RT8278 RICHTEK [Richtek Technology Corporation], RT8278 Datasheet
RT8278
Related parts for RT8278
RT8278 Summary of contents
Page 1
... Step-Down Converter General Description The RT8278 is a high voltage buck converter that can support an input voltage range from 4.5V to 24V with output current up to 2A. Current mode operation provides fast transient response and eases loop stabilization. The chip provides protection functions such as cycle-by- cycle current limiting and thermal shutdown protection. In shutdown mode, the regulator only draws 25μ ...
Page 2
... RT8278 Table 1. Recommended Component Selection for f V (V) R1 (kΩ) OUT 10 115 52.3 3.3 31.6 2.5 21.5 1.8 12.4 1.5 8.87 1.2 4.99 Functional Pin Description Pin No. Pin Name 1 BOOT 2 VIN GND 9 (Exposed Pad COMP www.richtek.com 2 R2 (kΩ) R (kΩ Bootstrap Power Pin ...
Page 3
... Function Block Diagram VIN Internal Regulator 1µ 10k - Shutdown 3V Comparator DS8278-02 March 2011 Oscillator V CC Foldback Control 0. Comparator Comparator 0. COMP RT Current Sense Slope Comp Amplifier + - Current 0. RT8278 V A BOOT SW GND www.richtek.com 3 ...
Page 4
... RT8278 Absolute Maximum Ratings V ---------------------------------------------------------------------------------------------------------------- IN SW --------------------------------------------------------------------------------------------------------------- −0. BOOT ----------------------------------------------------------------------------------------------------------- (V All Other Pins ------------------------------------------------------------------------------------------------- −0. Power Dissipation 25° SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------- 1.333W Package Thermal Resistance (Note 2) SOP-8 (Exposed Pad), θ --------------------------------------------------------------------------------- 75°C/W JA SOP-8 (Exposed Pad), θ -------------------------------------------------------------------------------- 28°C/W JC Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------ 260°C Junction Temperature ---------------------------------------------------------------------------------------- 150° ...
Page 5
... Note 4. The device is not guaranteed to function outside its operating conditions. DS8278-02 March 2011 Symbol Test Conditions 2V SHDN EN = 25° high effective thermal conductivity four-layer test board of A RT8278 Min Typ Max Unit 1 0.4 μ 0 μA -- ...
Page 6
... RT8278 Typical Operating Characteristics Efficiency vs. Output Current 100 0.0 0.4 0.8 Output Current (A) Output Voltage vs. Output Current 5.12 5.09 5.06 5.03 5.00 4.97 4.94 4.91 4.88 4.85 0.0 0.4 0.8 Output Current (A) Quiescent Current vs. Temperature 0.88 0.84 0.80 0.76 0.72 0.68 0.64 0.60 -50 - Temperature (°C) www.richtek.com 12V 19V 5V 2.2MHz OUT SW 1.2 1.6 2 19V 12V IN 1 ...
Page 7
... Output Ripple Voltage OUT Time (200ns/Div) Load Transient Response I OUT V = 12V 12V 2A 2A, f OUT OUT Time (100μs/Div) RT8278 = 2.2MHz 100 125 = 12V 3.3V OUT = 2A 2.2MHz SW = 3.3V = 3.3V OUT OUT = 2.2MHz = 2.2MHz SW S www.richtek.com 7 ...
Page 8
... RT8278 Power On from 12V 2A, f OUT (2V/Div) V OUT (1V/Div 12V (2A/Div) OUT I OUT Time (400μs/Div) www.richtek.com (2V/Div) = 3.3V, OUT = 2.2MHz S V OUT (1V/Div (2A/Div) = 3.3V, OUT = 12V 3.3V, IN OUT = 2A 2.2MHz 2.2MHz ...
Page 9
... Vout curve. Except the minimum on-time constraint, the limit of maximum duty also needs to be considered. In ideal case, the duty cycle of the RT8278 can be calculated by below equation, But in practical case it will be higher than the calculation result since all the components in a converter circuit are not ideal ...
Page 10
... RT input voltage. It can easily be solved by adding a voltage divider on the EN pin. The RT8278 will be enabled when the input voltage rises close to the nominal input voltage. Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and output voltage. The ripple current Δ ...
Page 11
... OUT , is determined by : OUT ⎡ ⎤ 1 ≤ Δ ESR OUT L ⎢ ⎥ 8fC ⎣ ⎦ OUT increases with input voltage. Multiple best, this ringing can couple to the output IN large enough to damage the IN RT8278 www.richtek.com 11 ...
Page 12
... OUT or ringing to indicate any stability problem. Compensation Parameters The switching frequency of RT8278 can be programmed from free running frequency to 3MHz. Table 1 only lists the recommended compensation parameters for 2.2MHz switching frequency. Optimized compensation parameters for other switching frequency can also be determined through below procedures ...
Page 13
... T is the maximum junction temperature, T J(MAX) the ambient temperature, and θ JA thermal resistance. For recommended operating condition specifications of the RT8278, the maximum junction temperature is 125°C and T is the ambient temperature. The junction to ambient A thermal resistance, θ layout dependent. For SOP-8 JA (Exposed Pad) packages, the thermal resistance, θ ...
Page 14
... Ambient Temperature (°C) Figure 8. Derating Curves for RT8278 Package capacitors. Keep the loop area small. Place the feedback components near the RT8278. Connect all analog grounds to a common node and then connect the common node to ground behind the output capacitors. ...
Page 15
... TAIYO YUDEN C IN MURATA C OUT TDK C OUT MURATA C OUT TDK C OUT DS8278-02 March 2011 Table 4. Suggested Capacitors for C Part No. GRM31CR61E106K C3225X5R1E106K TMK316BJ106ML GRM31CR60J476M C3225X5R0J476M GRM32ER71C226M C3225X5R1C226M RT8278 and C IN OUT Capacitance (μF) Case Size 10 1206 10 1206 10 1206 47 1206 47 1210 22 1210 22 1210 www.richtek.com 15 ...
Page 16
... RT8278 Outline Dimension EXPOSED THERMAL PAD (Bottom of Package) Symbol Option 1 Option 2 Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time ...