo io r1 r2 0.1f rsense v r r r v o 5 . 2 * 2 2 1 + = sense o r v i 05 . 0 max = out ld v ctrl isense + - + - 1.23 v 2.5 v 1 2 5 3 4 6 v cc 50mv osc gnd led am049 8 6v1 2 2 1 ) ( r r r vctrl v o + ? = vctrl vctrl v r r o ) ( 2 1 + ? =
sea05l application information doc id 18462 rev 1 7/12 current control the current loop is controlled via a transconductance 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 (p lim ) through it during full load operation. equation 5 as an example, with i omax = 1 a and v csth = 50 mv, p lim = 50 mw. therefore, for most adaptor and battery charger applications, a low-power resistor is suitable for the current sensing function. v csth threshold is achieved internally by a voltage divider tied to an internal precise voltage reference. its midpoint is tied to the positive input of the current control operational amplifier, and its endpoint is connected to gnd. the resi stors of this voltage divider are matched to provide the best precision possible. the current sinking outputs of the two transconductance operational amplifiers are common (to the output of the ic). this makes an or function which ensures that whenever the current or the voltage reaches excessively high values, the optocoupler is activated. the relationship 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). csth o sense v i r = ? max max o csth sense i v r = max lim o csth i v p ? =
application information sea05l 8/12 doc id 18462 rev 1 figure 4. output voltage versus output current 2.2 compensation the voltage control transconductance operationa l amplifier can be fully compensated. both its output and negative input are directly accessible for external compensation components. 2.3 ld pin function the device provides a unique feature that allows highly efficient driving of an led pilot-lamp. the main benefit of this new feature is to allow reducing the standby power consumption of the smps with the led pilot-lamp. the ld pin is an open-drain output able to sink 5 ma (peak), driven by the internal oscillator at 1 khz (typ.) square waveform with 12.5% duty cycle (see figure 6 ). the internal mosfet starts to switch when v cc is above the turn-on threshold (typ 3 v) and it is off (ld high impedance) when v cc is below the uvlo of the ic. connecting the led pilot-lamp, with a resistor in series in order to limit the led current, to pin ld (as shown in figure 5 ) reduces the power consumption of the led while keeping the same driving peak current. the led driving current modulation frequency of 1 khz (typ.) eliminates the visual perception of flickering. vout iout voltage regulation current regulation vcc of the device independent from output voltage) ( am049 8 7v1
sea05l application information doc id 18462 rev 1 9/12 figure 5. connection of led to pin ld figure 6. led current waveform with a typical frequency of 1 khz out ld vctrl isense + - + - 1.23 v 2.5 v 1 2 5 3 4 6 v cc 50mv osc gnd led r led v cc i led am049 88 v1 i t t=1ms (f=1khz) t on =125 s (t/8) i led am049 8 9v1
package mechanical data sea05l 10/12 doc id 18462 rev 1 3 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. note: dimensions per jedec mo178ab figure 7. sot23-6l (2.90 mm x 2.80 mm) package mechanical drawing table 6. sot23-6l (2.90 mm x 2.80 mm) package mechanical data sym mm inches min typ max min typ max a 1.45 0.057 a1 0.00 0.15 0.000 0.006 a2 0.90 1.15 1.30 0.035 0.045 0.051 b 0.30 0.50 0.012 0.020 c 0.08 0.22 0.003 0.009 d 2.90 0.114 e 2.80 0.110 e1 1.60 0.063 e 0.95 0.037 e1 1.90 0.075 l 0.30 0.45 0.60 0.012 0.018 0.024 0 4 8 0 4 8 n 6 6 7049717_g
sea05l revision history doc id 18462 rev 1 11/12 4 revision history table 7. document revision history date revision changes 23-feb-2011 1 initial release.
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