Embedded Systems

Power Supply

Consideration

• Voltage– Output voltage– In put voltage

• Current• Ripple• Power Consumption• Isolation• Interference• Protection

Linear Regulator

• Easy• Higher reliability• Low efficiency• Higher temperature

Linear Regulator

• LM78XX & LM79XX• Peak current (1A), change with voltage

difference • Vin < 35V• Vin – Vout > 5V• Thermal protection• Over current protection

Linear Regulator

Linear Regulator

Need enough voltage margin according to

working current

Linear Regulator

Linear Regulator

LDO

• Low drop voltage 15mV~150mV• Higher efficiency • Larger current (500mW)

LM1117

LM1117

LM1117 adj

LM1117

LDO

TPS60100

Charge Pump

3.3V I/O Voltage 200mA

TPS7301

LDO

1.8V Core Voltage

1N41

48

1N58

17

From Battery

From Battery

DC-DC Convert

• Why DC-DC convert?– High efficiency– Step-up

• Shortcomings– Complex– Noise– Start-up current– Inductor

DC-DC Convert

• Types– Step-up (boost)– Step-down (buck)– Invert

• Components– Inductor– Transformer– Capacitor– Diode– Feedback circuitry

Boost

Boost

Boost

Boost

Boost

Boost

Boost

Buck

Buck

Buck

Invert

Flyback

Flyback

Push-pull

DC-DC Convert Components

• MOSFETOn resistorMax currentVoltage

• DIODEOn voltagePeak currentSpeed

• InductorPeak Current

Charge Pump

• Simple• High efficient• Low current• Ripple

Charge Pump (Double Voltage)

V+

V+ 2V+

Charge Pump (Double Voltage)

- +

Charge Pump (Negative Voltage)

V+ V-V+

Charge Pump (Negative Voltage)

+

-

Charge Pump

Charge Pump (Negative Voltage)

Charge Pump

Multiple Voltage

Battery

• Type• Capacity• Voltage change during discharge• Current leakage• Charging circuits• Protection

Battery

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

Battery

Battery

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

Battery

• Li+– 4.2V– Larger energy density– Strict charge requirements– Internal protection circuit

Battery

Battery

Battery

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

Battery

Charge Protection

DC-DC LDO

LDO

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

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

Connection

2schemes

11 2 33 4 5 66 7 8Rx Tx TxRx

DC+ DC DC

11 22 33 4 5 66 7 8Rx Tx TxRx

DC+ DC

usign data pin

using idle pin

Implement of PoE

占用空闲管脚的连接

48V

PoE device probe

detect the value of RPD to determine whether it

support POE120nF capacitor parallel with

25KΩ±5%

Detect power class of PD

Apply different voltage and measure current to discover the

power class of PD

Power System Design

Steps1. Collect voltage & current data2. Construct power tree3. Verify current of each path4. Verify efficiency on each node5. Adjust tree structure

Module Voltage Current Note

CPU 1.8V 80mA Core voltage. Can be shut down in sleep mode

3.3V 100mA IO voltage, memory sub-system voltage. Should be stable enough

Audio 3.3V 10mA CODEC, analog sub-system voltage, can be shutdown. Low noise voltage

3.3V 10mA CODEC, digital sub-system voltage, can be shutdown

5V 20mA Power Amp, can be shutdown. Low noise voltage

LCD 3.3V 50mA Digital signal. Keep power-on sequence, can be shutdown

-12V 5~10mA Keep power-on sequence, can be shutdown

5V >100mA Backlight invert, can be shutdown

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

Bad Design Example

Step-up Step-down

Battery

5V

LCD Backlight

CPLD

CPU & Memory

1.8V

Buttons, LEDs

External Power in

Charge LDO

LDO

Step-up

3.3V

3.3V

Audio Power Amp.

Audio CODEC

LCD module

Step-up

Good Design Example

DC-DC

Battery

5V

LCD Backlight

CPLD

CPU & Memory

1.8V Buttons,

LEDs

External Power in

Charge LDO

Step-down

DC-DC

3.3V

3.3V

Audio Power Amp.

Audio CODEC

LCD module

DC-DC

Buttons

LDO

DC-DC

4V

4.2V ~ 2.7V

LDO

LDO LDO

3.3V

5V

12V

Charge Pump

5V

Design Example

LM317

LM7805

7v 2A

CPLD

CF

LCD

Audio, Touch screen, RS232,

IrDA, BSR, BCR, Bus

LEDs

TPS7333 TPS7333

TPS7333

LM7805

USB

Backlight voltage inverter

4.2v 1500mA

LM317 Processor

board

5v 1500mA

To extended

port

4.2v 1500mA

5v 1500mA

To extended

port

No limit on power efficiency

Hand held dev. using USB charging(example)

Power on order

TPS60100

Charge Pump

3.3V I/O Voltage 200mA

TPS7301

LDO

1.8V Core Voltage

1N41

48

1N58

17

From Battery

From Battery

Ensure on startup, Vcore won’t be higher than Vio too much

Viocannot be higher that Vcore too much

Vio

Vcore

Power on order——Implement by power tree