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OB2262 Current Mode PWM Controller
GENERAL DESCRIPTION
OB2262 is a highly integrated current mode PWM control IC optimized for high performance, low standby power and cost effective offline flyback converter applications in sub 30W range. PWM switching frequency at normal operation is externally programmable and trimmed to tight range. At no load or light load condition, the IC operates in extended `burst mode' to minimize switching loss. Lower standby power and higher conversion efficiency is thus achieved. www..com VDD low startup current and low operating current contribute to a reliable power on startup design with OB2262. A large value resistor could thus be used in the startup circuit to minimize the standby power. The internal slope compensation improves system large signal stability and reduces the possible subharmonic oscillation at high PWM duty cycle output. Leading-edge blanking on current sense(CS) input removes the signal glitch due to snubber circuit diode reverse recovery and thus greatly reduces the external component count and system cost in the design. OB2262 offers complete protection coverage with automatic self-recovery feature including Cycle-byCycle current limiting (OCP), over load protection (OLP), VDD over voltage clamp and under voltage lockout (UVLO). The Gate-drive output is clamped to maximum 18V to protect the power MOSFET. Excellent EMI performance is achieved soft switching control at the totem pole gate drive output. The tone energy at below 20KHZ is minimized in the design and audio noise is eliminated during operation. OB2262 is offered in SOT23-6, SOP-8 and DIP-8 packages.
FEATURES
Extended Burst Mode Control For Improved Efficiency and Minimum Standby Power Design Audio Noise Free Operation Programmable PWM Switching External Frequency Internal Synchronized Slope Compensation Low VDD Startup Current and Low Operating Current (1.4mA) Leading Edge Blanking on Current Sense Input Good Protection Coverage With Auto SelfRecovery o VDD Over Voltage Clamp and Under Voltage Lockout with Hysteresis (UVLO) o Gate Output Maximum Voltage Clamp (18V) o On-Bright Proprietary Line Input Compensated Cycle-by-Cycle Over-current Threshold Setting For Constant Output Power Limiting Over Universal Input Voltage Range. o Overload Protection (OLP).
APPLICATIONS
Offline AC/DC flyback converter for Battery Charger Power Adaptor Set-Top Box Power Supplies Open-frame SMPS
TYPICAL APPLICATION
EMI F i l te r
1
AC IN
4
2
+ + +
DC OUT
3
V DD
GATE RI
OB2262
S E NSE GND OB 43 1
FB
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OB2262 Current Mode PWM Controller
GENERAL INFORMATION
Pin Configuration The OB2262 is offered in SOT23-6, DIP8 and SOP8 packages, shown as below. Ordering Information Part Number OB2262MP OB2262AP OB2262CP
Description SOT23-6, Pb-free DIP8, Pb-free SOP8, Pb-free
Package Dissipation Rating RJA Package
(C/W)
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DIP8 SOP8 SOT23-6
90 150
200
Absolute Maximum Ratings Parameter Value VDD DC Supply Voltage 30 V VDD Zener Clamp VDD_Clamp+0.1V Note Voltage VDD DC Clamp Current 10 mA VFB Input Voltage -0.3 to 7V VSENSE Input Voltage to -0.3 to 7V Sense Pin VRI Input Voltage to RI Pin -0.3 to 7V Min/Max Operating -20 to 150 oC Junction Temperature TJ Min/Max Storage -55 to 160 oC Temperature Tstg Note: VDD_Clamp has a nominal value of 34V.
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied. Exposure to absolute maximum-rated conditions for extended periods may affect device reliability.
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OB2262 Current Mode PWM Controller
Marking Information
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TERMINAL ASSIGNMENTS
Pin Name GND FB RI SENSE VDD GATE I/O P I I I P O Description Ground Feedback input pin. The PWM duty cycle is determined by voltage level into this pin and the current-sense signal at Pin 6. Internal Oscillator frequency setting pin. A resistor connected between RI and GND sets the PWM frequency. Current sense input pin. Connected to MOSFET current sensing resistor node. Chip DC power supply pin. Totem-pole gate drive output for the power MOSFET.
RECOMMENDED OPERATING CONDITION
Symbol VDD RI TA Parameter VDD Supply Voltage RI Resistor Value Operating Ambient Temperature Min Max 10 to 30 100 -20 to 85 Unit V Kohm o C
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OB2262 Current Mode PWM Controller
BLOCK DIAGRAM
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OB2262 Current Mode PWM Controller
ELECTRICAL CHARACTERISTICS
(TA = 25OC if not otherwise noted) Symbol Parameter Supply Voltage (VDD) I_VDD_Stup VDD Start up Current I_VDD_Ops UVLO(ON) Operation Current Test Conditions VDD =12.5V, RI=100K Measure Leakage current into VDD VDD=16V, RI=100Kohm, VFB=3V 7.8 13 IVDD = 5 mA VFB /Vcs Short FB pin to GND and measure current VDD = 16V, RI=100Kohm Min Typ 3 1.4 8.8 14 34 2.0 4.8 1.2 0.75 3.7 35 VDD=18V, RI=100Kohm, FB=3V, CS=0 RI = 100 Kohm VDD = 16V, CS>VTH_OC, FB=3.3V FB=3.3V, RI=100 Kohm 6 75 9.8 15 Max 20 Unit uA mA V V V V/V V mA V V mSec Kohm %
VDD Under Voltage Lockout Enter www..com UVLO(OFF) VDD Under Voltage Lockout Exit (Recovery) VDD_Clamp VDD Zener Clamp Voltage Feedback Input Section(FB Pin) AVCS PWM Input Gain VFB_Open VFB Open Loop Voltage IFB_Short FB pin short circuit current VTH_0D Zero Duty Cycle FB Threshold Voltage VTH_PL Power Limiting FB Threshold Voltage TD_PL Power limiting Debounce Time ZFB_IN Input Impedance DC_MAX Maximum Duty Cycle
Current Sense Input(Sense Pin) T_blanking Leading edge blanking time ZSENSE_IN Input Impedance TD_OC Over Current Detection and Control Delay VTH_OC Over-Current Threshold Voltage or Equivalent maximum input voltage at SENSE Oscillator FOSC Normal Oscillation Frequency Frequency Temperature f_Temp Stability f_VDD RI_range V_RI_open Fosc_BM Frequency Voltage Stability Operating RI Range RI open load voltage Burst Mode Base Frequency
300 40 75 0.70 0.75 0.80
ns Kohm nSec V
RI = 100 Kohm VDD = 16V, RI=100Kohm, TA -20oC to 100 oC VDD = 12-25V, RI=100Kohm
60
65 5 5
70
KHZ % %
50 VDD = 16V, RI = 100Kohm
100 2 22
150
Kohm V KHZ
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OB2262 Current Mode PWM Controller
Gate Drive Output VOL Output Low Level VOH Output High Level V_Clamp Output Clamp Voltage Level T_r Output Rising Time T_f Output Falling Time VDD = 16V, Io = -20 mA VDD = 16V, Io = 20 mA VDD = 16V, CL = 1nf VDD = 16V, CL = 1nf 0.8 10 18 220 70 V V V nSec nSec
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CHARACTERIZATION PLOTS
VDD = 16V, RI = 100 Kohm, TA = 25oC condition applies if not otherwise noted.
VDD Startup Current vs. Voltage Ivdd_startup(uA ) 20
I_vdd_startup (uA)
5.0 4.6 4.2 3.8 3.4 3.0 -20
I_VDD_startup vs. Temp
15 10 5 0 0 2 4 6 8 10 12 14 16 VDD(V)
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10
40
70
100
130
Temp(C)
VDD UVLO and Ops Current 2 I(VDD) (mA) 1.6 1.2 0.8 0.4 0 0 5 10 15 VDD (V) 20 25 30
I(V D D ) (m A )
VDD Operation Current vs. Load(pF)
5 4 3 2 1 0 0
50KHz
65KHz
100KHz
500
Gate Load (pF)
1000
1500
2000
UVLO(ON) vs Temp
UVLO(OFF) vs Temp
14.5 14.4 14.3 14.2 14.1 14.0
9.0 UVLO(ON) (V)
UVLO(OFF) (V)
8.8 8.6 8.4 8.2 8.0
-20 10 40 70 100 130
-20
10
40
70
100
130
Temp(C)
Temp(C)
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Fosc(KHz) vs. RI(Kohm) 140 Fosc(K H z) 90 40 50 70 90 110 RI(Kohm) 130 150
Fosc (KHz) 66.5 66 65.5 65 64.5 64 63.5 -20 5
Fosc vs. Temp
115
65 www..com
30
55 80 Temp (C)
105
130
V th_O C (V )
1.2 1.1 1 0.9 0.8 0.7 0
Vth_OC(V) vs Duty_cycle(%)
10
20
30 40 50 Duty_cycle(%)
60
70
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OB2262 Current Mode PWM Controller
OPERATION DESCRIPTION
The OB2262 is a highly integrated PWM controller IC optimized for offline flyback converter applications in sub 30W power range. The extended burst mode control greatly reduces the standby power consumption and helps the design easily meet the international power conservation requirements. * Startup Current and Start up Control Startup current of OB2262 is designed to be very www..com low so that VDD could be charged up above UVLO threshold level and device starts up quickly. A large value startup resistor can therefore be used to minimize the power loss yet provides reliable startup in application. For AC/DC adaptor with universal input range design, a 2 M, 1/8 W startup resistor could be used together with a VDD capacitor to provide a fast startup and low power dissipation solution. * Operating Current The Operating current of OB2262 is low at 1.4mA. Good efficiency is achieved with OB2262 low operating current together with extended burst mode control features. * Extended Burst Mode Operation At zero load or light load condition, majority of the power dissipation in a switching mode power supply is from switching loss on the MOSFET transistor, the core loss of the transformer and the loss on the snubber circuit. The magnitude of power loss is in proportion to the number of switching events within a fixed period of time. Reducing switching events leads to the reduction on the power loss and thus conserves the energy. OB2262 self adjusts the switching mode according to the loading condition. At from no load to light/medium load condition, the FB input drops below burst mode threshold level. Device enters Burst Mode control. The Gate drive output switches only when VDD voltage drops below a preset level and FB input is active to output an on state. Otherwise the gate drive remains at off state to minimize the switching loss and reduces the standby power consumption to the greatest extend. The frequency control also eliminates the audio noise at any loading conditions. * Oscillator Operation A resistor connected between RI and GND sets the constant current source to charge/discharge the internal cap and thus the PWM oscillator frequency (c)On-Bright Electronics -9is determined. The relationship between RI and switching frequency follows the below equation within the specified RI in Kohm range at nominal loading operational condition.
FOSC =
6500 ( Khz ) RI ( Kohm)
* Current Sensing and Leading Edge Blanking Cycle-by-Cycle current limiting is offered in OB2262 current mode PWM control. The switch current is detected by a sense resistor into the sense pin. An internal leading edge blanking circuit chops off the sense voltage spike at initial MOSFET on state due to Snubber diode reverse recovery so that the external RC filtering on sense input is no longer required. The current limit comparator is disabled and thus cannot turn off the external MOSFET during the blanking period. PWM duty cycle is determined by the current sense input voltage and the FB input voltage. * Internal Synchronized Slope Compensation Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM generation. This greatly improves the close loop stability at CCM and prevents the sub-harmonic oscillation and thus reduces the output ripple voltage. * Gate Drive OB2262 Gate is connected to an external MOSFET gate for power switch control. Too weak the gate drive strength results in higher conduction and switch loss of MOSFET while too strong gate drive output compromises the EMI. A good tradeoff is achieved through the built-in totem pole gate design with right output strength and dead time control. The low idle loss and good EMI system design is easier to achieve with this dedicated control scheme. An internal 18V clamp is added for MOSFET gate protection at higher than expected VDD input. * Protection Controls Good power supply system reliability is achieved with its rich protection features including Cycle-byCycle current limiting (OCP), Over Load Protection (OLP) and over voltage clamp, Under Voltage Lockout on VDD (UVLO). With On-Bright Proprietary technology, the OCP threshold tracks PWM Duty cycles and is line voltage compensated to achieve constant output Confidential to Micro Bridge
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OB2262 Current Mode PWM Controller
power limit over the universal input voltage range with recommended reference design. At overload condition when FB input voltage exceeds power limit threshold value for more than TD_PL, control circuit reacts to shut down the output power MOSFET. Device restarts when VDD voltage drops below UVLO limit. VDD is supplied by transformer auxiliary winding output. It is clamped when VDD is higher than threshold value. The power MOSFET is shut down when VDD drops below UVLO limit and device enters power on start-up sequence thereafter.
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PACKAGE MECHANICAL DATA
SOT23-6
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OB2262 Current Mode PWM Controller
8-Pin Plastic DIP
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8-Pin Plastic SOP
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