CS2841BEDR14

CS2841B CS2841B Automotive Current Mode PWM Control Circuit Description The CS2841B provides all the necessary features to implement offline fixed frequency current-mode control with a minimum number of external components. The CS2841B (a variation of the CS-2843A) is designed specifically for use in automotive operation. The low start threshold voltage of 8.0V (typ), and the ability to survive 40V automotive load dump transients are important for automotive subsystem designs. The CS-2841 series has a history of quality and reliability in automotive applications. The CS2841B incorporates a precision temperature-controlled oscillator with an internally trimmed discharge current to minimize variations in frequency. Duty-cycles greater than 50% are also possible. On board logic ensures that VREF is stabilized before the output stage is enabled. Ion implant resistors provide tighter control of undervoltage lockout. Features s Optimized for Off-line Control s Internally Trimmed Temperature Compensated Oscillator s Maximum Duty-cycle Clamp s VREF Stabilized before Output Stage Enabled s Low Start-up Current s Pulse-by-pulse Current Limiting s Improved Undervoltage Lockout s Double Pulse Suppression s 1% Trimmed Bandgap Reference s High Current Totem Pole Output Absolute Maximum Ratings Supply Voltage (Low Impedance Source)...................................................40V Output Current ...............................................................................................±1A Output Energy (Capacitive Load) .................................................................5µJ Analog Inputs (VFB, Sense) ............................................................-0.3V to 5.5V Error Amp Output Sink Current...............................................................10mA Lead Temperature Soldering Wave Solder (through hole styles only) ..........10 sec. max, 260°C peak Reflow (SMD styles only) ...........60 sec. max above 183°C, 230°C peak Block Diagram V CC Undervoltage Lock-out Circuit Set/ 5V Reset Reference 8.0V/7.4V 2.50V OSC Internal Bias Output Enable NOR V OUT + V FB Error Amplifier COMP Sense – VC R 1V 2R S R Current Sensing Comparator PWM Latch Pwr Gnd V REF Package Options 8 Lead PDIP V CC P wr COMP VFB Sense OSC 1 2 3 4 8 7 6 5 VREF VCC VOUT Gnd Gnd 14 Lead SO Narrow COMP 1 NC 2 VFB 3 NC 4 Sense 5 NC 6 OSC 7 14 13 12 11 10 9 8 VREF NC VCC VCC Pwr VOUT Pwr Gnd Gnd Oscillator Cherry Semiconductor Corporation 2000 South County Trail, East Greenwich, RI 02818 Tel: (401)885-3600 Fax: (401)885-5786 Email: info@cherry-semi.com Web Site: www.cherry-semi.com Rev. 6/23/99 1 A ® Company CS2841B Electrical Characteristics: d -40≤TA≤85˚C RT=680kΩ, CT=0.022µF for triangular mode, VCC=15V (Note 1), RT=10kΩ, CT=3.3nF for sawtooth mode (See Fig. 3), unless otherwise stated. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT s Reference Section Output Voltage Line Regulation Load Regulation Temperature Stability Total Output Variation Output Noise Voltage Long Term Stability Output Short Circuit s Oscillator Section Initial Accuracy Sawtooth Mode: (See Fig. 3)TJ=25˚C Sawtooth Mode: -40˚C≤TA≤+85˚ Triangular Mode (See Fig. 3) TJ=25˚C 8.4V≤Vcc≤16V Sawtooth Mode TMIN≤TA≤TMAX Triangular Mode TMIN≤TA ≤TMAX (Note 2) VOSC (peak to peak) TJ=25˚C TMIN≤TA≤TMAX 7.4 7.2 47 44 44 52 52 52 0.2 5 8 1.7 8.3 9.2 9.4 57 60 60 1.0 kHz kHz kHz % % % V mA mA TJ=25˚C, IOUT=1mA 8.4≤VCC≤16V 1≤IOUT≤20mA (Note 2) Line, Load, Temp. (Note 2) 10Hz≤f≤10kHz, TJ=25˚C (Note 2) TA=125˚C, 1000 Hrs. (Note 2) TA=25˚C -30 4.82 50 5 -100 25 -180 4.90 5.00 6 6 0.2 5.10 20 25 0.4 5.18 V mV mV mV/˚C V µV mV mA Voltage Stability Temperature Stability Amplitude Discharge current s Error Amp Section Input Voltage Input Bias Current AVOL Unity Gain Bandwidth PSRR Output Sink Current Output Source Current VOUT High VOUT Low s Current Sense Section Gain Maximum Input Signal PSRR Input Bias Current Delay to Output Notes: VCOMP=2.5V VFB=0V 2≤VOUT≤4V (Note 2) 8.4V≤VCC≤16V VFB=2.7V, VCOMP=1.1V VFB=2.3V, VCOMP=5V VFB=2.3V, RL=15kΩ to ground VFB=2.7V, RL=15kΩ to VREF 2.42 65 0.7 60 2 -0.5 5 2.50 -0.3 90 1.0 70 6 -0.8 6 0.7 2.58 -2.0 V µA dB MHz dB mA mA V 1.1 V (Notes 3 & 4) VCOMP=5V (Note 3) 12V≤VCC≤25V (Note 3) VSense=0V TJ=25˚C (Note 2) 2.85 0.9 3.00 1.0 70 -2 150 3.15 1.1 -10 300 V/V V dB µA ns 1. Adjust Vcc above the start threshold before setting at 15V. 2.These parameters, although guaranteed, are not 100% tested in production. 3. Parameter measured at trip point of latch with VFB=0. 4. Gain defined as: A= ∆VCOMP ∆VSense ; 0 ≤ VSense ≤ 0.8V. 2 CS2841B Electrical Characteristics: continued PARAMETER TEST CONDITIONS MIN TYP MAX UNIT s Output Section Output Low Level Output High Level Rise Time Fall Time Output Leakage s Total Standby Current Start-Up Current Operating Supply Current ICC VFB=VSense=0V, RT=10kΩ, CT=3.3nF s Under-Voltage Lockout Section Start Threshold Min. Operating Voltage After Turn On 7.6 7.0 8.0 7.4 8.4 7.8 V V 0.5 11 1.0 17 mA mA ISINK=20mA ISINK=200mA ISOURCE=20mA ISOURCE=200mA TJ=25˚C, CL=1nF (Note 2) TJ=25˚C, CL=1nF (Note 2) Undervoltage Active, VOUT=0 13.0 12.0 0.1 1.5 13.5 13.5 50 50 -0.01 150 150 -10.00 0.4 2.2 V V V V ns ns µA Package Pin Description PACKAGE PIN # PIN SYMBOL FUNCTION 8L PDIP 1 2 3 4 5 14L SO Narrow 1 3 5 7 8 9 COMP VFB Sense OSC Gnd Pwr Gnd VOUT VCCPwr VCC VREF NC Error amp output, used to compensate error amplifier Error amp inverting input Noninverting input to Current Sense Comparator Oscillator timing network with Capacitor to Ground, resistor to VREF Ground Output driver Ground Output drive pin Output driver positive supply Positive power supply Output of 5V internal reference No Connection 6 10 11 7 8 12 14 2,4,6,13 3 CS2841B Typical Performance Characteristics: Oscillator Frequency vs CT 100 900 90 800 80 DUTY CYCLE (%) 70 60 50 40 30 20 Oscillator Duty Cycle vs RT RT =680Ω 700 FREQ. (kHz) 600 500 RT =1.5kΩ 400 300 200 100 RT =10kΩ 10 .0005 .001 .002 .003 .005 .01 .02 .03 .04 .05 100 200 300 400 500 700 1k 2k 3k 4k 5k 7k 10k CT (µF) RT (Ω) Test Circuit V REF RT 2N2222 100k Ω 4.7k Ω 1k Ω Error Amp Adjust 4.7k Ω 5k Ω A COMP V REF 0.1 µ F V CC V FB V CC 0.1 µ F 1k Ω 1W Sense Adjust Sense V OUT VO OSC Gnd Gnd CT Circuit Description Undervoltage Lockout V CC ON/OFF Command to reset of IC During Undervoltage Lockout (Figure 1), the output driver is biased to a high impedance state. The output should be shunted to ground with a resistor to prevent output leakage current from activating the power switch. V ON = 8 .0V V OFF = 7.4V PWM Waveform To generate the PWM waveform, the control voltage from the error amplifier is compared to a current sense signal which represents the peak output inductor current (Figure 2). An increase in VCC causes the inductor current slope to increase, thus reducing the duty cycle. This is an inherent feed-forward characteristic of current mode control, since the control voltage does not have to change during changes of input supply voltage. When the power supply sees a sudden large output current increase, the control voltage will increase allowing the duty cycle to momentarily increase. Since the duty cycle tends to exceed the maximum allowed to prevent trans4 I CC