RT8855
1
DS8855-00 July 2008 www.richtek.com
Ordering Information
Note :
Richtek Green products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
4/3/2/1-Phase PWM Controller for AMD AM2/AM2+ CPUs
General Description
The RT8855 is a 4/3/2/1-phase synchronous buck
controller with two integrated MOSFET drivers for CPU
power application and a single-phase buck with integrated
MOSFET driver for North-Bridge (NB) chipset.The RT8855
uses differential inductor DCR current sense to achieve
phase current balance and active voltage positioning. Other
features include adjustable operating frequency, power
good indication, external error-amp compensation, over
voltage protection, over current protection and enable/
shutdown for various applications. The RT8855 comes to
a small footprint with WQFN-48L 7x7 package.
Features
zzzzz 12V Power Supply Voltage
zzzzz 4/3/2/1-Phase Power Conversion for VCORE Power
zzzzz 3 Embedded MOSFET Drivers (2 for CPU and 1 for
NB)
zzzzz Internal Regulated 5V Output
zzzzz Support AMD AM2 6-bit Parallel and AM2+ 7-bit
Serial VID Tables
zzzzz Continuous Differential Inductor DCR Current Sense
zzzzz Adjustable Frequency (Typically at 300kHz)
zzzzz Selectable 1 or 2 Phase in Power-Saving (PS) Mode
zzzzz Phase-Interleaving for VCORE and NB Controller
zzzzz Power Good Indication
zzzzz Adjustable Over Current Protection
zzzzz Over Voltage Protection
zzzzz Small 48-Lead WQFN Package
zzzzz RoHS Compliant and Halogen Free
Applications
z Desktop CPU Core Power
z Low Voltage, High Current DC/ DC Converter
Pin Configurations
WQFN-48L 7x7
(TOP VIEW)
IM
A
X
_N
B
IM
AX
IS
N
1
IS
P1
IS
N
2
IS
P2
VC
C
5
IS
N
3
IS
P3
IS
N
4
IS
P4 PS
EN PG
O
O
D
VI
D
5
VI
D
4
VI
D
3/
SV
C
VI
D
2/
SV
D
U
G
AT
E_
N
B
VI
D
1/
PV
I
VI
D
0/
VF
IX
EN
VC
C
12
_N
B
LG
AT
E
_N
B
PH
A
SE
_N
B
BOOT_NB
PHASE1
UGATE1
PWM4
PWM3
BOOT2
UGATE2
PHASE2
LGATE2
LGATE1
VCC12
BOOT1
PWROK
FBRTN_NB
FBRTN
FB
COMP
OFS
ADJ
ISN_NB
ISP_NB
FB_NB
COMP_NB
RT
36
35
34
33
32
31
30
29
28
27
26
25
373839404142434445464748
1
2
3
4
5
6
7
8
9
10
11
12
242322212019181716151413
GND
49
Package Type
QW : WQFN-48L 7x7 (W-Type)
RT8855
Operating Temperature Range
G : Green (Halogen Free with Commer-
cial Standard)
RT8855
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DS8855-00 July 2008www.richtek.com
Typical Application Circuit
24
34 33 32
142
1 5
1 92 6
A
D
J
V
C
C
5
R
T
U
G
AT
E1
IS
N
1
R
T8
85
5
IM
A X
LG
AT
E1
9
35
B
O
O
T1
P
W
M
3
PH
A
S
E 1
IS
N
3
IS
P
1
16
L1
12
V
IS
P
3
20
P
W
M
4
25
N
TC
VC
C
P
W
M
B
O
O
T
U
G
A
TE
P
H
A
S
E
LG
A
TE
L2
12
V
12
V
G
N
D
VC
C
P
W
M
B
O
O
T
U
G
A
TE
P
H
A
S
E
LG
A
TE
L2
12
V
12
V
G
N
D
IS
N
4
IS
P
4
22 21
27 28 29 30 18
U
G
AT
E2
B
O
O
T2
IS
P2
P
H
A
S
E2
IS
N
2
17
LG
AT
E 2
L2
12
V
C
O
M
P
11
FB
12
LO
A
D
C
O
M
P_
N
B
6
FB
_N
B
536 37 38 39 7
U
G
AT
E_
N
B
B
O
O
T_
N
B
I S
P_
N
B
P H
A
S
E_
N
B
IS
N
_N
B
8
LG
AT
E_
N
B
L2
12
V
LO
A
D
V
C
C
12
31
12
V
V
C
C
12
_N
B
40
12
V
13
IM
AX
_N
B
1 0
O
F S
46
to
4
1
V
ID
[5
:0
]
48
E
N
1
P
W
R
O
K
47
P
G
O
O
D
3 4
FB
R
T N
_N
B
FB
R
TN
R
T9
61
9
R
T9
61
9
R
O
FS
P
S
23
RT8855
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DS8855-00 July 2008 www.richtek.com
Table 1. 7-bit VID Code Table for AM2+ CPU (Serial)
SVID[6:0] Voltage SVID[6:0] Voltage SVID[6:0] Voltage SVID[6:0] Voltage
0000000 1.5500 0100000 1.1500 1000000 0.7500 1100000 0.3500
0000001 1.5375 0100001 1.1375 1000001 0.7375 1100001 0.3375
0000010 1.5250 0100010 1.1250 1000010 0.7250 1100010 0.3250
0000011 1.5125 0100011 1.1125 1000011 0.7125 1100011 0.3125
0000100 1.5000 0100100 1.1000 1000100 0.7000 1100100 0.3000
0000101 1.4875 0100101 1.0875 1000101 0.6875 1100101 0.2875
0000110 1.4750 0100110 1.0750 1000110 0.6750 1100110 0.2750
0000111 1.4625 0100111 1.0625 1000111 0.6625 1100111 0.2625
0001000 1.4500 0101000 1.0500 1001000 0.6500 1101000 0.2500
0001001 1.4375 0101001 1.0375 1001001 0.6375 1101001 0.2375
0001010 1.4250 0101010 1.0250 1001010 0.6250 1101010 0.2250
0001011 1.4125 0101011 1.0125 1001011 0.6125 1101011 0.2125
0001100 1.4000 0101100 1.0000 1001100 0.6000 1101100 0.2000
0001101 1.3875 0101101 0.9875 1001101 0.5875 1101101 0.1875
0001110 1.3750 0101110 0.9750 1001110 0.5750 1101110 0.1750
0001111 1.3625 0101111 0.9625 1001111 0.5625 1101111 0.1625
0010000 1.3500 0110000 0.9500 1010000 0.5500 1110000 0.1500
0010001 1.3375 0110001 0.9375 1010001 0.5375 1110001 0.1375
0010010 1.3250 0110010 0.9250 1010010 0.5250 1110010 0.1250
0010011 1.3125 0110011 0.9125 1010011 0.5125 1110011 0.1125
0010100 1.3000 0110100 0.9000 1010100 0.5000 1110100 0.1000
0010101 1.2875 0110101 0.8875 1010101 0.4875 1110101 0.0875
0010110 1.2750 0110110 0.8750 1010110 0.4750 1110110 0.0750
0010111 1.2625 0110111 0.8625 1010111 0.4625 1110111 0.0675
0011000 1.2500 0111000 0.8500 1011000 0.4500 1111000 0.0500
0011001 1.2375 0111001 0.8375 1011001 0.4375 1111001 0.0375
0011010 1.2250 0111010 0.8250 1011010 0.4250 1111010 0.0250
0011011 1.2125 0111011 0.8125 1011011 0.4125 1111011 0.0125
0011100 1.2000 0111100 0.8000 1011100 0.4000 1111100 OFF
0011101 1.1875 0111101 0.7875 1011101 0.3875 1111101 OFF
0011110 1.1750 0111110 0.7750 1011110 0.3750 1111110 OFF
0011111 1.1625 0111111 0.7625 1011111 0.3625 1111111 OFF
RT8855
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DS8855-00 July 2008www.richtek.com
Table 2. 6-bit VID Code Table for AM2 CPU (Parallel)
VID[5:0] Voltage VID[5:0] Voltage VID[5:0] Voltage VID[5:0] Voltage
000000 1.5500 010000 1.1500 100000 0.7625 110000 0.5625
000001 1.5250 010001 1.1250 100001 0.7500 110001 0.5500
000010 1.5000 010010 1.1000 100010 0.7375 110010 0.5375
000011 1.4750 010011 1.0750 100011 0.7250 110011 0.5250
000100 1.4500 010100 1.0500 100100 0.7125 110100 0.5125
000101 1.4250 010101 1.0250 100101 0.7000 110101 0.5000
000110 1.4000 010110 1.0000 100110 0.6875 110110 0.4875
000111 1.3750 010111 0.9750 100111 0.6750 110111 0.4750
001000 1.3500 011000 0.9500 101000 0.6625 111000 0.4625
001001 1.3250 011001 0.9250 101001 0.6500 111001 0.4500
001010 1.3000 011010 0.9000 101010 0.6375 111010 0.4375
001011 1.2750 011011 0.8750 101011 0.6250 111011 0.4250
001100 1.2500 011100 0.8500 101100 0.6125 111100 0.4125
001101 1.2250 011101 0.8250 101101 0.6000 111101 0.4000
001110 1.2000 011110 0.8000 101110 0.5875 111110 0.3875
001111 1.1750 011111 0.7750 101111 0.5750 111111 0.3750
RT8855
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DS8855-00 July 2008 www.richtek.com
Functional Pin Description
Pin No. Pin Name Pin Function
1 PWROK PWROK Input Signal.
2 RT Connect this pin to GND by a resistor to adjust frequency.
3 FBRTN Remote sense ground for CORE.
4 FBRTN_NB Remote sense ground for NB.
5 FB_NB Inverting input of error-amp for NB.
6 COMP_NB Output of error-amp and input of PWM comparator for NB.
7 ISP_NB Positive current sense pin of NB
8 ISN_NB Negative current sense pin of NB
9 ADJ
Connect this pin to GND by a resistor to set load line of
VCORE.
10 OFS
Connect this pin to GND/5VCC by a resistor to set no-load
offset voltage of VCORE.
11 COMP Output of error-amp and input of PWM comparator of VCORE.
12 FB Inverting input of error-amp of VCORE.
13 IMAX_NB Connect this pin to GND by a resistor to set OCP of NB.
14 IMAX Connect this pin to GND by a resistor to set OCP of VCORE.
15, 17, 19, 21 ISN1, ISN2, ISN3, ISN4 Negative current sense pin of channel 1, 2, 3 and 4.
16, 18, 20, 22 ISP1, ISP2, ISP3, ISP4 Positive current sense pin of channel 1, 2, 3 and 4.
23 PS Power Saving Mode Selection Pin.
24 VCC5
Output of internal 5V regulator for control circuits power supply.
Connect this pin to GND by a ceramic capacitor larger than 1uF.
25,26 PWM4, PWM3 PWM output for channel 4 and channel 3.
27, 35, 36 BOOT2, BOOT1, BOOT_NB Bootstrap supply for channel 2 and channel 1 and NB.
28, 34, 37 UGATE2, UGATE1, UGATE_NB Upper gate driver for channel 2 and channel 1 and NB.
29, 33, 38 PHASE2, PHASE1, PHASE_NB Switching node of channel 2 and channel 1 and NB.
30, 32, 39 LGATE2, LGATE1, LGATE_NB Lower gate driver for channel 2 and channel 1 and NB.
31, 40 VCC12, VCC12_NB IC power supply. Connect this pin to 12V.
41 VID0/VFIXEN
PVI Mode : Used as voltage identification input for DAC.
SVI Mode : Functions as VFIXEN selection input.
42 VID1/PVI
This pin selects PVI/SVI mode based on the state of this pin
prior to EN signal.
PVI Mode : Used as voltage identification input for DAC.
43 VID2/SVD
PVI Mode : Used as voltage identification input for DAC.
SVI Mode : Serial data input.
44 VID3/SVC
PVI Mode : Used as voltage identification input for DAC.
SVI Mode : Serial clock input.
45, 46 VID4, VID5 PVI Mode : Used as voltage identification input for DAC.
47 PGOOD Power Good Indicator (open drain).
48 EN Enable Input Signal.
Exposed pad
(49) GND
Reference Ground for the IC. The exposed pad must be
soldered to a large PCB and connected to GND for maximum
power dissipation.
RT8855
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DS8855-00 July 2008www.richtek.com
Function Block Diagram
VCC12
VCC5
BOOT1
UGATE1
PHASE1
LGATE1
BOOT2
UGATE2
PHASE2
LGATE2
PWM3
PWM4
ISP1
ISN1
ISP2
ISN2
ISP3
ISN3
ISP4
ISN4
ADJ
FBRTN_NB
VID5 to VID0
I_SEN1
I_SEN2
I_SEN3
I_SEN4
IMAX OC
POR
POR
VIDOFF
PWROK
FB
1.8V
OV
COMP
OC
OV
RT
1.25V
EN
OFS
Power-On
Reset
5V
Regulator
MOSFET
Driver
MOSFET
Driver
CH3_EN
Detector
CH4_EN
Detector
CH1
Current
SENSE
CH2
Current
SENSE
CH3
Current
SENSE
CH4
Current
SENSE
AVG
VID
Table
Generator
Transient
Response
Enhancement
Soft Start
and
Fault
Logic
Transient
Response
Enhancement
Offset
Modulator
Waveform
Generator
+
-
+
-
+
-
+
-
+
-
+
+
-
+
+
-
EA
+
-
+
-
+-
+-
+-
PGOOD
FBRTN
ISP_NB
ISN_NB
I_SENNB NB
Current
SENSE
MOSFET
Driver
BOOT_NB
UGATE_NB
PHASE_NB
LGATE_NB
VCC12_NB
+
-RAMP_NB
-
+EA
FB_NB
OC_NBIMAX_NB
OV_NB-
+
+
1.8V
COMP_NB
PS
RAMP_NB
OC
Detection
OC_NB
Detection
RT8855
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DS8855-00 July 2008 www.richtek.com
Electrical Characteristics
Parameter Symbol Conditions Min Typ Max Unit
VCC Supply Input
VCC12 Supply Voltage VVCC12 10.8 12 13.2 V
VCC12 Supply Current IVCC12 -- 10 -- mA
VCC12_NB Supply Voltage VVCC12_NB 10.8 12 13.2 V
VCC12_NB Supply Current IVCC12_NB -- 5 -- mA
VCC5 Power
VCC5 Supply Voltage VVCC5 ILOAD = 10mA 4.9 5 5.1 V
VCC5 Output Sourcing IVCC5 10 -- -- mA
Power-On Reset
VCC12 Rising Threshold VVCC12TH VCC12 Rising 9.2 9.6 10 V
VCC12 Hysteresis VVCC12HY VCC12 Falling -- 0.9 -- V
Input Threshold
Enable Input High Threshold VENHI EN Rising 2 -- -- V
Enable Input Low Threshold VENLO EN Falling -- -- 0.8 V
To be continued
Recommended Operating Conditions (Note 3)
z Supply Voltage, VCC12 -------------------------------------------------------------------------------------------------- 12V ± 10%
z Junction Temperature Range-------------------------------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range-------------------------------------------------------------------------------------------- 0°C to 70°C
Absolute Maximum Ratings (Note 1)
z Supply Input Voltage------------------------------------------------------------------------------------------------------ −0.3V to 15V
z BOOTx to PHASEx ------------------------------------------------------------------------------------------------------- −0.3V to 15V
z BOOTx to GND
DC----------------------------------------------------------------------------------------------------------------------------- −0.3V to 30V
<200ns ----------------------------------------------------------------------------------------------------------------------- −0.3V to 42V
z PHASEx to GND
DC----------------------------------------------------------------------------------------------------------------------------- −2V to 15V
<200ns ----------------------------------------------------------------------------------------------------------------------- −5V to 30V
z Input/Output Voltage or I/O Voltage ----------------------------------------------------------------------------------- −0.3V to 7V
z Power Dissipation, PD @ TA = 25°C
WQFN−48L 7x7 ------------------------------------------------------------------------------------------------------------ 3.226W
z Package Thermal Resistance (Note 4)
WQFN-48L 7x7, θJA ------------------------------------------------------------------------------------------------------- 31°C/W
z Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- 260°C
z Storage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 2)
HBM (Human Body Mode) ---------------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ------------------------------------------------------------------------------------------------------ 200V
(VCC12 = 12V, GND = 0V, TA = 25°C, unless otherwise specified)
RT8855
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DS8855-00 July 2008www.richtek.com
Parameter Symbol Conditions Min Typ Max Unit
PWROK Input High Threshold VPOKHI PWROK Rising 2 -- -- V
PWROK Input Low Threshold VPOKLO PWROK Falling -- -- 0.8 V
VID5 to VID0 Rising Threshold VVID5 to 0 VID5 to VID0 Rising 0.75 0.8 0.85 V
VID5 to VID0 Hysteresis V VID5 to 0 HYS VID5 to VID0 Falling -- 25 -- mV
VID5 to VID0 Pull-Down
Current IVID5 to 0 VVID5 to 0 = 1.5V -- 16 30 uA
Reference Voltage accuracy
DAC Accuracy
1V to 1.55V −0.5 -- +0.5 %
0.8V to 1V −8 -- +8 mV
0.5V to 0.8V −10 -- +10 mV
Error Amplifier
DC Gain ADC No Load -- 80 -- dB
Gain-Bandwidth GBW CLOAD = 10pF -- 10 -- MHz
Slew Rate SR CLOAD = 10pF 10 -- -- V/us
Output Voltage Range VCOMP RLOAD = 47kΩ 0.5 -- 3.6 V
Power Good
Over-Voltage Threshold VPGOOD-OV FB Rising
VDAC
+210mV
VDAC
+240mV
VDAC
+270mV
V
Under-Voltage Threshold VPGOOD-UV FB Falling
VDAC
−330mV
VDAC
−300mV
VDAC
−270mV V
Over-Voltage Threshold_NB VPGOOD-OV_NB FB_NB Rising
VDAC
+210mV
VDAC
+240mV
VDAC
+270mV
V
Under-Voltage Threshold_NB VPGOOD-UV_NB FB_NB Falling
VDAC
−330mV
VDAC
−300mV
VDAC
−270mV V
Power Good Low Voltage VPGOOD IPGOOD = 4mA -- -- 0.4 V
Current Sense Amplifier
Max Current IGMMAX
VCSP = 1.3V
Sink Current from CSN
100 -- -- uA
Input Offset Voltage VOSCS −2 0 +2 mV
Oscillator
Running Frequency fOSC RRT = 40kΩ 270 300 330 kHz
Ramp Amplitude VRAMP -- 1.6 -- V
Soft Start
Soft Start Slew Rate SRSS Slew Rate 2.5 3.25 4 mV/us
VID change Slew Rate SRVID Slew Rate 2.5 3.25 4 mV/us
Protection
Over-Voltage Threshold
VOVP Sweep FB Voltage 1.7 1.8 1.9 V
VOVP_NB Sweep FB_NB Voltage 1.7 1.8 1.9 V
To be continued
RT8855
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DS8855-00 July 2008 www.richtek.com
Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
Note 2. Devices are ESD sensitive. Handling precaution is recommended.
Note 3. The device is not guaranteed to function outside its operating conditions.
Note 4. θJA is measured in the natural convection at TA = 25°C on a effective single layer thermal conductivity test board of
JEDEC thermal measurement standard.
Parameter Symbol Conditions Min Typ Max Unit
Over-Current Threshold
IOCP RIMAX = 40kΩ 68 80 92 uA
VIMAX RIMAX = 40kΩ 1.44 1.6 1.76 V
IOCP_NB RIMAX_NB = 40kΩ 68 80 92 uA
VIMAX_NB RIMAX_NB = 40kΩ 1.44 1.6 1.76 V
Gate Driver
UGATE Drive Source RUGATEsr
BOOT − PHASE = 8V
250mA Source Current
-- 1 -- Ω
UGATE Drive Sink RUGATEsk
BOOT − PHASE = 8V
250mA Sink Current
-- 1 -- Ω
LGATE Drive Source RLGATEsr VLGATE = 8V -- 1 -- Ω
LGATE Drive Sink RLGATEsk 250mA Sink Current -- 0.9 -- Ω
RT8855
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DS8855-00 July 2008www.richtek.com
Figure 1. SVI Communication-Send Byte
Application Information
The RT8855 is a dual output PWM controller supports
hybrid power control of AMD processors which operate
from either a 6-bit parallel VID interface (PVI) or a serial
VID interface (SVI). One of the outputs is a 4/3/2/1-phase
PWM controller with two integrated MOSFET drivers to
support CPU core voltage (VDD) and another is a single-
phase buck controller with an integrated MOSFET driver
to power North-Bridge (NB) chipset (VDDNB) in SVI mode.
In PVI mode, only multiphase PWM controller is active
for single-plane VDD only processor.
Richtek's proprietary Burst Transient Response(BTRTM),
provides fastest initial response to high di/dt load transients
and less bulk and ceramic output capacitance is required
to meet transient regulation specifications. The RT8855
incorporates differential voltage sensing, continuous
inductor DCR phase current sensing, programmable load-
line voltage positioning and offset voltage to provide high
accuracy regulated power for both VDD and VDDNB. While
VDDNB is enabled in SVI mode, it will be automatically
phase-shifted with respect to the CPU Core phases in
order to reduce the total input RMS current amount.
CPU_TYPE Detection and System Start-Up
At system Start-up, on the rising-edge of EN signal,
RT8855 monitors the status of VID1 and latches the PVI
mode (VID1 = 1) or SVI mode (VID1 = 0).
PVI Mode
PVI is a 6-bit-wide parallel interface used to address the
CPU Core section reference. According to the selected
code, the device sets the Core section reference and
regulates its output voltage according to Table 2. In this
mode, NB section is kept in high impedance. Furthermore,
PWROK information is ignored as well since the signal
only applies to the SVI protocol.
SVI Mode
SVI is a two wire, Clock and Data, bus that connect a
single master (CPU) to one slave (RT8855). The master
initiates and terminates SVI transactions and drives the
clock, SVC, and the data, SVD, during a transaction. The
slave receives the SVI transactions and acts accordingly.
SVI wire protocol is based on fast-mode I2C as shown in
Figure1. SVI interface also consider two additional signals
needed to manage the system start-up. These signals
are EN and PWROK. The device asserts a PGOOD signal
if the output voltages are in regulation.
Set VID Command
The Set VID Command is defined as the command
sequence that the CPU issues on the SVI bus to modify
the voltage level of the Core section and NB section, as
shown is Figure 1. During a Set VID Command, the
processor sends the start (Start) sequence followed by
the address of the Section which the Set VID Command
applies. The processor then sends the write (WRITE) bit.
After the write bit, The Voltage Regulator (VR) sends the
acknowledge (ACK) bit. The processor then sends the
VID bits code during the data phase. The VR sends the
acknowledge (ACK) bit after the data phase. Finally, the
processor sends the stop (Stop) sequence. After the VR
has detected the stop, it performs an On-the-Fly VID
transition for the addressed section(s). Refer to Table 3
for the details of SVI send byte.
RT8855 is able to manage individual power off for both
VCORE and NB sections. The CPU may issue a serial
VID command to power off or power on one section while
the other one remains powered. In this case, the PGOOD
signal remains asserted.
Start Slave Addressing + W ACK ACKData Phase Stop
SVC
SVD
Start Slave Addressing
(7 Clocks)
Write
(1Ck)
A
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