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
From Battery
TPS7301
LDO
1N4148
Charge Pump
1.8V Core Voltage
1N5817
From Battery
3.3V I/O Voltage
200mA
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
• MOSFET
On resistor
Max current
Voltage
• DIODE
On voltage
Peak current
Speed
• Inductor
Peak Current
Charge Pump
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•
•
•
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
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•
•
•
•
•
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
DC-DC
LDO
LDO
Charge
Protection
Main
voltage
outputs
booster
control
on/off
standby
voltage
•
•
•
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
Rx Rx
1 2
Tx
3 4
Tx
5 6
DC+ DC-
7 8
usign
data pin
7 8
using
idle pin
DC-
2schemes
Rx Rx
1 2
Tx
3 4
Tx
5 6
DC+
DC-
Implement of PoE
48V
占用空闲管脚的连接
PoE device probe
120nF capacitor parallel with
25KΩ±5%
detect the value of RPD to
determine whether it
support POE
Detect power class of PD
Apply different voltage and
measure current to discover the
power class of PD
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
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
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
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
Audio
LCD
Design
• Power tree
– Source
• Battery
• Wall adapter
– Different branched for different voltages
– Separate one voltage branches if necessary
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•
•
•
•
Analog-Digital
Shutdown function
Interference
Current
Protection
– Move branches to reduce power consumption
– Select chipsets for the implementation
Bad Design
Example

Step-up
5V
Step-up
3.3V
External
Power in
Step-up
Step-down
LDO
Audio
Power
Amp.
LCD
Backlight
Charge
LDO
CPLD
1.8V
Battery
LCD
module
3.3V
CPU & Memory
Buttons,
LEDs
Audio
CODEC
12V

Good Design
Example
DC-DC
5V
5V
4V
External
Power in
Charge
Pump
DC-DC
DC-DC
3.3V
LDO
Charge
LDO
DC-DC
4.2V ~ 2.7V
LDO
Battery
5V
LDO
LCD
module
Stepdown
1.8V
LDO
CPLD
Buttons,
LEDs
3.3V
CPU & Memory
Buttons
Audio
Power
Amp.
3.3V
Audio
CODEC
LCD
Backlight
Design
Example7v
2A
LM317
LM317
4.2v
1500mA
Processor
board
4.2v 1500mA
TPS7333
CPLD
No limit on
power efficiency
To
extended
port
TPS7333
Audio, Touch
screen, RS232,
IrDA, BSR,
BCR, Bus
LEDs
TPS7333
CF
LCD
LM7805
To
extended
port
5v
1500mA
USB
LM7805
5v
1500mA
Backlight
voltage
inverter
Hand held dev. using USB charging
(example)
Power on order
TPS60100
From Battery
TPS7301
1N4148
Charge Pump
Vio
1.8V Core Voltage
1N5817
From Battery
3.3V I/O Voltage
200mA
Vcore
LDO
Ensure on startup, Vcore won’t be higher than Vio too much
Viocannot be higher that Vcore too much
Power on order——Implement by
power tree