S3842

S3842 AUK | Alldatasheet

Document overview

• Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
• PDF pages: 8

Technical content

Features

• Optimized for off -line control • Current mode operation to 500 ㎑
• Low start up and operating current • Under voltage lockout with 6V hysteresis
• Pulse by pulse current limiting • Internally trimmed bandgap reference about 5V
• Enhanced load response characteristic • Automatic feed forward compensation

Ordering Information

Type NO. Marking Package Code S3842 S3842 SOP-8 O u t l i n e D i m e n s i o n s u n i t : mm SSeemmiiccoonndduuccttoorr PIN Connections 1. Output / Compensation 2. Voltage feedback. Input 3. Current sense Input 4. Rt/Ct 5. GND 6. Output 7. Vcc 8. Vref

A b s o l u t e M a x i m u m R a t i n g s Ta=25°C Characteristic Symbol Ratings Unit Supply voltage V cc 30 V Current Sense and Vfb Input V IN -0.3 to V cc V Total Power Supply and Zener Current I CC+ IZ 30 mA Output Sink of Source Current I o 1 A Error AMP Output Sink Current I eo 10 mA Operating Ambient Temperature T a 0 to 70 °C Storage Temperature Range T stg -65 to 150 °C Power Dissipation at Ta≤ 50°C Pd 1 W note) All voltages are with respect to PIN5, and current are positive into the specified pin. PIN Description PIN NO Function Description 1 Compensation Error amplifier output and is made available for loop compensation.

2 Voltage

Inverting input of error amplifier, normally connected to the switching power supply output through a resistor driver. 3 Current sense A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output.

4 R t/Ct

The oscillator frequency and maximum output duty cycle are programmed by connecting resistor Rt to Vref and capacitor Ct to ground. 5 Ground This pin is the combined control circuitry and power ground. 6 Output This output directly drives the ga te of a power MOSFET. Peak current up to 1.0A are sourced and sinked by this pin. 7 V CC This pin is the positive supply of the control IC. 8 Vref This is the reference output. it prov ides charging current for capacitor Ct through resistor Rt. Block Diagram

Electrical Characteristics

(Unless otherwise stated, these specifications apply for 0 ≤ Ta ≤ 70°C; VCC =15V(Note.4), RL =10 ㏀, CL =3.3nF) Characteristic Symbol Test Co ndition Min. Typ. Max. Unit 1. Reference Section Output Voltage Vref Ta=25°C, IO=1mA 4.90 5.00 5.10 V Line Regulation △Vref 12V ≤ VCC ≤ 25V - 6 20 mV Load Regulation △Vref 1mA ≤ IO ≤ 20mA - 6 25 mV Temperature Stability △VT /△VT (Note 1) - 0.2 0.4 mV/°C Output Noise Voltage V n 10Hz ≤ f ≤10KHz,Ta=25°C(Note 1) - 50 - uV Long Term Stability S Ta=125°C, 1000Hrs (Note 1) - 5 - mV Output Short Circuit I SC - -30 -100 -180 mA 2. Oscillator Section Initial Accuracy f SC Ta=25°C 47 52 57 KHz Voltage Stability △f /△V 12 ≤ Va ≤25V - 0.05 1.0 % Temperature Stability △f /△T Tmin ≤ Ta ≤ Tmax (Note 1) - 5 - % Amplitude V 4 V PIN4 Peak to Peak - 1.7 - V 3. Error Amp Section Input Voltage V 2 V PIN1=2.5V 2.42 2.50 2.58 V Input Bias Current I b - - -0.3 -2.0 ㎂ Open Loop Voltage Gain A VO1 2V ≤ VO ≤ 4V 65 90 - ㏈ Supply Voltage Rejection SVR 12V ≤ Va ≤ 25V 60 70 - ㏈ Output Sink Current I O V PIN2=2.7V, VPIN1=1.1V 2 6 - mA Output Source Current I O V PIN2=2.3V, VPIN1=5V -0.5 -0.8 - mA VOUT High V ch VPIN2=2.3V, RL=15 ㏀ to Ground 5 6 - V VOUT Low V c1 VPIN2=2.7V, RL=15 ㏀ Pin8 - 0.7 1.1 V 4. Current Sense Section Gain G V (Note 2 & 3) 2.8 3.0 3.2 V/V Maximum Input Signal V 3 V PIN 1=5V (Note 2) 0.9 1.0 1.1 V Supply Volt Rejection SVR 12 ≤ Va ≤ 25V (Note 2) - 70 - ㏈ Input Bias Current I b - - -2 -10 ㎂ 5.Output Section ISINK=20mA - 0.1 0.4 V Output Low Level V Ol ISINK=200mA - 1.5 2.2 V ISOURCE=20mA 13.0 13.5 - V Output High Level V Oh ISOURCE=200mA 12.0 13.5 - V Rise time t r Ta=25°C, Cl=1nF (Note 1) - 50 150 ns Fall time t f Ta=25°C, Cl=1nF (Note 1) - 50 150 ns

Electrical Characteristics(continued) Characteristic Symbol Test Co ndition Min. Typ. Max. Unit 6. Under-Voltage Lockout Section Start Threshold V th VPIN7 where VPIN8 ≥ 4.9V 14.5 16.0 17.5 V Min. Operation Voltage After Turn-On VCC(min) VPIN7 where VPIN8 ≤ 1V 8.5 10.0 11.5 V 7. PWM Section Maximum Duty Cycle DC max - 93 97 100 ns 8. Total Standby Section Start-Up Current I st V CC = 15V before turn on - 0.4 0.7 mA Operating Supply Current I CC VPIN2= VPIN3=0V - 11 20 mA Zener Voltage V Z I CC=25mA - 36 - V NOTE: 1.Thes parameters, although guaranteed.are not 100% tested in production 2.Parameter measured at trip piont of latch with V pin2= 0 3.Gain defined as : A = △VPIN1/△VPIN3 ; 0 ≤ VPIN3 ≤ 0.8V 4.Adjust V CC above the start threshold before setting at 15V Information in Using IC 1. Under voltage Lockout To prevent erratic output behavior which activating the power switch with extraneous leakage currents, during under voltage lockout. Output(pin6) should be shunted to ground with a bleeder resister. The Vcc comparator upper and lower threshold are 16V/10V . The large hysteresis and low start up currents makes it ideally suited in off-line converter application where efficient bootstrap start-up techniques are required. ON/ OFF COMMAND TO RESET OF IC Vcc V on-16V V off-10V Vcc Icc <17mA <1mA 10V 16V

1. Oscillator Waveforms and Maximum Duty Cycle The oscillator frequency is programmed by the values selected for the timing components Rt and Ct. Ct is charged from 5V , Vref, through resistor Rt to a p p r o x i m a t e l y 2 . 8 V a n d d i s c h a r g e d t o 1 . 2 V b y a n i n t e r n a l c u r r e n t s i n k . During the discharge of Ct, the oscillator generates an internal blanking pulse and the center input NOR gate high. T h i s m a k e s o u t p u t t o b e i n a l o w s t a t e a n d c o n t r o l t h e amount of output dead time. 3. Error AMP Configuration Error amp output(Pin1) is provided for external loop C o m p e n s a t i o n a n d e r r o r a m p c a n s o u r c e o r s i n k u p t o 0 . 5 m A . The non-inverting input is internally biased at 2.5V and is not pinned out. The converter output voltage is typically d i v i d e d d o w n a n d m o n i t o r e d b y t h e i n v e r t i n g i n p u t ( p i n 2 ) . 4. Current Sense Circuit A normal operating conditions occurs when the power supply ou tput is overloaded or if output voltage to 1.0V Therefore the maximum peak switch current is lpk(max)=1.0V/R s, and under the normal operating conditions the peak inductor current controlled by the voltage at pin1. S3842 Rt Ct LARGE Rt SMALL Ct SMALL Rt LARGE Ct Vpin4 INTERNAL CLOCK INTERNAL CLOCK Vpin4 COMP ERROR AMP GND CURRENT SENSE Rs R C R IV Iβ Ipeak = R(Vpin1 - 2Vbe) 3R x Rs 0.5mA 1Zf Zt 2.50V Vin COMP

1. Shutdown Techniques Shutdown of the S3842 can be accomplished by two methods; either raise pin3 above 1V or pull p i n 1 b e l o w a v o l t a g e t w o d i o d e s drops above ground. Either causes the output of the PWM method c o m p a r a t o r t o b e h i g h ( r e f e r t o block diagram). The PWM latch is reset dominant so that the output will remain low until the next clock cycle after the shutdown condition at pins 1 and/or 3 is removed. In one example, an externally latched shutdown may be accomplished by adding an SCR which turn off, allowing the SCR to reset. 6. Open Loop Test High peak currents associated with cap acitive leads necessitate careful groun ding techniques. Timing and bypass capacitors should be connected close to Pin5 in a single point ground. The transistor and 5 ㏀ potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to Pin3. 7. Slope Compensation A fraction of the oscillator ramp can be resistively s u m m e d w i t h t h e c u r r e n t s e n s e s i g n a l t o p r o v i d e s l o p e c o m p e n s a t i o n f o r c o n v e r t e r s r e q u i r i n g d u t y c y c l e o v e r 5 0 % . N o t e t h a t c a p a c i t o r C , f o r m s a f i l t e r w i t h R 2 to suppress the leading edge switch s p i k e s . 3ISENSE RT /CT V REF ISENSE RT CT C 0.1uF RSENSE S3842 V REF ISENSE TO CURRENT SENSE RESISTOR SHUT DOWN 4.7K 4.7K 5.00

1 COMP

ISENSE4.7K COMP Vcc OUTPUT GROUND ERROR AMP ADJUST 2N2222 RT 4.7K 1K 0.1uF 0.1uF 1K/1W RT /CT Vin Vcc OUTPUT 100K

Electrical Characteristic Curves %DT PERCENT OUTPUT DEAD-TIME OUTPUT DEAD-TIME vs. OSCILLATOR FREQUENCY fOSC OSCILLATOR FREQUENCY (KHz) 1.0 2.0 5.0 100 10K 20K 50K 100K 200K 500K 1.0M Vcc=15V Ta = 25 oC Ct=10nF 2.0nF 5.0nF 1.0nF 500pF 200pF 100pF RT TIMING RESISTOR (KΩ) TIMING RESISTOR vs. OSCILLATOR FREQUENCY fOSC OSCILLATOR FREQUENCY (KHz) 0.8 2.0 5.0 8.0 10K 20K 50K 100K 200K 500K 1.0M Vcc=15V Ta = 25 oC CT=10nF 2.0nF 5.0nF 1.0nF 500pF 200pF 100pF 10 100 1K 10K 100K 1M 10M FREQUENCY (Hz) VOLTAGE GAIN (dB) Error Amplifier Open-Loop Frequency Response PHASE (o) -135 -90 -45 -180 AV φ SATURATION VOLTAGE (V) Output Saturation Characteristics OUTPUT CURRENT SOURCE OR SINK (A) Vcc=15V Ta = 25 oC Ta=-55oC SINK SAT(VOL) SOURCE SAT(Vcc-VOH)

These AUK products are intended for usage in general electronic equipments(Office and communication equipment, measuring equipment, domestic electrification, etc.). Please make sure that you consult with us before you use these AUK products in equipm- ents which require high quality and/or reliabi lity, and in equipments which could have major impact to the welfare of human life(atomic energy control, airplane, spaceship, traffic signal, combustion central, all types of safety device, etc.). AUK cannot accept liability to any damage which may occur in case these AUK products were used in the mentioned equipments without prior consultation with AUK.