VICOR PI33 EVAL1 Series User manual

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PI33xx‑xx‑EVAL1
ZVS Switching Regulators
I2C™ Digital Interface Guide
Introduction
The PI33xx‑xx I2C digital interface guide provides an overview of how to read and write to the user
accessible registers within the PI33xx‑xx series. This guide details use of the Vicor I2C digital interface
software tool coupled with a USB based I2C hardware interface device. Information is also provided for
I2C communication protocol using generic tools and/or embedded hardware.
Program Capability
The PI33xx‑xx devices provide an I2C digital interface that enables the user to program the EN pin
polarity (from high to low assertion) and input switching frequency synchronization phase/delay.
Margining the output is also available via the I2C interface.
All settings are one‑time programmable except for the VOUT margining, which settings are stored in
volatile memory only and not retained by the device.
Fault Telemetry
The PI33xx‑xx can report when a fault is detected via the I2C interface.
Reported faults include:
n Input Undervoltage Lockout (UVLO)
n Input Overvoltage Lockout (OVLO)
n Output Voltage Overvoltage (OVP)
n Overtemperature Protection (OTP)
n Slow Current Limit
n Fast Current Limit
n VCC (internal to the SiP) Undervoltage
I2C Communication Compatibility
The PI33xx‑xx is hardware‑compatible with the NXP I2C bus specification Version 2.1 Standard Mode
(100kHz) January 2000 for all bus timing and voltage resistors levels up to 5.5V maximum. The
PI33xx‑xx is configured as an I2C child device with no internal bus pull up or pull down.
Interface Software Tool
The Buck GUI software tool offered by Vicor allows quick access to the one time programmable
parameters and user adjustable parameters. The one time user programmable parameters include
enable (EN) polarity, synchronization (SYNCI) delay and edge trigger. User‑adjustable parameters include
output margin (MRGN) level percentage and the ability to clear the fault (FLT) register. This software also
provides the user with the ability to read and decode fault telemetry information.
The Buck GUI operates under the Windows™ 7 or XP (Service Pack 3) environment. Java™ version 1.5
or greater 32‑bit version is required. This software has been tested using Windows 7, 32 bit and 64 bit
and Windows XP with service pack 3.
USER GUIDE | UG:309
Contents Page
Introduction 1
Program Capability 1
Fault Telemetry 1
I2C Communication
Compatibility 1
Interface Software Tool 1
USB Interface Hardware 2
Addressing &
Register Mapping 3
Software Installation
and Operation 4
Fault Telemetry
Command Structure 7
Configuration Programming 10
Programming
Initial Conditions 16
Configuration Examples 16
Sync Delay 16
Enable Polarity 18
Setting Kill Bit 19
Error Messages 20

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SCL
SDA
VCC
(not used)
SGND
SCL
SDA
VCC
(not used)
SGND
Figure 1
LinkM with case removed
USB Interface Hardware
The Buck GUI software is designed to work with the LinkM™ USB to I2C™ interface device
manufactured by ThingM. Information about the LinkM can be found at the ThingM website. A
Windows‑based PC is required with a dedicated USB port. The use of USB expansion ports, especially
those that are heavily loaded, is not recommended.
The LinkM interface can be mounted directly to the PI33xx‑xx evaluation board using a straight
4‑pin header (see Figure 1). Users who wish to connect the LinkM in this manner will need to use a
male‑to‑female USB extension cable. This method works very well and is the preferred method. Other
users may wish to probe the I2C bus or connect to it with ball clips. For this option, the LinkM data
sheet describes the recommended connectors to build such a cable.

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Figure 2
PI33xx‑xx block diagram
showing I2C hardware interface
Addressing & Register Mapping
Figure 2 shows the PI33xx‑xx I2C™ hardware interface. The PI33xx‑xx supports floating addressing so
that two address lines allows for up to eight programmable addresses. The address is 7 bit with the
read/write bit not included. Table 1 shows the address range that can be achieved using all possible
combinations of ADR0 and ADR1. Bits A[6] – A[3] are fixed internally and may not be changed.
The least significant 3 bits; A[2] – A[0], will assume the values in the table based on the decoding of
ADR1 and ADR0. A zero or one indicates the logic strength of the bit and “NC” indicates that the pin
is floating or not connected. The HEX column indicates the final address in hexadecimal, while the DEC
column is the decimal address value.
Table 1
Addressing options
(See Table 3 where
VCC = PI33xx‑xx fixed,
internal 5.1V bias rail)
PGND
SGND
SYNCO
PGD
Q1 Q2
ADR0
SDA
VCC
ADR1
EN
SYNCI
TRK
EAO
ADJ
VS1
Power
Control
InterfaceMemory
+
–
VOUT
REM
SCL
R4
R2
R3
VOUT
0Ω
R1
ZVS Control
1V
VIN
I2C Hardware Interface Signals
A[6] A[5] A[4] A[3] A[2] A[1] A[0] R/W ADR1 ADR0 HEX DEC
1 0 0 1 0 0 0 X 0 0 48 72
1 0 0 1 0 0 1 X 0 NC 49 73
1 0 0 1 0 1 0 X 0 1 4A 74
1 0 0 1 0 1 1 X NC 0 4B 75
1 0 0 1 1 0 0 X NC NC 4C 76
1 0 0 1 1 0 1 X NC 1 4D 77
1 0 0 1 1 1 0 X 1 0 4E 78
1 0 0 1 1 1 1 X 1 1 or NC 4F 79

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Software Installation and Operation
Users downloading the Buck GUI should save the compressed file in a desired directory. The user should
unzip the compressed file and run the executable installation file “PicorBuckGuiFull_setup.exe”. The
installer will then install the Buck GUI in either the default Programs directory or to a directory specified
by the user. Once the software is installed, the user should next plug in the LinkM™ into a dedicated
USB port. The LinkM will detect and use a valid driver without the need of installing one. If the LinkM
device is not detected, the user should consult the LinkM homepage. If the LinkM is not installed, the
Buck GUI will not start and an error message will be generated like the one shown in Figure 3.
Successful installation of the LinkM Interface should result in a successful start up screen of the Buck
GUI as shown in Figure 4. First a dialog box will pop up indicating proper detection of the LinkM. When
the user clicks the “OK” button, that box will disappear. The Buck GUI program screen will appear as
shown in the bottom half of Figure 4.
Table 2
User‑accessible registers
Table 3
I2C™ port specifications
Figure 3
Error message due to missing
LinkM upon software start
Name Address HEX # Bits Description
TSTMDE[2:0] 18 3 Test mode register used for burning bits into non‑volatile memory
MRGN[3:0] 19 4 Volatile register for output voltage margining
FLT[7:0] 1A 8 Fault Register read only
FREG_CLR 1B 0 Register for clearing the Fault Register‑writing address clears register
ENA_POL 20 1 EN pin polarity programming bit
SYN[3:0] 21 4 SYNC programming. SYN[3] = SYNC polarity
KBIT2 22 1 User kill bit for SYN[3:0] and ENA_POL – can not be reversed;
register is write only, can not be read
Parameter Conditions Min Typ Max Units
SCL, SDA VIH Rising, 3.3V & 5V bus compatible 2.1 V
SCL, SDA VIL Falling 3.3V & 5V bus compatible 1.5 V
SCL, SDA input current
(sink to hold open pins low) At 5V 1.8 5 10 µA
SDA VOL 3mA 0.4 V
ADDR0,1VMID VCC = PI33xx‑xx fixed, internal 5.1V 0.4VCC 0.6VCC V
ADDR0,1VIH VCC = PI33xx‑xx fixed, internal 5.1V 0.8VCC V
ADDR0,1VIL VCC = PI33xx‑xx fixed, internal 5.1V 0.1VCC 0.2VCC V
ADDR0,1 hysteresis 0 mV
ADDR0,1 Output resistance
from ½ VCC
0.3VCC < ADDRx < 0.7VCC
VCC = PI33xx‑xx fixed, internal 5.1V 6k kΩ
ADDR0,1 Output resistance
from ½ VCC
ADDRx < 0.2VCC, ADDRx > 0.8VCC
VCC = PI33xx‑xx fixed, internal 5.1V 70k kΩ

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After the user observes a successful main screen like the one shown in Figure 4 and the LinkM is
installed to the target board as shown in Figure 1, it is possible to use the Buck GUI to monitor and
configure the PI33xx‑xx. The target PI33xx‑xx unit should be powered on using the proper input voltage
value and enabled by the user. Failure to apply input voltage will result in the error message shown in
Figure 28 (see Buck GUI error messages section) upon pressing any of the “soft” buttons on the screen.
The LinkM should not be removed or installed with the power already applied to the PI33xx‑xx. Always
power down the PI33xx‑xx prior to installing or removing the LinkM.
Figure 4
LinkM™ detection followed by
Buck GUI main screen

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The following information is intended to provide the user with a description of the various “soft”
buttons and user menus available in the Buck GUI.
The “File” menu provides “Exit” as the only option available when left clicking on it. If the user chooses
“Exit”, a dialog box will pop up to allow the user to confirm their selection. If “Yes” is chosen, the GUI
will close and Buck GUI will terminate. If “No” is selected, the user will be returned to the main program
without exiting the GUI.
The “Help” menu provides the current revision of the Buck GUI. There is no interactive user help or
search utility provided at this time, although there may be expanded help facilities in the future build
releases of the software.
The “Address” menu will produce a drop down dialog box for the user to be able to select the
decimal address of the PI33xx‑xx determined by the ADR0 and ADR1 decodes in Table 1. For example,
if the PI33xx‑xx unit has both ADR0 and ADR1 floating or not connected, the child address will be
76 decimal or 4C. Configuring ADRO and ADR1 allow for eight addressable locations from 72d to
79d or 48h to 4Fh.
The “FAULT” button allows the user to read the PI33xx‑xx fault telemetry information. The fault register
is 8 bits wide with the most significant bit set to logic 0 always. The gray indicator panels for each fault
on the Buck GUI display will illuminate bright red to indicate the decoded fault(s) for the user, so they
don’t have to refer to Table 4 for the decoded value. In addition, the binary value of the register will be
displayed in the “FAULT” window.
The PI33xx‑xx fault logging only occurs when the controller is in normal operation mode. After a fault
is detected and assessed, the fault is latched into the register so long as the controller VCC is active and
above the minimum threshold. The controller will take the appropriate action to protect the PI33xx‑xx
and system based on the type of fault. If for example, the input voltage is high enough to power the
controller but below the minimum under voltage lock out threshold, the controller will prevent the unit
from enabling and remain in a low‑power state. Since it has not entered operate mode, the UVLO fault
will not be logged. If the input voltage is higher than the undervoltage lockout threshold but drops to
zero, the fault will remain latched as long as there is VCC to the controller. Once the controller VCC dips
below the minimum value, the fault data will not remain valid. The fault register will be cleared upon
power on reset. If VCC remains after a logged fault, the fault register must be cleared in order to log any
new events. A description of the logged faults is as follows:
FLT[0] – VCC_UV: if this bit is set, it indicates that the internal power supply for the PI33xx‑xx has gone
into undervoltage.
FLT[1] – UVLO: if this bit is set, the indication is that the input voltage decreased below the
undervoltage lock outthreshold (UVLO) at some point while the unit was in operate mode. The UVLO
threshold is defined as the minimum value required for a PI33xx‑xx to be able to meet all specified
parameters of operation.
FLT[2] – OVLO: if set indicates that the input voltage exceeded the over voltage lockout threshold
(OVLO) at some point while the unit was in operate mode. The OVLO threshold is that value where the
input voltage is too high for a PI33xx‑xx to be able to meet all specified parameters of operation.
FLT[3] – VOUT_HI: if this bit is set, it indicates that the error amplifier input was higher than it should
be for the programmed output voltage during operate mode, indicating that the output voltage
may be too high.
FLT[4] – SLOW_IL: if this bit is set, it indicates that the error amplifier output was at the positive rail for
more than 1 ms during operate mode. This means that the load current demand was higher than the
maximum output current available from the PI33xx‑xx.
FLT[5] – FAST_IL: if this bit is set, it indicates that the peak current in the output inductor was higher
than the maximum peak current allowed during operate mode. It is an indicator of output short circuit
or inductor failure.
FLT[6] – OTP: if this bit is set, it indicates that the PI33xx‑xx internal temperature exceeded the
maximum temperature for safe operation during operate mode and that the PI33xx‑xx shut down to
prevent damage.
Table 4
Fault register assignments FLT[7] FLT[6] FLT[5] FLT[4] FLT[3] FLT[2] FLT[1] FLT[0]
0 OTP FAST_IL SLOW_IL VOUT_HI OVLO UVLO VCC_UV

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The “Clear” button allows the user to clear the PI33xx‑xx fault telemetry information.
The “ENA POL” button allows the user to read the EN polarity by left clicking on it. Changing the
polarity can be accomplished by entering the desired value in the dialog box and then left clicking the
“BURN” button. The Buck GUI will then instruct the user for the remaining steps. The burn function
is irreversible and requires careful consideration. For that reason, further details can be found in the
section “Configuration Programming”.
The “SYNC” button allows the user to read the SYNC polarity and delay settings by left clicking on it.
Changing the polarity can be accomplished by entering the desired value in the dialog box and then left
clicking the “BURN” button. The Buck GUI will then instruct the user for the remaining steps. The burn
function is irreversible and requires careful consideration. For that reason, further details can be found in
the section “Configuration Programming”.
The “KILL BIT2” button allows the user to prevent further changes to any programmed register value
when used in conjunction with the “BURN” button. The burn function is irreversible and requires careful
consideration. For that reason, further details can be found in the section “Configuration Programming”
The “MARGIN” button operates using volatile memory. Any changes made to this register are dynamic
and will change as soon as the command is sent. The user simply enters the value they wish to margin
and then clicks margin. Any value sent to this register will be lost as soon as power is removed. Note
that margining down 20% or more in one step may cause a VOUT_HI fault, which is a normal condition.
Fault Telemetry Command Structure
The PI33xx‑xx command structure is always a 2‑byte write and a 1‑byte read following the start
condition and the base address when using Buck GUI and the LinkM interface. The second data byte is
either 00h or additional data based on the command being sent. Figure 5 is an example of an I2C™ bus
command to read the fault register and it can be implemented using the Buck GUI by left‑clicking the
“FAULT” button. In a similar fashion, the actual fault register can be read from a generic I2C™ device
as shown in Figure 6 by sending the commands shown followed by stop bits. The I2C device used for
sending the command required a R/W bit for addressing so the address of 4Ch was sent as 98h.
In Figure 5, the address of 4Ch was sent followed by the first data byte. “4Ch” represents the base
address of the PI33xx‑xx as determined by ADR0 and ADR1. The first data byte is the address decode
of the internal register to be read (or written); in this case, read. “1Ah” is address of the fault register as
shown in Table 2.
Table 5
PI33xx‑xx margin
register assignments
Figure 5
Fault register read no fault
MRGN[3:0] % VOUT
1100 –20
1101 –15
1110 –10
1111 –5
0000 0
1000 5
1001 10
1010 15
1011 20

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The sequence for sending the data in Figure 6 applies to a generic I2C interface, not the Buck GUI
software. There are many devices available on the market (including microcontrollers) that may be
configured for this function. In the end, the final result is the same. The sequence was:
START WRITE 98h 2 Bytes 1Ah,00h followed by STOP
START READ 99h 1 Byte followed by STOP
The returned value in the data field is the actual fault register value sent by the PI33xx‑xx.
Figure 7 shows the bus capture of the instructions sent after clicking on the “Clear” button using Buck
GUI. Here there are four I2C messages sent. The address field shows the address of the PI33xx‑xx and
then there are two bytes of data. The first byte is the address of the FREG_CLR register. The second byte
is the data. The next message is a read of the address. This read is performed by the LinkM and is not
needed to make the transaction complete. This command could be sent by a generic I2C interface as:
START WRITE 98h 2 Bytes 1Bh,00h followed by STOP
START WRITE 98h 2 bytes 1Ah,00 followed by STOP
START READ 99h 1 Byte followed by STOP
The data returned should be the same as seen previously. In the event an actual fault occurs, the
Buck GUI will indicate the fault graphically as a result of decoding the fault register. Figure 8 shows
the I2C bus capture of the event, while the Buck GUI decodes the fault and gives a visual indication as
shown in Figure 9.
Figure 6
Bus capture read fault register
with generic I2C™ interface
Figure 7
I2C bus capture clear fault
register using the Buck GUI
and LinkM™

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Figure 10 shows several more common faults displayed by the Buck GUI along with the corresponding
I2C bus capture of each event. The first fault SLOW_IL, the second fault is VOUT_HI and the third
fault is OVLO.
Figure 11 shows the I2C bus capture of dynamically margining the PI33xx‑xx output voltage down –20%
by entering “1100” in the “MARGIN” dialog box and clicking the “MARGIN” button. Note that “0Ch”
is sent in the second data byte, which is the margin value.
Figure 8
I2C™ bus capture input
undervoltage fault register
read using Buck GUI
and LinkM™
Figure 9
Buck GUI capture of input
undervoltage fault

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Configuration Programming
The PI33xx‑xx has three programming registers that can be changed by the user as a one‑time change
only. Of each register, any bit that is not set may be set. The programming requires burning internal fuse
links as permanent memory. Once they are burned there is no way to change or reset the settings back
to default. For this reason, it is critical to be sure the settings are correct prior to clicking on the
burn button. The three registers are ENA_POL, SYN[3:0] and KBIT2. ENA_POL is programmed by using
the “ENA POL” soft key and dialog box. SYN[3:0] is programmed by the “SYNC” soft key and dialog
box. KBIT2 is programmed using the “KILL BIT2” soft key and dialog box.
The programmable values for the SYN[3:0] register are shown in Table 6. Bits 0 through 2 define the
delay setting between a synchronizing signal (rising or falling edge as selected) applied to the SYNCI
input and the SYNCO output rising edge, applied as a fraction of the main system clock period (MP).
The most significant bit SYN[3] determines which edge trigger occurs. A “1” indicates rising edge and a
“0” indicates falling edge. As an example, if the MP value is 1µs, and the SYNC dialog box reads “1101”,
the programmed delay is 500ns from the rising edge of the SYNCI input. The actual programmed value
does not take effect until the bits are actually burned so there is no way to measure the delay without
actually burning the value in. For this reason, the user should review the waveform plots in
Figures 12 – 19 to understand the timing relationship prior to attempting to burn the values into the
register. The value of main system clock can be found in the PI33xx‑xx data sheet for each part number.
Figure 10
Buck GUI capture of
common faults with
corresponding I2C™ Data
Figure 11
I2C bus capture

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To understand the relationship between the synchronization timing and the PI33xx‑xx operation, an
overview of the PI33xx‑xx power train timing is shown in Figure 12. There are three main timing states
in the ZVS buck topology, T1, T3 and T4 as defined below:
T1: T1 defines the start of a power cycle when the clamp switch has opened and the zero voltage
switching resonant action has started, followed by the turn on of Q1 and continuing until Q1 turns off.
During T1, current ramps up to a positive peak value, charge is delivered to the output capacitor and
energy is stored in the output inductor.
T3: Q1 has turned off, Q2 has turned on and energy stored in the inductor is delivered to the load. As
the current in the inductor passes through zero, energy is stored in the inductor to provide zero‑voltage
switching for the next time Q1 is required to turn on.
T4: After Q2 turns off, the clamp switch turns on to preserve the energy stored in the inductor to be
used for the next T1, while clamping VS to VOUT. At the end of T4 and beginning of T1, the clamp
switch opens and the parasitic capacitance of Q1 and Q2 resonates with the output inductor to provide
zero‑voltage switching.
The rising edge of SYNCO defines the beginning of T1 and can be observed in Figure 13. The rising
edge of SYNCO is synchronized to SYNCI rising or falling edge as programmed plus any delay desired.
Figure 13 shows the timing relationship of SYNCO, SYNCI and the phase node VS with default timing
and phase delay. Note that the node VS in the schematic of Figure 12 is called VS1 in Figure 13 and can
be observed on Channel 3 of the plot.
= Clamp open
Q1
Q2
Cin
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
Q1
Q2
Cin
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
Q1
Q2
Cin
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
Sync at T1
T1 T3 T4
Q1
Q2
CLAMP
SWITCH
VS
ON ON
ON ON
ON ON
I_L
IQ1
= Clamp open= Clamp open
Q1
Q2
Cin
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
Q1
Q2
Cin
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
Q1
Q2
Cin
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
Q1
Q2
Cin
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
Q1
Q2
Cin
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
V
OUT
Q1
Q2
CinC
OUT
VS
LS
Driver
HS
Driver
ZVS-Buck
Vin
Clamp
Switch
Sync at T1
T1 T3 T4
Q1
Q2
CLAMP
SWITCH
VS
ON ON
ON ON
ON ON
I_L
IQ1
T1 T3 T4
Q1
Q2
CLAMP
SWITCH
VS
V
OUT
V
IN
ON ON
ON ON
ON ON
I_L
IQ1
I
OUT
C
OUT
C
OUT
V
OUT
V
OUT
Figure 12
ZVS buck topology
timing diagram

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The ENA_POL and KBIT2 registers are single bit registers. A “0” in the ENA_POL register is the default
value. This means the PI33xx‑xx will enable when the ENA pin is floating or logic high. Pulling down
ENA pin will disable the PI33xx‑xx. If a “1” is programmed into the ENA_POL register, the ENA polarity
reverses. If the ENA pin is floating or logic low, the PI33xx‑xx is enabled. Pulling the ENA pin high will
disable the PI33xx‑xx.
The KBIT2 register may only be written with a “1” entered into the dialog box. This register can not be
read, it is write only. Burning this register will prevent making any more changes to any register, even if
there are unused bits available to burn.
Start of T1 (ZVS)
Turn on of high side
MOSFET
External sync pulse
falling edge
Start of T1 (ZVS)
Turn on of high side
MOSFET
External sync pulse
falling edge
Figure 13
PI33xx‑xx ZVS buck sync to
T1 timing relationship
where VS = Ch3 VS1
SYN[3:0]
SYN[3] SYN[2:0]
Polarity Bit Control Bits SYNC Delay
0 = Falling 000 NONE
1 = Rising 001 3/4MP
100 2/3MP
101 1/2MP
110 1/3MP
111 1/4MP

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Figure 14
PI33xx‑xx
SYNC = “1000” timing
Figure 15
PI33xx‑xx
SYNC = “1111” 1/4MP

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Figure 16
PI33xx‑xx
SYNC = “1110” 1/3MP
Figure 17
PI33xx‑xx
SYNC = “1101” 1/2MP

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Figure 18
PI33xx‑xx
SYNC = “1100” 2/3MP
Figure 19
PI33xx‑xx
SYNC = “1001” 3/4MP

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Programming Initial Conditions
Once the user has selected the configuration for the timing register, the burn process can be initiated.
To begin this process, the user must be ready to be able to enable and disable the PI33xx‑xx, since this
is required to enter the burn mode and actually burn the bits. The initial conditions to begin the burn
process are as follows:
1. Proper input voltage should be applied to the target PI33xx‑xx.
2. The unit can be either enabled and producing output voltage or disabled with the output voltage
at zero. The preferred method is disabled since in some cases multiple units may depend on proper
phase delay for best performance. The user must adhere to the instructions from the GUI to
ensure proper burn results.
The burn process consumes power from the internal bias for the controller, so only a single bit can be
burned at a time. Buck GUI takes care of this for the user and will generate the appropriate number of
bus commands to ensure each bit is burned correctly. Users that write their own software or operate
from a different GUI will need to consider this. In addition, power should not be removed from the
PI33xx‑xx during the burn process. The Buck GUI will prompt the user when to enable and disable the
target. Enabling and disabling is done using the EN pin. One important note to consider is that if the
enable polarity has been changed already due to a separate operation, the new enable polarity must be
used when enabling and disabling. The procedure along with the Buck GUI commands, for changing the
SYN[3:0] register so that the synchronization polarity is falling edge and the delay is 3/4MP is as follows.
Configuration Example – Sync Delay
Type “0001” into the SYNC dialog box. Left‑click on the “BURN” button.
The first four writes and reads ensure that the three user registers are cleared. Then the test mode
register is selected at address 18h and the test mode 05h is entered. Next, the user is prompted to
disable the unit using the enable pin. The target can be enabled or disabled prior to being prompted to
disable. See Figures 20 and 21.
Figure 20
SYNC “0001” burn phase 1
while unit enabled or disabled
Figure 21

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When the user disables the target, another prompt will provide notification to enable the target again
as shown in Figure 22. When the unit is enabled, the output voltage will remain low as if the PI33xx‑xx
was still disabled. This is normal. The Buck GUI will next write “01h” into the SYN[3:0] register.
The next step prompts the user to disable the target again. After clicking “OK”, Buck GUI will reset
from test mode 5 and then clear the other user registers as shown in Figure 23. Buck GUI will display a
dialog box to inform the user of the successful burn completion. When the user enables the PI33xx‑xx, it
should power up normally and the burned in changes shall take effect.
The user may read the register that was just programmed by clicking on the “SYNC” button. Buck GUI
should show the new burned in values read back from the SYN[3:0] register as shown in Figure 24. If
an error message occurs or the incorrect results are obtained, refer to the section titled “PI33xx‑xx Error
Messages” for more information.
It is important to note that the data sent here is the value shown in the dialog window. The actual
read is the burned in value of the register. Sending “4Ch 21h FFh” or “4Ch 21h 00h” would
also work properly.
Figure 22
SYNC “0001” burn phase 2
unit must be enabled
Figure 23
SYNC “0001” burn phase 3
unit must be disabled
Figure 24
Read SYN[3:0]
after burning “0001”

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Configuration Example – Enable Polarity
Figure 25 shows the complete procedure for changing the enable polarity along with the I2C™ bus
capture of all of the commands required to make the changes using Buck GUI or some other generic
software. Since the enable polarity is not changed until AFTER the burn is completed, always use the
default polarity of the signal before the burn process to enable and disable the target PI33xx‑xx. It
should be pointed out that the SYN[3:0] register had already been programmed to “0010” on the
PI33xx‑xx target prior to the enable polarity change. Note that the first two bus transactions occur when
the target PI33xx‑xx is enabled and the final transaction occurs when it is disabled. Failure to follow
this exact sequence will prevent successful storage of the desired configuration settings. If an error
message occurs or the incorrect results are obtained, refer to the section titled “Error Messages” for
more information.
Figure 25
Changing EN_POL register to
“1” with SYN[3:0]
programmed to “0010”

UG:309 Page 19
Configuration Example – Setting Kill Bit
The procedure for setting the KBIT2 register to prevent any further programming is outlined in sequence
in Figure 26. The SYN[3:0] register has been programmed to “1111” and the ENA_POL register has
been programmed to “1” in advance. Like the previous procedures, the first two bus transactions occur
while the PI33xx‑xx is enabled and the final transaction occurs while the PI33xx‑xx is disabled. After
completing this step, no further changes can be made to the PI33xx‑xx. It is very important to double
check all settings before clicking the “BURN” button. If the user makes a mistake in a setting after
clicking on the “BURN” button, the instructions for enabling and disabling the unit that are prompted
by Buck GUI should be IGNORED by leaving the target enabled and clicking “OK” to each pop‑up dialog
box. This will prevent the burn from occurring and give the user another chance to correct the mistake.
Buck GUI will report the failed burn with a pop up dialog box.
Figure 26
Setting KBIT2 register after
setting ENA_POL Register to “1”
with SYN[3:0]
progr a mmed to “1111”

UG:309 Page 20
Error Messages
Missing or Malfunctioning I2C™ Interface Error
The error message shown in Figure 27 occurs only at the first boot of the Buck GUI each time the
program is executed. During program initialization, the software determines the existence of the
LinkM™ USB interface. If the hardware or software interface from the computer USB port to the LinkM
is either not connected, missing or malfunctioning, Buck GUI will display this error message. If some
error occurs with this interface during program execution, a different error message will be displayed.
This error ONLY applies to the USB portion of the LinkM and does not indicate any problem with
the PI33xx‑xx or the LinkM I2C bus interface.
Incorrect I2C Address or Missing Unit Error
The error message shown in Figure 28 occurs during Buck GUI program execution if either the PI33xx‑xx
or LinkM I2C interface is malfunctioning. It will also occur during program execution if the PC to USB
or LinkM USB hardware or software interface is malfunctioning. If the USB portion of the interface
is at fault, Buck GUI can not recover and will continue to display this error even if the USB interface
problem is corrected. Buck GUI will need to be closed and restarted to reestablish USB connectivity
with Buck GUI. If the I2C interface is the problem, the error will clear without restarting Buck GUI
once the problem is corrected. It is very important to note that a failure of the critical interface
to either the LinkM or the PI33xx‑xx during a programming operation can result in the
incorrect or unintentional programming of parameters. If the user encounters this error during a
programming operation:
1. Remove input power to the PI33xx
2. Exit Buck GUI
3. Restore power to the PI33xx‑xx
4. Restart Buck GUI
Figure 27
Fatal error message at
Buck GUI boot
Figure 28
I2C bus or USB error message
during Buck GUI execution