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CR6848
Novel Low Cost Green-Power PWM Controller
Features
Low Cost, PWM&PFM&CRM Low Start-up Current (about 10A) Low Operating Current (about 2mA) Current Mode Operation Under Voltage Lockout (UVLO) Built-in Synchronized Slope Compensation Programmable PWM Frequency Leading edge Blanking on Sense input Constant output power limiting for universal AC input Cycle-by-cycle current limiting Clamped gate output voltage 16.5V Over voltage protect 26.7V High-Voltage CMOS Process with ESD SOT-23-6L SOP-8 & DIP-8 Pb-Free Packaging Compatible with SG5701 & SG5848 & LD7535 &OB22632/63
Applications
Switching AC/DC Adaptor Battery Charger Open Frame Switching Power Supply 384X Replacement
General Description
The CR6848 is a highly integrated low cost current mode PWM controller, which is ideal for small power current mode of offline AC-DC fly-back converter applications. Making use of external resistors, the IC changes the operating frequency and automatically enters the PFM/CRM under light-load/zero-load conditions. This can minimize standby power consumption and achieve green-power functions. With a very low start-up current, the CR6848 could use a large value start-up resistor (1.5Mohm). Built-in synchronized slope compensation enhances the stability of the system and avoids sub-harmonic oscillation. Dynamic peak limiting circuit minimizes output power change caused by delay time of the system over a universal AC input range. Leading edge blanking circuit on current sense input could remove the signal glitch due to snubber circuit diode reverse recovery and thus greatly reduces the external component count and system cost in the design. Pulse-by-pulse current limiting ensures safe operation even during short-circuit. The CR6848 offers more protection like OVP (Over Voltage Protection) and OCP (Over current protection). The CR6848's output driver is clamped to maximum 16.5V to protect the power MOSFET. Excellent EMI performance is achieved soft switching control at the totem pole gate driver output. CR6848 is offered in SOT-23-6, SOP-8 and DIP-8 packages.
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CR6848
CR68XX Series
Part Number CR6848 PWM Frequency External Adjustable External Adjustable External Adjustable Package DIP-8 SOP8 SOT-23-6L DIP-8 SOP8 SOT-23-6L DIP-8 SOP8 SOT-23-6L Description PWM&PFM&CRM Current Mode Slope Compensation Leading-edge Blanking Gate Clamped Over-voltage Protection Over-current Protection Soft Drive. With All Functions of CR6848 Gate soft Clamped With All Functions of CR6850 Frequency jitter Soft start Sense Fault Protect OLP SCP OTP
CR6850 CR6851
TYPICAL APPLICATION
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CR6848
Pin Assignment
Pin Descriptions
Name GND FB RI SEN VDD GATE Description GND Pin Analog Input. Voltage feedback pin (same as the COMP pin in UC384X), This pin is to program the switching frequency. By connecting a resistor to ground to set the switching frequency. Current sense pin, connect to sense the MOSFET current. Supply voltage pin. Gate output to drive the external power MOSFET.
Block Diagram
Simplified Internal Circuit Architecture
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CR6848
Absolute Maximum Ratings
Symbol VDD IOVP VFB VSEN PD Parameter Supply voltage Pin Voltage VDD OVP maximal enter current Input Voltage to FB Pin Input Voltage to SEN Pin Power Dissipation ESD Capability, HBM Model ESD Capability, Machine Model 20 second Lead Temperature SOT-23-6L (Soldering) 10 second DIP-8 Storage Temperature Range Rating 40 20 -0.3 to 6V -0.3 to 6V 300 2000 200 220 ae ae ae 260 -55 to + 150 Unit V mA V V mW V V
TL
TSTG
RECOMMENDED OPERATION CONDITION
Symbol VDD RI TOA PO FPWM Parameter VDD Supply Voltage RI PIN Resistor Value Operation Ambient Temperature Output Power Frequency of PWM Min ~ Max 11~20 58~120 -20~85 0~60 48~100 Unit V K ohm ae W kHz
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CR6848
Electrical Characteristics (Ta=25C unless otherwise noted, VDD = 15V.)
Symbol Parameter Conditions Min. Typ. Max. Unit
Supply Voltage (VDD Pin) IST Startup Current VFB=0V ISS Operating Current VFB=3V VFB=Open VDDON VDDOFF VDCLAMP Turn-on Threshold Voltage Turn-off Threshold Voltage VDD Clamp Voltage IVDD=20mA 10 2.8 2.3 1.46 16.1 11.1 26.7 A mA mA mA V V V
Voltage Feedback (FB Pin) IFB VFB IPFM ICRM Short Circuit Current Open Loop Voltage Enter PFM, FB current Enter CRM, FB current VFB=0V VFB=Open 2.8 4.8 0.92 1.5 mA V mA mA
Current Sensing (SEN Pin) VTH_L VTH_H TPD RCS Minimum Voltage Lever Maximum Voltage Lever Delay to Output Input Impedance 0.83 0.87 1.0 300 50 1.05 V V ns K
Oscillator (RI Pin) FOSC FPFM DCMAX | FTEMP TBLANK Normal Frequency PFM Frequency Maximum Duty Cycle Frequency Temp. Stability Leading-Edge Blanking Time RI=100Kohm RI=100Kohm RI=100Kohm -30-85ae 53 58 11.6 75 5 300 63 KHz KHZ % % nS
GATE Drive Output (GATE Pin) VOL VOH TR TF VGCLAMP
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Output Low Level Output High Level Rising Time Falling Time Output Clamp Voltage
VDD=15V, IO=20mA VDD=15V, IO=20mA CL=1000pF CL=1000pF VDD=20V 8 450 130 16.5
1
V V ns ns V
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CR6848
TYPICAL CHARACTERISTICS
VDD startup Current VS Temperature
VDD startup Current VS Temperature
VDD (OFF) VS Temperature
VDD Operation Current VS Temperature
OVP VS Temperature
PWM frequency VS Temperature
Duty cycle VS Temperature FOSC VS FB Current
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CR6848
FOSC VS RI pin resistor
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CR6848
OPERATION DESCRIPTION Current Model
Compared to voltage model control, current model control has a current feedback loop. When the voltage of the sense resistor peak current of the primary winding reaches the internal setting value VTH, comparator reverse, register reset and power MOSFET cut-off. So that to detect and modulate the peak current cycle by cycle could control the output of the power supply. The current feedback has a good linear modulation rate and a fast input and output dynamic impact avoid the pole that the output filter inductance brings and the second class system descends to first class and so it widens the frequency range and optimizes overload protection and short circuit protection.
suggested operating frequency range of CR6848 is within 48KHz to 100KHz.
Green Power Operation
The power dissipation of switching mode power supply is very important in zero load or light load condition. The major dissipation result from conduction loss switching loss and consume of the control circuit. However, all of them related to the switching frequency. There are many difference topologies has been implemented in different chip. The basic operation theory of all these approaches intended to reduce the switching frequency under light-load or no-load condition. CR6848s green power function adapts PWM PFM and CRM combining modulation. When RI resistor is 100k, the PWM frequency is 58kHz in medium or heavy load operation. Through modifying the pulse width, CR6848 could control output voltage. The current of FB pin increases when the load is in light condition and the internal mode controller enters PFM&PWM when the feedback current is over 0.92mA. The operation frequency of oscillator is to descend gradually. The invariable frequency of oscillator is 11.6kHz when the feedback current is over 1.05mA. To decrease the standby consumption of the power supply , Chip-Rail introduces the Cycle Reset Mode technology If the feedback current were over 1.1mA, mode controller of CR6848 would reset internal register all the time and cut off the gate pin, while the output voltage is lower than the set value, it would set register, gate pin operating again. Although the frequency of the internal OSC is invariable, the register would reset some pulses so that the practical frequency is decreased at the gate pin.
Startup Current and Under Voltage Lockout
The startup current of CR6848 is set to be very low so that a large value startup resistor can therefore be used to minimize the power loss. For AC to DC adaptor with universal input range design, a 1.5 M, 1/8 W startup resistor and a 10uF/25V VDD hold capacitor could be used. The turn-on and turn-off threshold of the CR6848 is designed to 16.1V/11.1V. During startup, the hold-up capacitor must be charge to 16.1V through the startup resistor. The hysteresis is implemented to prevent the shutdown from the voltage dip during startup.
Internal Bias and OSC Operation
A resistor connected between RI pin and GND pin set the internal constant current source to charge or discharge the internal fixed cap. The charge time and discharge time determine the internal clock speed and the switching frequency. Increasing the resistance will reduce the value of the input current and reduce the switching frequency. The relationship between RI pin and PWM switching frequency follows the below equation within the RI allowed range.
FOSC =
5800 (kHz ) RI ( K)
CR6848 Green-Power Function
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For example, a 100k resistor RI could generate a 50uA constant current and a 58kHz PWM switching frequency. The
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CR6848
Internal Synchronized Compensation
Slop
Although there are more advantages of the current mode control than conventional voltage mode control, there are still several drawbacks of peak-sensing current-mode converter. Especially the open loop instability when it operates in higher than 50% of the duty-cycle. CR6848 is introduced an internal slope compensation adding voltage ramp to the current sense input voltage for PWM generation to solve this problem. It improves the close loop stability greatly at CCM, prevents the sub-harmonic oscillation and thus reduces the output ripple voltage.
primary wind inductance. V IN ranges from 85VAC to 264VAC. To guarantee the output power is a constant for universal input AC voltage, there is a dynamic peak limit circuit to compensate the system delay T that the system delay brings on.
Leading-edge Blanking (LEB)
Each time the power MOSFET is switched on, a turn-on spike will inevitably occur at the sense pin, which would disturb the internal signal from the sampling of the RSENSE. There is a 300n sec leading edge blanking time built in to avoid the effect of the turn-on spike and the power MOSFET cannot be switched off during this time. So that the conventional external RC filtering on sense input is no longer required.
VSLOP = 0.33 x
DUTY = 0.4389 x DUTY DUTYMAX
Current Sensing & Dynamic peak limiting
The current flowing by the power MOSFET comes in to being a voltage VSENSE on the sense pin cycle by cycle, which compares to the internal reference voltage, controls the reverse of the internal register, limits the peak current IMAX of the primary of the transformer. The energy E =
Over Voltage Protection (OVP)
There is a 26.7V over-voltage protection circuit in the CR6848 to improve the credibility and extend the life of the chip. The GATE is to shutdown immediately when the voltage of the VDD is over 26.7V and the voltage of VDD is to descend rapidly.
1 2 x L x I MAX 2
deposited by the transformer. So adjusting the RSENSE can set the Max output power of the power supple mode. The current flowing by the power MOSFET has an extra value
Gate Driver & Soft Clamped
CR6848' output designs a totem pole to drive a periphery power MOSFET. The dead time is introduced to minimize the transfixion current when the output is drove. The NMOS is shut off when the other NMOS is turned on. The clamp technology is introduced to protect the periphery power MOSFET from breaking down.
I =
V IN x TD due to the system delay T LP
that the current detected from the sense pin to power MOSFET cut off in the CR6848 (Among these, VIN is the primary winding voltage of the transformer and LP is the
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CR6848
PACKAGE DEMENSIONS DIP-8L
Dimensions
Symbol
A A1 A2 b b1 D E E1 e L eB
Millimeters Min.
0.381 3.175 3.302 1.524 0.457 9.017 9.271 7.620 6.223 6.350 2.540 2.921 8.509 0 3.302 9.017 7 3.810 9.525 15 0.115 0.335 0 6.477 0.245 10.160 0.355 3.429
Inches Max.
5.334 0.015 0.125 0.130 0.060 0.018 0.365 0.300 0.250 0.100 0.130 0.355 7 0.150 0.375 15 0.255 0.400 0.135
Typ.
Min.
Typ.
Max.
0.210
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CR6848
SOT-23-6L
Symbol A A1 B b C D e H L
Dimensions In Millimeters Min 0.700 0.000 1.397 0.300 2.591 2.692 0.838 0.080 0.300 Max 1.000 0.100 1.803 0.559 3.000 3.099 1.041 0.254 0.610
Dimensions In Inches Min 0.028 0.000 0.055 0.012 0.102 0.106 0.033 0.003 0.012 Max 0.039 0.004 0.071 0.022 0.118 0.122 0.041 0.010 0.024
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CR6848
SOP-8L
Dimensions DISCLAIMERS
Symbol
A A1 b c D E e F H L 5.791 0.406 0a 4.648 3.810 1.016 1.270 0.381X45 a
Min.
1.346 0.101
Millimeter Typ.
Max.
1.752 0.254
Min.
0.053 0.004
Inch Typ.
Max.
0.069 0.010
0.406 0.203 4.978 3.987 1.524 0.183 0.150 0.040
0.016 0.008 0.196 0.157 0.050 0.015X45 a 0.060
6.197 1.270 8a
0.228 0.016 0a
0.244 0.050 8a
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CR6848
REFERENCE CIRCUIT 1 CR6848 drives a periphery Power MOSFET. 5V/6A 30W Power Supply
Quantity
Part Number
C1 C2 C3 C4 C5 C7 C8 C6 C7 C8 BD1 D1 D2 D3 D4 T1 T2
Description
102/1000V 103/1000V 104 33uF/400V 223/1000V 103/1000V 102/100V 1000 uF/25V 104 KBL406 FR107 1N4007 Y2010D LED 20mH EI-22
Quantity
Part Number
F1 L1 R1 R2 R4 R5 R6
Description
0.25A 10uH 20R 1K 100K 100K/0.5W 47R 1.5M 0R51 20R 3.3K CR6848 PC817 TL431 2N60
1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1
1 1 1 2 1 1 1 1 1 1 2 1 1 1 1
R3
R7 R8 R9 R11 R12 U1 U2 U3 Q1
Notice: Q1 is a Power MOSFET
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CR6848
REFERENCE CIRCUIT 2 CR6848 drives a periphery Power BJT
5V/3A 15W Power Supply(c)
Quantity
Part Number
C1 C3 C4 C5 C6 C7 C8 C9 C10 C12 D1 D4 D6 D8 D9 D10 T1 T2 F1 C2
Description
104/400V 472 102 33uF/400V 10uF/50V 103/1000V 102/100V 223/1000V 220uF/16V 1.0uF/16V 1N4007 1N4148 18V SB560 FR107 20mH EI-22 0.25A
Quantity
Part Number
R2 R3 R4 R5 R6 R8 R9 R12 R13 R14 U1 U2 U3 U4 Q1 Q2
Description
100K 100K/0.5W 1K 1.5M 220R/1W 220R 20K 20R 1R2/1W 20K 2K2 CR6848 PC817 TL431 LM358 13003 9013
2 1 1 1 1 1 1 1 2 1 5 2 1 1 2 1 1 1
1 1 1 1 2 1 1 2 1 1 1 1 1 1 1 1 1
R7
R10 R11
C11 D2 D5 D7 D3
D11
Notice: Q1 is a Power BJT
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