AN8021L

AN8021L PANASONIC | Alldatasheet

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AN8021L, AN8021SB AC-DC switching power supply control IC n Overview The AN8021L and AN8021SB are ICs which are suitable for controlling the switching power supply us- ing primary side control method. Those are most suited for a switching power supply of relatively small capacity. Less frequently used func- tions are removed and only the necessary minimum func- tions are incorporated, so that they are compact and very easy to use. Moreover, the internal settings are incorporated as much as possible, thus cost down can be realized by de- creasing the peripheral parts. n Features

• It operates at a control frequency up to 700 kHz, realiz- ing the output rise time of 35 ns and the output fall time of 25 ns.
• Pre-start operating current is as small as 70 mA (typical) so that it is possible to use a miniaturized start resistor.
• Output block employs totem pole method. The absolute maximum rating of –1.0 A (peak) allows the direct drive of power MOSFET.
• Built-in pulse-by-pulse overcurrent protection circuit
• Built-in protection circuit against malfunction at low voltage (on/off: 14.2 V/9.2 V)
• Equipped with timer latch function and overvoltage pro- tection circuit.
• Two kinds of packages: 9-pin SIP, 16-pin SOP n Applications
• Various power supply equipment SIP009-P-0000D AN8021L Unit: mm SSOP016-P-0225B AN8021SB Unit: mm 21.7±0.3 4.3±0.3 1.0±0.25 2.7±0.25 1.4±0.25 1.35±0.25 0.4±0.25 0.5±0.1 1.2±0.25 2.54 0.3+0.1 –0.05 0.65(0.45)0.80 6.30±0.30 4.30±0.30 0.35±0.10 6.50±0.30 +0.10-0.05 0.15 0.50±0.05 1.00±0.20 Seating plane 16 9 Seatng plane

AN8021L, AN8021SB Voltage Regulators Pin No. Symbol Description

1 SS Soft start pin

2 RT Resistor connection pin that determines charge and discharge current of triangular wave

3 CT Triangular wave generating capacitor connection pin

4 CLM( -) Pulse-by-pulse overcurrent protection input pin

5 GND Grounding pin

6V OUT Power MOSFET direct drive pin 7V CC Power supply voltage pin

8 TIM/OVP Pin for overvoltage protection and timer latch (joint use)

9 IFB Current feedback signal input pin from power-supply-output photocoupler

• AN8021L n Block Diagram Note) The number in ( ) shows the pin number for the AN8021SB. (4)SVCC V REFStart/Stop DrivePWM Reset 4.1 V V CC (3)PVCC V OUT (2) CLM( -) (15) GND (1)PGND (16)SGND TIM/OVP (5) SS (11) IFB (6) OVP CLM OSC OCL FBCT (13) RT (12)
• AN8021SB Pin No. Symbol Description

1 PGND Grounding pin

2V OUT Power MOSFET direct drive pin 3P V CC Power supply voltage pin 4S V CC Power supply voltage pin

5 TIM/OVP Pin for overvoltage protection and

6 IFB Power supply output photocoupler

current feedback signal input pin 7 N.C. N.C. 8 N.C. N.C. 9 N.C. N.C. Pin No. Symbol Description 10 N.C. N.C.

11 SS Soft start pin

12 RT Charge and discharge current of

triangular wave determining resistance connection pin

13 CT Triangular wave generating capacitor

14 N.C. N.C.

15 CLM( -) Pulse-by-pulse overcurrent protection

16 SGND Grounding pin

Voltage Regulators AN8021L, AN8021SB n Absolute Maximum Ratings Parameter Symbol Rating Unit Supply voltage V CC 35 V OVP terminal allowable application voltage VOVP V CC V CLM terminal allowable application voltage VCLM - 0.3 to +7.0 V SS terminal allowable application voltage VSS - 0.3 to +7.0 V Constant output current I O –150 mA Peak output current I OP –1 000 mA IFB terminal allowable application voltage IFB -5m A Power dissipation AN8021L P D 658 mW AN8021SB 340 Operating ambient temperature * T opr -30 to +85 °C Storage temperature * Tstg -55 to +150 °C n Recommended Operating Range Parameter Symbol Range Unit Timing resistor RT R 7 15 to 20 k W Note) *: Expect for the operating ambient temperature and storage temperature, all ratings are for Ta = 25°C. n Electrical Characteristics at Ta = 25°C Parameter Symbol Conditions Min Typ Max Unit Start voltage V CC-START 13.0 14.2 15.4 V Stop voltage V CC-STOP 8.5 9.2 9.9 V Standby bias current I CC-STB V CC = 12 V 50 70 105 mA Operating bias current I CC-OPR V CC = 34 V 6.4 8.0 9.6 mA OVP operating bias current 1 I CC-OVP1 V CC = 20 V 2.4 3.0 3.6 mA OVP operating bias current 2 I CC-OVP2 V CC = 10 V 0.44 0.55 0.66 mA OVP operating threshold voltage V TH-OVP V CC = 18 V 5.4 6.0 6.6 V OVP release supply voltage V CC-OVPC 7.6 8.4 9.2 V Timer latch charge current I CH-TIM V CC = 18 V, RT = 19 kW- 20 -30 -40 mA Timer latch start feedback current IFB-TIM V CC = 18 V - 0.37 - 0.5 - 0.63 mA Soft-start charge current I CH-SS V CC = 18 V, RT = 19 kW- 20 -30 -40 mA Overcurrent protection threshold voltage 1V TH-CLM1 V CC = 18 V -180 -200 -220 mV Pre-start low-level output voltage VOL-STB V CC = 12 V, IO = 10 mA ¾ 0.8 1.8 V Low-level output voltage V OL V CC = 18 V, IO = 100 mA ¾ 1.3 1.8 V High-level output voltage V OH V CC = 18 V, IO = -100 mA 15.0 16.5 ¾ V Oscillation frequency 1 f OSC1 V CC = 18 V 175 200 225 kHz Maximum duty 1 Du max1 V CC = 18 V 62 66 70 % Feedback current at 0% duty I FB-Du min V CC = 18 V -1.1 -1.5 -1.9 mA Feedback current at maximum duty IFB-Du max V CC = 18 V - 0.37 - 0.5 - 0.63 mA

AN8021L, AN8021SB Voltage Regulators Pin No. Equivalent circuit Description I/O

1 SS: ¾

(11) Soft start terminal. When V CC is applied, the capacitor connected to this pin is charged, and the output duty is de- creased by inputting the capacitor voltage to the PWM.

2 RT: ¾

(12) The terminal for connecting a resistor to deter- mine the charge and discharge current of the triangular wave.

3 CT: ¾

(13) The terminal for connecting a capacitor to gen- erate the triangular wave.

4 CLM( -): I

(15) The input terminal for pulse-by-pulse overcurrent protection. It is usually required to attach an external filter. 5 ¾ GND, (PGND), (SGND): ¾ (1)(16) Grounding terminal. 500 W (11)1 PWMcomp. 500 W (12) 2 V REF n Terminal Equivalent Circuits (13) V REF IO 2IO PWMcomp. Reset (15) V REF Parameter Symbol Conditions Min Typ Max Unit Oscillation frequency 2 f OSC2 Ta = -30°C to +85°C 160 ¾ 240 kHz Overcurrent protection delay time tDry-CLM V CC = 18 V under no load ¾ 200 ¾ ns Output voltage rise time t r V CC = 18 V under no load ¾ 35 ¾ ns Output voltage fall time t f V CC = 18 V under no load ¾ 25 ¾ ns n Electrical Characteristics at Ta = 25°C (continued)

• Design reference data Note) The characteristics listed below are theoretical values based on the IC design and are not guaranteed. Note) The number in ( ) shows the pin number for the AN8021SB.

Voltage Regulators AN8021L, AN8021SB Pin No. Equivalent circuit Description I/O 6V OUT :O (2) The terminal for directly driving a power MOSFET. 7 ¾ V CC , (PVCC ), (SVCC ): ¾ (3)(4) Supply voltage terminal. It monitors the supply voltage and has operat- ing threshold value for start/stop/OVP reset.

8 TIM/OVP: I

(5) The terminal with double functions such as OVP (overcurrent protection) and timer latch termi- nal. [OVP] When it receives the overvoltage signal of the power supply output and high is input to the terminal, internal circuit is turned off. At the same time, this condition (latch) is hold. To re- set the OVP latch, it is necessary to reduce V CC under the release voltage. [Timer latch] The output voltage drop due to the overcurrent condition of power supply output is detected through the current level for IFB-input. When I IFB becomes less than current of a certain value, charge current flows into the capacitor con- nected to this terminal. When the capacitor is charged to the threshold voltage of OVP, OVP starts to operate and the IC stays stop.

9 IFB : I

(6) The terminal into which the current feedback signal is input from the photocoupler of the power supply output. n Terminal Equivalent Circuits (continued) 6 V 500 W (5) Comp. SV CC 5 mA I/V conversion 500 W (6) V REF PWMcomp. Note) The number in ( ) shows the pin number for the AN8021SB. (2) PV CC

AN8021L, AN8021SB Voltage Regulators n Application Notes [1] Main characteristics [Load: CL = 3 300 pF, RL = 20 W ] Start/stop voltage characteristics OVP operation threshold voltage characteristics Standby bias current characteristics Operating bias current characteristics Overcurrent protection threshold voltage characteristics OVP release voltage characteristics -50 -25 100 Ambient temperature (°C) Start/stop voltage (V) 0 25 50 75 V CC = 18 V 5.0 -50 -25 100 Ambient temperature (°C) Threshold voltage (V) 5.5 6.0 6.5 7.0 0 25 50 75 V CC = 18 V -50 -25 100 Ambient temperature (°C) Bias current (mA) 0 25 50 75 V CC = 12 V 6.5 -50 -25 100 Ambient temperature (°C) Bias current (mA) 7.0 7.5 8.0 8.5 0 25 50 75 V CC = 34 V -180 -50 -25 100 Ambient temperature (°C) Threshold voltage (mV) -190 -200 -210 -220 0 25 50 75 V CC = 18 V 7.5 -50 -25 100 Ambient temperature (°C) OVP release voltage (V) 8.0 8.5 9.0 9.5 0 25 50 75 V CC = 18 V

Voltage Regulators AN8021L, AN8021SB n Application Notes (continued) [1] Main characteristics [Load: CL = 3 300 pF, RL = 20 W ] (continued) OVP operating bias current characteristics 1 OVP operating bias current characteristics 2 Feedback current at 0% duty characteristics Feedback current at maximum duty characteristics Timer latch feedback current characteristics Pre-start low-level output voltage characteristics 2.5 -50 -25 100 Ambient temperature (°C) Bias current (mA) 3.0 3.5 4.0 4.5 0 25 50 75 V CC = 20 V 0.5 -50 -25 100 Ambient temperature (°C) Bias current (mA) 1.0 1.5 2.0 2.5 0 25 50 75 V CC = 10 V 0.5 -50 -25 100 Ambient temperature (°C) Feedback current (mA) 1.0 1.5 2.0 2.5 0 25 50 75 V CC = 18 V 300 -50 -25 100 Ambient temperature (°C) Feedback current (mA) 400 500 600 700 0 25 50 75 V CC = 18 V 300 -50 -25 100 Ambient temperature (°C) Feedback current (mA) 400 500 600 700 0 25 50 75 V CC = 18 V 0.65 -50 -25 100 Ambient temperature (°C) Output voltage (V)0.70 0.75 0.80 0.85 0 25 50 75 V CC = 12 V

AN8021L, AN8021SB Voltage Regulators n Application Notes (continued) [2] Operation descriptions 1. Start/stop circuit block

• Start mechanism When AC voltage is applied and the sup- ply voltage reaches the start voltage through the current from the start resistor, the IC starts operation. Then the power MOSFET driving starts. Thereby, bias is generated in the trans- former and the supply voltage is given from the bias coil to the IC. (This is point a in figure 1.) During the period from the time when the start voltage is reached and the voltage is gen- erated in the bias coil to the time when the IC is provided with a sufficient supply voltage, the supply voltage of the IC is supplied by the capacitor (C1) connected to V CC . Since the supply voltage continuously decreases during the above period (area b in figure 1), the power supply is not able to start (state c in figure 1), if the stop voltage of the IC is reached before the sufficient supply voltage is supplied from the bias coil.
• Function The start/stop circuit block is provided with the function to monitor the V CC voltage, and to start the operation of IC when VCC voltage reaches the start voltage (14.2 V typical), and to stop when it decreases under the stop voltage (9.2 V typical). A large voltage difference is set between start and stop (5.0 V typical), so that it is easier to select the start resistor and the capacitor to be 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 450 mA. 2. Oscillation circuit The PWM is an abbreviation of pulse width modulation. In this IC, the smaller voltage between the voltage level which is converted from the current input to IFB terminal and dead-time control level which is fixed internally is compared with the internal triangular oscillation level through PWM comparator, and optimal duty is determined, and then it is output via output driving stage.
• Triangular wave oscillation The triangular waveform oscillation is performed through constant current charge/constant current discharge to/from the external capacitor connected to the CT. The ratio of the charge current to the discharge current is set inside, and the current value is determined by the external resistor connected to the RT terminal. The RT terminal voltage is determined by the level which is a resistor-divided voltage of the internal reference voltage (which is determined by Zener diode and V BE of NPN transistor, and temperature- compensated). For this reason, the effect of fluctuation with temperature and dispersion is small. By the use of a temperature-compensated external resistor, the effect of the fluctuation with temperature and dispersion on the charge and discharge current value will be reduced further. Moreover, since the upper/lower voltage level of the triangular wave oscillation is given by the resistor- division of internal reference voltage, the effect of fluctuation with temperature and dispersion has been suppressed. As described above, the sufficient consideration has been given to the effect of fluctuation with tempera- ture and dispersion in the design of the triangular wave oscillation frequency. (Reference calculation of oscillation frequency) f OSC = 5 [Hz]6 · CT · RT Start voltage After AC rectification Stop voltage a b Start condition Start failurec V oltage supplied from bias coil Before start Start Figure 1 V OUT Start resistance V CC GND

1. Overcurrent protection circuit (OVP)

current flowing in the main switch, the circuit protects the parts which are easily damaged by the overcurrent. which is equivalently formed at turning-on of the power MOSFET.

• Notes on the detection level precision This overcurrent detection level is reflected on the operating current level of the power supply overcurrent protection. Therefore, if this detection level fluctuates with temperature or dispersion, the operating current level of the power supply overcurrent protection also fluctuates. Since such level fluctuation increases the necessity of withstand capability for the parts to be used and in the worst case it means the cause of destruction, the accuracy of detection level is raised as much as possible for these ICs, the AN8021L and AN8021SB. Figure 5 R4GND CLM Power MOSFET current Time

0 Time

Figure 6. Pulse-by-pulse overcurrent detector operation waveform

rises with gradually widening duty from the minimum one (0%) at the power supply start is adopted. life of parts and raise the reliability of the power supply. signals of the non-reverse input, the lowest one is selected for input to the PWM comparator. this capacitor is set to be sufficiently discharged by the transistor inside the IC. the constant current source inside the IC. Therefore VSS gradually rises from 0 V. However, when the VSS exceeds the VFB or VDTC , the duty of the output pulse depends on the VFB or VDTC . The soft start function works only up to that point and after that the normal control comes. Figure 7. Soft start operation waveform

the power supply by hitting the OVP, when the overcurrent condition continues for a certain period. reverses and the constant current flows to the TIM/OVP terminal.

• Timer period The period from the time when an error of the power supply output is detected to the time when the OVP starts operation (hereinafter referred to as timer period) should be longer than the rise time of the power supply. Since at operation start the IC is in the same condition as the overload or output short-circuit condition, if the timer period is shorter, the power supply works latch and can not start. Therefore, the IC is designed so that the timer period can be set to any desired value with capacitance value of the external capacitor connected to the TIM/OVP terminal. However, particular care should be taken, because too large value of this capacitance may cause the breakdown of the power supply. Power supply output voltage V O Power supply stop Time Power MOSFET current IDS Power supply stop Time TIM/OVP terminal voltage V OVP Power supply stop Time OVP V TH = 6 V (typ.)

Figure 8. Timer latch basic operation

AN8021L, AN8021SB Voltage Regulators n Application Notes (continued) [2] Operation descriptions (continued) 7. Output Block The AN8021L and AN8021SB employ the out- put circuit using the totem pole (push-pull) method, by which sink/source of current is performed with the NPN transistor as shown in figure 9, in order to drive the power MOSFET at high speed. The maximum sink/source current is –0.1 A (DC) and –1.0 A (peak). Even when the supply voltage V CC is under the stop voltage, the sink function works to ensure that the power MOSFET be turned off. For the current capability, the peak current is major concern, and the particularly large current is not required normally: the power MOSFET which works as load on the output is capacitive load. Therefore, in order to drive it at high speed, the large peak current is required. However, after charge/discharge, particularly large current is not required to keep that condition. For the AN8021L or AN8021SB, capacitance value of the power MOSFET used is taking into account, and the capability of peak value –1 A is ensured. The parasitic LC of the power MOSFET may produce ringing which makes the output pin go under the GND potential. When the decrease of the output pin becomes larger than the voltage drop of diode and its voltage becomes negative, the parasitic diode consisting of the substrate and collector of the output NPN turns on. This phenomenon may cause the malfunction of the device. In such a case, the Schottky barrier diode should be connected between the output and GND. [3] Design reference data 1. Setting the output frequency The output is controlling the triangular oscillation with PWM control: Triangular oscillation frequency = output frequency CT (C6) = capacitor terminal for triangular oscillation RT (C7) = resistor terminal for triangular oscillation [Reference calculation formula] T 1 = T2 = C 6 · V 2IRT (charge/discharge current) Since the IRT is given by rough calculation of 2.5 V/RT , and V becomes approximately 3 V, the output frequency is obtained in the following equation: f OUT = 1 = IRT = 5 T1 + T2 C 6 · V 6 · C 6 · R7 However, it may deviate a little from the design value due to delay of the internal circuit. (Reference value) fOUT = approximately 200 kHz at CT (C6) = 220 pF and RT (R7) = 19 kW Figure 9 Schottky barrier diode T2T1 V OSC - H- V OSC - L- V

Voltage Regulators AN8021L, AN8021SB n Application Notes (continued) [3] Design reference data (continued) 2. Setting the timer latch period The timer latch period t, the period from the time when an abnormality of the power supply output is detected to the time when the overvoltage protector is activated, can be set to any desired value by using the external capacitance C TIM (C2) based on the following equation: TIM/OVP = capacitor terminal for timer latch period setting [Reference calculation formula] t = C 2 · VTIM [s] V TIM = 6 V (typ.): Overvoltage protection threshold value ITIM ITIM = timer latch charge current (Varies depending on R7 value, at R7 = 19 kW ) ITIM = 30 mA (typ.) 3. Setting the soft start time

• Soft start charge current Most of the conventional ICs are charged by using the internal resistor from the internal reference voltage, or by using the constant current source which is determined by the internal resistance. However, the above charging method suffers from problems on dispersion or temperature change and can not ensure the soft start time. For this reason, the AN8021L and AN8021SB use the following method: The soft start charge current is given from the constant current source used in the internal triangular wave oscillation circuit. In addition, the above constant current source is stable with respect to dispersion or fluctuation with temperature because it has the current value which is determined by the external resistor and the terminal voltage given from the resistor-divider of internal reference voltage. However, for this method, particular care should be taken on the application: Since each time the setting of oscillation frequency is changed, the soft start constant should be also changed. SS (C5) = capacitor terminal for soft start [Reference calculation formula] t = C 5 · VSS [s] ISS = soft start charging current ISS (Varies depending on R7 value, at RT (R7) = 19 kW ) ISS = 30 mA (typ.) V SS = 2.0 V, at duty = 0% V SS = 4.1 V, at maximum duty 4. Start circuit The start time from the power-on to the actual start can be set by using the values of R1 and C1. Too long start time makes the power supply to rise slowly. [Setting the start resistor R1] 1) When the overload shutting-off condition is kept, the shut-off bias current (OVP operating bias current) of the AN8021L and AN8021SB is 550 mA (typical) at VCC = 10 V. Therefore, set the R1 as shown in the following equation : R 1 < V IN - 10 V 550 mA 2) When automatic reset is desired after the overload shut-off, the standby current of the AN8021L and AN8021SB is 70 mA (typical) at VCC = 12 V. Therefore, set the R1 as shown in the following equation : V IN - 10 V < R1 < V IN - 12 V 550 mA 70 mA [Setting the C1] When the AN8021L or AN8021SB is started, the operating supply current of 7.5 mA is required at VCC = 18 V. The current should be supplied with the discharge current of the C1 during the period from the soft start time up to the time when the supply current is supplied from the auxiliary bias coil. Therefore set the C1 as shown in the following equation: (VCC(START) - VCC(STOP) ) · C1 > Soft start time7.5 mA

AN8021L, AN8021SB Voltage Regulators n Application Circuit Example C5R7 R2 DI DZ1 V IN FRD Filter Photocoupler R86 Start-up resistor V OUT TIM/ OVP AN8021L 7V CC CT RT SS IFB CLM GND AC input