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• Low Start-Up Current (<0.5 mA)• Trimmed Oscillator Discharge Current• Current Mode Operation to 500 kHz• Automatic Feed-Forward Compensation• Latching PWM for Cycle-by-Cycle Current
The TL284xB and TL384xB series of control integrated circuits provide the features that are necessary toimplement off-line or dc-to-dc fixed-frequency current-mode control schemes, with a minimum number ofexternal components. Internally implemented circuits include an undervoltage lockout (UVLO) and a precisionreference that is trimmed for accuracy at the error amplifier input. Other internal circuits include logic to ensurelatched operation, a pulse-width modulation (PWM) comparator that also provides current-limit control, and atotem-pole output stage designed to source or sink high-peak current. The output stage, suitable for drivingN-channel MOSFETs, is low when it is in the off state.
The TL284xB and TL384xB series are pin compatible with the standard TL284x and TL384x with the followingimprovements. The start-up current is specified to be 0.5 mA (max), while the oscillator discharge current istrimmed to 8.3 mA (typ). In addition, during undervoltage lockout conditions, the output has a maximumsaturation voltage of 1.2 V while sinking 10 mA (VCC = 5 V).
Major differences between members of these series are the UVLO thresholds and maximum duty-cycle ranges.Typical UVLO thresholds of 16 V (on) and 10 V (off) on the TLx842B and TLx844B devices make them ideallysuited to off-line applications. The corresponding typical thresholds for the TLx843B and TLx845B devices are8.4 V (on) and 7.6 V (off). The TLx842B and TLx843B devices can operate to duty cycles approaching 100%. Aduty-cycle range of 0% to 50% is obtained by the TLx844B and TLx845B by the addition of an internal toggleflip-flop, which blanks the output off every other clock cycle.The TL284xB-series devices are characterized foroperation from –40°C to 85°C. The TL384xB-series devices are characterized for operation from 0°C to 70°C.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of TexasInstruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
(1) Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratingsonly, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operatingconditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) All voltages are with respect to the device GND terminal.(3) Maximum power dissipation is a function of TJ(max), θJA, and TA. The maximum allowable power dissipation at any allowable ambient
temperature is PD = (TJ(max) – TA)/θJA. Operating at the absolute maximum TJ of 150°C can impact reliability.(4) The package thermal impedance is calculated in accordance with JESD 51-7.
MIN NOM MAX UNIT
VCC 30VCC Supply voltage V
VC (1) 30
RT/CT 0 5.5VI Input voltage V
VFB and ISENSE 0 5.5
OUTPUT 0 30VO Output voltage V
POWER GROUND (1) –0.1 1
ICC Supply current, externally limited 25 mA
IO Average output current 200 mA
IO(ref) Reference output current –20 mA
fosc Oscillator frequency 100 500 kHz
TL284xB –40 85TJ Operating free-air temperature °C
TL384xB 0 70
(1) The recommended voltages for VC and POWER GROUND apply only to the 14-pin D package.
Voltage stability VCC = 12 V to 25 V 0.2 1 0.2 1 %
Temperature stability 5 5 %
Amplitude Peak to peak 1.7 1.7 V
TJ = 25°C, RT/CT = 2 V 7.8 8.3 8.8 7.8 8.3 8.8Discharge current mA
RT/CT = 2 V 7.5 8.8 7.6 8.8
(1) Output frequency equals oscillator frequency for the TL3842B and TL3843B. Output frequency is one-half the oscillator frequency for theTL3844B and TL3845B.
(2) Adjust VCC above the start threshold before setting it to 15 V.(3) All typical values are at TJ = 25°C.
Supply-voltage rejection VCC = 12 V to 25 V 70 70 dBratio (3)
Input bias current –2 –10 –2 –10 μA
Delay time to output VFB = 0 V to 2 V 150 300 150 300 ns
(1) Adjust VCC above the start threshold before setting it to 15 V.(2) All typical values are at TJ = 25°C.(3) Measured at the trip point of the latch, with VFB at 0 V.(4) Measured between ISENSE and COMP, with the input changing from 0 V to 0.8 V.
TL284xB, TL384xBHIGH-PERFORMANCE CURRENT-MODE PWM CONTROLLERSSLVS610B–AUGUST 2006–REVISED JULY 2007
APPLICATION INFORMATION (continued)
In the open-loop laboratory test fixture (see Figure 4), high peak currents associated with loads necessitatecareful grounding techniques. Timing and bypass capacitors should be connected close to the GND terminal in asingle-point ground. The transistor and 5-kΩ potentiometer sample the oscillator waveform and apply anadjustable ramp to the ISENSE terminal.
The PWM controller (see Figure 5) can be shut down by two methods: either raise the voltage at ISENSE above1 V or pull the COMP terminal below a voltage two diode drops above ground. Either method causes the outputof the PWM comparator to be high (refer to block diagram). The PWM latch is reset dominant so that the outputremains low until the next clock cycle after the shutdown condition at the COMP or ISENSE terminal is removed.In one example, an externally latched shutdown can be accomplished by adding an SCR that resets by cyclingVCC below the lower UVLO threshold. At this point, the reference turns off, allowing the SCR to reset.
Figure 5. Shutdown Techniques
A fraction of the oscillator ramp can be summed resistively with the current-sense signal to provide slopecompensation for converters requiring duty cycles over 50% (see Figure 6). Note that capacitor C forms a filterwith R2 to suppress the leading-edge switch spikes.
TL3844BD-8 ACTIVE SOIC D 8 75 Green (RoHS& no Sb/Br)
CU NIPDAU Level-1-260C-UNLIM 0 to 70 3844B
TL3844BDR ACTIVE SOIC D 14 2500 Green (RoHS& no Sb/Br)
CU NIPDAU Level-1-260C-UNLIM 0 to 70 TL3844B
TL3844BDR-8 ACTIVE SOIC D 8 2500 Green (RoHS& no Sb/Br)
CU NIPDAU Level-1-260C-UNLIM 0 to 70 3844B
TL3844BP ACTIVE PDIP P 8 50 Pb-Free(RoHS)
CU NIPDAU N / A for Pkg Type 0 to 70 TL3844BP
TL3844BPE4 ACTIVE PDIP P 8 50 Pb-Free(RoHS)
CU NIPDAU N / A for Pkg Type 0 to 70 TL3844BP
TL3845BD ACTIVE SOIC D 14 50 Green (RoHS& no Sb/Br)
CU NIPDAU Level-1-260C-UNLIM 0 to 70 TL3845B
TL3845BD-8 ACTIVE SOIC D 8 75 Green (RoHS& no Sb/Br)
CU NIPDAU Level-1-260C-UNLIM 0 to 70 3845B
TL3845BDG4-8 ACTIVE SOIC D 8 75 Green (RoHS& no Sb/Br)
CU NIPDAU Level-1-260C-UNLIM 0 to 70 3845B
TL3845BDR ACTIVE SOIC D 14 2500 Green (RoHS& no Sb/Br)
CU NIPDAU Level-1-260C-UNLIM 0 to 70 TL3845B
TL3845BDR-8 ACTIVE SOIC D 8 2500 Green (RoHS& no Sb/Br)
CU NIPDAU Level-1-260C-UNLIM 0 to 70 3845B
TL3845BP ACTIVE PDIP P 8 50 Pb-Free(RoHS)
CU NIPDAU N / A for Pkg Type 0 to 70 TL3845BP
(1) The marketing status values are defined as follows:ACTIVE: Product device recommended for new designs.LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.PREVIEW: Device has been announced but is not in production. Samples may or may not be available.OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availabilityinformation and additional product content details.TBD: The Pb-Free/Green conversion plan has not been defined.Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement thatlead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used betweenthe die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weightin homogeneous material)
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuationof the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finishvalue exceeds the maximum column width.
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In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
OTHER QUALIFIED VERSIONS OF TL2843B :
• Automotive: TL2843B-Q1
NOTE: Qualified Version Definitions:
• Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects
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