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AX3842P / AX3842S
High Performance Current Mode Pwm Controlers
Description
The AX3842 Series is high performance fixed frequency current mode controllers. That is specifically designed for Off-Line and DC To DC converter applications offering the designer a costeffective solution with minimal external components. These integrated circuits feature a trimmed oscillator for precise duty cycle control. A temperature compensated reference, high gain error amplifier, current sensing compara-tor, and a high current totem pole output ideally suited for driving a power MOSFET. Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle-by-cycle current limiting, programmable output deadtime, and a latch for single pulse metering.
8-Lead Plastic DIP-8 Package Code: P •
8-Lead Plastic SO-8 Package Code: S
Features
• Trimmed Oscillator for Precise Frequency Control • Oscillator Frequency Guaranteed at 250 kHz • Current Mode Operation to 500 kHz • Automatic Feed Forward Compensation • Latching PWM for Cycle-By-Cycle Current Limiting • Internally Trimmed Reference with Undervoltage Lockout • High Current Totem Pole Output • Undervoltage Lockout with Hysteresis • Low Startup and Operating Current
Absolute Maximum Ratings
Symbol Vi Vi IO EO Parameter Supply Voltage (low impedance source) Supply Voltage (Ii<30mA) Output Current Output Energy (capacitive load) Analog Inputs (pin 2, 3) Error Amplifier Output Sink Current Ptot Tstg TJ TL Power Dissipation at Tamb≤25oC Storage Temperature Range Junction Operating Temperature Lead Temperature (soldering 10s) Value 30 Self Limiting ±1 5 -0.3 to 5.5 10 800 -65 to 150 -40 to 150 300 A uJ V mA mW
o o o
Unit V
C C C
Thermal Data
Symbol Rth j-amb Description Thermal Resistance Junction-ambient DIP-8 100 SO-8 150 Units
o
C/W
AVANTICS - AX3842 Series
Specification No.: 050308-FE0008
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Block Diagram
Vcc
7 34V
UVLO S/R 5V REF Internal Bias VREF Good Logic T 2R R S R 1V Current Sense Comparator 6 8 VREF 5V 50mA
Ground
5 2.50V
RT/CT
4
Error AMP. + -
OSC
Output
VFB COMP Current Sense
2 1 3
PWM Latch
Pin Connection (Top View)
Package Function Pin1: Compensation
8 7 6 5
Description This pin is the Error Amplifier output and is made available for loop compensation. This is the inverting input of the Error Amplifier. It’s normally connected to the switching power supply output through a resistor divider. A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction. 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. This pin is the combined control circuitry and power ground. This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced and sunk by this pin. This pin is the positive supply of the control IC. This is the reference output. It provides charging current for capacitor CT through resistor RT.
Pin2: Voltage Feedback
1
2
3
4
Pin3: Current Sense
DIP-8
8 7 6 5
Pin4: RT/CT Pin5: Ground
1
2
3
4
Pin6: Output Pin7: Vcc Pin8: Vref
SO-8
AVANTICS - AX3842 Series
Specification No.: 050308-FE0008
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Electrical Characteristics
Unless otherwise stated, specifications apply for 0≤Tamb≤70°C VCC=15V (Note 1); RT=680Ω, CT=0.022uF for triangular mode, RT=10k, CT=3.3nf for sawtooth mode
Symbol Reference Section VREF ∆VREF ∆VREF
Parameter Reference Output Voltage Line Regulation Load Regulation Total Output Variation
Test Conditions Tj=25°C,Io=1mA 12V≤Vin≤25V 1mA≤Io≤20mA
(Note 2)
Min. 4.90 -
Typ. 5 2.0 3.0 0.2 50 5 -100 52 52 0.2 5 0.5 1.7 8.3 2.50 -0.1 90 1.0 70 12 -1.0 6 0.7 3.0 1.0 70 -2.0 150
Max. 5.1 20 25 5.18 -180 57 60 1 9.3 9.5 2.58 -2.0 1.1 3.15 1.1 -10 300
Units V mV mV mV/°C V uV mV mA KHz KHz % % % V mA mA V uA dB MHz dB mA mA V V V/V V dB uA nS
∆VREF/∆T Temperature Stability eN ISC Output Noise Voltage Long Term Stability Output Short Current Oscillator Section fOSC ∆fOSC/∆V ∆fOSC/∆T VOSC Idischg Frequency Frequency Change with Volt. Frequency Change with Temp. Oscillator Voltage Swing Discharge Current (VOSC=2V)
Line, Load, Temp
(Note 2) (Note 2)
4.82 -30 47 46 7.8 7.2 2.42 65 0.7 60 2.0 -0.5 5 2.85
10Hz≤f≤10kHz,Tj=25°C Ta=25°C TJ=25°C Tlow≤TA≤Thigh 12V≤VCC≤25V Tlow≤TA≤Thigh TJ=25°C Peak to Peak TJ=25°C Tlow≤TA≤Thigh VO=2.5V VFB=5.0V 2≤VO≤4 V TJ=25°C (Note 2) 12V≤VCC≤25V
(Note 2)
Ta=125°C,1000Hrs (Note 2)
Error Amplifier Section V2 Ib AVOL BW PSRR IO VOUT-High VOUT-Low GV V3 SVR Ib Voltage Feedback Input Input Bias Current Open Loop Voltage Gain Unity Gain Bandwidth Power Supply Rejection Ratio Output Current Output Voltage Swing High State Output Voltage Swing Low State Current Sense Input Voltage Gain Maximum Input Signal Supply Voltage Rejection.