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| CS2844/3845 SERIES CS2844/CS3844 CS2845/CS3845 Current Mode PWM Control Circuit with 50% Max Duty Cycle Description The CS3844/45 provides all the necessary features to implement off-line fixed frequency current-mode control with a minimum number of external components. The CS3844 family incorporates a new precision temperature-controlled oscillator to minimize variations in frequency. An internal toggle flip-flop, which blanks the output every other clock cycle, limits the duty-cycle range to less than 50%. An undervoltage lockout ensures that VREF is stabilized before the output stage is enabled. In the CS2844/CS3844 turn on occurs at 16V and turn off at 10V. In the CS2845/CS3845 turn on is at 8.4V and turn off at 7.6V. Other features include low start-up current, pulse-by-pulse current limiting, and a high-current totem pole output for driving capacitive loads, such as gate of a power MOSFET. The output is low in the off state, consistent with N-channel devices. Features s Optimized for Offline Control s Temp. Compensated Oscillator s 50% Max Duty-cycle Clamp s VREF Stabilized before Output Stage is Enabled s Low Start-up Current s Pulse-by-pulse Current Limiting s Improved Undervoltage Lockout s Double Pulse Suppression s 1% Trimmed Bandgap Ref. s High Current Totem Pole Output Absolute Maximum Ratings Supply Voltage (ICC<30mA).........................................................................Self Limiting Supply Voltage (Low Impedance Source) .................................................................30V Output Current..............................................................................................................1A Output Energy (Capacitive Load) ................................................................................5J Analog Inputs (VFB, VSENSE) .........................................................................-0.3V to 5.5V Error Amp Output Sink Current .............................................................................10mA Package Options 8 Lead PDIP & SO Narrow COMP VFB Sense OSC 1 2 3 4 8 7 6 5 Lead Temperature Soldering Wave Solder (through hole styles only) ...................10 sec. max, 260C peak Reflow (SMD styles only) ....................60 sec. max above 183C, 230C peak Block Diagram VREF VCC VOUT Gnd 14 Lead SO Narrow V CC V CC Undervoltage Lock-out COMP 1 14 13 12 11 10 9 8 VREF NC VCC VCC Pwr VOUT Gnd Pwr Gnd V CC Pwr NC 2 VFB 3 34V Gnd 16V/10V (8.4V/7.6V) V FB Error Amplifier + OSC 2.50V Set/ 5.0 Volt Reset Reference Internal Bias R V REF Undervoltage Lockout Toggle Flip-Flop V REF NC 4 Sense 5 NC 6 OSC 7 COMP 16 Lead SO Wide NC 1 NC 2 16 15 14 13 12 11 10 9 NC VREF VCC VCCPwr VO Gnd Pwr Gnd NC R NOR V OUT COMP 3 VFB 4 Oscillator 2R R Sense 1V S Pwr Gnd R Current PWM Sensing Latch Comparator SENSE 5 OSC 6 NC 7 NC 8 ( ) indicates CS-2845/3845 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. 3/17/99 1 A (R) Company CS2844/3845 SERIES Electrical Characteristics: -25 TA 85C for CS2844/2845, 0 TA 70C for CS3844/3845. VCC = 15V (Note 1); RT = 10k, CT = 3.3nF for sawtooth mode., unless otherwise stated. CS2844/CS2845 MIN TYP MAX CS3844/CS3845 MIN TYP MAX UNITS PARAMETER TEST CONDITIONS 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 Voltage Stability Temperature Stability Amplitude 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 s Output Section Output Low Level Output High Level Rise Time Fall Time ISINK=20mA ISINK=200mA ISOURCE=20mA ISOURCE=200mA TJ=25C, CL=1nF (Note 2) TJ=25C, CL=1nF (Note 2) 13.0 12.0 0.1 1.5 13.5 13.5 50 50 150 150 0.4 2.2 13.0 12.0 0.1 1.5 13.5 13.5 50 50 150 150 0.4 2.2 V V V V ns ns (Notes 3 & 4) VCOMP=5V (Note 3) 12VCC25V (Note 3) VSense=0V TJ=25C (Note 2) 2.85 0.9 3.00 1.0 70 -2 150 -10 300 3.15 1.1 2.85 0.9 3.00 1.0 70 -2 150 -10 300 3.15 V/V 1.1 V dB A ns VCOMP=2.5V VFB=0V 2VOUT4V (Note 2) 12VCC25V VFB=2.7V, VCOMP=1.1V VFB=2.3V, VCOMP=5V VFB=2.3V, RL=15k to Gnd VFB=2.7V, RL=15k to VREF 65 0.7 60 2 -0.5 5 2.45 2.50 -0.3 90 1.0 70 6 -0.8 6 0.7 1.1 2.55 -1.0 65 0.7 60 2 -0.5 5 2.42 2.50 -0.3 90 1.0 70 6 -0.8 6 0.7 1.1 2.58 V -2.0 A dB MHz dB mA mA V V Sawtooth Mode, TJ=25C 12VCC25V Sawtooth Mode TMINTATMAX (Note 2) VOSC (peak to peak) 47 52 0.2 5 1.7 57 1.0 47 52 0.2 5 1.7 57 1.0 kHz % % V TJ=25C, IREF=1mA 12VCC25V 1IREF20mA (Note 2) Line, Load, Temp. (Note 2) 10Hz f10kHz, TJ=25C (Note 2) TA=125C, 1000 Hrs. (Note 2) TA=25C -30 4.90 50 5 -100 25 -180 -30 4.95 5.00 6 6 0.2 5.05 20 25 0.4 5.10 4.82 50 5 -100 25 4.90 5.00 6 6 0.2 5.10 V 20 25 0.4 mV mV mV/C V mV -180 mA 5.18 V 2 CS2844/3845 SERIES Electrical Characteristics: -25TA85C for CS2844/2845, 0TA70C for CS3844/3845. VCC=15V (Note 1); RT=10k, CT=3.3nF for sawtooth mode., unless otherwise stated. PARAMETER TEST CONDITIONS CS2844/CS2845 MIN TYP MAX CS3844/CS3845 MIN TYP MAX UNITS s Total Standby Current Start-Up Current Operating Supply Current VCC Zener Voltage s PWM Section Maximum Duty Cycle Minimum Duty Cycle CS2844 TYP MAX 0.5 VFB=VSense=0V RT=10k, CT=3.3nF ICC=25mA 11 34 1.0 17 0.5 11 34 1.0 17 mA mA V 46 48 50 0 46 48 50 0 % % PARAMETER TEST CONDITIONS MIN MIN CS3844 TYP MAX CS2845/CS3845 MIN TYP MAX UNITS s Under-Voltage Lockout Section Start Threshold Min. Operating Voltage Notes: 15 After Turn On 9 16 10 17 11 14.5 8.5 16 10 17.5 11.5 7.8 7.0 8.4 7.6 9.0 8.2 V V 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. Package Pin Description PACKAGE PIN # PIN SYMBOL FUNCTION 8L PDIP/SO 1 2 3 4 5 14L SO Narrow 1 3 5 7 9 8 16L SO Wide 3 4 5 6 11 10 12 13 14 15 1,2,7,8,9,16 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 CS2844/3845 SERIES Test Circuit Open Loop Laboratory Test Fixture V REF RT 2N2222 100k 4.7k 1k Error Amp Adjust 4.7k 5k A COMP V REF 0.1F V CC V FB V CC 0.1F 1k 1W Sense Adjust Sense V OUT V OUT OSC Gnd Gnd CT Circuit Description Undervoltage Lockout During Undervoltage Lockout (Figure 1), the output driver is biased to sink minor amounts of current. The output should be shunted to ground with a resistor to prevent activating the power switch with extraneous leakage currents. 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 transformer saturation in some power supplies, the internal oscillator waveform provides the maximum duty cycle clamp as programmed by the selection of OSC components. V CC ON/OFF Command to reset of IC CSX844 V ON V OFF 16V 10V CSX845 8.4V 7.6V I CC <15mA <1mA V ON V OFF V CC Figure 1: Startup voltage for CSX844 and CSX845. 4 CS2844/3845 SERIES Circuit Description: continued Setting the Oscillator VOSC OSC RESET Toggle F/F Output EA Output Switch Current VCC The times Tc and Td can be determined as follows: t c = RTCT ln t d = RTCT ln ( ( VREF - Vlower VREF - Vupper ) ) VREF - IdRT - Vlower VREF - IdRT - Vupper IO Substituting in typical values for the parameters in the above formulas: VREF = 5.0V, Vupper = 2.7V, Vlower = 1.0V, Id = 8.3mA, then tc 0.5534RTCT td = RTCT ln VO Figure 2: Timing Diagram ( 2.3 - 0.0083 RT 4.0 - 0.0083 RT ) For better accuracy RT should be 10k. Vupper Vlower ton tC ton = tC toff = tC+2td Figure 3: Duty Cycle parameters. Grounding toff td High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected close to Gnd in a single point ground. The transistor and 5k potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to Sense. 5 CS2844/3845 SERIES Package Specification PACKAGE DIMENSIONS IN mm (INCHES) PACKAGE THERMAL DATA D Lead Count 8 Lead PDIP 8 Lead SO Narrow 14L SO Narrow 16L SO Wide Metric Max Min 10.16 9.02 5.00 4.80 8.75 8.55 10.50 10.10 English Max Min .400 .355 .197 .189 .344 .337 .413 .398 Thermal Data RJC typ RJA typ 8L 8L SO 14 L SO 16L SO PDIP Narrow Narrow Wide 52 45 30 23 C/W 100 165 125 105 C/W Plastic DIP (N); 300 mil wide Surface Mount Narrow Body (D); 150 mil wide 7.11 (.280) 6.10 (.240) 4.00 (.157) 3.80 (.150) 6.20 (.244) 5.80 (.228) 8.26 (.325) 7.62 (.300) 3.68 (.145) 2.92 (.115) 1.77 (.070) 1.14 (.045) 2.54 (.100) BSC 0.51 (.020) 0.33 (.013) 1.27 (.050) BSC 1.75 (.069) MAX .356 (.014) .203 (.008) 0.39 (.015) MIN. .558 (.022) .356 (.014) REF: JEDEC MS-001 D Some 8 and 16 lead packages may have 1/2 lead at the end of the package. All specs are the same. 1.57 (.062) 1.37 (.054) 1.27 (.050) 0.40 (.016) 0.25 (.010) 0.19 (.008) D REF: JEDEC MS-012 0.25 (0.10) 0.10 (.004) Ordering Information Part Number 0C to -25C 70C to 85C CS2844LN8 * CS2844LD14 * CS2844LDR14 * CS2844LDW16 * CS2844LDWR16 * CS2845LN8 * CS2845LDW16 * CS2845LDWR16 * CS3844GN8 * CS3844GD8 * CS3844GDR8 * CS3844GD14 * CS3844GDR14 * CS3844GDW16 * CS3844GDWR16 * CS3845GN8 * CS3845GD8 * CS3845GDR8 * CS3845GD14 * CS3845GDR14 * CS3845GDW16 * CS3845GDWR16 * Rev. 3/17/99 Description 8L PDIP 14L SO 14L SO (Tape & Reel) 16L SO Wide 16L SO Wide (Tape & Reel) 8L PDIP 16L SO Wide 16L SO Wide (Tape & Reel) 8L PDIP 8L SO 8L SO (Tape & Reel) 14L SO 14L SO (Tape & Reel) 16L SO Wide 16L SO Wide (Tape & Reel) 8L PDIP 8L SO 8L SO (Tape & Reel) 14L SO 14L SO (Tape & Reel) 16L SO Wide 16L SO Wide (Tape & Reel) 6 Surface Mount Wide Body (DW); 300 mil wide 7.60 (.299) 7.40 (.291) 10.65 (.419) 10.00 (.394) 0.51 (.020) 0.33 (.013) 1.27 (.050) BSC 2.49 (.098) 2.24 (.088) 2.65 (.104) 2.35 (.093) 1.27 (.050) 0.40 (.016) REF: JEDEC MS-013 0.32 (.013) 0.23 (.009) D 0.30 (.012) 0.10 (.004) Cherry Semiconductor Corporation reserves the right to make changes to the specifications without notice. Please contact Cherry Semiconductor Corporation for the latest available information. (c) 1999 Cherry Semiconductor Corporation |
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