AN3302 STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 13
Technical content
Datasheet sections
- 1 Block diagram
- 2 Recommended PCB Iayout
- 2.1 Layout considerations
- 2.2 Programming the output voltage
- 3 Test results
- 3.1 S-wire protocol
- 3.2 Inductor selection
- 3.3 Input and output capacitor selection
- 4 Revision history
digital services and high definition digital media content. down converters and one step-up. dissipation may cause an overheating of the application environment. the range of 6.5 V to 14 V, with a current capability of 0.7 A. Figure 1. Blu-ray disc player power management architecture based on STODD01 voltage, make the device particularly suitable for optical storage applications. topology and by the use of X7R or X5R and low ESR SMD ceramic capacitors. damage due to accidental overload.
3.3 V 700 mA
1 Block diagram
Figure 2. Block diagram and reference circuit Table 1. List of external components (1)
- Components listed above refer to a typica l application. Operation of the STODD01 is not limited to the choice of these
- R 1 and R2 are calculated according to the following formula: R1 = R2 (VOUT1 / VFB1-1)
It is recommended to use resistors with values in the range of 1 kΩ to 50 kΩ.
- R 3 and R4 are calculated according to the following formula: R3 = R4 (VOUT3 / VFB3-1)
It is recommended to use resistors with values in the range of 1 kΩ to 50 kΩ.
- It is recommended to use resistors with values in the range of 100 k Ω to 1 MΩ.
2 Recommended PCB Iayout
2.1 Layout considerations
parameters such as efficiency and output voltage ripple may be out of specification. Short, wide traces must be implemented for the main current and for power ground paths. inductor and output capacitor. placed very close to the device. connected to the common ground node. Figure 3. Recommended PCB layout
AN3302 Recommended PCB Iayout Doc ID 18163 Rev 1 5/13
2.2 Programming the output voltage
The output voltage for the step-up (ch1) can be adjusted from 6.5 V up to 14 V by connecting a resistor divider between the VOUT1 and GND, the middle point of the divider must be connected to the FB1 pin, as shown in Figure 2. The resistor divider should be chosen according to the following equation: Equation 1 where VFB1 is programmable, by using S-wire protocol, in the range of 0.8 V to 1.25 V (see Figure 11). It is recommended to use a resistor with a value in the range of 1 kΩ to 50 kΩ. Lower values may also be suitable, but increase current consumption. For ch2 the device integrates the resistor divider needed to set the correct output voltage (3.3 V). This allows to save 2 external components. The FB2 pin must be connected directly to V OUT2. The output voltage for ch3 can be adjusted from 0.8 V up to 94 % of the input voltage value by connecting a resistor divider between the VOUT3 and GND, the middle point of the divider must be connected to the FB3 pin, as shown in Figure 2. The resistor divider should be chosen according to the following equation: Equation 2 It is recommended to use a resistor with a value in the range of 1 kΩ to 50 kΩ. Lower values may also be suitable, but increase current consumption. ⎛ +⋅= 1R RVV 11FB1OUT ⎛ +⋅= 1R RVV 33FB3OUT
3 Test results
Figure 4. Inrush current of step-up Figure 5. Enable startup time of step-up Figure 6. Efficiency ch1 step-up Figure 7. Efficiency ch2-ch3 step-down Figure 8. Step-down load transient OUT2 Figure 9. Step-down load transient OUT3
3.1 S-wire protocol
from the microprocessor to program the STODD01 output voltage (see Figure 10). power during read and write operation. If this function isn't used, the TX pin must be connected to GND. the VFB1 is programmed to 0.8 V. Figure 10. Wire connection Table 2. Feedback one voltage level
Figure 11. Single wire programming Figure 12. Example of S-wire programming
5 PULSES SEQUENCE
30 PULSES SEQUENCE
3.2 Inductor selection
The inductor is the key passive component for switching converters. The inductor selection must take the boundary conditions in which the converter works into consideration; for the buck, the maximum input voltage, and for the boost, the minimum input voltage. The critical inductance values are then obtained according to the following formulas: for the step-down: Equation 3 and for the step-up: Equation 4 where: F SW: switching frequency. ΔIL = the peak-to-peak inductor ripple current. As a rule of thumb, the peak-to-peak ripple can be set at 20 % - 40 % of the output current for the step-down and can be set at 20 % - 40 % of the input current for the step-up. The peak current of the inductor must be calculated as: Equation 5 Equation 6 In addition to the inductance value, in order to avoid saturation, the maximum saturation current of the inductor must be higher than that of the IPEAK.
3.3 Input and output capacitor selection
It is recommended to use ceramic capacitors with X5R or X7R dielectric and Iow ESR as input and output capacitors in order to filter any disturbance present in the input line and to obtain stable operation. The output capacitor is very important to satisfy the output voltage ripple requirement. ( ) LSWMAX_IN OUTMAX_INOUT MIN IFV VVVL Δ⋅⋅ −⋅= ( ) LSWOUT MIN_INOUTMIN_IN MIN IFV VVVL Δ⋅⋅ −⋅= () ( ) LFV2 VVV8.0II SWMAX_IN OUTMAX_INOUT OUTDOWNSTEPPEAK ⋅⋅⋅ −⋅+=−− ( ) LFV2 VVV V IVI SWOUT MIN_INOUTMIN_IN MIN_IN OUTOUTUPSTEPPEAK ⋅⋅⋅ −⋅+⎟⎟ ⋅=−−
where: ΔIL is the ripple current and FSW is the switching frequency. where FSW is the switching frequency. maximum input or output voltage is recommended. Figure 13. Inductor with high I SAT current Figure 14. Inductor with low I SAT current
4 Revision history
Table 3. Document revision history 03-Jan-2011 1 Initial release.