THOMSON SEMICONDUCTORS UAA4006A SWITCH MODE POWER SUPPLY CONTROL CIRCUIT The UAA4006A is a regulation and control device for fly-back switch mode power supplies using one external switching transistor. Includes oscillator, PWM and error amplifier Soft start SWITCH MODE POWER SUPPLY CONTROL CIRCUIT Direct drive of the switching transistor Self-regutated positive base current (peak 1.5 A) Negative base current providing fast turn-off and allowing the best use of the safe operating area (peak 1.5 A) Switching transistor protected against saturation failure Instantaneous collector current limitation Positive power supply monitoring On chip thermal protection Adjustable minimum conducting time for use of a snubber circuit Internal reference voltage Start up with very low supply current * Application note available ANO27R1 ORDERING INFORMATION PART NUMBER PACKAGE op sp UAA4006A e e Example : UAA4006ADP CASES CB-79 DP SUFFIX PLASTIC PACKAGE SP SUFFIX PLASTIC PACKAGE PIN ASSIGNMENTS (Top view} CB-79 C, : Oscillator timing capacitor cy hjt 4 161] GND Rt: Oscillator timing resistor Vcc : Supply voltage Ar G 2 16 7 E Vce : VCEisat) Sensing Vec G3 0 Sop vt: Power stage positive supply V og 4 H Vo_ : Power stage output cE 13 LU ton V7: Power stage negative supply vt o 5 12 Ic Ig : Secondary current monitoring input (s Primary current limit input vo 6 Whigs ton: ton{max) limit access v-Q7 yf N.c. Sop : Amplifier output E : Amplifier input n.c. 8 of] n.c. GND : Ground {Front view) CB-501 3 21a he | PLR biel t R E 183 7 gh OE OS Nc. IC Sop GND Cy Voc VNC. THOMSON SEMICONDUCTORS Sales headquarters 45, av. de l'Europe - 78140 VELIZY - FRANCE Tel. : (3) 946 97 19 / Telex : 204780 F 633 y.\ THOMSON @ COMPONENTS Ref. 00420UAA4006A MAXIMUM RATINGS Rating Symbol Vatue Unit Supply voltage Vec +18 Vv Supply voltages (Power stage) Positive vt +15 v Negative vo -6 v Voltage between pins 11 and 13 vt-vo +18 Vv Output current lo 16 A Current into input Ic (internal protection diodes) - +5 mA Current into input Ig = 5 mA Minimum value of resistance R; Re(max) 18 ka Junction temperature range fi -40 to +150 C Storage temperature range Tstg -40 to +190 C THERMAL CHARACTERISTICS Characteristic Symbot CB-79 CB-501 Unit Junction-ambient thermal resistance Rtnij ~a) 50 4a C/W Junction-case thermat resistance Rinijc) 7 2.5 C/W BLOCK DIAGRAM Rr CG} Vec VCE HW Oscillato Thermal vec J Protection Monitor Y Y ye PWM Logic processor Tontmax) - -0.16V | 0.1 V rts SF LS fon Ic ts vo case | Rt | Vee | Voce | V* | Vo j v nc Is ic | ton | Sop | E | GNO CB-79 1 2 3 4 5 6 7 8,9, 10 it 12 13 14 18 16 C8-501 9 10 iB) 12 13 14 8 1,15 2 3 4 5 6 7 2:8 THOMSON SEMICONDUCTORS 634UAA4006A CIRCUIT DESCRIPTION OSCILLATOR The oscillator provides a triangular waveform with a fail tirne much smalter than the rise time. The voltage swings bet- ween + 1.5 V and about Vcc/2. The maximum operating frequency is 60 kHz, the period being given by Tose = 90.5RCy Resistor Ry adjusts the frequency, but determines also the value of ton(min) (see logic processor). PULSE WIDTH MODULATOR (PWM) The variable duty-cycle signal is elaborated by comparing the oscillator voltage (pin C;) to the inverted error amplifier output voltage. Another comparator determines the maxi- mum value of the duty-cycle by comparing the oscillator signal with the voltage on pin ton. If Viton) = 0, then the maximum duty-cycle is internally set to 0.9 T ogc, otherwise, the maximum duty-cycle is given by : ton Rton Tose 2Rt (valid only if Rtpp >0.2 Ry, where Rton is the resistor inser- ted between top, pin and ground). max=1 CURRENT LIMITATION A level lower than 0.15 V on pin Ic involves two actions : a direct action through the logic processor which stops the drive until the end of the oscillator period ; an indirect action through the ton funtion. The change of state at the output of comparator Ic is applied to pin ton as long as the overioad current persists. By inserting capa- citor Cg between pin ton and Vcc (about 0.1 pF), the vol- tage at this point rises by a quantity AV proportional to the duration and the frequency of the overcurrent. This will consequently lower the maximum conduction ratio, thus decreasing the frequency of the overcurrent. At the end of an overload condition, capacitor Cg slowly charges up through a 20k internal impedance, in order to return pro- gressively to normal operation. NOTE : If capacitor Cp is omitted, direct action will only be implemented. SUPERVISION OF THE SECONDARY CURRENT In order to avoid the magnetization of the transformer core in case of short-circuits or heavy overloads on the secon- dary winding, 3 new cycle of conduction can only begin after the secondary current has completly fallen to zero. This task is accomplished by comparator Ig whose thres- hold is 0.1 V and detects the zero crossing of the secon- dary current. 3/8 THOMSON SEMICONDUCTORS 635 PROTECTION AGAINST DESATURATION If, because of a too low base current or a too heavy load, the collector to emitter voltage of the switching transistor rises above 4 V approximately, the output of comparator VCE changes state, and the drive is interrupted. ERROR AMPLIFIED This is an operational amplifier whose open loop gain is about 1000. The input current are less than 3 4A, and the input offset voltage is lower than mV. The input common-mode voltage range is 0 V to (Vcc -3V). Due to an internal limitation the output source current of the amplifier can not exceed 2 mA. START SWITCH An internal switch is inserted between pin Vcc supply line and internal voitage. During power-up, this switch closes when Vcc reaches +7.2V. The leakage current (Ic)L is about 0.4 mA before the switch closes. This original feature enables starting the converter by means of a high value resistance directly con- nected between Vcc and the high supply voltage. The smoothing capacitor on Vcc supply provides the energy required for the start. The turn-off of the internal switch requires that Vcc falis below +6.2 V. THERMAL PROTECTION This protection becomes active when the junction tempe- rature reaches + 160C. LOGIC PROCESSOR A logic unit processes the information coming from the fault detectors, and ensures that the output signal fulfils two conditions : No double pulsing with a period : the occurrence of a hault detection is memorized until the end of the period. * To allow the discharge of a snubber network, the mini- mum width of the output pulse is set at a given value ton{min) by an intemal monostable. if this monostable is not triggered, there will be no conduction. The duration ton(min) is programmable by resistor Ry using the relationship : ton(min) = 0.144 Ry - 2@(Vcc= +12 V) us (ko)UAA4006A ELECTRICAL CHARACTERISTICS Tamb = +25C, Vec= +10 V, V7 = -5V {Unless otherwise specified) Characteristic Symbol Min Typ Max Unit Supply voltage Vec _ - 14 Vv Rise supply voltage threshold Ycocr 6.5 7.2 79 v Fall supply voltage threshold Vccr 5.3 6.0 6.7 Vv Hysteresis on Vcc threshold AVcc 1 1.2 1.7 v Current Icc (Vcc under threshold voltage} _ - 0.4 1 mA Supply current (Vcc = + 10 V) lec _ 10 ~ mA Positive supply voltage {Power stage) vt. 4 - 15 v Negative supply voltage (Power stage) vO ~6 - -1 Vv Threshold of input Ic lotthy | 0.176] -0.16 | -0.144 v i input current (Vijq)=0 V) - - 5 20 pA Threshold of input Ig Istthy 0.065 0.1 0.135 v lg input current (Vig) =0 Vv} _ - 5 20 uA Error amplifier open-loop gain Ay 60 - - dB Error amplifier offset voltage Vio = 5 - mV Internai reference voltage Viref} 21 2.2 2.3 v Oscillator frequency fog =! fose | 2/R,C,} 60 kHz Tose Value of resistance Ry (Vcc = + 14 V) (See figure 1) Re 39 50 100 kQ (Vec=+8V) 18 50 100 7 Output current (V* Vg=3V, Vg - V7 =3 V) lo 15 - ~- A VCE comparator threshold voltage VCE(th) 3.6 4 4.4 v ton(min) adjustment range (Vcc = + 14 V) (See figure 1) = 4 = 8 us (Voc = +8 V} 1 - 13 Max duty cycle : (2) (Rtg, > 0.2 Re) - Note 1 _ = 1-oe ~ ~ me Rta <0-2 Rel ~ - 0.9 - - Oscillator frequency drift with temperature (Vcc = 12 V) = - 0.02 0.05 %/C Oscillator frequency drift with Voc - _ 0.2 0.5 %/IV Note 1: Rt, n externally connected between pin toy and GND Ry externally connected between pin Ry and GND FIGURE 1 - ton(min) ADJUSTMENT RANGE ton(min} (us) 10 20 30 18 kQ Ry (ka) 48 636 THOMSON SEMICONDUCTORSUAA4006A OUTPUT STAGE ON-state The positive stage achieves a very efficient drive of the swit- ching transistor. its features are essentially : Direct drive (neither inductor, nor tranformer) ; The transistor stays in a quasi-saturation mode, and thus has a reduced storage time ; * The drive energy is strictly limited to the required amount ; * Easy implementation. K1 is closed to turn the positive stage on. The maximum value of the positive base current is determined by the exter- nal limitation resistor R (between Vcc and vii. Diode D maintains Q in a quasi-saturation mode : the more Q is saturated, the more diode D will shunt an important part of the drive current Igy, through diode Dj. Resistor Rg has a low value (about 1 0), and is used to sta- bilize the regulation loop. For a good efficiency of the nega- tive drive, the value of this resistor should be as low as possible. Integrated Darlington T is able to supply a peak current of 1.5 A with a 2 V saturation voltage. The voltage VcE on transistor Q is : Vce=Vp + Rep !p1 OFF-state The turn off is accomplished in two steps : an immediate action through K2 which connects the base of the switching transistor to the negative supply through a 120 Q integrated resistor (current Ip) : * a detayed action through K3 which is closed only after the desaturation of the external transistor. This is detected by comparator Vc_, when the collector to emitter voltage rea- ches 4.5 V. Darlington T3 can supply 1.5 A with a 2 V saturation vol- tage (current Ip3). NOTE : The negative drive Ig3 for the removal of the sto- red charges is delayed in order to limit the slope dig/dt at the on-off transition. A high dig/dt might indeed lead to a destructive overheating of the base-collector junction (see The power transistor in its environment published by Thomson-CSF Division Semiconducteurs Discrets). SELF REGULATED BASE CURRENT Ig =f(Vce)} Voce +4V J UAA4006 5/8 THOMSON SEMICONDUCTORS 637UAA4006A TYPICAL WAVEFORMS LIMITS OF THE DUTY CYCLE Vic) - 0.6 Viton) Vcc VSop - 3 V | No | conduction | ' in +__+ >t ton(max) ton(min) CURRENT LIMITATION Viton) Viton! VIC) - 0.6V VIC) - 0.8 WITH Cg CAPACITOR WITHOUT Cg CAPACITOR Viton) Vic) - 0.6V I | | I { l Collector current ! Vilgh 1 O1V --F+]- - ---------- 4tre---- ov ~ Secondary current (short-circuit) 6/8 THOMSON SEMICONDUCTORS 638UAA4006A 50 W FLY-BACK CONVERTER ow BAI59 BUV 46 T 2.2 nF/1000 V = 2.22 1w EXTERNAL SYNCHRONIZATION The oscillator may be synchronized to an external frequency fext so that : foge < fext< 1.2 fose UAA4006A Ct Re Vcc 2 2x 1N4148 Rt CQ ~0Vv T Tose <1<_lose 78 639 THOMSON SEMICONDUCTORS ""UAA4006A Bsmar_, baum } ee J 11 Nominal dimension Oo 1 | 02) True geometrical position o MILI TITI CII a 2244 mor | L6.35_ Z ~ ny 16 pres DIN Y ASOE Fz CB-79 Cel OATA JEDEC SITELESC SEMICONDUCTORS mm _ 198 _ 44 * 201 ae fF oF ee S| BZ oh pe 1S 29 160 \ Y | 7 ( : q Vf a 7 4 ia 2.75 176 38 2338 oe =a + 0.60 Oxtpst afl H 075 fer tig 2 2 ! PS ee eR a a ne ay cee et a [J 15 pins DIN Y cB-501 CEL DATA JEDEC SITELESC SEMICONDUCTORS CB-79 OP SUFFIX PLASTIC PACKAGE CB-501 SP SUFFIX PLASTIC PACKAGE These specitications are subject to change without notice. Please inquire with our sales offices about the availability of the different packages. 8:8 THOMSON SEMICONDUCTORS 640