Pin SMD Data
DC / DC converters
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FAN6862 = ABx
LD7550IL_BL = xxP/50
OB2252 = 52xxx
OB2262 = 62xxx
OB2273 = 73xxx
SG6858TZ = AAIxx
UC3863G_L = U863
USING CERAMIC OUTPUT CAPACITORS WITH THE MAX1734 VOLTAGE-MODE BUCK CONVERTER
Abstract: The MAX1734 voltage-mode buck DC-DC converter was design to work with medium ESR tantalum capacitors; however, by slightly changing the feedback scheme, small, low-ESR ceramic capacitors may be used. A schematic, design equations, and load-transient response waveforms are provided.
Figure 1. In this simple application circuit, a stepdown DC-DC converter operates with a ceramic output capacitor.
A ceramic-capacitor circuit offers several benefits over the standard application circuit. First, ceramic capacitors are more readily available than tantalum types. Second, (see Figure 2) they cause less output ripple (<5mVPP vs. >20mVPP), and less load-transient overshoot (<50mVPP vs. >100mVPP). IC11 needs 20mVPP or more at the OUT pin for stable operation under load. To meet this requirement, first calculate the R1 value:
Figure 2. Load-transient response waveforms (top traces) show that a ceramic output capacitor produces lower output ripple and less overshoot.
Per the MAX1734 data sheet, VOUT is 1.5V or 1.8V, L1 is 10µH, Tmin is 0.4µsec, ILOADMAX is 250mA, and IOUTSENSE is 4µA. The result is R1 = 4.3kΩ for VOUT = 1.8V, and R1 = 5.2kΩ for VOUT = 1.5V. R1 may therefore be rounded to 5kΩ. Next, calculate the feedforward-capacitor value:
If R1 = 5kΩ and VOUT = 1.5V, then Cff < 12nF. Select Cff = 10nF. Choosing a much smaller value will cause excessive load-transient overshoot, and choosing a larger value will cause instability under loaded conditions. For optimized load transients, the inductor series resistance should be
In this case the RL value should be about 200mΩ, which allows use of a small inductor and causes an approximate efficiency drop of only 3% at maximum load. Because the inductor time constant L1/RL is matched to the feedback time constant R1 × Cff, the short-term load-transient response equals the DC load regulation (Figure 2). If RL is chosen less than 200mΩ, the peak-to-peak load-transient voltage will increase but the DC load regulation will decrease.
Finally, choose COUT large enough for stability:
where ΔIL is approximately 100mA when the MAX1734 operates with a 10µH inductor. In this case, COUT should be greater than 4µF.
1The MAX1734 stepdown DC-DC converter supplies a fixed 1.8V or 1.5V output at 250mA from an input voltage range of 2.7V to 5.5V. Its 5-pin SOT23 package and internal synchronous rectifier allows a small application circuit with a minimum number of external components.
RT9266B
The RT9266B is a compact, high efficiency, and low voltage step-up DC/DC converter with an Adaptive Current Mode PWM control loop, includes an error amplifier, ramp generator, comparator, switch pass element and driver in which providing a stable and high efficient operation over a wide range of load currents. It operates in stable waveforms without external compensation.The low start-up input voltage below 1V makes RT9266B suitable for 1 to 4 battery cells applications with a 500mA internal switch. The 550kHz high switching rate minimized the size of external components. Besides, the 25μA low quiescent current together with high efficiency maintains long battery lifetime.
What is the Ic number for marking 6116A & IA029 (SOT23-6) LG home theater model LDH457 .Thanks
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