UC2842B STMICROELECTRONICS | Alldatasheet
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HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER .TRIMMED OSCILLATOR FOR PRECISE FRE- QUENCY CONTROL .OSCILLATOR FREQUENCY GUARANTEED AT 250kHz .CURRENT MODE OPERATION TO 500kHz .AUTOMATIC FEED FORWARD COMPENSA- TION .LATCHING PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING .INTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT .HIGH CURRENT TOTEM POLE OUTPUT .UNDERVOLTAGE LOCKOUT WITH HYSTER- ESIS .LOW START-UP AND OPERATING CURRENT
DESCRIPTION
TheUC384xBfamilyofcontrolICsprovidesthenec- essary features to implement off-line or DC to DC fixed frequencycurrent mode control schemes with a minimal external parts count. Internally imple- mented circuits includea trimmed oscillator for pre- cise DUTY CYCLE CONTROL under voltage lock- outfeaturingstart-upcurrentless than0.5mA,a pre- cision reference trimmed for accuracy at the error amp input, logicto insurelatchedoperation,a PWM comparatorwhich alsoprovidescurrentlimit control, and a totem pole output stage designed to source or sink high peakcurrent. Theoutputstage,suitable for driving N-Channel MOSFETs, is low in the off- state. Differences between members of this family are the under-voltagelockout thresholdsand maximum duty cycle ranges. The UC3842B and UC3844B have UVLO thresholds of 16V (on) and 10V (off), ideally suitedoff-lineapplicationsThecorrespondingthresh- oldsfortheUC3843BandUC3845Bare8.5Vand7.9 V. The UC3842B and UC3843B can operate to duty cycles approaching 100%. A range of the zero to < 50 % is obtained by the UC3844B and UC3845B by theadditionofan internaltoggleflip flopwhich blanks the outputoff everyotherclock cycle. BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B) UVLO S/R 5V REF 34V INTERNAL BIAS VREF GOOD LOGIC 2.50V T S R OSC R1 V CURRENT SENSE COMPARATOR 2R+ - PWM LATCH ERROR AMP. Vi GROUND RT/CT VFB COMP CURRENT SENSE VREF 5V 50mA OUTPUT D95IN331 Minidip SO8 UC3842B
- All voltages are with respect to pin 5, all currents are positive into the specified terminal. PIN CONNECTION (top view) COMP VFB ISENSE R T/CT GROUND OUTPUT Vi VREF1 D95IN332 Minidip/SO8 ORDERING NUMBERS SO8 Minidip UC2842BD1; UC3842BD1 UC2843BD1; UC3843BD1 UC2844BD1; UC3844BD1 UC2845BD1; UC3845BD1 UC2842BN; UC3842BN UC2843BN; UC3843BN UC2844BN; UC3844BN UC2845BN; UC3845BN ABSOLUTE MAXIMUM RATINGS Symbol Parameter Value Unit Vi Supply Voltage (low impedance source) 30 V Vi Supply Voltage (Ii < 30mA) Self Limiting IO Output Current ±1 A EO Output Energy (capacitive load) 5 µJ Analog Inputs (pins 2, 3) – 0.3 to 5.5 V Error Amplifier Output Sink Current 10 mA P tot Power Dissipation at Tamb ≤ 25 °C (Minidip) 1.25 W Ptot Power Dissipation at Tamb≤ 25 °C (SO8) 800 mW Tstg Storage Temperature Range – 65 to 150 °C TJ Junction Operating Temperature – 40 to 150 °C TL Lead Temperature (soldering 10s) 300 °C PIN FUNCTIONS No Function Description 1 COMP This pin is the Error Amplifier output and is made available for loop compensation. 2V FB This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider. 3I SENSE A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction. 4R T/CT The oscillator frequency and maximum Output duty cycle are programmed by connecting resistor RT to Vref and cpacitor CT to ground. Operation to 500kHz is possible. 5 GROUND This pin is the combined control circuitry and power ground. 6 OUTPUT This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced and sunk by this pin. 7V CC This pin is the positive supply of the control IC. 8V ref This is the reference output. It provides charging current for capacitor CT through resistor RT. UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
ELECTRICAL CHARACTERISTICS ( [note 1] Unless otherwise stated, these specifications apply for -25 < Tamb <8 5°C for UC284XB; 0 < Tamb <7 0°C for UC384XB; Vi= 15V (note 5); RT = 10K; CT = 3.3nF) Symbol Parameter Test Conditions UC284XB UC384XB Unit REFERENCE SECTION ΔV REF Line Regulation 12V ≤ Vi≤ 25V 22 0 22 0 m V ΔV REF Load Regulation 1 ≤ Io ≤ 20mA 32 5 32 5 m V ΔVREF /Δ T Temperature Stability (Note 2) 0.2 0.2 mV/°C Total Output Variation Line, Load, Temperature 4.9 5.1 4.82 5.18 V eN Output Noise Voltage 10Hz ≤ f≤ 10KHz Tj =2 5°C (note 2) 50 50 µV Long Term Stability Tamb = 125 °C, 1000Hrs (note 2) 52 5 52 5 m V ISC Output Short Circuit -30 -100 -180 -30 -100 -180 mA OSCILLATOR SECTION fOSC Frequency Tj =2 5°C TA =T low to Thigh TJ =2 5°C( RT =6 . 2 k ,CT =1 n F ) 225 250 275 225 250 275 KHz KHz KHz Δ fOSC /Δ V Frequency Change with Volt. VCC = 12V to 25V – 0.2 1 – 0.2 1 % Δ fOSC /Δ T Frequency Change with Temp. TA =T low to Thigh –1–– 0 . 5 –% VOSC Oscillator Voltage Swing (peak to peak) – 1.6 – – 1.6 – V Idischg Discharge Current (VOSC =2V) TJ =2 5°C TA =T low to Thigh 7.8 7.5 8.3 8.8 8.8 7.8 7.6 8.3 8.8 8.8 mA mA ERROR AMP SECTION V Ib Input Bias Current V FB = 5V -0.1 -1 -0.1 -2 µA AVOL 2V ≤ Vo ≤ 4V 65 90 65 90 dB BW Unity Gain Bandwidth T J =2 5°C 0.7 1 0.7 1 MHz PSRR Power Supply Rejec. Ratio 12V ≤ Vi≤ 25V 60 70 60 70 dB Io Output Sink Current V PIN2 = 2.7V V PIN1 = 1.1V 2 12 2 12 mA Io Output Source Current V PIN2 = 2.3V VPIN1 = 5V -0.5 -1 -0.5 -1 mA VOUT High V PIN2 = 2.3V; R L = 15KΩ to Ground 5 6.2 5 6.2 V VOUT Low V PIN2 = 2.7V; R L = 15KΩ to Pin 8 0.8 1.1 0.8 1.1 V CURRENT SENSE SECTION G V Gain (note 3 & 4) 2.85 3 3.15 2.85 3 3.15 V/V V3 Maximum Input Signal V PIN1 = 5V (note 3) 0.9 1 1.1 0.9 1 1.1 V SVR Supply Voltage Rejection 12 ≤ Vi≤ 25V (note 3) 70 70 dB Ib Input Bias Current -2 -10 -2 -10 µA Delay to Output 150 300 150 300 ns THERMAL DATA Symbol Description Minidip SO8 Unit R th j-amb Thermal Resistance Junction-ambient. max. 100 150 °C/W UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
Notes : 1. Max packag e power dissipation limitsmust be respected; low duty cycle pulse techniques are used during test maintain Tjas close to Tamb as possible. 2. These paramete rs, although guaranteed, are not 100% tested in production. 3. Parameter measure d at trip point of latch with V PIN2 =0 . 4. Gain definedas : Δ VPIN1 A= ;0 ≤ VPIN3 ≤ 0.8 V Δ VPIN3 5. Adjust Viabove the start threshold before setting at 15 V. ELECTRICAL CHARACTERISTICS (continued) Symbol Parameter Test Conditions UC284XB UC384XB Unit OUTPUT SECTION VOL Output Low Level I SINK = 20mA 0.1 0.4 0.1 0.4 V ISINK = 200mA 1.6 2.2 1.6 2.2 V VOH Output High Level I SOURCE = 20mA 13 13.5 13 13.5 V ISOURCE = 200mA 12 13.5 12 13.5 V VOLS UVLO Saturation VCC = 6V; I SINK = 1mA 0.1 1.1 0.1 1.1 V tr Rise Time Tj =2 5°CC L = 1nF (2) 50 150 50 150 ns tf Fall Time Tj =2 5°CC L = 1nF (2) 50 150 50 150 ns UNDER-VOLTAGE LOCKOUT SECTION Start Threshold X842B/4B 15 16 17 14.5 16 17.5 V Min Operating Voltage After Turn-on X842B/4B 9 10 11 8.5 10 11.5 V PWM SECTION Maximum Duty Cycle X842B/3B 94 96 100 94 96 100 % X844B/5B 47 48 50 47 48 50 % Minimum Duty Cycle 0 0 % TOTAL STANDBY CURRENT Vi = 14V for UCX842B/44B 0.3 0.5 0.3 0.5 mA Ii Operating Supply Current VPIN2 =V PIN3 =0 V 1 2 1 7 1 2 1 7 m A V iz Zener Voltage I i = 25mA 30 36 30 36 V UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
-55 -25 0 25 50 75 100 T A(°C) 7.0 7.5 8.0 8.5 I dischg (mA) D95IN335 V i=15V V OSC =2V Figure 4:Oscillator Discharge Current vs. Tem- perature. 12 3 5 Dmax (%)
0.8 R T(KΩ )
Vi=15V C T=3.3nF TA=25°C Idischg=7.5mA Idischg=8.8mA Figure 5:Maximum Output Duty Cycle vs. Tim- ing Resistor. 10 100 1K 10K 100K 1M f(Hz) -20 (dB) 180 150 120 φ D95IN337 Vi=15V VO =2V to4V R L=100K TA=25°CGain Phase Figure 6:Error Amp Open-Loop Gain and Phase vs. Frequency.
0246 V O (V)
0.0 0.2 0.4 0.6 0.8 1.0 V th (V) D95IN338 Vi=15V TA=-40°C TA=125°C TA=25°C Figure 7:Current Sense Input Threshold vs. Er- ror Amp Output Voltage. 0 2 04 06 08 0 1 0 0 I ref(mA) D95IN339 Vi=15V TA=-40°C TA=125°C TA=25°C Figure 8:Reference Voltage Change vs. Source Current. -55 -25 0 25 50 75 100 T A(°C) D95IN340 100 I SC (mA) Vi=15V R L≤0.1Ω Figure 9:Reference Short Circuit Current vs. Temperature. UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
Figure 15 :ErrorAmp Configuration. Zi Zf 1mA VFB COMP 2.5V D95IN345 Figure 16 :Under Voltage Lockout. UC3842B UC3844B UC3843B UC3845B 16V 8.4V 10V 7.6V VON VOFF Vi ON/OFF COMMAND TO REST OF IC <0.5mA <17mA ICC VCC VOFF VON D95IN346 Figure 17 :Current Sense Circuit . ERROR AMPL. 2R R1 V CURRENT SENSE COMPARATOR CURRENT SENSE COMP CR S R 3 GND IS D95IN347 Peak current (is) is determined by the formula
1.0 VIS max ≈ R S
A small RC filter may be required to suppress switch transients. During UVLO, the Output is low UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
DIM. mm inch A 1.75 0.069 a1 0.1 0.25 0.004 0.010 a2 1.65 0.065 a3 0.65 0.85 0.026 0.033 b 0.35 0.48 0.014 0.019 b1 0.19 0.25 0.007 0.010 C 0.25 0.5 0.010 0.020 c1 45 ° (typ.) D (1) 4.8 5.0 0.189 0.197 E 5.8 6.2 0.228 0.244 e 1.27 0.050 e3 3.81 0.150 F (1) 3.8 4.0 0.15 0.157 L 0.4 1.27 0.016 0.050 M 0.6 0.024 S8 ° (max.) (1) D and F do not include mold flash or protrusion s. Mold flash or potrusio ns shall not exceed 0.15m m (.006inch) . SO8 OUTLINE AND MECHANICAL DATA UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
DIM. mm inch A 3.32 0.131 a1 0.51 0.020 B 1.15 1.65 0.045 0.065 b 0.356 0.55 0.014 0.022 b1 0.204 0.304 0.008 0.012 D 10.92 0.430 E 7.95 9.75 0.313 0.384 e 2.54 0.100 e3 7.62 0.300 e4 7.62 0.300 F 6.6 0.260 I 5.08 0.200 L 3.18 3.81 0.125 0.150 Z 1.52 0.060 OUTLINE AND MECHANICAL DATA UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
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