APPLICATION NOTE Maximum Peak Current: NCP101X series, peak curre

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APPLICATION NOTE Maximum Peak Current: NCP101X series, peak curre

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AND8125/D Evaluating Power Capability NCP101X Members
APPLICATION NOTE Maximum Peak Current: NCP101X series,
peak current internally fixed. This parameter plays obvious role maximum transmitted power since obeys Flyback formula, Pout Fsw. input process selection will thus reference peak current, Once theoretical power capability been evaluated, will finally necessary check power dissipation switcher itself (given conduction losses, switching losses, etc.) what remains available reliable operation.
Operating
NCP101X series available various combinations peak current switching frequencies. help designer quickly picking right part, important present guidelines aimed simplify selection process. This application note details evaluate power handled each device offers overview each part capability. Each reference affected parameter that needs accounted very beginning like switching frequency, maximum peak current Rds(ON). Among these parameters, also find another constraints linked adopted topology, i.e. current mode case: Operation: device operates current-mode, mandatory keep operating discontinuous mode with duty-cycle bounded below avoid sub-harmonic oscillations when accidentally entering Continuous Conduction Mode (CCM). will 0.45 maximum value examples. Nonnegative Reflection: built-in lateral MOSFET does accept body diode forward biased excessive Flyback voltage greater than bulk voltage during time. Hence, universal mains operation, turn ratio Ns:Np will selected keep Vreflect (Ns/Np) (Vout below very minimum operating input voltage your converter (including input 120/100 ripple offline applications). instance, have input, becomes once rectified minus selected ripple. choose "20% ripple, then very minimum voltage 141-20% select maximum reflection voltage (noted safe operation wide mains, whereas this number will grow-up above European mains operation (230 "15%).
When switch closes, applied across primary inductance until current reaches level imposed feedback loop. duration this event called time defined
(eq.
primary inductance, input voltage, operating peak current.
switch opening, primary energy transferred secondary flyback voltage appears across resetting transformer core with slope
(Vout Toff, time thus: Toff (Vout
(eq.
primary inductance, Vout output voltage, operating peak current, secondary rectifier voltage drop, transformer turn ratio, Ns:Np.
Semiconductor Components Industries, LLC, 2003
July, 2003 Rev.
Publication Order Number: AND8125/D
AND8125/D
wants keep only, still need pass maximum power, will allow dead-time after core reset, rather immediately restart (fixed frequency boundary mode operation). switching period expressed
(eq.
Extracting from equation gives:
Lpcritical (Vin Vr)2 [Pout (Vr2 Vin2)]
Toff
(Vout
(eq. with (Vout reflected voltage. Selecting primary inductance value lower than given equation ensures discontinuous operation lowest line given reflected voltage.
Nonnegative Reflection
with input voltage
Flyback transfer formula dictates that:
Pout (eq. which, extracting
(with converter efficiency)
plugging into equation leads
Pout (Vout
(eq.
operate universal mains from VAC, then maximum reflected voltage VinAC 1.414 ripple with selected "20% ripple (eq. take include safety margin. Running part from single Europeans mains offers greater flexibility. voltage "15%, which leads minimum operating voltage 230-15% VAC. maximum reflected voltage thus: VinAC 1.414 ripple with selected "10% ripple (eq. take include safety margin.
Maximum Peak Current
maximum peak current given particular part reference. follow data sheet, these values are:
NCP1010 NCP1011 NCP1012 NCP1013 NCP1014 Rdson Ipeak (mA) Freq (kHz)
Combining these parameters together, finally calculate what theoretical maximum power pass satisfying three bullets expressed beginning this document. From maximum peak current, duty-cycle constraint minimum input voltage (universal narrow mains), deduce maximum inductor Lpmax use:
Lpmax
Vinput (eq.
apply following parameters (45% minimum voltage, switching frequency peak current), gives upper inductance boundary 0.45 15.4 m/0.1
equate equation with equation obtain maximum power constrained duty-cycle, maximum peak current given minimum input voltage:
Pmax Tsw2 Vinmin2 Lpmax Lpmax Vinmin Lpmax Vinmin2)
(eq.
Keep same parameters above, obtain, Pmax Please note that increasing switching frequency will expand power capability given converter will reduce inductance allow smaller magnetic element (the goes down). Running same chart with listed references, gives first following correspondence between given peak current theoretical maximum power obtained from converter operated high line line:
Table Theoretical Transmitted Power Depending Peak Current Only
Peak Current Wide Mains Operation Operation 18.6 14.5 10.3
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AND8125/D
Accounting Part Parameters Power Dissipation PDIP7 Package
need refine these calculations knowing thermal constraints internal power dissipation (conduction switching losses, Dynamic Self-Supply, etc.) order offer final selection table. following chart will used assess possible power combinations given NCP101X family:
Select frequency
Capacitive losses Coss
power dissipated PDIP7 package dependent upon internal consumption total thermal resistance junction-to-ambient RqJA. start from 70°C ambient temperature RqJA 75°C/W (which measured demoboard with added copper please data sheet suggested layout), then maximum dissipation from PDIP7 (Max Tj-Ta)/ RqJA (125-70)/75 which grows lower maximum ambient temperature 50°C. Calculating total power consumption monolithic circuit implies splitting budget with various contributors: Dynamic Self Supply (DSS): average current flowing through directly current needed chip operate (neglecting switching losses itself. Therefore, PDSS ICC1 VHV. Therefore, average, parts exhibit average ICC1 consumption then maximum dissipated power 0.37 (This number drops with auxiliary winding thus offers better margin MOSFET.) Switching Losses: Theoretically, turn-on losses null since turn MOSFET zero current (DCM). However, there still parasitic capacitance MOSFET (Coss Crss) which play role power dissipation budget. assess value this capacitor, measure time taken current come back zero:
used?
Vbulk ICC1 Package dependency Conduction losses
Pdmax Ta)/RqJA Dissipation room MOSFET Pcond Pdmax
IdRMS (Pcond, Rdson) Compute available since
available NCP101Xmin
final available
final NCP101Xmin
Compute Pmax using equations
Figure Power Flowchart Used methodology assessing maximum power capability from particular part number.
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AND8125/D
Current MOSFET
Capacitive Contribution
Figure Typical Turn Behavior NCP101X Series Member
presence "square" corresponds capacitive current flowing inside MOSFET.but also through scope probe. This current does create turn-off losses (except losses ohmic paths) reveals existence capacitor that will create additional losses during turn-on. Based Figure this capacitor roughly equals: ns/300 pF-10 This pretty typical lateral MOSFETs. DCM, this capacitor charged worse case. Therefore, energy stored capacitor 3702 1.03 Depending switching frequency, will have following average losses:
1.03 65000 1.03 100000 1.03 130000 Conduction Losses: These losses dependent device Rds(ON) current flowing into lack internal ramp compensation, converter operate Discontinuous Conduction Mode (DCM) avoid sub-harmonic oscillations. powers described bullets have remaining power MOSFET alone different ambient temperatures (Ploss previous chart):
Table Available Losses Budget Function Switching Frequency Selection
Fswitching 505C 705C A.W. 505C A.W. 705C
from Table applications needing maximum power high ambient temperature will require auxiliary improve room MOSFET power dissipation. definition, know that Pcond Idrms2 Rds(ON), hence maximum allowable current deducted from previous table. instance, Idrms2 Rds(ON) Idrms
Pcond Rds(ON) 0.49 (eq.
definition, value triangular current waveform (SMPS operated DCM) Irms Ipeak sqrt (d/3). Since maximum, then Ipeak Irms computing peak values different versions, obtain following arrays (RMS current/ Peak current):
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Rdson 1255C (NCP1012/13/14) Table Available RMS/Peak Current Version, Respecting Table Figures
Fswitching 505C mA/361 mA/346 mA/335 705C mA/242 mA/225 mA/200 A.W. 505C mA/498 mA/490 mA/479 A.W. 705C mA/423 mA/410 mA/400
Rdson 1255C (NCP1010/11) Table Available RMS/Peak Current Version, Respecting Table Figures
Fswitching 505C mA/250 mA/240 mA/232 705C mA/168 mA/156 mA/139 A.W. 505C mA/345 mA/340 mA/332 A.W. 705C mA/293 mA/284 mA/277
Final Selection Table
From above tables compute maximum power handled component applying equations where duty-cycle constrained 45%, Vreflec universal mains rises single mains, offering more flexibility. device offers peak current capability greater than value recommended table then unfortunately table priority flow chart indicated. opposite, available peak current room exceeds maximum part peak setpoint, then part peak current takes lead. short examples detail this methodology with kHz, device featuring Rds(ON): Table states that maximum peak current 70°C equals when used. peak current
Universal Mains Applications (100 VAC)
value entered equation thus which gives maximum power 3.41 (eq. 10). Here, cannot full dynamic because dissipation constraint imposed table wire auxiliary winding, peak current room given table rises this time, peak limit bounded part setpoint (350 This value will therefore entered into equation gives maximum power These calculations were performed universal mains application (Vreflect also narrow mains input with Vreflect results gathered table offering power handling capability device device.
Table Power Capability Selected Device Universal Mains Applications
Part Reference NCP1012P06 NCP1013P06 NCP1014P06 NCP1012P10 NCP1013P10 NCP1014P10 NCP1012P13 NCP1013P13 NCP1010P06 NCP1011P06 NCP1010P10 NCP1011P10 NCP1010P13 NCP1011P13 Parameters 505C 705C A.W. 505C A.W. 705C
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AND8125/D
Narrow Mains Applications (230 15%) Table Power Capability Selected Device Narrow Mains Applications
Part Reference NCP1012P06 NCP1013P06 NCP1014P06 NCP1012P10 NCP1013P10 NCP1014P10 NCP1012P13 NCP1013P13 NCP1010P06 NCP1011P06 NCP1010P10 NCP1011P10 NCP1010P13 NCP1011P13 Parameters 505C 10.6 14.8 17.3 10.6 14.8 16.6 10.6 14.8 10.6 10.6 10.6 705C 10.6 11.7 11.7 10.6 10.6 10.7 A.W. 505C 10.6 14.8 10.6 14.8 10.6 14.8 10.6 10.6 10.6 A.W. 705C 10.6 14.8 10.6 14.8 10.6 14.8 10.6 10.6 10.6
Taking Right Part
see, there overlap between part themselves. this characteristic fine tune final design reach optimal price/performance ratio. instance, there questions which, once answered, will naturally push toward exact reference. need accurate Over Current Protection point?": answer yes, then option only. answer auxiliary winding will help passing more power with cooler part. filtering constraint design?": means need provide frequency jittering. not, auxiliary winding option point Also, filtering pattern easier than kHz.
need operate converter highest ambient temp!": that case, auxiliary winding. application requires protection against optocoupler failures0": sensing auxiliary current flowing into pin, part selfprotects against open-loop runaways. auxiliary winding option. have converter that already runs with auxiliary winding!": that case, option, provided that power budget compatible. need smallest possible size0": frequency increase does help pass more power, certainly provides size reduction magnetic element. version.
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Notes
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APPLICATION NOTE Maximum Peak Current: NCP101X series, peak curre

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