ST7570
S-FSK power line networking system-on-chip
Datasheet — production data
Features
■
Fully integrated narrow-band power line
networking system-on-chip
■
High performing PHY processor with
embedded turn-key firmware for spread
frequency shift keying (S-FSK) modulation:
– Programmable bit rate up to 2.4 Kbps (@
50 Hz)
– 1 Hz step programmable carriers up to
148.5 kHz
– Signal to noise ratio estimation
– Received signal strength indication
■
Protocol engine embedding:
– IEC61334-5-1 PHY and MAC layers
– Alarm management
– Repeater Call procedure
– Intelligent search initiator process
6&1&0.XX,
PITCH
■
Suitable for EN50065 and FCC part 15
compliant applications
■
VFQFPN48 package with exposed pad
■
-40 °C to +85 °C temperature range
Applications
■
Smart metering applications
■
Street lighting control
Command and control networking
■
On chip peripherals:
– Host controller UART interface
■
■
Fully integrated analog front end:
– ADC and DAC
– PGA with automatic gain control for high
receiving sensitivity
– High linearity modulated signal generation
Description
■
Fully integrated single-ended power amplifier
for line driving
– Up to 1 A rms, 14 V p-p output
– Configurable Active filtering topology
– Very high linearity
– Embedded temperature sensor
– Current control feature
■
8 to 18 V power amplifier supply
■
3.3 V or 5 V digital I/O supply
■
Integrated 5 V and 1.8 V linear regulators for
AFE and digital core supply
■
Mains zero crossing synchronization
September 2012
This is information on a product in full production.
The ST7570 is a powerful power line networking
system-on-chip. It combines a high-performance
PHY processor core and a protocol controller core
with a fully integrated analog front end (AFE) and
line driver.
The ST7570 features allow the most costeffective, single-chip power line communication
solution based on IEC61334-5-1 S-FSK standard.
Table 1.
Device summary
Order codes
Package
ST7570
Packaging
Tube
VFQFPN48
ST7570TR
Doc ID 17526 Rev 2
Tape and reel
1/26
www.st.com
26
Contents
ST7570
Contents
1
Device overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1
3
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5
Analog front end (AFE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1
Reception path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2
Transmission path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3
Power amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.4
Current and voltage control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.5
Thermal shutdown and temperature control . . . . . . . . . . . . . . . . . . . . . . . 16
5.6
Zero-crossing PLL and delay compensation . . . . . . . . . . . . . . . . . . . . . . 16
6
Power management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7
Clock management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8
Functional overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1
9
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Physical layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1
S-FSK principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.2
Bit timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.3
Frame structure at physical level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.4
Frame timing and time-slot synchronization . . . . . . . . . . . . . . . . . . . . . . . 22
10
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
11
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2/26
Doc ID 17526 Rev 2
ST7570
1
Device overview
Device overview
Realized using a multi-power technology with state-of-the-art VLSI CMOS lithography, the
ST7570 is based on dual digital core architecture (a PHY processor engine and a protocol
controller core) to guarantee outstanding communication performance with a high level of
flexibility and programmability.
The on-chip analog front end, featuring analog to digital and digital to analog conversion and
automatic receiver gain control, plus the integrated Power Amplifier delivering up to 1Arms
output current, makes the ST7570 the first complete system-on-chip for power line
communication.
Line coupling network design is also simplified, leading to a very low cost BOM. Safe and
performing operations are guaranteed while keeping power consumption and distortion
levels very low, thus making ST7570 an ideal platform for the most stringent application
requirements and regulatory standards compliance.
Figure 1.
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Doc ID 17526 Rev 2
3/26
Pin connection
Pin connection
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ST7570
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4/26
Doc ID 17526 Rev 2
ST7570
Pin connection
2.1
Pin description
Table 2.
Pin description
Pin
Name
Type
Reset state Pull-up
1
TXD
Digital output
High Z
Disabled
2
RXD
Digital input
High Z
Disabled UART data in
3
VDDIO
Power
-
4
TRSTN
Digital input
Input
Enabled System JTAG interface reset (active low)
5
TMS
Digital input
Input
Enabled System JTAG interface mode select
6
GND
Power
-
-
7
TCK
Digital input
High Z
Disabled
8
TDO
Digital output
High Z
Disabled System JTAG interface data out
9
TDI
Digital input
Input
Enabled System JTAG interface data in
10
RESETN
Digital input
Input
Disabled System reset (active low)
11
VDD
Power
-
-
1.8 V digital supply.
Internally connected to VDD_REG_1V8
Externally accessible for filtering purposes only
12
XIN
Analog
-
-
Crystal oscillator input / external clock input
13
XOUT
Analog
-
-
Crystal oscillator output
(if external clock supplied on XIN, XOUT must be
left floating)
14
GND
Power
-
-
Digital ground
15
VSSA
Power
-
-
Analog ground
16
VDD_PLL
Power
-
-
1.8 V PLL supply voltage.
Connect externally to VDD
17
VCCA
Power
-
-
5 V analog supply / internal regulator output
Externally accessible for filtering purposes only
18
ZC_IN_A
Analog input
-
-
Analog zero-crossing input
19
RX_IN
Analog input
-
-
Reception analog input
20
TX_OUT
Analog output
-
-
Transmission analog output
21
PA_IN+
Analog input
-
-
Power amplifier
Non-inverting input
22
PA_IN-
Analog input
-
-
Power amplifier
Inverting input
23
CL
Analog input
-
-
Current limit sense input
24
VCC
Power
-
-
Power supply
25
VSS
Power
-
-
Power ground
-
Description
UART data out
External pull-up to VDDIO required
3.3 V – 5 V I/O external supply
Digital ground
System JTAG interface clock.
External pull-up to VDDIO required
Doc ID 17526 Rev 2
5/26
Pin connection
Table 2.
ST7570
Pin description (continued)
Pin
Name
Type
Reset state Pull-up
Description
26
PA_OUT
Analog output
-
-
Power amplifier output
27
VDD_REG_1V8
Power
-
-
1.8 V digital supply / internal regulator output
Externally accessible for filtering purposes only
28
VDDIO
Power
-
-
3.3 V – 5 V I/O external supply
29
NC
-
-
-
Not used, leave floating
30
NC
-
-
-
Not used, leave floating
31
RESERVED6
-
-
-
Pull up to VDDIO
32
NC
-
-
-
Not used, leave floating
33
GND
Power
-
-
Digital ground
34
VDDIO
Power
-
-
3.3 V – 5 V I/O supply
35
VSSA
Power
-
-
Analog ground
36
PRESLOT
/ZC/TS/BIT
Digital output
High Z
Configurable digital output:
- Slot synchronization (PRESLOT),
- Zero Crossing (ZC),
- Timeslot (TS),
Disabled - Bit synchronization (BIT),
- Transmission in progress (TXP),
- Reception in progress (RXP),
- Transmission or Reception in progress (TXRXP).
If not used, this pin can be left floating.
37
ZC_IN_D
Digital input
High Z
Disabled
38
T_REQ
Digital input
High Z
Disabled UART communication control line
39
BR1
Digital input
High Z
40
BR0
Digital input
High Z
Disabled UART baud rate selection
Disabled (sampled after each reset event) see Table 3
41
RESERVED0
-
-
-
Connect to GND
42
RESERVED1
-
-
-
Pull up to VDDIO
43
RESERVED2
-
-
-
Pull up to VDDIO
44
RESERVED3
-
-
-
Pull up to VDDIO
45
GND
Power
-
-
Digital ground
Digital zero-crossing input.
Pull up to VDDIO if not used
46
VDD
Power
-
-
1.8 V digital supply.
Internally connected to VDD_REG_1V8
Externally accessible for filtering purposes only
47
RESERVED4
-
-
-
Connect to VDDIO
48
RESERVED5
-
-
-
Pull up to VDDIO
6/26
Doc ID 17526 Rev 2
ST7570
Pin connection
Table 3.
UART baud rate selection
BR1
BR0
Baud rate
0
0
9600
0
1
19200
1
0
38400
1
1
57600
Doc ID 17526 Rev 2
7/26
Maximum ratings
ST7570
3
Maximum ratings
3.1
Absolute maximum ratings
Figure 3.
Absolute maximum ratings
Value
Symbol
Parameter
VCC
VSSA-GND
VDDIO
Max
Power supply voltage
-0.3
20
V
Voltage between VSSA and GND
-0.3
0.3
V
I/O supply voltage
-0.3
5.5
V
VI
Digital input voltage
GND-0.3
VDDIO+0.3
V
VO
Digital output voltage
GND-0.3
VDDIO+0.3
V
V(PA_IN)
PA inputs voltage range
VSS-0.3
VCC+0.3
V
V(PA_OUT)
PA_OUT voltage range
VSS-0.3
VCC+0.3
V
RX_IN voltage range
-(VCCA+0.3)
VCC+0.3
V
ZC_IN_A voltage range
-(VCCA+0.3) VCCA+0.3
V(RX_IN)
V(ZC_IN_A)
V(TX_OUT, CL) TX_OUT, CL voltage range
V(XIN)
VSSA-0.3
VCCA+0.3
V
GND-0.3
VDDIO+0.3
V
Power amplifier output non-repetitive peak
current
5
A peak
I(PA_OUT)
Power amplifier output non-repetitive rms
current
1.4
A rms
Tamb
Operating ambient temperature
-40
85
°C
Tstg
Storage temperature
-50
150
°C
Maximum withstanding voltage range
Test condition: CDF-AEC-Q100-002 “Human
Body Model”
Acceptance criteria: “Normal Performance”
-2
+2
kV
Thermal data
Table 4.
Symbol
8/26
XIN voltage range
V
I(PA_OUT)
V(ESD)
3.2
Unit
Min
Thermal characteristics
Parameter
Value
Unit
RthJA1
Maximum thermal resistance junction-ambient steady state
(1)
50
°C/W
RthJA2
Maximum thermal resistance junction-ambient steady state (2)
42
°C/W
1.
Mounted on a 2-side + vias PCB with a ground dissipating area on the bottom side.
2.
Same conditions as in Note 1, with maximum transmission duration limited to 100 s.
Doc ID 17526 Rev 2
ST7570
4
Electrical characteristics
Electrical characteristics
TA = -40 to +85°C, TJ < 125°C, VCC = 18 V unless otherwise specified.
Table 5.
Electrical characteristics
Symbol
Parameter
Note
Min.
Typ.
Max.
Unit
8
13
18
V
0.35
0.5
mA
22
30
mA
Power supply
VCC
Power supply voltage
VCCA externally
supplied
I(VCC) RX
Power supply current - Rx mode
I(VCC) TX
Power supply current - Tx mode, no VCCA externally
load
supplied
VCC UVLO_TL
VCC under voltage lock out low
threshold
6.1
6.5
6.95
V
VCC UVLO_TH
VCC under voltage lock out high
threshold
6.8
7.2
7.5
V
250 (1)
700
VCC
UVLO_HYST
VCC under voltage lock out
hysteresis
I(VCCA) RX
Analog supply current - Rx mode
I(VCCA) TX
Analog supply current - Tx mode
I(VDD)
I(VDD) RESET
mV
5
6
mA
8
10
mA
Digital core supply current
35
41
mA
Digital core supply current in
RESET state
8
mA
V
V(TX_OUT) =5 V p-p,
No load
VDD_PLL
PLL supply voltage
VDD
I(VDD_PLL)
PLL supply current
0.4
0.45
mA
-10%
3.3 or 5
+10%
V
VDDIO
Digital I/O supply voltage
Externally supplied
VDDIO UVLO_TL
VDDIO under voltage lock out low
threshold
2.2
2.4
2.6
V
VDDIO UVLO_TH
VDDIO under voltage lock out high
threshold
2.45
2.65
2.85
V
VDDIO under voltage lock out
hysteresis
180
240
mV
VCC/2
V
VDDIO
UVLO_HYST
Analog front end
Power amplifier
V(PA_OUT) BIAS
GBWP
I(PA_OUT) MAX
Power amplifier output bias voltage
- Rx mode
Power amplifier gain-bandwidth
product
Power amplifier maximum output
current
Doc ID 17526 Rev 2
100
MHz
1000
mA
rms
9/26
Electrical characteristics
Table 5.
ST7570
Electrical characteristics (continued)
Symbol
Parameter
Note
V(PA_OUT) TOL
Power amplifier output tolerance
V(PA_OUT) HD2
Power amplifier output 2nd
harmonic distortion
V(PA_OUT) HD3
Power amplifier output 3rd
harmonic distortion
V(PA_OUT) THD
Power amplifier output total
harmonic distortion
Min.
(2)
-3%
VCC=18 V,
V(PA_OUT) = 14 V pp (typ), V(PA_OUT)
BIAS = VCC/2,
RLOAD=50Ω, T = 25°C
See Figure 3
PA_IN+ vs. VSS (3)
C(PA_IN)
CL_TH
CL_RATIO
Power supply rejection ratio
Max.
Unit
+3%
-70
-63
dBc
-66
-63
dBc
0.1
0.15
%
10
pF
10
pF
50 Hz
100
dB
1 kHz
93
dB
100 kHz
70
dB
Power amplifier input capacitance
PA_IN- vs. VSS
PSRR
Typ.
(3)
Current sense high threshold on CL
pin
2.25
Ratio between PA_OUT and CL
output current.
2.35
2.4
V
80
Transmitter
V(TX_OUT) BIAS
Transmitter output bias voltage - Rx
mode
V(TX_OUT) MAX
Transmitter output maximum
voltage swing
TX_GAIN
VCCA/
2
TX_GAIN = 31, No
load
Transmitter output digital gain range
TX_GAIN TOL
Transmitter output digital gain
tolerance
R(TX_OUT)
Transmitter output resistance
V(TX_OUT) HD2
Transmitter output 2nd harmonic
distortion
V(TX_OUT) HD3
Transmitter output 3rd harmonic
distortion
V(TX_OUT) THD
Transmitter output Total harmonic
distortion
4.8
4.95
V
VCCA
0
31
-0.35
0.35
1
V(TX_OUT) = 4.5
Vpkpk (typ.), no load,
T = 25°C
V p-p
dB
kΩ
-72
-55
dBc
-70
-67
dBc
0.1
0.2
%
Receiver
V(RX_IN) MAX
Receiver input maximum voltage
V(RX_IN) BIAS
Z(RX_IN)
V(RX_IN) MIN
10/26
16
V p-p
Receiver input bias voltage
VCCA/
2
V
Receiver input Impedance
10
kΩ
45
dBµV
rms
Receiver input sensitivity
VCC = 18 V
Bit rate = 1200 bps @
50 Hz,
BER = 10-3, SNR =
20 dB
Doc ID 17526 Rev 2
ST7570
Table 5.
Electrical characteristics
Electrical characteristics (continued)
Symbol
Parameter
Note
Min.
Typ.
Max.
Unit
PGA_MIN
PGA minimum gain
-18
dB
PGA_MAX
PGA maximum gain
30
dB
Oscillator
V(XIN)
V(XIN) TH
f(XIN)
Clock frequency
supplied externally
Oscillator input voltage swing
Oscillator input voltage threshold
1.8
0.8
Crystal oscillator frequency
0.9
VDDIO V p-p
1
8
f(XIN) TOL
External quartz crystal frequency
tolerance
ESR
External quartz crystal ESR value
-150
V
MHz
+150
ppm
100
Ω
20
pF
External quartz crystal load
capacitance
16
fCLK_AFE
Internal frequency of the analog
front end
8
MHz
fCLK_PROT_ctrl
Internal frequency of the protocol
Ctrl core
28
MHz
56
MHz
CL
fCLK_PHY_proces Internal frequency of the PHY
sor
processor core
Temperature sensor
T_TH1
Temperature threshold 1
63
70
77
°C
T_TH2
Temperature threshold 2
90
100
110
°C
T_TH3
Temperature threshold 3
112
125
138
°C
T_TH4
Temperature threshold 4
153
170
187
°C
10
V p-p
Zero crossing comparator
V(ZC_IN_A) MAX
Zero crossing analog input voltage
range
V(ZC_IN_A) TL
Zero crossing analog input low
threshold
-40
-30
-20
mV
V(ZC_IN_A) TH
Zero crossing analog input high
threshold
30
40
50
mV
Zero crossing analog input
hysteresis
62
70
78
mV
V(ZC_IN_A)
HYST
ZC_IN_D d.c.
Zero crossing digital input duty
cycle
50
%
Digital section
Digital I/O
Doc ID 17526 Rev 2
11/26
Electrical characteristics
Table 5.
ST7570
Electrical characteristics (continued)
Symbol
Parameter
RPULL-UP
Note
Min.
Typ.
Max.
Unit
VDDIO = 3.3 V
66
kΩ
VDDIO = 5 V
41
kΩ
Internal pull-up resistors
VIH
High logic level input voltage
0.65*V
DDIO
VDDIO
+0.3
V
VIL
Low logic level input voltage
-0.3
0.35*V
DDIO
V
VOH
High logic level output voltage
IOH= -4 mA
VOL
Low logic level output voltage
IOL= 4 mA
VDDIO
-0.4
V
0.4
V
UART interface
-1.5%
57600
+1.5%
BAU
D
-1.5%
38400
+1.5%
BAU
D
-1.5%
19200
+1.5%
BAU
D
-1.5%
9600
+1.5%
BAU
D
Baud rate
Reset and power on
tRESETN
Minimum valid reset pulse duration
1
µs
tSTARTUP
Start-up time at power on or after a
reset event
60
ms
1. Referred to TA = -40 °C
2. This parameter does not include the tolerance of external components
3. Guaranteed by design
Figure 4.
12/26
Power amplifier test circuit
Doc ID 17526 Rev 2
ST7570
Analog front end (AFE)
5
Analog front end (AFE)
5.1
Reception path
Figure 4 shows the block diagram of the ST7570 input receiving path. The main blocks are a
wide input range analog programmable gain amplifier (PGA) and the analog to digital
converter (ADC).
Figure 5.
reception path block diagram
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The PGA is controlled by an embedded loop algorithm, adapting the PGA gain to amplify or
attenuate the input signal according to the input voltage range for the ADC.
The PGA gain ranges from -18 dB up to 30 dB, with steps of 6 dB (typ.), as described in
Table 5.
Table 6.
5.2
PGA gain table
PGA code
PGA gain (typ) [dB]
RX_IN max range [V p-p]
0
-18
16
1
-12
8
2
-6
4
3
0
2
4
6
1
5
12
0.500
6
18
0.250
7
24
0.125
8
30
0.0625
Transmission path
Figure 5 shows the transmission path block diagram. it is mainly based on a digital to analog
converter (DAC), capable to generate a linear signal up to its full scale output. A gain control
block before the DAC gives the possibility to scale down the output signal to match the
desired transmission level.
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Analog front end (AFE)
Figure 6.
ST7570
Transmission path block diagram
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The amplitude of the transmitted signal can be set on a 32-step logarithmic scale through
the TX_GAIN parameter, introducing an attenuation ranging from 0 dB (typ.), corresponding
to the TX_OUT full range, down to -31 dB (typ.).
The attenuation set by the TX_GAIN parameter can be calculated using the formula of
Equation 1:
Equation 1 Output attenuation A [dB] vs. TX GAIN
A [ dB ] = ( TX_GAIN – 31 ) + TX_GAINTOL
5.3
Power amplifier
The integrated power amplifier is characterized by very high linearity, required to be
compliant with the different international regulations (CENELEC, FCC etc.) limiting the
spurious conducted emissions on the mains, and a current capability of 1 A rms that allows
the amplifier driving even very low impedance points of the network.
All the pins of the power amplifier are accessible, making it possible to build an active filter
network to increase the linearity of the output signal.
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ST7570
5.4
Analog front end (AFE)
Current and voltage control
The power amplifier output current sensing is performed by mirroring a fraction of the output
current and making it flow through a resistor RCL connected between the CL pin and VSS.
The following relationship can be established between V(CL) and I(PA_OUT):
Equation 2 V(CL) vs. I(PA_OUT)
R CL ⋅ I ( PA_OUT )
V ( CL ) = -----------------------------------------------CL_RATIO
The voltage level V(CL) is compared with the internal threshold CL_TH. When the V(CL)
exceeds the CL_TH level, the V(TX_OUT) voltage is decreased by one TX_GAIN step at a
time until V(CL) goes below the CL_TH threshold.
The current sense circuit is depicted in Figure 6.
Figure 7.
PA_OUT current sense circuit
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The RCL value to get the desired output current limit I(PA_OUT)LIM can be calculated
according to Equation 3:
Equation 3 RCL calculation
CL_TH
R CL = --------------------------------------------------------------------------I(PA_OUT) LIM ⁄ CL_RATIO
Note that I(PA_OUT)LIM is expressed as peak current, so the corresponding rms current
value shall be calculated according to the transmitted signal waveform.
The RCL value to get 1 A rms output current limit, calculated with typical values for CL_TH
and CL_RATIO parameters, is indicated in Table 7.
Table 7.
Parameter
RCL
CL resistor typical values
Description
Resistor value for I(PA_OUT) MAX = 1 A rms (1.41 A peak)
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Value
Unit
133
Ω
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Analog front end (AFE)
5.5
ST7570
Thermal shutdown and temperature control
The ST7570 performs an automatic shutdown of the power amplifier circuitry when the
internal temperature exceeds T_TH4. After a thermal shutdown event, the temperature must
get below T_TH3 before the ST7570 power amplifier comes back to operation.
Moreover, a digital thermometer is embedded to identify the internal temperature among
four zones, as indicated in Table 8.
Table 8.
5.6
Temperature zones
Temperature zone
Temperature value
1
T < T_TH1
2
T_TH1 < T < T_TH2
3
T_TH2 < T < T_TH3
4
T > T_TH3
Zero-crossing PLL and delay compensation
In operating mode, ST7570 needs to be synchronized with an external signal period through
zero crossing detection.
The user can select among two input pins for the external zero-crossing reference:
●
Analog input (ZC_IN_A): it requires a bipolar analog input signal which is internally
squared through a Schmidt Trigger comparator with symmetrical thresholds;
●
Digital input (ZC_IN_D): it requires a 50% duty-cycle square-wave digital signal (with
two levels).
The desired input can be selected by accessing a dedicated management information base
(MIB) object.
The ST7570 embeds a phase-locked loop (PLL) to generate the internal reference based on
the external zero-crossing. In case of delay due to external zero crossing coupling circuits
(i.e. based on optocouplers) or to improve interoperability, it is possible to introduce delay
compensation through a dedicated MIB object.
Figure 8.
Zero crossing detection
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ST7570
6
Power management
Power management
Figure 9 shows the power supply structure for the ST7570 device. The ST7570 operates
from two external supply voltages:
●
VCC (8 to 18 V) for the power amplifier and the analog section;
●
VDDIO (3.3 or 5 V) for interface lines and digital blocks.
Two internal linear regulators provide the remaining required voltages:
●
5 V analog front end supply: generated from the VCC voltage and connected to the
VCCA pin;
●
1.8 V digital core supply: generated from the VDDIO voltage and connected to
VDD_REG_1V8 (direct regulator output) and VDD pins.
The VDD_PLL pin, supplying the internal clock PLL, must be externally connected to VDD.
All supply voltages must be properly filtered to their respective ground, using external
capacitors close to each supply pin, in accordance to the supply scheme depicted in
Figure 9.
Note that the internal regulators connected to VDD_REG_1V8 and to VCCA are not
designed to supply external circuitry; their outputs are externally accessible for filtering
purpose only.
Figure 9.
Power supply internal scheme
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Clock management
7
ST7570
Clock management
The main clock source is an 8 MHz crystal connected to the internal oscillator through XIN
and XOUT pins. Both XIN and XOUT pins have a 32 pF integrated capacitor, in order to
drive a crystal having a load capacitance of 16 pF with no additional components.
Alternatively, an 8 MHz external clock can be directly supplied to XIN pin, leaving XOUT
floating.
A PLL internally connected to the output of the oscillator generates the fCLK_PHY, required by
the PHY processor block. fCLK_PHY is then scaled down by two to obtain fCLK_PC, required
by the protocol controller.
8
Functional overview
The ST7570 embeds complete physical (PHY) and a medium access control (MAC)
protocol layers and services compliant with the open standard IEC61334-5-1, mainly
developed for smart metering applications, but suitable also for other command and control
applications and remote load management in CENELEC B and D bands.
A local port (UART) is available for communication with an external host, exporting all the
functions and services required to configure and control the device and its protocol stack.
Below a list of the protocol layers and functions embedded in the ST7570 (Figure 10):
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●
Physical layer: implemented in the PHY processor and exporting all the primitive
functions listed in the international standard document IEC61334-5-1, plus additional
services for configuration, alarm management, signal and noise amplitude estimation,
phase detection, statistical information;
●
MAC layer: implemented on the protocol controller and exporting all the primitive
functions listed in the international standard document IEC61334-5-1, Repeater Call
and Intelligent search initiator process together with additional services.
●
Management information base (MIB): an information database with all the data
required for proper configuration of the system (at both PHY and MAC layer);
●
Host interface: all the services of the PHY, MAC and MIB are exported to an external
host through the local UART port.
Doc ID 17526 Rev 2
ST7570
Functional overview
Figure 10. Functional overview
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8.1
References
Additional information regarding the PHY and MAC layers, the MIB and the HOST interface,
including a detailed description of all services, extended functionalities and commands can
be found in the following documents:
1.
ST7570 user manual, www.st.com/powerline
2.
International standard CEI-IEC-61334-5-1
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Physical layer
9
ST7570
Physical layer
The ST7570 embeds a IEC-61334-5-1 PHY layer, which is based on the S-FSK (spread
FSK) modulation technique.
9.1
S-FSK principles
The S-FSK modulation technique is aimed at strengthening the classical FSK by adding
higher robustness against narrow-band interferers typical of a spread-spectrum approach.
Non-return-to-zero (NRZ) coding is used to map the binary data “0” or “1” to sinusoidal
carriers at frequencies f0 and f1 (Figure 11).
Figure 11. S-FSK waveform (time domain)
The absolute frequency deviation |f0 - f1| is at least 10 kHz, in order to reduce the probability
that a narrow-band interferer could corrupt both carriers at the same time.
f0 and f1 can be set at any value in CENELEC bands A, B, D.
Figure 12. S-FSK waveform (frequency domain)
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ST7570
Bit timing
The data communication is synchronized to the mains zero-crossing through an internal
PLL. The bit time is dynamically adapted in order to have always 24 or 48 bits in each mains
cycle, according to the desired configuration (Figure 13). The resulting bit-rate is thus
dependent on the instantaneous mains frequency. With a nominal frequency of 50 Hz, the
resulting bit-rate is 1200 bps in the case of 24 bit/mains cycle, while 2400 bps in the case of
48 bit/mains cycle.
Figure 13. Bit timing
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9.2
Physical layer
BITMAINSCYCLE
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Physical layer
9.3
ST7570
Frame structure at physical level
The frame at physical level is compliant with the IEC61334-5-1 and is composed of 45 bytes
(360 bits) as follows:
●
2 byte preamble (PRE) (AAAAh);
●
2 byte start subframe delimiter (SSD) (54C7h);
●
38 byte physical service data unit (P_sdu);
●
3 byte for pause or alarm;
The bytes are sent from the most significant byte (MSB) to the least significant byte (LSB).
Bits within the byte are packed with the same order (msb to lsb).
Figure 14. Physical frame format
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