AN8026 PANASONIC

Document overview

  • Manufacturer or author: Provided By digicamel.com
  • PDF pages: 12

Technical content

Self-excited RCC pseudo-resonance type AC-DC switching power supply control IC n Overview The AN8026 is an IC developed for controlling the self-excited switching power supply employing the RCC pseudo-resonance type control method. It is compact, equipped only with the necessary mini- mum functions. The maximum on-period and the minimum off-pe- riod can be set separately by using the external capacitor and resistor respectively. It is suitable for the power supply of AV equipment. n Features

  • Operating supply voltage range: Stop voltage (8.6 V typical) to 34 V
  • Output block employs the totem pole system.
  • Power MOSFET can be directly driven. (output peak current: –1 A maximum)
  • Small pre-start operating current (80 mA typical) allows using a small size start resistor.
  • Built-in pulse-by-pulse overcurrent protection function
  • Incorporating protection circuit against malfunction at low voltage (start/stop: 14.9 V/8.6 V)
  • Built-in overvoltage protection function (externally resettable)
  • Equipped with frequency (VF) control function.
  • 9-pin single inline package expands the freedom of board design. n Applications
  • Televisions, facsimiles, printers, scanners, video equipment n Block Diagram 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° V REF (7.1 V) U.V.L.O. 8.6V 1.5V Current source 0.1 V CLM QIFB Switch diode Q R S RS latch Signal IN IN V OUT GND5 CLM4 TDL 1 FB 9 OVP 8 V CC TOFF 2 TON 3 0.7 V

0.7 VLow-side

2.8 V

n Absolute Maximum Ratings Parameter Symbol Rating Unit Supply voltage V CC 35 V Peak output current I 6PEAK –1A Power dissipation P D 874 mW Operating ambient temperature * T opr -30 to +85 °C Storage temperature * Tstg -55 to +150 °C Pin No. Symbol Description

1 TDL Transformer reset detection

2 TOFF Pin for connecting C and R to set minimum off-period

3 TON Pin for connecting C to set minimum on-period

4 CLM Input pin for overcurrent protection detection

5 GND Grounding pin

7V CC Power supply voltage pin

8 OVP Input pin for overvoltage protection circuit

9 FB Photocoupler connection pin for error voltage feedback

Note) *: Expect for the operating ambient temperature and storage temperature, all ratings are for Ta = 25°C. n Recommended Operating Range Parameter Symbol Range Unit Supply voltage V CC From stop voltage to 34 V n Electrical Characteristics at VCC = 18 V, Ta = 25°C Parameter Symbol Conditions Min Typ Max Unit OVP operation threshold voltage V 8OVP 6.7 7.9 9.1 V OVP operation threshold current I 8OVP 0.5 0.75 1 mA OVP release voltage V 7OVP 7.4 8.2 9 V OVP operating circuit current 1 I 7OVP1 V CC = 10 V, VOVP = 9.1 V 0.66 0.89 1.12 mA OVP operating circuit current 2 I 7OVP2 V CC = 20 V, VOVP = 9.1 V 3.5 4.7 5.9 mA TDL threshold voltage V 1TDL 0.5 0.7 0.9 V TDL upper limit clamp voltage V 1TDL/H ITDL = 3mA 2 2.8 3.6 V TDL lower limit clamp voltage V 1TDL/L ITDL = -3mA - 0.3 0 0.3 V CLM threshold voltage V 4CLM 0.7 0.75 0.8 V

n Electrical Characteristics at VCC = 18 V, Ta = 25°C (continued) Parameter Symbol Conditions Min Typ Max Unit TON maximum on-period current I 3TON FB terminal = open -125 -100 -75 mA TON terminal = GND TON upper limit voltage V 3TON/H FB terminal = open 0.55 0.7 0.8 V TON lower limit voltage V 3TON/L FB terminal = open - 0.1 0.05 0.2 V TOFF upper limit voltage V 2TOFF/H 0.7 0.9 1.1 V TOFF lower limit voltage V 2TOFF/L - 0.1 0.05 0.2 V Output oscillation frequency f OSC C ON = 2 200 pF, ROFF = 1.5 kW 50 60 70 kHz C OFF = 1 000 pF Output current feedback current gain GIFB IFB = -1 mA 5.25 7 8.75 ¾ Pre-start low-level output voltage V6STB/L V CC = 10 V, IOUT = 10 mA ¾ 1 1.25 V Low-level output voltage 1 V 6L(1) IOUT = 10 mA ¾ 0.9 2 V Low-level output voltage 2 V 6L(2) IOUT = 100 mA ¾ 1.1 2.2 V High-level output voltage 1 V 6H(1) IOUT = -10 mA 15.7 16.5 ¾ V High-level output voltage 2 V 6H(2) IOUT = -100 mA 15.5 16.3 ¾ V Pre-start circuit current I 7STB V CC = 12 V 40 80 120 mA Circuit current 1 I 7OPR(1) V CC = 18 V 7.4 9.5 11.6 mA TON terminal = GND FB terminal = open Circuit current 2 I 7OPR(2) V CC = 34 V 7.8 10 12.2 mA TON terminal = GND FB terminal = open TDL flowing-out current I 1TDL V TDL = 0.3 V -28 -20 ¾m A Pin No. Equivalent circuit Description I/O

1 TDL: I

Transformer reset detection terminal. When the transformer reset is detected and low is inputted into the terminal, the output of the IC (VOUT ) becomes high. However, low-level sig- nal under the minimum off-period determined by the TOFF is ignored.

2 TOFF: ¾

Terminal for connecting the resistor and capaci- tor for determining the minimum off-period (low) of the IC output (VOUT ). An equation for approximate calculation of the minimum off-period (T OFF ) is as follows: TOFF = 2.2 · C · R C: external capacitance R: external resistance n Terminal Equivalent Circuits V REF High- side clamp Low- side clamp V CC Comp. 0.1 V

Pin No. Equivalent circuit Description I/O

3 TON: ¾

Terminal for connecting the capacitor for deter- mining the maximum on-period (high) of the IC output (VOUT ). An equation for approximate calculation of the maximum on-period (TON ) is as follows: TON = 6 500 · C C: External capacitance

4 CLM: I

Input terminal for detection of the pulse-by- pulse overcurrent protection. Normally, it is recommended that a filter be attached externally.

5 GND: ¾

Grounding terminal. 6V OUT :O Output terminal for directly driving the power MOSFET. It uses the totem pole type output. The maximum rating of the output current: Peak: –1 A DC: –150 mA 7V CC : ¾ Terminal for applying power supply voltage. It monitors the supply voltage and has the op- eration threshold of start/stop/OVP reset.

8 OVP: I

When overvoltage of the power supply output is detected and high is inputted to the terminal, it turns off the internal circuit. At the same time, it holds that condition (latch). To reset the OVP latch, the terminal voltage should be decreased to low, or the VCC should be decreased to a voltage lower than the release voltage.

9 FB: I

Terminal for connecting the photocoupler for error voltage feedback of the power supply out- put. It is possible to cancel about 150 mA of the dark current of photocoupler. n Terminal Equivalent Circuits (continued) FBComp. 0.7 V V CC V REF (+) Comp. V CC Comp. TON 9 V CC

[1] Main characteristics Operating circuit current temperature characteristics Overvoltage protection operation circuit current temperature characteristics Overvoltage protective threshold voltage Overvoltage protective operation threshold current temperature characteristics temperature characteristics Overvoltage protective threshold voltage temperature characteristics TDL threshold voltage temperature characteristics -50 -25 100 Ambient temperature (°C) Operating circuit current (mA) 0 25 50 75 V CC = 18 V -50 -25 100 Ambient temperature (°C) Overvoltage protection operation circuit current (mA) 0 25 50 75 V CC = 18 V -50 -25 100 Ambient temperature (°C) Overvoltage protective threshold voltage (V) 8.0 7.5 8.5 9.5 0 25 50 75 V CC = 18 V -50 -25 100 Ambient temperature (°C) Overvoltage protective operation threshold current (mA) 0.4 0.2 0.6 0.8 1.0 0 25 50 75 V CC = 18 V -50 -25 100 Ambient temperature (°C) Overvoltage protective threshold voltage (V) 0.6 0.5 0.7 0.8 0.9 0 25 50 75 V CC = 18 V -50 -25 100 Ambient temperature (°C) TDL threshold voltage (V) 0.5 0.4 0.6 0.7 0.8 0 25 50 75 V CC = 18 V

n Application Notes (continued) [2] Operation descriptions (continued) 6. Overcurrent protection circuit The overcurrent of the power supply output is proportional to the value of current flowing in the main switch in the primary side (the power MOSFET). Taking advantage of the above fact, the overcurrent of the power supply output is restricted by regulating the upper limit of the pulse current flowing in the main switch to protects the parts easily damaged by the overcurrent. The current flowing in the main switch is detected by monitoring the voltage of both ends of the low resistor which is connected between the source of power MOSFET and the power supply GND. When the power MOSFET is turned on and the threshold voltage of CLM (current limit) is detected, the circuit turns off the output and turns off the power MOSFET to control so as not to allow further current flow. The threshold voltage of CLM is approximately 0.75 V (typical) under T a = 25°C with respect to GND. This control is repeated for each cycle. Once the overcurrent is detected, the off condition is kept during that cycle and it can not be turned on until the next cycle. The overcurrent detection method described in the above is called "pulse-by-pulse overcurrent detection". The R6 and C6 in figure 7 construct the filter circuit for removing the noise generated by the parasitic capacitance equivalently accompanied when turn- ing on the power MOSFET. For the earth point, it is recommended that the connection between GND of the IC and GND of the AC rectifier capacitor should be shortest.

  • Notes on the detection level precision This overcurrent detection level reflects 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 overcurrent protection of power supply itself also fluctuates. Since such level fluctuation means the neces- sity for an increase in the withstanding capability of used parts and in the worst case it means the cause of destruction, the accuracy of detection level is increased as much as possible for the AN8026 (approximately –4%). 7. Overvoltage protection circuit (OVP) OVP is an abbreviation of over voltage protection. It refers to a self-diagnosis function, which stops the power supply to protect the load when the power supply output generates abnormal voltage higher than the normal output voltage due to failure of the control system or an abnormal voltage applied from the outside. (Refer to figure 8.) Basically, it is set to monitor the voltage of supply voltage V CC terminal of the IC. Normally, the VCC voltage is supplied from the transformer drive coil. Since this voltage is proportional to the secondary side output voltage, it still operates even when the secondary side output has overvoltage. 1) When the voltage input to the OVP terminal exceeds the threshold voltage (7.9 V typical) as the result of power supply output abnormality, the protective circuit shuts down the internal reference voltage of the IC to stop all of the controls and keeps this stop condition. 2) The OVP is released (reset) under the following two conditions: (1) Setting the OVP terminal voltage at low from outside (lower than approximately 7 V) (2) Decreasing the supply voltage (V CC < 8.2 V typical: OVP release supply voltage) When the IC starts its operation, the open bias of approximately 6.5 V is generated in the OVP terminal.
  • When the supply voltage becomes lower than the stop voltage,
  • When the supply voltage becomes lower than the OVP release voltage, The discharge circuit is incorporated so that the electric charge which is charged in the capacitor connected to the OVP terminal can be discharged momentarily for the next re-start. V th(OUT) = secondary side output voltage under normal operation VOUT
  • V7V CC terminal voltage under normal operation V 7 = Vth(OVP) + VZ V th(OUT) : Secondary side output overvoltage threshold value V th(OVP) : OVP operation threshold value V Z : Zener voltage (externally attached to OVP terminal) Figure 7 R7C6 R6CLM GND

n Application Circuit Example 68 kW 10 kW AC 4.7 kW 22 W 82 mF R10 PC1C10 2 200 pF R11 R12 AN1431T/M FRD 1 800 pF 1 000 pF 560 mF Out6 CLM4 OVP 8 TDL 1 V CC 7 GND5 TON3 FB9 TOFF2 R6 680 W 1.5 kW 1.5 kW 2 200 pF 0.01 mF 1 mF 470 pF SBD To CLM terminal PCI 0.11 W OVP TDL High-clamp Low-clamp FB CLM VF control U.V .L.O. V REF Drive