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NCP1217, NCP1217A Enhanced PWM Current-Mode Controller for High-Power Universal Off-Line Supplies
Housed in an SO-8 or PDIP-7 package, the NCP1217 represents the enhanced version of the NCP1203-based controllers. Thanks to its high drive capability, NCP1217 drives large gate-charge MOSFETs, which together with internal ramp compensation and built-in overvoltage protection, ease the design of modern AC/DC adapters. NCP1217 offers a true alternative to UC384X-based designs. With an internal structure operating at different fixed frequencies (65-100-133 kHz), the controller features a high-voltage startup FET, which ensures a clean and loss less startup sequence. Its current-mode control topology provides an excellent input audio-susceptibility and inherent pulse-by-pulse control. Internal ramp compensation easily prevents subharmonic oscillations from taking place in continuous conduction mode designs. When the current setpoint falls below a given value, e.g. the output power demand diminishes, the IC automatically enters the so-called skip cycle mode and provides excellent efficiency at light loads. Because this occurs at a user adjustable low peak current, no acoustic noise takes place. The NCP1217 features two efficient protective circuitries: 1) In presence of an overcurrent condition, the output pulses are disabled and the device enters a safe burst mode, trying to restart. Once the default has gone, the device auto-recovers. 2) If an external signal (e.g. a temperature sensor) pulls Pin 1 above 3.2 V, output pulses are immediately stopped and the NCP1217 stays latched in this position. Reset occurs when the VCC collapses to ground, e.g. the user unplugs the power supply.
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MARKING DIAGRAMS
8 8 1 SOIC-8 D1, D2 SUFFIX CASE 751 1 17xxx ALYW G
PDIP-8 N SUFFIX CASE 626 8 1 1
P1217xxxx AWL YYWWG
* * * * * * * * * * * * * * * * * *
Current-Mode with Adjustable Skip-Cycle Capability Built-in Internal Ramp Compensation Auto-Recovery Internal Output Short-Circuit Protection Internal 1.0 ms Soft-Start (NCP1217A Only) Limited Duty-Cycle to 50% (NCP1217A Only) Full Latchoff if Adjustment Pin is Brought High Extremely Low No-Load Standby Power Internal Temperature Shutdown 500 mA Peak Current Capability Fixed Frequency Versions at 65 kHz, 100 kHz and 133 kHz Direct Optocoupler Connection Internal Leading Edge Blanking SPICE Models Available for TRANsient and AC Analysis Pb-Free Packages are Available High Power AC/DC Converters for TVs, Set-Top Boxes, etc. Offline Adapters for Notebooks Telecom DC-DC Converters All Power Supplies
xxxx A L, WL Y, YY W, WW G or G
= = = = = =
Specific Device Code Assembly Location Wafer Lot Year Work Week Pb-Free Package
PIN CONNECTIONS
Adj 1 FB 2 8 7 6 5 (Top View) HV NC VCC Drv
CS 3 GND 4
DEVICE MARKING INFORMATION
See detailed device marking information in the ordering information section on page 16 of this data sheet.
Typical Applications
ORDERING INFORMATION
See detailed ordering and shipping information in the ordering information section on page 16 of this data sheet.
(c) Semiconductor Components Industries, LLC, 2005
1
September, 2005 - Rev. 4
Publication Order Number: NCP1217/D
NCP1217, NCP1217A
See Application Section + NCP1217 1 2 EMI FILTER UNIVERSAL INPUT 3 4 Adj FB CS VCC Gnd Drv HV 8 7 6 5 Aux.
VOUT +
Ramp Adjustment
+
Figure 1. Typical Application Example
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PIN FUNCTION DESCRIPTION
Pin No. 1 Pin Name Adj Function Description Adjust the skipping peak current This pin lets you adjust the level at which the cycle skipping process takes place. Shorting this pin to ground permanently disables the skip cycle feature. By bringing this pin above 3.1 V, you permanently shut off the device. By connecting an optocoupler to this pin, the peak current setpoint is adjusted accordingly to the output power demand. This pin senses the primary current and routes it to the internal comparator via an L.E.B. By inserting a resistor in series with the pin, you control the amount of ramp compensation you need. - The driver's output to an external MOSFET. This pin is connected to an external bulk capacitor of typically 22 mF. - Ensures a clean and lossless startup sequence This unconnected pin ensures adequate creepage distance. Connected to the high-voltage rail, this pin injects a constant current into the VCC capacitor during the startup sequence. 2 3 FB CS Sets the peak current setpoint Current sense input 4 5 6 7 8 Gnd Drv VCC NC HV The IC ground Driving pulses Supplies the IC
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NCP1217, NCP1217A
Adj 1 + -
+ -
Latchoff Comparator
HV 8 HV Current Source
3.1 V
Set Reset Latch
UVLO
FB 2
80 k
1.1 V
+ -
Skip Cycle Comparator UVLO High and Low Internal VCC
NC 7
24 k Current Sense 3 250 ns L.E.B. 19 k Ramp Compensation 20 k Ground 4 + - VREF 57 k + - Drv 25 k 1V 1ms SS* 500 mA 5 65-100-133 kHz Clock Set Reset Q Flip-Flop DCmax = 74% Reset VCC Q Overload Management 6
* Available for "A" version only
Figure 2. Internal Circuit Architecture
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MAXIMUM RATINGS
Rating Symbol VCC - Value 16 Unit V V V V mA C/W C/W C C C C kV V Power Supply Voltage Power Supply Voltage on All Other Pins Except Pin 8 (HV), Pin 6 (VCC) and Pin 5 (Drv) Maximum Voltage on Pin 8 (HV), Pin 6 (VCC) Decoupled to Ground with 10 mF Maximum Voltage on Pin 8 (HV), Pin 6 (VCC) Grounded Maximum Current into All Pins Except VCC (6) and HV (8) when 10 V ESD Diodes are Activated Thermal Resistance, Junction-to-Case Thermal Resistance, Junction-to-Air, PDIP-7 Version Thermal Resistance, Junction-to-Air, SO-8 Version Maximum Junction Temperature Temperature Shutdown Hysteresis in Shutdown Storage Temperature Range ESD Capability, HBM Model (All Pins Except VCC and HV) ESD Capability, Machine Model -0.3 to 10 500 450 5.0 57 100 178 150 155 30 -60 to +150 2.0 200 VHV VHV - RqJC RqJA RqJA TJMAX - - - - - Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage may occur and reliability may be affected.
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NCP1217, NCP1217A
ELECTRICAL CHARACTERISTICS (For typical values TJ = 25C, for min/max values TJ = 0C to +125C, Max TJ = 150C,
VCC = 11 V unless otherwise noted.) Characteristic SUPPLY SECTION (All frequency versions, unless otherwise noted) Turn-On Threshold Level, VCC Going Up Minimum Operating Voltage After Turn-On VCC Decreasing Level at which the Latchoff Phase Ends Internal IC Consumption, No Output Load on Pin 5, FSW = 65 kHz Internal IC Consumption, No Output Load on Pin 5, FSW = 100 kHz Internal IC Consumption, No Output Load on Pin 5, FSW = 133 kHz Internal IC Consumption, 1.0 nF Output Load on Pin 5, FSW = 65 kHz Internal IC Consumption, 1.0 nF Output Load on Pin 5, FSW = 100 kHz Internal IC Consumption, 1.0 nF Output Load on Pin 5, FSW = 133 kHz Internal IC Consumption, Latchoff Phase, VCC = 6.0 V INTERNAL STARTUP CURRENT SOURCE (TJ u 0C) High-Voltage Current Source, VCC = 10 V High-Voltage Current Source, VCC = 0 DRIVE OUTPUT Output Voltage Rise-Time @ CL = 1.0 nF, 10-90% of a 12 V Output Signal Output Voltage Fall-Time @ CL = 1.0 nF, 10-90% of a 12 V Output Signal Source Resistance Sink Resistance CURRENT COMPARATOR (Pin 5 Unloaded) Input Bias Current @ 1.0 V Input Level on Pin 3 Maximum Internal Current Setpoint Default Internal Current Setpoint for Skip Cycle Operation Propagation Delay from Current Detection to Gate OFF State Leading Edge Blanking Duration INTERNAL OSCILLATOR (VCC = 11 V, Pin 5 Loaded by 1.0 kW) Oscillation Frequency, 65 kHz Version Oscillation Frequency, 100 kHz Version Oscillation Frequency, 133 kHz Version Maximum Duty-Cycle, NCP1217 Maximum Duty-Cycle, NCP1217A 1. Maximum Value @ TJ = 0C. 2. Minimum Value @ TJ = 125C. - - - - - fOSC fOSC fOSC Dmax Dmax 58.5 90 120 69 42 65 100 133 74 46.5 71.5 110 146 80 50 kHz kHz kHz % % 3 3 3 3 3 IIB ILimit ILskip TDEL TLEB - 0.9 - - - 0.02 1.0 330 90 250 - 1.1 - 150 - mA V mV ns ns 5 5 5 5 Tr Tf ROH ROL - - 15 5.0 60 20 20 10 - - 35 18 ns ns W W 8 8 IC1 IC2 3.5 (Note 2) - 6.0 7.0 7.8 - mA mA 6 6 6 6 6 6 6 6 6 6 VCCON VCCmin VCClatch ICC1 ICC1 ICC1 ICC2 ICC2 ICC2 ICC3 11.8 6.9 - - - - - - - - 12.8 7.6 5.6 960 1020 1060 1.7 2.1 2.4 230 13.8 8.3 - 1110 (Note 1) 1180 (Note 1) 1200 (Note 1) 2.0 (Note 1) 2.4 (Note 1) 2.9 (Note 1) - V V V mA mA mA mA mA mA mA Pin Symbol Min Typ Max Unit
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NCP1217, NCP1217A
ELECTRICAL CHARACTERISTICS (continued) (For typical values TJ = 25C, for min/max values TJ = 0C to +125C,
Max TJ = 150C, VCC = 11 V unless otherwise noted.) Characteristic FEEDBACK SECTION (VCC = 11 V, Pin 5 Loaded by 1.0 kW) Internal Pull-Up Resistor Pin 2 (FB) to Internal Current Setpoint Division Ratio SKIP CYCLE GENERATION Default Skip Mode Level Pin 1 Internal Output Impedance INTERNAL RAMP COMPENSATION Internal Ramp Level @ 25C (Note 3) Internal Ramp Resistance to CS Pin ADJUSTMENT LATCHOFF LEVEL Latching Level 3. A 1.0 MW resistor is connected to the ground for the measurement. 1 Vlatch 2.69 3.10 3.42 V 3 3 Vramp Rramp 2.6 - 2.9 19 3.2 - V kW 1 1 Vskip Zout 0.93 - 1.1 27 1.26 - V kW 2 - Rup Iratio - - 19 3.3 - - kW - Pin Symbol Min Typ Max Unit
TYPICAL CHARACTERISTICS
HV PIN LEAKAGE CURRENT @ 500V (mA) 80 70 60 50 40 30 20 10 0 -50 0 50 TEMPERATURE (C) 100 150 11.5 11.0 -50 VCCOFF, (V) 13.0 12.5 12.0 14.0 13.5
0
50 TEMPERATURE (C)
100
150
Figure 3. High Voltage Pin Leakage Current vs. Temperature
9.0 3.0 2.8 8.5 VCCMIN, (V) ICC 1.0 nF LOAD, (mA) 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 7.0 -50 0 50 TEMPERATURE (C) 100 150 1.0 -50
Figure 4. VCCOFF vs. Temperature
133 kHz 100 kHz
8.0
7.5
65 kHz
0
50 TEMPERATURE (C)
100
150
Figure 5. VCCMIN vs. Temperature
Figure 6. ICC 1.0 nF Load vs. Temperature
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NCP1217, NCP1217A
TYPICAL CHARACTERISTICS (continued)
150 133 kHz 130 VCClatch, (V) 100 150 FOSC, (kHz) 5.90 5.80 5.70 5.60 5.50 5.40 5.30 -50
110
100 kHz
90 65 kHz
70
50 -50
0
50 TEMPERATURE (C)
0
50 TEMPERATURE (C)
100
150
Figure 7. Switching Frequency vs. Temperature
500 450 400 350 300 250 200 -50 DRIVE SOURCE RESISTANCE, (W) 30 25 20 15 10 5 0 -50
Figure 8. VCClatch vs. Temperature
ICC3, (mA)
0
50 TEMPERATURE (C)
100
150
0
50 TEMPERATURE (C)
100
150
Figure 9. ICC3 vs. Temperature
Figure 10. Drive Source Resistance vs. Temperature
1.10 CURRENT SENSE LIMIT, (V)
30 DRIVE SINK RESISTANCE, (W) 25 20 15 10 5 0 -50
1.05
1.00
0.95
0
50 TEMPERATURE (C)
100
150
0.90 -50
0
50 TEMPERATURE (C)
100
150
Figure 11. Drive Sink Resistance vs. Temperature
Figure 12. Current Sense Limit vs. Temperature
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NCP1217, NCP1217A
TYPICAL CHARACTERISTICS (continued)
1.20 INT COMP RAMP LEVEL (V) 150 3.10 3.05 3.00 2.95 2.90 2.85 2.80 2.75 2.70 -50 0 50 TEMPERATURE (C) 100 150
DSKIP MODE LEVEL (V)
1.15
1.10
1.05
1.00 -50
0
50 TEMPERATURE (C)
100
Figure 13. Skip Mode Level vs. Temperature
Figure 14. Int Comp Ramp Max Level vs. Temperature
8.0 HV SOURCE CURRENT (mA)
7.0
6.0
5.0
4.0
3.0 -50
0
50 TEMPERATURE (C)
100
150
Figure 15. High Voltage Current Source (@ VCC = 10V) vs. Temperature
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NCP1217, NCP1217A
APPLICATION INFORMATION
Introduction
The NCP1217 implements a standard current mode architecture where the switch-off event is dictated by the peak current setpoint. This component represents the ideal candidate where low part-count is the key parameter, particularly in low-cost AC/DC adapters, TV power supplies, etc. Due to its high-performance High-Voltage technology, the NCP1217 incorporates all the necessary components normally needed in UC384X based supplies: timing components, feedback devices, low-pass filter and startup device but also enhances the original component by offering: 1) an externally triggerable latchoff 2) ramp compensation and finally, 3) short-circuit protection. Due to its high-voltage current source, ON Semiconductor's NCP1217 does not need an external startup resistance but supplies the startup current directly from the high-voltage rail. On the other hand, more and more applications are requiring low no-load standby power, e.g. for AC/DC adapters, VCRs, etc. UC384X series have a lot of difficulty to reduce the switching losses at low power levels. NCP1217 elegantly solves this problem by skipping unwanted switching cycles at a user-adjustable power level. By ensuring that skip cycles take place at low peak current, the device ensures quiet, noise-free operation: Current-Mode Operation: As the UC384X series, the NCP1217 features a well-known current mode control architecture which provides superior input audio- susceptibility compared to traditional voltage-mode controllers. Primary current pulse-by-pulse checking together with a fast over current comparator offers greater security in the event of a difficult fault condition, e.g. a saturating transformer. Ramp Compensation: By inserting a resistor between the current-sense (CS) pin and the actual sense resistor, it becomes possible to inject a given amount of ramp compensation since the internal saw tooth clock is routed to the CS pin. Subharmonic oscillations in Continuous Conduction Mode (CCM) can thus be compensated via a single resistor. Adjustable Skip Cycle Level: By offering the ability to tailor the level at which the skip cycle takes place, the designer can make sure that the skip operation only occurs at low peak current. This point guarantees a noise-free operation with cheap transformers. Skip cycle offers a proven mean to reduce the standby power in no or light loads situations. Wide Switching-Frequency Offer: Three different options are available: 65 kHz - 100 kHz-133 kHz. Depending on the application, the designer can pick up the right device to
help reducing magnetics or improve the EMI signature before reaching the 150 kHz starting point. Overcurrent Protection (OCP): By continuously monitoring the VCC auxiliary winding voltage, NCP1217 enters burst mode as soon as the power supply undergoes an overload: when the VCC voltage goes down until it crosses the undervoltage lockout level (VCCmin). When the NCP1217 reaches this level (typically 7.6 V), it stops the switching pulses until the VCC pin voltage reaches VCClatch (5.6 V). At VCClatch, the NCP1217 attempts to restart. As soon as the default disappears, the power supply resumes operation. Overvoltage Protection (OVP): If pin1 is brought to a level higher than the internal 3.2 V reference voltage, the controller is permanently shut down until the user cycles the VCC OFF and ON again. This allows the building of efficient and low-cost over voltage protection circuits. Wide Duty-Cycle Operation: Wide mains operation requires a large duty-cycle excursion. The NCP1217 can go up to 74% typically. Low Standby-Power: If SMPS naturally exhibit a good efficiency at nominal load, they begin to be less efficient when the output power demand diminishes. By skipping unneeded switching cycles, the NCP1217 drastically reduces the power wasted during light load conditions. In no-load conditions, the NPC1217 allows the total standby power to easily reach next International Energy Agency (IEA) recommendations. No Acoustic Noise While Operating: Instead of skipping cycles at high peak currents, the NCP1217 waits until the peak current demand falls below a user-adjustable 1/3 of the maximum limit. As a result, cycle skipping can take place without having a singing transformer ... You can thus select cheap magnetic components free of noise problems. External MOSFET Connection: By leaving the external MOSFET external to the IC, you can select avalanche proof devices, which in certain cases (e.g. low output powers), let you work without an active clamping network. Also, by controlling the MOSFET gate signal flow, you have an option to slow down the device commutation, therefore reducing the amount of ElectroMagnetic Interference (EMI). SPICE Model: A dedicated model to run transient cycle-by-cycle simulations is available but also an averaged version to help you closing the loop. Ready-to-use templates can be downloaded in OrCAD's Pspice and INTUSOFT's IsSpice from ON Semiconductor web site, NCP1217 related section.
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NCP1217, NCP1217A
Startup Sequence
When the power supply is first powered from the mains outlet, the internal current source (typically 7.0 mA) is biased and charges up the VCC capacitor. When the voltage on this VCC capacitor reaches the VCCON level (typically
12.8 V), the current source turns off and no longer wastes any power. At this time, the VCC capacitor only supplies the controller and the auxiliary supply is supposed to take over before VCC collapses below VCCmin. Figure 16 shows the internal arrangement of this structure.
8 12.8 V/5.6 V + - 6 mA or 0 6 CVCC 4
HV
Aux
Figure 16. The Current Source Brings VCC Above 12.8 V and then Turns Off
Once the power supply has started, the VCC shall be constrained below 16 V, which is the maximum rating on Pin 6. Figure 17 portrays a typical startup sequence with a VCC regulated at 12.5 V.
13.5 12.8 V REGULATION
12.5
11.5
10.5
9.5 3.00 M 8.00 M 13.0 M t, TIME (sec) 18.0 M 23.0 M
Figure 17. A Typical Startup Sequence for the NCP1217 Overload Operation
In applications where the output current is purposely not controlled (e.g. wall adapters delivering raw DC level), it is interesting to implement a true short-circuit protection. A short-circuit actually forces the output voltage to be at a low
level, preventing a bias current to circulate in the optocoupler LED. As a result, the auxiliary voltage also decreases because it also operates in Flyback and thus duplicates the output voltage, providing the leakage inductance between windings is kept low. To account for this situation and properly protect the power supply, NCP1217 hosts a dedicated overload detection circuitry. Once activated, this circuitry imposes to deliver pulses in a burst manner with a low duty-cycle. The system auto-recovers when the fault condition disappears. During the startup phase, the peak current is pushed to the maximum until the output voltage reaches its target and the feedback loop takes over. The auxiliary voltage takes place after a few switching cycles and self-supplies the IC. In presence of a short circuit on the output, the auxiliary voltage will go down until it crosses the undervoltage lockout level of typically 7.6 V. When this happens, NCP1217 immediately stops the switching pulses and unbiases all unnecessary logical blocks. The overall consumption drops, while keeping the gate grounded, and the VCC slowly falls down. As soon as VCC reaches typically 5.6 V, the startup source turns-on again and a new startup sequence occurs, bringing VCC toward 12.8 V as an attempt to restart. If the default has gone, then the power supply normally restarts. If not, a new protective burst is initiated, shielding the SMPS from any runaway. Figure 18 portrays the typical operating signals in short circuit.
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NCP1217, NCP1217A
VCCON = 12.8 V
VCCmin = 7.6 V VCC
VCClatch = 5.6 V
DRIVING PULSES
Figure 18. Typical Waveforms in Short Circuit Conditions
Calculating the VCC Capacitor
The
theoretical
power
transfer
is
therefore:
The VCC capacitor can be calculated knowing the IC consumption as soon as VCC reaches 12.8 V. Suppose that a NCP1217P065 is used and drives a MOSFET with a 30 nC total gate charge (Qg). The total average current is thus made of ICC1 (750 mA) plus the driver current, Fsw * Qg + 1.95 mA. The total current is therefore 2.7 mA. The DV available to fully startup the circuit (e.g. never reach the 8.2 V VCCmin during power on) is 13.7-8.2 + 5.5 V best case or 4.9 V worse case (11.9-7.0). We have a capacitor that then needs to supply the NCP1217 with 2.7 mA during a given time until the auxiliary supply takes over. Suppose that this time was measured at around 15 ms. CVCC is calculated using the equation C + Dt * i or DV C w 8.3 mF. Select a 22 mF/25 V and this will fit.
Skipping Cycle Mode
1 * Lp * Ip2 * Fsw + 4.1 W. If this IC enters skip cycle 2
mode with a bunch length of 10 ms over a recurrent period of 100 ms, then the total power transfer is:
4.1 * 0.1 + 410 mW.
To better understand how this skip cycle mode takes place, a look at the operation mode versus the FB level immediately gives the necessary insight.
FB 4.2 V, FB Pin Open NORMAL CURRENT MODE OPERATION 3.2 V, Upper Dynamic Range
The NCP1217 automatically skips switching cycles when the output power demand drops below a given level. This is accomplished by monitoring the FB pin. In normal operation, pin 2 imposes a peak current accordingly to the load value. If the load demand decreases, the internal loop asks for less peak current. When this setpoint reaches a determined level (Vpin 1), the IC prevents the current from decreasing further down and starts to blank the output pulses: the IC enters the so-called skip cycle mode, also named controlled burst operation. The power transfer now depends upon the width of the pulse bunches (Figure 20). Suppose we have the following component values: Lp, primary inductance = 350 mH Fsw, switching frequency = 65 kHz Ip skip = 600 mA (or 333 mV/Rsense)
SKIP CYCLE OPERATION IP(min) = 333 mV/RSENSE
1V Time
Figure 19.
When FB is above the skip cycle threshold (1.0 V by default), the peak current cannot exceed 1.0 V/Rsense. When the IC enters the skip cycle mode, the peak current cannot go below Vpin1/3.3. The user still has the flexibility to alter this 1.0 V by either shunting pin 1 to ground through a resistor or raising it through a resistor up to the desired level. In this later case, care must be taken to keep sufficient margin between this pin 1 adjustment level and the latchoff level. Grounding pin 1 permanently invalidates the skip cycle operation.
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NCP1217, NCP1217A
Power P1
Power P2
Power P3
Figure 20. Output Pulses at Various Power Levels (X = 5.0 ms/div) P1 t P2 t P3
300 M
MAX PEAK CURRENT
200 M
SKIP CYCLE CURRENT LIMIT
100 M
0
315.40 U
882.70 U
1.450 M
2.017 M
2.585 M
Figure 21. The Skip Cycle Takes Place at Low Peak Currents which Guarantees Noise-Free Operation
Sufficient margin shall be kept between normal Pin1 level and the latchoff point in order to avoid false triggering.
Ramp Compensation
Ramp compensation is a known mean to cure subharmonic oscillations. These oscillations take place at half the switching frequency and occur only during
Continuous Conduction Mode (CCM) with a duty-cycle greater than 50%. To lower the current loop gain, one usually injects between 50 and 100% of the inductor down-slope. Figure 22 depicts how internally the ramp is generated.
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NCP1217, NCP1217A
Duty Cycle Typ = 74% 2.9 V 0V
Latching Off the NCP1217
19 k Rcomp + - L.E.B. CS Rsense From Setpoint
Total latched shutdown can easily be implemented through a simple PNP bipolar transistor as depicted by Figure 23. When OFF, Q1 is transparent to the operation. When forward biased, the transistor pulls the Adj pin toward VCC and permanently latches-off the IC as soon Vadj goes above the latching level (typical 3.1 V). Figure 23 shows how to wire the bipolar transistor to activate the latchoff. A typical candidate for Q1 could be an MMBT3906 from ON Semiconductor.
VCC
Figure 22. Inserting a Resistor in Series with the Current Sense Information Brings Ramp Compensation
Off Q1
In the NCP1217, the ramp features a swing of 2.9 V with a duty cycle max at 74%. Over a 65 kHz frequency, for instance, it corresponds to a 254 mV/ms ramp. In our FLYBACK design, let's suppose that our primary inductance Lp is 350 mH, delivering 12 V with a Np:Ns ratio of 1:0.1. The OFF time primary current slope is thus given by:
(Vout ) Vf) * Lp
Np Ns
Rlimit
1 2 3 4
8 7 6 5 CVCC
+ 371 mA ms or 37 mV ms when
projected over an Rsense of 0.1 W, for instance. If we select 75% of the downslope as the required amount of ramp compensation, then we shall inject 27 mV/ms. Our internal compensation being of 254 mV/ms, the divider ratio (divratio) between Rcomp and the 19 kW is 0.106. A few lines of algebra to determine Rcomp:
19 k * divratio + 2.26 kW. (1-divratio)
Figure 23. A Simple Bipolar Transistor Totally Disables the IC
VCC
The startup current source keeps the device latched until reset occurs. VCCON = 12.8 V
VCCmin = 7.6 V VCClatch = 5.6 V Reset level
Time Drv
Driver Pulses Adj
Latched-off
Time
Default adj level Fault brings adj above latching level
Time
Figure 24. When Vadj is Pulled Above 3.1 V, NCP1217 Permanently Latches-Off the Output Pulses http://onsemi.com
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NCP1217, NCP1217A
In normal operation, the Adj pin level is kept at a fixed level, the default one or lower. As soon as some external signal pulls this Adj pin level above 3.1 V typical, the output pulses are permanently disabled. Care must be taken to limit the injected current into pin 1 to less than 2.0 mA, e.g. through a series resistor of 5.6 k with a 10 V VCC. The startup switch is activated every time VCC reaches 5.6 V and maintains a VCC voltage ramping up and down between 5.6 V and 12.8 V. Reset occurs when VCC falls below 5.6 V, e.g. when the user cycle the SMPS down. Figure 25 illustrates the operation. Adding a zener diode from Q1 base to ground makes a cheap OVP, protecting the supply from any lethal open-loop operation. If a thermistor (NTC) is added in parallel with the Zener-diode, overtemperature protection is also ensured.
Vaux
output pulses are disabled as long as FB is pulled below Pin 1. As soon as FB is relaxed, the IC resumes its operation. Figure 26 depicts the application example.
1 2 3 ON/OFF Q1 4 8 7 6 5
Figure 26. Another Way of Shutting Down the IC Without a Definitive Latchoff State
Protecting the Controller Against Negative Spikes
1 T OVP 2 3 4
8 7 6 5 CVCC Laux t16 V
Figure 25. A Thermistor and a Zener Diode Offer Both OVP and Overtemperature Latched-Off Protection
Nonlatching Shutdown
In some cases, it might be desirable to shut off the part temporarily and authorize its restart once the default has disappeared. This option can easily be accomplished through a single NPN bipolar transistor wired between FB and ground. By pulling FB below the Adj Pin 1 level, the
As with any controller built upon a CMOS technology, it is the designer's duty to avoid the presence of negative spikes on sensitive pins. Negative signals have the bad habit to forward bias the controller substrate and induce erratic behaviors. Sometimes, the injection can be so strong that internal parasitic SCRs are triggered, engendering irremediable damages to the IC if a low impedance path is offered between VCC and GND. If the current sense pin is often the seat of such spurious signals, the high-voltage pin can also be the source of problems in certain circumstances. During the turn-off sequence, e.g. when the user unplugs the power supply, the controller is still fed by its VCC capacitor and keeps activating the MOSFET ON and OFF with a peak current limited by Rsense. Unfortunately, if the quality coefficient Q of the resonating network formed by Lp and Cbulk is low (e.g. the MOSFET Rdson + Rsense are small), conditions are met to make the circuit resonate and thus negatively bias the controller. Since we are talking about ms pulses, the amount of injected charge (Q = I * t) immediately latches the controller that brutally discharges its VCC capacitor. If this VCC capacitor is of sufficient value, its stored energy damages the controller. Figure 27 depicts a typical negative shot occurring on the HV pin where the brutal VCC discharge testifies for latchup.
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NCP1217, NCP1217A
Vcc 5 V/DIV Vlatch 1 V/DIV Time 10 ms/DIV
Figure 27. A Negative Spike Takes Place on the Bulk Capacitor at the Switch-Off Sequence
Simple and inexpensive cures exist to prevent from internal parasitic SCR activation. One of them consists in inserting a resistor in series with the high-voltage pin to keep the negative current to the lowest when the bulk becomes negative (Figure 28). Please note that the negative spike is clamped to (-2*Vf) thanks to the diode bridge. Also, the power dissipation of this resistor is extremely small since it only heats up during the startup sequence.
Another option (Figure 29) consists in wiring a diode from VCC to the bulk capacitor to force VCC to reach VCCON sooner and thus stops the switching activity before the bulk capacitor gets deeply discharged. For security reasons, two diodes can be connected in series.
3 Rbulk u4.7 k + Cbulk + Cbulk 1 + CVCC
1 2 3 4
8 7 6 5
2
1 2 3 4
8 7 6 5
3
D3 1N4007 1 + CVCC
Figure 28. A simple resistor in series avoids any latch-up in the controller . . .
Figure 29. . . . or one diode forces VCC to reach VCCON sooner.
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NCP1217, NCP1217A
Soft-Start (NCP1217A only)
The NCP1217A features an internal 1.0 ms soft-start activated during the power on sequence (PON). As soon as VCC reaches VCCOFF, the peak current is gradually increased from nearly zero up to the maximum clamping level (e.g. 1.0 V). This situation lasts during 1.0 ms and further to that time period, the peak current limit is blocked to 1.0 V until the supply enters regulation. The soft-start is
also activated during the Over Current Burst (OCP) sequence. Every restart attempt is followed by a soft-start activation. Generally speaking, the soft-start will be activated when VCC ramps up either from zero (fresh power-on sequence) or 5.6 V, the latchoff voltage occurring during OCP. Figure 30 portrays the soft-start behavior. The time scales are purposely shifted to offer a better zoom portion.
Figure 30. Soft-start is activated during a startup sequence or an OCP condition
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NCP1217, NCP1217A
ORDERING INFORMATION
Device NCP1217D65R2 NCP1217D65R2G NCP1217D100R2 NCP1217D100R2G NCP1217D133R2 NCP1217D133R2G NCP1217P65 NCP1217P65G NCP1217P100 NCP1217P100G NCP1217P133 NCP1217P133G NCP1217AD65R2 NCP1217AD65R2G NCP1217AD100R2 NCP1217AD100R2G NCP1217AD133R2 NCP1217AD133R2G NCP1217AP65 NCP1217AP65G NCP1217AP100 NCP1217AP100G NCP1217AP133 NCP1217AP133G Version 65 kHz 65 kHz 100 kHz 100 kHz 133 kHz 133 kHz 65 kHz 65 kHz 100 kHz 100 kHz 133 kHz 133 kHz 65 kHz 65 kHz 100 kHz 100 kHz 133 kHz 133 kHz 65 kHz 65 kHz 100 kHz 100 kHz 133 kHz 133 kHz Marking 17D06 17D06 17D10 17D10 17D13 17D13 P1217P065 P1217P065 P1217P100 P1217P100 P1217P133 P1217P133 17A06 17A06 17A10 17A10 17A13 17A13 P1217AP06 P1217AP06 P1217AP10 P1217AP10 P1217AP13 P1217AP13 Package SO-8 SO-8 (Pb-Free) SO-8 SO-8 (Pb-Free) SO-8 SO-8 (Pb-Free) PDIP-7 PDIP-7 (Pb-Free) PDIP-7 PDIP-7 (Pb-Free) PDIP-7 PDIP-7 (Pb-Free) SO-8 SO-8 (Pb-Free) SO-8 SO-8 (Pb-Free) SO-8 SO-8 (Pb-Free) PDIP-7 PDIP-7 (Pb-Free) PDIP-7 PDIP-7 (Pb-Free) PDIP-7 PDIP-7 (Pb-Free) Shipping 2500 / Tape & Reel 2500 / Tape & Reel 2500 / Tape & Reel 2500 / Tape & Reel 2500 / Tape & Reel 2500 / Tape & Reel 50 Units / Rail 50 Units / Rail 50 Units / Rail 50 Units / Rail 50 Units / Rail 50 Units / Rail 2500 / Tape & Reel 2500 / Tape & Reel 2500 / Tape & Reel 2500 / Tape & Reel 2500 / Tape & Reel 2500 / Tape & Reel 50 Units / Rail 50 Units / Rail 50 Units / Rail 50 Units / Rail 50 Units / Rail 50 Units / Rail
For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specification Brochure, BRD8011/D.
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16
NCP1217, NCP1217A
PACKAGE DIMENSIONS
SOIC-8 NB CASE 751-07 ISSUE AG
-X- A
8 5
B
1 4
S
0.25 (0.010)
M
Y
M
-Y- G C -Z- H D 0.25 (0.010)
M SEATING PLANE
K
NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DIMENSION A AND B DO NOT INCLUDE MOLD PROTRUSION. 4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER SIDE. 5. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE DAMBAR PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN EXCESS OF THE D DIMENSION AT MAXIMUM MATERIAL CONDITION. 6. 751-01 THRU 751-06 ARE OBSOLETE. NEW STANDARD IS 751-07. MILLIMETERS MIN MAX 4.80 5.00 3.80 4.00 1.35 1.75 0.33 0.51 1.27 BSC 0.10 0.25 0.19 0.25 0.40 1.27 0_ 8_ 0.25 0.50 5.80 6.20 INCHES MIN MAX 0.189 0.197 0.150 0.157 0.053 0.069 0.013 0.020 0.050 BSC 0.004 0.010 0.007 0.010 0.016 0.050 0_ 8_ 0.010 0.020 0.228 0.244
N
X 45 _
0.10 (0.004)
M
J
ZY
S
X
S
DIM A B C D G H J K M N S
SOLDERING FOOTPRINT*
1.52 0.060
7.0 0.275
4.0 0.155
0.6 0.024
1.270 0.050
SCALE 6:1 mm inches
*For additional information on our Pb-Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D.
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17
NCP1217, NCP1217A
PACKAGE DIMENSIONS
PDIP-7 P SUFFIX CASE 626B-01 ISSUE A
J
8 5
M B L
1
4
NOTES: 1. DIMENSIONS AND TOLERANCING PER ASME Y14.5M, 1994. 2. DIMENSIONS IN MILLIMETERS. 3. DIMENSION L TO CENTER OF LEAD WHEN FORMED PARALLEL. 4. PACKAGE CONTOUR OPTIONAL (ROUND OR SQUARE CORNERS). 5. DIMENSIONS A AND B ARE DATUMS. DIM A B C D F G H J K L M N MILLIMETERS MIN MAX 9.40 10.16 6.10 6.60 3.94 4.45 0.38 0.51 1.02 1.78 2.54 BSC 0.76 1.27 0.20 0.30 2.92 3.43 7.62 BSC --- 10 0.76 1.01
F
NOTE 2
A
C -T-
SEATING PLANE
N D G K B
M
H 0.13 (0.005)
M
TA
M
The product described herein (NCP1217), may be covered by the following U.S. patents: 6,271,735, 6,362,067, 6,385,060, 6,429,709, 6,587,357. There may be other patents pending.
ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. "Typical" parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT: N. American Technical Support: 800-282-9855 Toll Free Literature Distribution Center for ON Semiconductor USA/Canada P.O. Box 61312, Phoenix, Arizona 85082-1312 USA Phone: 480-829-7710 or 800-344-3860 Toll Free USA/Canada Japan: ON Semiconductor, Japan Customer Focus Center 2-9-1 Kamimeguro, Meguro-ku, Tokyo, Japan 153-0051 Fax: 480-829-7709 or 800-344-3867 Toll Free USA/Canada Phone: 81-3-5773-3850 Email: orderlit@onsemi.com ON Semiconductor Website: http://onsemi.com Order Literature: http://www.onsemi.com/litorder For additional information, please contact your local Sales Representative.
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18
NCP1217/D

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