AN8027

AN8027 PANASONIC

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Technical content

AN8027, AN8037 AC-DC switching power supply control IC with standby mode n Overview The AN8027 and AN8037 are ICs developed for self- excited switching regulator of RCC local resonance con- trol type. These ICs are designed to achieve stability and high efficiency over a wide input voltage range and loads range (light loads to heavy loads), for supporting input levels used worldwide and improved conformance with energy conservation laws. n Features

• Support improved conformance with energy conserva- tion laws by providing two operating modes.
• Standby mode (light loads): Achieves better efficiency due to reduced frequency .
• Normal mode: Achieves high efficiency in RCC local resonance op- eration with zero-cross detection.
• Incorporating an input voltage compensation function available to a wide input range for worldwide use.
• This function compensates the maximum on-period in inverse proportion to the input voltage.
• Incorporating a timer latch function.
• The time period can be adjusted according to the overload in normal mode or standby mode.
• This function makes it possible to protect the IC from damage that may be caused by the short-circuiting of the IC's external capacitor for the timer.
• Incorporating an overvoltage protection function. (detects at V CC pin)
• Incorporating a pulse-by-pulse overcurrent protection function, which makes latch protection possible at the time of the short-circuiting of the transformer's primary winding.
• Adopting a 9-pin single inline package (E-9S: available to manufacturing in overseas).
• AN8027: Transformer resetting is detected from the high- or low-level signal on the TR pin.
• AN8037: Transformer resetting is detected from the falling edge of the high-level signal on the TR pin. Refer to the "[1] operation descriptions 7. local resonance operation" section in the application notes. n Applications
• Televisions, VCRs, facsimiles, and printers SIP009-P-0000C Unit: mm 0.3+0.1 –0.05 23.3±0.3 6.0±0.3 2.4±0.25 3.3±0.25 1.5±0.25 0.5±0.1 2.541.5±0.25 1.4±0.3 3.0±0.3 30°

AN8027, AN8037 Voltage Regulators Parameter Symbol Rating Unit Supply voltage V CC 24 V Constant output current I OUT –150 mA Peak output current I OP –1 000 mA TR pin allowable application current ITR –5m A OCP pin allowable application voltage VOCP - 0.3 to +7.0 V CLM pin allowable application voltage VCLM - 0.3 to +7.0 V SD pin allowable application voltage V SD - 0.3 to +7.0 V FB pin allowable application current IFB 0 to -2.0 mA Power dissipation (Ta £ 25°C) P D 874 mW Power dissipation (Ta = 85°C) 454 mW Operating ambient temperature * Topr -30 to +85 °C Storage temperature * Tstg -55 to +150 °C Parameter Symbol Range Unit Supply voltage V CC From the stop voltage to the OVP supply voltage V Note) 1. *: Except for the operating ambient temperature and storage temperature, all ratings are for Ta = 25°C. 2. Do not apply external currents or voltages to any pins not specifically mentioned. For circuit current, '+' denotes current flowing into the IC, and '-' denotes current flowing out of the IC. n Absolute Maximum Ratings n Recommended Operating Range n Block Diagram OVP 3.8 V 0.5 V 7.1 V - 0.2 V 1.0 V 0.35 V V FB (- 0.15 V) (0.7 V) To timer Out Drive TON TOFF INIT(SD latch) Start Current reviser (IFB ) High-side clamp Start pulse One shotLow-side clamp High-side clamp I/V conv. Current reviser (ITR ) Timer 2 6 Out GND CLM

7 V CC

Q Q Q Q R S Q CF latch In In Stop Q Q R Q

Voltage Regulators AN8027, AN8037 n Electrical Characteristics at VCC = 18 V, Ta = 25°C Parameter Symbol Conditions Min Typ Max Unit initial startup supply voltage operation stop supply voltage Overvoltage protection (OVP) V CC-OVP 19.4 20.5 21.6 V operating supply voltage Overvoltage protection (SD) V TH1-SD 3.5 3.9 4.3 V operating threshold voltage Overvoltage protection (SD) V TH2-SD 0.4 0.8 1.2 V reset threshold voltage Remote (RM) operating V TH1-RM 0.05 0.15 0.3 V threshold voltage Shutdown (SD) standby voltage V STB-SD SD pin = Open 1.0 1.5 2.0 V Overvoltage protection (OVP) V CC-OVPC 7.3 8.1 8.9 V reset supply voltage Remote (RM) operating time I CC-RM V CC = 18 V, VSD = 0 V 3.0 4.0 5.0 mA circuit current Overvoltage protection (SD) I CC1-SD V CC = 10 V, VSD = 4.3 V fi Open 1.2 1.5 1.8 mA operating time circuit current 1 Overvoltage protection (SD) I CC2-SD V CC = 18 V, VSD = 4.3 V fi Open 3.6 4.5 5.4 mA operating time circuit current 2 Timer latch (SD) charge current 1 ISD1-TIM FB pin = Open, ITR = -270 mA 68 102 136 mA Timer latch (SD) charge current 2 ISD2-TIM FB pin = Open, ITR = -1.64 mA 179 267 355 mA Timer latch (SD) start feedback IFB-TIM ITR = -1 mA, ROCP = 30 kW- 0.95- 0.75- 0.55 mA current Transformer reset detection (TR) VTH-TR 0.15 0.25 0.35 V threshold voltage Transformer reset detection (TR) VCLH-TR ITR = 3 mA 0.55 0.7 0.85 V upper limit clamp voltage Transformer reset detection (TR) VCLL-TR ITR = -3 mA - 0.3 - 0.15 0 V lower limit clamp voltage Overcurrent protection (CLM) V TH-CLM -220 -200 -180 mV threshold voltage Oscillator (CF) upper limit voltageV H-CF FB pin = Open, CF = 2 200 pF 3.8 4.2 4.6 V Oscillator (CF) lower limit voltage 1V L1-CF FB pin = Open, CF = 2 200 pF 0.8 1.0 1.2 V Oscillator (CF) lower limit voltage 2V L2-CF IFB = - 0.5 mA, CF = 2 200 pF 0 0.1 0.3 V Oscillator (CF) maximum G ION-CF FB pin = Open, ITR = -750 mA 0.8 1.0 1.2 ¾ on-period current gain Oscillator (CF) maximum I ON-CF ITR = 0 mA 200 250 300 mA on-period current Oscillator (CF) minmum I OFF1-CF IFB = - 0.4 mA -880 -660 -440 mA off-period current 1

AN8027, AN8037 Voltage Regulators n Electrical Characteristics at VCC = 18 V, Ta = 25°C (continued) Parameter Symbol Conditions Min Typ Max Unit Oscillator (CF) minmum I OFF2-CF IFB = - 0.8 mA -210 -160 -110 mA off-period current 2 Minimun off-period threshold I FB-TOFF - 0.78 - 0.6 - 0.42 mA feedback current Overcurrent protection (OCP) pin IOCP-OCP -130 -100 -70 mA source current Output oscillator frequency F OSC C F = 2 200 pF, ITR = 475 mA, 50 65 80 kHz IFB = - 0.5 mA Pre-startup low-level output voltage VOL-STB V CC = 13.5 V, IOUT = 1 mA ¾ 1.0 1.25 V Low-level output voltage V OL IOUT = 0.1 A ¾ 0.9 2.0 V High-lebel output voltage V OH IOUT = - 0.1 A 15.5 16.3 ¾ V Pre-startup circuit current 1 ICC-STB1 V CC = 13.5 V 75 100 125 mA Circuit current 1 I CC1-OPR1 V CC = 10 V 8.5 11.5 14.5 mA Circuit current 2 I CC2-OPR2 V CC = 18 V 9.0 12.0 15.0 mA Circuit current durring startup 1 ISTART1 ¾ 200 380 mA Parameter Symbol Conditions Min Typ Max Unit start/stop supply voltage difference Remote (RM) reset threshold voltage VTH2-RM ¾ 0.1 ¾ V Timer latch (SD) overcurrent T CLM-SD ¾ 0.1 ¾ s protection time Transformer reset detection (TR)DV TH-TR ¾ 0.05 ¾ V threshold hysteresis width Maximum on-period T ON(max) ITR = 0 mA, IFB = - 0.2 mA ¾ 26.5 ¾m s Minimum off-period T OFF(min) ITR = 0 mA, IFB = - 0.2 mA ¾ 5 ¾m s Overcurrent protection (OCP) TSD(ON)-OCP IFB = - 0.5 mA, ROCP = 22 kW¾ 1.8 ¾m s power-on charge period Overcurrent protection (OCP) TSD(OFF)-OCP IFB = - 0.5 mA, ROCP = 30 kW¾ 8.8 ¾m s power-off charge period Output rise time t r 10% to 90%, IOUT = 0 mA ¾ 60 ¾ ns Output fall time t f 10% to 90%, IOUT = 0 mA ¾ 20 ¾ ns TR output response time T TR ¾ 800 ¾ ns CLM output response time T CLM ¾ 100 ¾ ns Pre-startup circuit current 2 ICC-STB2 V CC = 13.5 V, 50 100 150 mA Ta = -30°C to +85°C Only for AN8037 Timer period during startup T START ¾ 100 ¾m s

• Design reference data Note) The characteristics listed below are theoretical values based on the IC design and are not guaranteed.

Voltage Regulators AN8027, AN8037 Pin No. Pin name I/O Explanation Equivalent Circuit 1 TR I Transformer reset detection input. When the IC detects transformer resetting and the fall- ing edge of a high-level signal is input to this pin of the AN8037 or a low-level signal is input to the same pin of the AN8027, the level of the Out pin becomes high. However, the transformer reset signal is ignored if the signal is shorter than the minimum off-pe- riod determined by the CF pin. Also note that the maximum on-period is corrected ac- cording to the source currents.

2 OCP ¾ Connection for the resistor that determines

the overload level of the IC to activate the timer latch protection circuit. By judging the operating mode (i.e., the nor- mal or standby mode) of the IC from the secondary side, the timer period is adjusted with the selection of external resistance ac- cording to the operating mode. 3C F ¾ Connection for the capacitor that determines the on- and off-periods of the IC output (Out). The on- and off-periods are corrected by ION which is proportional to the flowing out cur- rent at the TR pin, and IOFF which corre- sponds to the current at FB pin.

4 CLM I Input to the pulse-by-pulse overcurrent pro-

tection circuit. Normally, we recommend adding an external filter for this input. If overcurrent continues for several cycles, the IC determines that the operation is erroneous, thus triggering the latch protection function. 5 GND ¾ IC ground. n Pin Descriptions High-side clamp Low-side clamp V REF V REF CF Comp. V REF V FB IOFF ION Comp. V REF CLM( -) Comp.

AN8027, AN8037 Voltage Regulators Pin No. Pin name I/O Explanation Equivalent Circuit 6 Out O Output used to directly drive a power MOSFET. A totem pole structure is adopted in this output circuit. The absolute maximum ratings for the output current are: Peak: –1 A DC: –150 mA 7V CC ¾ Power supply. This pin monitors supply voltage and has the threshold for the start, stop, OVP, and OVP reset levels.

8 SD I This pin is used in RM (remote), OVP (over-

voltage protection), and timer latch. RM: The IC is in remote operation if this pin is short-circuited to the ground and the output of the IC is turned off. OVP: When overvoltage signal of the power sup- ply is detected and high is inputted to the ter- minal, it turns off the internal circuit. At the same time, it holds that condition (latch). Timer latch: It detects the output voltage fall due to the overcurrent condition of the power supply output through the current level inputted to FB. When the I FB decreases under the current of certain value, the charge current flows in the capacitor which is connected to this ter- minal. Then, when the capacitor is charged up to the threshold voltage of the OVP, the OVP works so that the IC could keep the op- eration stop condition.

9 FB I Connection for the photocoupler used for the

power supply output error-voltage feedback. This input can decrease the photocoupler dark current by about 200 mA. V CC V CC OVP 3.9 V 25 mA ITIMComp. RM 0.1 V Comp. V REF V FB IFB 9 n Pin Descriptions (continued)

Voltage Regulators AN8027, AN8037 n Application Notes [1] Operation descriptions 1. Start/stop circuit block

• Startup mechanism After the AC voltage is applied and the supply voltage due to the current in the startup resistor reaches the startup voltage and the IC begins to operate, drive of the power MOSFET begins. This causes a bias in the transformer, and the supply voltage is provided to the IC from the bias winding. (This is point a in figure 1.) During the period between the point when the startup voltage is reached, and the point when the bias winding can generate a voltage enough to supply the IC, the IC supply voltage is pro- vided by the capacitor (C8) connected to V CC . Since the supply voltage falls during this period (area b in figure 1), if the supply voltage falls below the IC stop-voltage before an adequate supply voltage can be provided by the bias wind- ing, it will not be possible to start the power sup- ply. (This is the state at point c in figure 1.)
• Functions This IC includes a function that monitors the V CC voltage. It starts IC operation when VCC reaches the startup voltage (14.9 V typical), and stops operation when the voltage falls below the stop voltage (8.6 V typical). Since a large voltage difference (6.3 V typical) is taken between the start and stop voltages, it is easy to select values for the start resistor and the capacitor connected to V CC . Note) To start up the IC operation, the startup current which is a pre-start current plus a circuit drive current is necessary. Set the resistance value so as to supply a startup current of 400 mA. 2. Oscillation circuit The oscillation circuit makes use of the charge and discharge of current to and from the capacitor CCF connected to the CF pin (pin 3) to determine the switching timing of the power MOSFET. The IC is in constant voltage control by changing the on-period of the power MOSFET without making off- period change while the IC is in normal (RCC continuous) operation mode. At that time, the on-period is con- trolled by directly changing the output pulse width of the oscillation circuit, and the maximum on-period can be adjusted with input voltage compensation by detecting the input voltage with the flow of current from the TR pin (TR source current). Refer to figure 2. When the IC is in standby mode (for light loads), the stable, efficient control of the IC is ensured by detecting the flow of current from the FB pin (I FB ) and changing the off-period for a decrease in frequency. Refer to figure 3. The following provides information on how to set on- and off-period.
• Setting the on-period The output on-period is the discharge period when the CF pin is between the peak value oft VH-CF = 4 V (typical) and VFB . An approximate on-period of the power MOSFET is obtained from the following formula. Refer to figure 2. TON = CCF · (VH-CF - VFB )/ION whereas, VH-CF = 4 V typ. ION = ITR + 250 mA typ. ITR = (EIN · NB/NP - VZ)/RTR V FB = 0.7 V typ. (IFB £ 200 mA) V FB = 4 kW · IFB typ. (IFB > 200 mA) GND b Figure 1 Startup failure Startup state V oltage supplied from bias winding StartupStandby Startup voltage Stop voltage a c Rectified AC Startup resistor V CC V OUT

1. Oscillation circuit (continued)

• Setting the on-period (continued) TON : On-period C CF : Value of a capacitor connected to CF pin V FB : Voltage internally converted from feedback signal IFB V H-CF : CF upper limit voltage ION : On-period discharge current ITR : Flowing current at TR pin EIN : Voltage on primary winding NB : Number of turns in the bias winding NP : Number of turns in the primary winding V Z : Voltage on Zener diode connected to bias winding R TR : Value of a resistor connected to the TR pin The power MOSFET is turned off if the voltage at the CLM pin reaches the pulse-by-pulse overcurrent protection threshold voltage (i.e., -200 mV typical) when the overcurrent protection function of the IC is operating. AN8027, AN8037 TON is shortened because large EIN increases ITR . Current mirror ITR =ION V CC ION V FB TR FB PC C CF CF V ZR TRITR EIN+ EIN- NP NB Out GND The minimum current is guaranteed to prevent a limitless increase in TON .

Figure 2. On-period block diagram and control waveform The maximum on-period can be used for overcurrent protection. When the input voltage is low, the maximum on-period overcurrent protection is possible. When the input voltage is high, the CLM pulse-by-pulse overcurrent protection is possible.

1. Oscillation circuit (continued)

• Setting the off-period The minimum off-period is the charge period from VL-CF = 0.2 V (typical) to VTH(OFF) or VFB . An approximate minimum off-period of the power MOSFET is obtained from the following formula. Refer to figure 3. TOFF(min) = CCF · VTH(OFF) /IOFF1 (IFB £ 0.6 mA) = {CCF · VTH(OFF) / IOFF1 } + {CCF · (VFB - VTH(OFF) ) / IOFF2 }( IFB > 0.6 mA) V TH(OFF) = 2.4 V typ. IOFF1 = 660 mA typ. IOFF2 = 160 mA typ. TOFF(min) : Minimum off-period C CF : Value of a capacitor connected to the CF pin V FB : Voltage internally converted from feedback signal IFB V TH(OFF) : Threshold voltage of VFB to extend off-period IOFF1 : Charge current until CF pin voltage increases from 0.2 V to 2.4 V IOFF2 : Charge current until CF pin voltage increases from 2.4 V to VFB When the IC is in local resonance operation, the off-period is determined by the longer one of either the time required for the input voltage on the TR pin to drop below the threshold voltage or the minimum off- period (T OFF(min)) specified by the CCF . Thus the power MOSFET is in continuous on/off operation. AN8027, AN8037 IOFF = 660 mA typ. (IFB < 0.6 mA) IOFF = 160 mA typ. (IFB > 0.6 mA) V CC IOFFV FB FBPC C CF CF EIN+ NP NB Out GND Current mirror 1 : 5 20 kW CF pin voltage Out pin voltage V H -CF = 4 V V TH(OFF) = 2.4 V V L2-CF = 0.2 V V CC - 1.5 V 0 V V FB 0 V

Figure 3. Off-period block diagram and control waveform

AN8027, AN8037 Voltage Regulators n Application Notes (continued) [1] Operation descriptions (continued) 3. Control waveform timing chart 1) Normal (RCC contiuous) operation mode (A)Voltage on bias winding (B)TR pin voltage (C)CF pin voltage 0 V 0 V 0 V 2.4 V Off OnOn OffOff Off 0 V 0 A Current on bias winding Off OnOn OffOff On On Off LoadHeavy Light (D)Out pin voltage V FB voltage (E)Current on primary winding (F)Current on secondary winding V CC - 1.5 V 4 V <Circuit diagram> IFB correction V FB ; large TOFF(min); long AN8027, AN8037 (D) (G) (A) (E) (F) CLM CF TR V CC Out (C) (B) Input voltage correction EIN; large TON ; short

Voltage Regulators AN8027, AN8037 n Application Notes (continued) [1] Operation descriptions (continued) 3. Control waveform timing chart (continued) 2) Standby (Intermittent) mode (for light loads) (A)Voltage on bias winding (B)TR pin voltage (C)CF pin voltage 0 V 0 V TOFF(min) T(OFF) 0 V 2.4 V Off On OffOff 0 V 0 A Off On Off On Off (D)Out pin voltage V FB voltage (E)Current on primary winding 4 V TON is acceptable only after CF pin voltage reaches 4 V. TON is unacceptable during TOFF(min) period. <Circuit diagram> AN8027, AN8037 (D) (G) (A) (E) (F) CLM CF TR V CC Out (C) (B) Current on bias winding (F)Current on secondary winding

AN8027, AN8037 Voltage Regulators n Application Notes (continued) [1] Operation descriptions (continued) 3. Control waveform timing chart (continued) 3) Pulse-by-pulse overcurrent protection (CLM) operation (A)Voltage on bias winding (B)TR pin voltage (C)CF pin voltage 0 V 0 V 0 A 0 V - 0.2 V 2.4 V Off OnOn OffOff On Off On Off Off OnOn OffOff On Off On Off 0 V 0 A (E) Current on primary winding (H)CLM pin voltage CLM threshold voltage (D)Out pin voltage V FB voltage V CC - 1.5 V 4 V <Circuit diagram> AN8027, AN8037 (D) (G) (A) (E) (F) CLM CF TR V CC Out (C) (B)

AN8027, AN8037 Voltage Regulators n Application Notes (continued) [1] Operation descriptions (continued) 6. Notes on the feedback control (continued) [Countermeasures] If an application exhibits the symptoms of the case described above, or similar symptoms, first insert a Schottky barrier diode between VOUT and GND. It is not possible to completely remove the mechanism described above from a power supply system. It is also not possible to prevent levels from being pulled down to negative voltages in the control IC itself. Therefore, the most important point in designing countermeasures is to prevent such negative voltages from reaching the parasitic device conductance voltage. Note) If a Schottky barrier diode is added to the circuit and the condition improves initially but the symptoms reappear when the input voltage or other parameter is increased, try replacing the Schottky barrier diode with one that has a larger forward current (both peak and average values). The current capacity of the Schottky barrier diode is sometime insufficient. (Reference) The following our Schottky diodes are available. Part No. Reverse voltage Forward current (average) Forward current (peak) MA2C700A (MA700A*) 30 V 30 mA 150 mA MA2C723 (MA723*) 30 V 200 mA 300 mA MA2C719 (MA719*) 40 V 500 mA 1 A 7. Local resonance operation (power MOSFET turn-on delay circuit) Local resonance operation by using the AN8027 or AN8037 is possible with circuits as shown in figure 13. C7 is the resonance capacitor, and R9 and C9 form a delay circuit for adjusting the power MOSFET turn on time. When the power MOSFET is off, the voltage that occurs in the drive winding is input to the TR pin (pin 1) through R9 and C9. The power MOSFET will be held in the off state while a high level (a level higher than the threshold voltage, which is 0.25 V typical) is input to the TR pin. The TR pin also has a clamping capability for upper and lower limit voltages. The upper limit voltage is clamped at 0.7 V (typical) (sink current: -3 mA), and the lower limit voltage is clamped at about - 0.15 V typical (source current: 3 mA). (Refer to figure 11.) The power MOSFET off-period is determined by the longer period of the following two periods: the period until the TR pin input voltage becomes lower than the threshold voltage as the bias winding voltage falls after the transformer discharges its energy, and the minimum off-period (T OFF(min)) stipulated by the internal oscillator. (Refer to the "Setting the off-period" section in the "Operating descriptions, 2. Oscillation circuit.") As a result, ringing in the bias winding does not be regarded as a turn on signal during the minimum off-period. Note) *: Former part number

AN8027, AN8037 Voltage Regulators n Application Notes (continued) [1] Operation descriptions (continued) 8. Bottom-on function (AN8037 only) (continued) Select the constants of R9 and C9 to determine the turn-on delay time so that the power MOSFET will be turned on at a frequency of half the resonant frequency. Practically, refer to figure 12 and determine the turn-on delay time so that the power MOSFET will be turned on at V DS = 0 V. The approximate resonant frequency can be obtained from the following formula. fSYNC = 1 [Hz] C: resonant capacitance 2p ÖL · C L: inductance of primary winding of transformer The turn-on delay time tpd(ON) to turn on the power MOSFET at a frequency of half the resonant frequency is, therefore, as follows. tpd(ON) = p ÖL · C [s] Note that since insertion of the resonance capacitor results in increased losses, using the parasitic capacitance of the power MOSFET itself should also be considered. However, in this case the sample-to-sample variations and temperature variations should be considered. 9. Notes on R9 and C9 value selection If an excessively low value is used for R9, the current flowing into the TR pin after power supply startup will exceed the maximum rating for the IC, and incorrect operation (in the worst case, destruction of the device) may occur. We recommend using a value of R9 in the range that satisfies the following conditions. V B(-) - The TR lower limit clamp voltage (- 0.15 V typical) ‡ -3 mA R9 V B(-): negative peak voltage V B(+) - The TR upper limit clamp voltage (1.5 V typical) £ 3 mA R9 V B(+): positive peak voltage Adjust tPD(ON) with C9 by taking the inductance and resonant capacitance of the transformer into consideration. tpd V P V IN V DS 0 V 0 V 0 V 0.25 V V TR ID V TR 0.7 V typ. Figure 14Figure 13 ID SBD SBD R9 V B V P V CC Out6 TR V IN Rectified AC To AC -

AN8027, AN8037 Voltage Regulators n Application Notes (continued) [1] Operation descriptions (continued) 13. Overvoltage protection (OVP) circuit OVP stands for overvoltage protection. The overvoltage protection circuit is a self-diagnostic function that shuts down the power supply to protect the load if a voltage that is significantly and abnormally higher than the normal output voltage occurs in the power supply output, due to, for example, a malfunction in the control system or an abnormal voltage applied externally. (Refer to figure 22.) Basically, the overvoltage protection circuit should be designed so that the V CC pin voltage of the IC can be monitored. Since the VCC pin voltage is normally supplied from the transformer bias winding, this voltage is proportional to the secondary side output voltage. Thus the overvoltage protection circuit operates when an overvoltage occurs in the secondary side output. 1) If, as a result of an abnormality in the power supply output, the voltage input to the V CC pin exceeds the threshold value (20.5 V typical), the IC internal reference voltage is shut down, and all control operation is stopped. The IC then holds this state. If latching at a voltage lower than the threshold value is required, connect a Zener diode between the V CC and SD pins as shown in figure 22 and take method 2) below to set the voltage. 2) If the SD pin input voltage exceeds a threshold value of 3.9 V typical, the IC internal reference voltage is shut down, and all control operation is stopped. The IC then holds this state. 3) OVP is reset in two methods. One is to decrease the output voltage on the secondary side so that the VCC pin voltage is less than the OVP reset voltage, i.e., 8.1 V typical. The other is to decrease the SD pin input voltage V typical, however, the IC will be in remote operation to shut off the output. The IC incorporates a circuit that discharges a constant current of approximately 25 mA from the capacitor connected to the SD pin for the re-start operation. The operation of this circuit is stopped when the SD pin voltage drops to 1.5 V or below. Refer to figure 21. Figure 21 AN8027, AN8037 NBV CC OVP C TIM ZOVP D B GND SDShut- down Latch V OVP-SD 3.9 V typ. V OVP-VCC 20.5 V typ. Timer capacitor discharging conditions Timer capacitor discharging transistor V CC < U.V .L.O. stop voltage V CC < OVP reset voltage OVP reset conditions V CC < OVP reset voltage V SD < SD reset voltage On The following is a formula to allow the IC to be in OVP operation with the SD pin in the above method 2). V th(OUT) = V (OUT) Secondary side output voltage under normal operation· V7V CC pin voltage under normal operation V7 = VTH-SD1 + VZ V th(OUT) : Secondary side output overvoltage threshold value V TH-SD1 : SD operating threshold value V Z : Zener voltage (externally connected to OVP pin)

Voltage Regulators AN8027, AN8037 n Application Notes (continued) [2] Package power dissipation PD ¾ Ta Power dissipation PD (mW) 0 25 150 Ambient temperature Ta (°C) 50 75 100 125 100 200 300 400 500 600 700 800 900 874 1 000 Independent IC without a heat sink R th j-a = 143°C/W PD = 874 mW (25°C) n Application Circuit Examples

• Circuit Diagram L1 L2 C1 C3 2 200 pF/250 V R19 68 kW · 2 68 kW · 2 C14 22 mF/50 V C16 1 000 mF/25 V D6 SBD MA3F760 (MA760*) D7 SBD MA3F750 (MA750*) D8 SBD MA3D798 (MA10798*) D9 SBD MA3D760 (MA7D60*) D10 SBD MA3D798 (MA10798*) 38 V 13 V C5 180 mF /250 V2 200 pF C12 2 200 pF 100 V 0.22 mF /250 V 0.1 mF /250 V FBI MA2C166 (MA166*) 75 kW C17 1 000 mF 6 V C18 22 mF/50 V C19 47 mF/16 V GND AN1431M/T -30 V 4.6 V 0 V R10

750 W R12

1.8 kW PC1 Q3 R13 1.5 kW R11 510 W C15 1.5 mF 2 200 pF 47 W 47 W 820 W MA2C166 (MA166*) MA2C700 (MA700*) SBD 0.22 W R15 51 W AN8027, AN8037 MA2C700 (MA700*) SBD R9 18 kW C11 1 800 pF 10 mF/50 V 100 mF/50 V 15 kW 3300 pF C10 PC1 C16 Note) *: Former part number

AN8027, AN8037 Voltage Regulators n Application Circuit Examples (continued)

• Evaluation board chart AN8027/AN8037 Application Board TN1 N L C4C3C1 C12 JP C13 R19 C11 C7 R15 R3 D2 N.C. 0 V 4.6 V 30 V GND 6 V 13 V 38 V TN2 R17 JP Q1 9JP C10S2 Z1 C16 C15 A Q3KR A A A A A D8 JP K K K D10 C18 C19 C14 C16 C17 R16 R10 R13 R14 R12 (Adj.) S G DQ2 R2 R15 PC1 0.8 ˘ R11 R18D1 AA K AA T1FB1 FB2 K