1. Embedded Systems Power Supply

2. Consideration Voltage – Output voltage – In put voltage Current Ripple Power Consumption Isolation Interference Protection

3. Linear Regulator Easy Higher reliability Low efficiency Higher temperature

4. Linear Regulator LM78XX & LM79XX Peak current (1A), change with voltage difference Vin < 35V Vin – Vout > 5V Thermal protection Over current protection

5. Linear Regulator

6. Need enough voltage margin according to working current

7. Linear Regulator

9. LDO Low drop voltage 15mV~150mV Higher efficiency Larger current (500mW)

10. LM1117

11. LM1117 adj LM1117

12. LDO

13. DC-DC Convert Why DC-DC convert? – High efficiency – Step-up Shortcomings – Complex – Noise – Start-up current – Inductor

14. DC-DC Convert Types – Step-up (boost) – Step-down (buck) – Invert Components – Inductor – Transformer – Capacitor – Diode – Feedback circuitry

15. Boost

22. Buck

25. Invert

26. Flyback

28. Push-pull

29. DC-DC Convert Components MOSFET On resistor Max current Voltage DIODE On voltage Peak current Speed Inductor Peak Current

30. Charge Pump Simple High efficient Low current Ripple

31. Charge Pump (Double Voltage) V+ 2V+

32. Charge Pump (Double Voltage) - +

33. Charge Pump (Negative Voltage) V+ V- V+

34. Charge Pump (Negative Voltage) +-+-

35. Charge Pump

36. Charge Pump (Negative Voltage)

37. Charge Pump

38. Multiple Voltage

39. Battery Type Capacity Voltage change during discharge Current leakage Charging circuits Protection

40. Battery Ni-Cd – Long history – Low self-discharge current – Relative low capacity – Memory effect – Charge stops at dv/dt<0

41. Battery

42. Ni-MH – Relative high capacity – No memory effect – Higher self-discharge current – Charge stops at dv/dt=0

43. Battery Li+ – 4.2V – Larger energy density – Strict charge requirements – Internal protection circuit

44. Battery

47. Charge steps Waiting for battery attached (Li+) Start charge cycle If battery voltage to low (2.45V), start trickle charge (40mA) Normal charge Enter intermittence mode when battery voltage reach float voltage Stop charge when timer-out

48. Battery Charge Protection DC-DCLDO booster control Main voltage outputs standby voltage on/off inputted voltage may be higher or lower that 3.3V Never cutoff standby voltage Need battery charging protection circuits

49. Power over Ethernet (PoE) IEEE P802.3af Category 5 Cable 44~57V,typically 48V 。 Max current 550mA, Max startup current 500mA 。 Provide 5 stage power supply: 3.84~12.95W

50. Connection 2schemes 1 12 3 345 6 678 Rx Tx Rx DC+ DC  1 1 2 2 3 3 45 6 6 78 Rx Tx Rx DC+ DC  usign data pin using idle pin

51. Implement of PoE 占用空闲管脚的连接 48V

52. PoE device probe detect the value of R PD to determine whether it support POE 120nF capacitor parallel with 25KΩ±5%

53. Detect power class of PD Apply different voltage and measure current to discover the power class of PD

54. Power System Design Steps 1.Collect voltage & current data 2.Construct power tree 3.Verify current of each path 4.Verify efficiency on each node 5.Adjust tree structure

55. ModuleVoltageCurrentNote CPU1.8V80mACore voltage. Can be shut down in sleep mode 3.3V100mAIO voltage, memory sub-system voltage. Should be stable enough Audio3.3V10mACODEC, analog sub-system voltage, can be shutdown. Low noise voltage 3.3V10mACODEC, digital sub-system voltage, can be shutdown 5V20mAPower Amp, can be shutdown. Low noise voltage LCD3.3V50mADigital signal. Keep power-on sequence, can be shutdown -12V5~10mAKeep power-on sequence, can be shutdown 5V>100mABacklight invert, can be shutdown

56. Design Power tree – Source Battery Wall adapter – Different branched for different voltages – Separate one voltage branches if necessary Analog-Digital Shutdown function Interference Current Protection – Move branches to reduce power consumption – Select chipsets for the implementation

57. Bad Design Example 

58. Good Design Example

59. Design Example No limit on power efficiency

60. Hand held dev. using USB charging (example)

61. Power on order Ensure on startup, V core won’t be higher than V io too much V io cannot be higher that V core too much V io V core

62. Power on order——Implement by power tree