CS3842B

CS3842B ONSEMI | Alldatasheet

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Technical content

Features

I Very low Start Up Current (300µA typ) I Optimized Off-line Control I Internally Trimmed, Temperature Compensated Oscillator I Maximum Duty-cycle Clamp I V REF stabilization before Output Enable I Pulse-by-pulse Current Limiting I Improved Undervoltage Lockout I Double Pulse Suppression I 1% Trimmed Bandgap Reference I High Current Totem Pole Output Package Options CS3842B/3843B Off-Line Current Mode PWM Control Circuit with Very Low Start Up Current CS3842B/CS3843B

Description

8 Lead PDIP & SO Narrow

December, 2001 - Rev. 4 ON Semiconductor

2000 South County Trail, East Greenwich, RI 02818

Tel: (401)885–3600 Fax: (401)885–5786 N. American Technical Support: 800-282-9855 Web Site: www.cherry–semi.com ARCHIVE DEVICE NOT RECOMMENDED FOR NEW DESIGN The CS384XB provides all the neces- sary features to implement off-line fixed frequency current-mode control with a minimum number of external components. The family has been opti- mized for very low start up current (300µA, typ). The CS384XB family incorporates a precision temperature-controlled oscil- lator with an internally trimmed dis- charge current to minimize variations in frequency. A precision duty-cycle clamp eliminates the need for an exter- nal oscillator when a 50% duty-cycle is used. Duty-cycles of almost 100% are possible. On board logic ensures that VREF is stabilized before the output stage is enabled. Ion-implant resistors provide tighter control of undervoltage lockout. Other features include pulse-by-pulse current limiting, and a high-current totem pole output for driving capaci- tive loads, such as the gate of a power MOSFET. The output is LOW in the off state, consistent with N-channel devices. These ICs are available in 8 and 14 lead surface mount (SO) and 8 lead PDIP packages. Analog Inputs (V Lead Temperature Soldering V CC Gnd OSC V FB COMP Sense V REF V OUT Output Enable Reference Internal Bias NOR S R PWM Latch Current Sense Comparator Oscillator 1 VR 2 R V CError Amplifier 2.50V Set/ Reset Undervoltage Lock-out Circuit 34V ( ) Indicates CS-3843B 16V/10V (8.4V/7.6V) V CC Pwr Pwr Gnd REF

Electrical Characteristics: 0≤TA≤70°C, V CC=15V (Note 1); RT=680Ω , CT=.022µF for triangular mode, RT=10kΩ , CT=3.3nF for sawtooth mode (see Fig. 3), unless otherwise stated PARAMETER TEST CONDITIONS MIN TYP MAX UNITS CS3842B/3843B I Reference Section Output Voltage T J=25°C, I OUT=1mA 4.90 5.00 5.10 V Line Regulation 12 ≤VIN≤25V 6 20 mV Load Regulation 1 ≤IOUT≤20mA 6 25 mV Temperature Stability (Note 2) 0.2 0.4 mV /°C Total Output Variation Line, Load, Temperature (Note 2) 4.82 5.18 V Output Noise Voltage 10Hz ≤f≤10kHz, T J=25°C (Note 2) 50 µV Long Term Stability T A=125°C, 1kHrs. (Note 2) 5 25 mV Output Short Circuit T A=25°C -30 -100 -180 mA I Oscillator Section Initial Accuracy Sawtooth Mode (see Fig. 3), T J=25°C 47 52 57 kHz Triangular Mode (see Fig. 3), TJ=25°C 44 52 60 kHz Voltage Stability 12 ≤VCC≤25V 0.2 1.0 % Temp. Stability Sawtooth Mode T MIN≤TA≤TMAX (Note 2) 5 % Triangular Mode TMIN≤TA≤TMAX (Note 2) 8 % Amplitude Oscillator peak to peak 1.7 V Discharge Current T J=25°C 7.5 8.3 9.3 mA TMIN≤TA≤TMAX 7.2 9.5 mA I Error Amp Section Input Voltage V COMP=2.5V 2.42 2.50 2.58 V Input Bias Current -0.3 -2.0 µA A VOL 2≤VOUT≤4V 65 90 dB Unity Gain Bandwidth (Note 2) 0.7 1.0 MHz PSRR 12 ≤V CC≤25V 60 70 dB Output Sink Current V FB=2.7V, VOSC=1.1V 2 6 mA Output Source Current V FB=2.3V, VOSC=5V -0.5 -0.8 mA VOUT High V FB=2.3V, RL=15kΩ to ground 5 6 V VOUT Low V FB=2.7V, RL=15kΩ to VREF 0.7 1.1 V I Current Sense Section Gain (Notes 3 & 4) 2.85 3.00 3.15 V/V Maximum Input Signal V COMP=5V (Note 3) 0.9 1.0 1.1 V PSRR 12 ≤VCC≤25V (Note 3) 70 dB Input Bias Current -2 -10 µA Delay to Output T J=25°C (Note 2) 150 300 ns I Output Section Output Low Level I SINK=20mA 0.1 0.4 V ISINK=200mA 1.5 2.2 V Output High Level I SOURCE=20mA 13.0 13.5 V ISOURCE=200mA 12.0 13.5 V

Electrical Characteristics: continued PARAMETER TEST CONDITIONS MIN TYP MAX UNITS CS-3842B CS-3843B PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX UNITS Notes: 1. Adjust V CC 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 V FB=0. 4. Gain defined as: A = ; 0 ≤ VSense ≤ 0.8V. ∆VCOMP ∆VSense Package Pin Description PACKAGE PIN # PIN SYMBOL FUNCTION 8L PDIP/SO 14L SO Narrow 1 1 COMP Error amp output, used to compensate error amplifier 23 V FB Error amp inverting input 3 5 Sense Noninverting input to Current Sense Comparator 4 7 OSC Oscillator Timing Network with Capacitor to Ground, resistor to V REF 5 8 Gnd Ground

9 Pwr Gnd Output driver Ground

61 0 V OUT Output drive pin

11 V CCPwr Output driver positive supply

71 2V CC Positive power supply 81 4V REF Output of 5V internal reference 2,4,6,13 NC No Connection I Output Section: continued Rise Time T J=25°C, C L=1nF (Note 2) 50 150 ns Fall Time T J=25°C, C L=1nF (Note 2) 50 150 ns Output Leakage UVLO Active, V OUT=0 -0.01 -10.00 µA I Total Standby Current Start-Up Current 0.3 0.5 mA Operating Supply Current V FB=VSense=0V RT=10kΩ , CT=3.3nF 11 17 mA VCC Zener Voltage I CC=25mA 34 V I Under-Voltage Lockout Section Voltage

During Undervoltage Lockout (Figure 1), the output driv- er is biased to a high impedance state. VOUT should be shunted to ground with a resistor to prevent output leak- age current from activating the power switch. 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 V CC causes the inductor current slope to increase, thus reducing the duty cycle. This is an inherent feed-forward characteristic of current mode con- trol, since the control voltage does not have to change during changes of input supply voltage. When the power supply sees a sudden large output cur- rent increase, the control voltage will increase allowing the duty cycle to momentarily increase. Since the duty CS3842B/3843B Test Circuit V REF V CC V OUT 1kΩ 0.1µ F 0.1µ F V REF V CC V OUT Gnd V FB Sense OSC COMP 5kΩ 100k Ω 4.7kΩ 1kΩ ERROR AMP ADJUST 4.7kΩ Sense ADJUST R T 2N2222 C T Gnd A CS-3842B CS-3843B Circuit Description Typical Performance Characteristics: Oscillator Duty Cycle vs RTOscillator Frequency vs CT V CC ON/OFF Command to reset of IC V ON 16V 8.4V V OFF 10V 7.6V CS3842B CS3843B <0.5mA <15mA V ON V OFF ICC V CC Figure 1: Typical Undervoltage Characteristics 800 900 FREQ. (kHz) C T (µF) 700 600 500 400 300 200 100 .05 R T =1.5kΩ R T =680Ω R T =10kΩ 100 200 700 1k 2k 5k 7k 10k DUTY CYCLE (%) R T (Ω ) 4k3k500400300 100

D Lead Count Metric English Max Min Max Min 8 L PDIP 10.16 9.02 .400 .355 8 L SOIC Narrow 5.00 4.80 .197 .189 14L SOIC Narrow 8.75 8.55 .344 .337 Part Number Description CS3842BGN8 8L PDIP CS3842BGD8 8L SO Narrow CS3842BGDR8 8L SO Narrow (tape & reel) CS3842BGD14 14L SO Narrow CS3842BGDR14 14L SO Narrow (tape & reel) CS3843BGN8 8L PDIP CS3843BGD8 8L SO Narrow CS3843BGDR8 8L SO Narrow (tape & reel) CS3843BGD14 14L SO Narrow CS3843BGDR14 14L SO Narrow (tape & reel) Thermal Data 8 L 8L 14 L PDIP SO Narrow SO Narrow RΘ JC typ 52 45 30 °C/W RΘ JA typ 100 165 125 °C/W Package Specification PACKAGE DIMENSIONS IN mm (INCHES)

Ordering Information

ON Semiconductor and the ON Logo are trademarks of Semiconductor Components Industries, LLC (SCILLC). ON Semiconductor reserves the right to make changes without further notice to any products herein. For additional infor- mation and the latest available information, please contact your local ON Semiconductor representative. © Semiconductor Components Industries, LLC, 2000 ARCHIVE DEVICE NOT RECOMMENDED FOR NEW DESIGN Plastic DIP (N); 300 mil wide 0.39 (.015) MIN. 1.14 (.045) D Some 8 and 16 lead packages may have 1/2 lead at the end of the package. All specs are the same. .203 (.008) .356 (.014) REF: JEDEC MS-001 3.68 (.145) 2.92 (.115) 8.26 (.325) 7.62 (.300) 7.11 (.280) 6.10 (.240) .356 (.014) .558 (.022) Surface Mount Narrow Body (D); 150 mil wide 0.33 (.013) 6.20 (.244) 5.80 (.228) 4.00 (.157) 3.80 (.150) 1.57 (.062) 1.37 (.054) D 0.25 (0.10) 0.10 (.004) 1.75 (.069) MAX 1.27 (.050) 0.40 (.016) REF: JEDEC MS-012 0.25 (.010) 0.19 (.008)