LINER LTC3887 Total power management: hot swap, intermediate bus, point-of-load Datasheet

DEMO MANUAL DC2578A
LTC4281, LTC3886, LTC2975, LTC3887
Total Power Management:
Hot Swap, Intermediate Bus, Point-of-Load
BOARD FEATURES
Complete Power Tree from Input Hot Swap to Pointof-Load
nn Hot Swap Controller for Input Power Safety and
Telemetry (LTC®4281)
nn Intermediate Bus Controller for Precise, Complete
Power Control Over Two Separate Buses (LTC3886)
nn Point-of-Load Managers/Controllers Cooperatively
Sequence, Manage, Measure, and Manage Faults on
All Output Supplies (LTC2975 and LTC3887)
nn Built-In Load Step Generator for Transient Response
Tuning
nn I2C/SMBus/PMBus Compatible Interface for Complete Control and Read Back of Telemetry, Including
Voltages, Currents, and Temperatures, as well as
Status and Faults
LTpowerPlay® PC GUI Software
nn Linduino Firmware Platform Support
nn Powered from 12V/1A Wall Supply
nn
nn
Table 1. DC2578A Board Parameters
PARAMETER
MIN
TYP
MAX
VIN
11V
12V
13.8V
Output Power
(Total Over All Outputs)
10W
0°C
Ambient Temperature
25°C
60°C
Design files for this circuit board are available at
http://www.linear.com/demo/DC2578A
All registered trademarks and trademarks are the property of their respective owners.
POINT-OF-LOAD
2.5V
LTC3887
12V HS
12V
8V
LTC3886
2V
SHARED
TIMING
5V
INTERMEDIATE
BUS
LTC2975
LTC4281
CONTROL
HOT SWAP
1.8V
1.5V
1.2V
1V
LTC3370
POINT-OF-LOAD
DC2578a F01
Figure 1. DC2578A Power Tree
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DEMO MANUAL DC2578A
BOARD FEATURES
Table 2. Channel Capabilities
PARAMETER
Manager/Controller
HOT SWAP
IBV_8V, IBV_5V
CH0, CH1
CH2 TO CH5
LTC4281
LTC3886
LTC3887
LTC2975
Nominal Channel Output Voltage
12V, VOUT = VIN
8V, 5V
(Defined by Config)
2.5V, 2V
(Defined by Config)
1.8V, 1.5V, 1.2V, 1V
Configured Voltage Trim Range
N/A
±5%
±5%
±5%
Output Current Limit (Configured)
1A
4A
2.5A
2A
Load Pulser Current
N/A
1A on IBV_8V
N/A
N/A
Temperature Monitor
N/A
1 Internal,
2 External*
1 Internal,
2 External*
1 Internal,
4 External*
*External temperature sensors are located near each inductor.
DESCRIPTION
The DC2578A is a complete power chain, including a
hot swap controller, an intermediate bus controller, and
six point-of-load channels with power system management. The board demonstrates how to safely transfer
power from a backplane, through an LTC4281 hot swap
controller, through an LTC3886 step-down intermediate
bus controller (IBC), and out through the point-of-load
converters (POLs) that regulate load voltages. It shows
the comprehensive set of power management, cooperation, and safety features of the Analog Devices solution,
and showcases how easy it is to configure and manage
the whole power hierarchy. Each regulated supply has the
ability to sequence, trim, margin, supervise, measure,
respond cooperatively to faults, and log fault information in nonvolatile memory. In addition, the onboard load
pulser helps with optimizing the adjustable LTC3886 control loop response. The rich set of status and telemetry
information provided by the entire system is consolidated
and presented under one GUI interface — LTpowerPlay.
Figure 2. DC2578A Board Layout
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DEMO MANUAL DC2578A
IC FEATURES
LTC4281
• Fast OV/UV and OC Supervisors per Channel
• Allows Safe Board Insertion into Live Backplane
• PMBus/I2C Compliant Serial Interface
• MOSFET Power Limiting with Current Foldback
• Automatically Coordinate Sequencing and Fault
Management Across Multiple ADI PSM Devices
• Programmable Current Limit with 2% Accuracy
• Input Overvoltage/Undervoltage Protection
• Monitor Current, Voltage, Power, Energy, and FET Health
• 16-Bit ADC with ±0.7% Total Unadjusted Error
• Wide Operating Voltage Range: 2.9V to 33V
• Internal EEPROM for Nonvolatile Configuration
LTC3886
• Sequence and Trim Supplies to within ±0.5% of Target
• Programmable Voltage, Current Limit, Digital SoftStart/Stop, Sequencing, Margining, OV/UV/OC Limits,
Frequency, and Control Loop Compensation
• Telemetry Read Back Includes Accurate VIN, IIN, VOUT,
IOUT, Temperature and Faults per Channel
• PMBus/I2C Compliant Serial Interface
• Internal EEPROM and Fault Logging
• Automatically Coordinate Sequencing and Fault Management Across Multiple ADI PSM Devices
• Integrated N-Channel MOSFET Gate Drivers
• VIN Range: 4.5V to 60V; VOUT Range: 0.5V to 13.8V
LTC2975
• Sequence and Trim Supplies to within ±0.25% of Target
• Programmable Voltage, Current Limit, Digital SoftStart/Stop, Sequencing, Margining, and OV/UV/OC
Limits
• Automatic Fault Logging to Internal EEPROM
• VIN Range: 3.3V, or 4.5V to 15V
LTC3887
• Sequence and Trim Supplies to within ±0.5% of Target
• Programmable Voltage, Current Limit, Digital SoftStart/Stop, Sequencing, Margining, OV/UV/OC Limits,
and Frequency Synchronization
• Telemetry Read Back Includes Accurate VIN, IIN, VOUT,
IOUT, Temperature and Faults per Channel
• PMBus/I2C Compliant Serial Interface
• Internal EEPROM and Fault Logging
• Automatically Coordinate Sequencing and Fault
Management Across Multiple ADI PSM Devices
• Integrated N-Channel MOSFET Gate Drivers
• VIN Range: 4.5V to 24V; VOUT Range: 0.5V to 5.5V
The DC2578A board is supported by the LTpowerPlay
graphical user interface (GUI), which demonstrates the
complete set of control and telemetry registers in each
IC. The entire system can be controlled and observed
in real time through the LTpowerPlay GUI. LTpowerPlay
makes it easy to see and control all of the behaviors in
the system, to update EEPROM registers, to measure and
visualize telemetry from the ICs, to debug any problems
that arise, and to store configuration information on the
Windows PC for use later.
• Telemetry Read Back Includes Accurate VIN, IIN, VOUT,
IOUT, Temperature and Faults per Channel
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DEMO MANUAL DC2578A
DC2578A BOARD STRUCTURE
Refer to Figure 1.
HOT SWAP INPUT
The DC2578A represents a typical power chain similar to
a plug-in card or industrial scenario where the primary
power distribution bus is at a high voltage, and must be
processed down to a level and quality factor suitable for
the loads. In such a system the bus voltage might be 28V
or higher, which is much too high for most loads, and
which presents challenging plug-in and unplug conditions. A hot swap controller is the first mechanism to
control potentially hazardous voltages and currents in
this environment. On the DC2578A board, the hot swap is
an LTC4281, which controls and monitors the 12V input
supply voltage and current, and manages the health of
the FET.
INTERMEDIATE BUS
In many scenarios the high voltage input bus is not suitable to apply directly to the down-stream point-of-load
(POL) controllers. The voltage may be too high, too noisy,
or too unpredictable, so an intermediate bus controller
stands between the hot swap and the POLs, providing
a first level of voltage conditioning. On this board the
LTC3886 controls two separate intermediate buses, one
8V and the other 5V, which power the down-stream supplies and which can be coordinated through the LTC3886’s
timing and fault response mechanisms.
POINT-OF-LOAD CONTROL
After the intermediate bus, the point-of-load controllers
provide the final step-down and signal conditioning step
to supply clean, predictable power to each load at its
preferred voltage. The job of each POL is to power and
protect its load.
There are two classes of POL on this board: a powersupply controller (LTC3887) and a 4-channel switching supply (LTC3370) with a power-supply manager
(LTC2975). The power-supply controller is a switching
regulator with power-system management (PSM) features
built-in. It has built-in gate drivers and can monitor and
control its output voltages and currents in real time. The
Figure 3. DC2578A with DC1613
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DEMO MANUAL DC2578A
DC2578A BOARD STRUCTURE
power-supply manager, on the other hand, wraps around
any power supply and provides PSM features such as
enhanced accuracy, control, telemetry monitoring, and
fault response. On this board, the LTC2975 manages a
4-channel LTC3370 switching regulator.
Note that all of the voltages and currents on the DC2578A
board are for demonstration purposes and not inherent
limits of the LTC4281, the LTC3886, the LTC3887, or the
LTC2975. Input voltages as high as 33V are possible with
the LTC4281 and as high as 60V for the LTC3886. Much
higher and more flexible voltages and currents are achievable as required by each system. See the individual device
data sheets for complete details.
GETTING STARTED
POWERING THE BOARD
Begin with 12V power. Plug in a supply rated for at least
12W (1A) to the J2 connector, or clip to the 12VIN and
GND leads. The green LED near the 12V turret will illuminate when power is applied. Also at power-up, an auxiliary
keep alive 3.3V supply powers the onboard I2C bus.
THE SEQUENCE OF EVENTS
The board is configured to sequence-up autonomously
and deliver power to the loads on the CH0 to CH5 output
turrets. A combined total of 10W is available at the POL
IBC
T=0
PLUG
IN
12V INPUT
1
12V HOT SWAP
IBC_8V
IBC_5V
2
DELAY0
DELAY1
3
CH0
CH1
PROGRAMMABLE
SEQUENCE
ORDER
CH2
CH3
CH4
CH5
SHARE_CLK
POL
T=0
DC2578a F04
Figure 4. DC2578A Power Sequence
Figure 5. Hot Swap Voltage Ramp
outputs. The associated LEDs light as each output channel powers up in sequence. There is a lot going on during
power-up, so let’s take a look at the sequence.
(1) When the LTC4281 hot swap controller receives
power, it automatically begins the sequence of events.
On this board, the LTC4281 is enabled by default, so it
begins charging the capacitors at a (configurable) measured rate, preventing excessive inrush current from collapsing the 12V input supply. The LTC4281 monitors the
inrush current and the input and output voltages, as well
as the health of the FET, maintaining power if all system
parameters are within programmed limits and the FET is
healthy.
(2) When the hot swap output voltage rises above the
VIN_ON input threshold of the LTC3886, and the LTC3886
is finished with its boot up from EEPROM, the two intermediate buses begin their sequence. The LTC3886 has
two independent outputs, one programmed to operate
at 8V and one at 5V. On this demo board, the LTC3886
sequencer is programmed to bring up the 8V rail at the
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DEMO MANUAL DC2578A
GETTING STARTED
same time as the 5V rail. Because these two rails are
intended to operate in tandem their sequence spacing
must be nearly coincident in order to maintain sequencing
coherence between the two intermediate power domains.
The scope trace in Figure 6 shows the hot swap (yellow),
the 8V (blue) and 5V (green) intermediate buses, and one
of the loads (pink) as the systems powers up.
CH4, and CH5). Because the sequence timing is programmable, and because the LTC2975 and LTC3887 share a
common time base, any sequence order is achievable.
Sequence timing at the loads is coordinated between
the LTC2975 and the LTC3887 with the SHARE_CLK
signal, which sets the TIME = 0 moment at which both
ICs agree that they are ready and can begin sequencing.
The LTC3886 intermediate bus controller does not share
SHARE_CLK, and the LTC4281 does not have such a signal, so timing of up-stream events is independent.
Once powered up, each output channel can source up to
1A to its load, and will generate a fault under excessive
load current. Both the LTC3887 and the LTC2975 maintain
better than 0.5% accuracy at their respective outputs,
accurately measure current in their output channels, and
can respond to overcurrent with programmable fault
responses. The LTC3887 and LTC2975 can also coordinate their fault responses so that CH0 to CH5 all respond
appropriately in response to any fault.
Figure 6. Sequence Timing from Board Power
(3) When the 8V and 5V intermediate bus voltages rise,
they power the down-stream point-of-load regulators and
cause them to turn on. The LTC3887 sequences its two
outputs (CH0 and CH1), and the LTC2975 sequences its
four supplies during the same time period (CH2, CH3,
Each regulator output has its own turret to make access
easy. The POL output turrets are located on the upper and
lower right hand side of the board, the two intermediate
bus outputs are located in the center of the board, labeled
IBV_5V and IBV_8V, and the hot swap turret is located
center left. Each turret has an associated green LED to
indicate when the corresponding power supply is active.
14
12
HS
IBV_8V
VOLTS
10
IBV_5V
8
CH0
6
CH2
CH1
CH3
4
CH4
CH5
2
0
–2
–0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
TIME (s)
Figure 7. Sequence Up Timing
6
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DEMO MANUAL DC2578A
DC2578A BUTTONS AND FUNCTIONS
The DC2578A can demonstrate many important features
of the ICs onboard. There are several pushbuttons to activate these features.
respond to other faults as well, such as voltage and current faults by turning off and retrying after a cooldown
delay.
4281 DISABLE BUTTON
The red MOS STRESS LED may illuminate briefly when
the 4281 FAULT button is pressed. This indicates that the
LTC4281 has detected the event and is responding appropriately. Press the 4281 DISABLE button momentarily to
re-enable after a hot swap fault.
The LTC4281 on this board is enabled by default, so it
powers up the FET as soon as 12V input power is good.
To momentarily disable the LTC4281 press the button
labeled 4281 DISABLE (Figure 8) which commands the
LTC4281 hot swap to shut down its FET. Pressing this
button will momentarily interrupt power to everything
down stream of the hot swap. When powering down, the
down-stream LTC3886, LTC2975, and LTC3887 will not
communicate over the I2C bus. Only the LTC4281 will
communicate. The LTC3886, LTC2975, and LTC3887
are configured to only communicate when they have VIN
power available. Since the hot swap removes this power,
no communication is possible.
The green LED near the hot swap turret illuminates when
the LTC4281 PGOOD output is active.
Figure 9. LTC4281 Fault Button
POL DISABLE BUTTON
The LTC3887 and LTC2975 share a common control input
that commands them to turn on their outputs. Normally
this signal pulls high as soon as the intermediate buses
power up. Pressing the POL DISABLE button (Figure 10)
momentarily disrupts this control signal and causes all
of the POL outputs to sequence down in a coordinated
fashion. The hot swap and intermediate buses remain up.
Figure 8. LTC4281 Disable Button
4281 FAULT BUTTON
The LTC4281 constantly monitors the FET for any conditions that may cause damage, including a short that pulls
down on the gate. The button labeled 4281 FAULT (Figure 9)
simulates a FET bad fault for the LTC4281. Pressing this
button momentarily pulls down the FET gate through a
resistor to GND. In response the hot swap controller turns
off the FET and latches off, since retrying with a bad FET
could be damaging. The LTC4281 is programmable to
Figure 10. POL Disable Button
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DEMO MANUAL DC2578A
DC2578A BUTTONS AND FUNCTIONS
The pin labeled RUN in the header at the bottom of the
board carries this same signal, which can be monitored
or pulled low at the pin.
Figure 11. CREATE FAULT Button
CREATE FAULT BUTTON
All of the PSM ICs on this demo board monitor for faults
and have programmable fault responses. The button
labeled CREATE FAULT (Figure 11) produces an undervoltage fault on CH2 at the load, causing the LTC2975
to respond according to its programmed fault response,
bringing down all of its controlled channels (CH2 to CH5),
then restarting them when the fault button is released and
the fault is gone. This behavior is configurable, including
fault responses and fault sharing between the LTC2975
and LTC3887.
Figure 12. LOAD PULSE Jumper
LOAD PULSE JUMPER
Figure 13. IBV_8V Response to a 1A Current Step
The LTC3886 has a set of special loop stability tuning
features that allow the user to change the gain, resistance,
and gm components of the control loop. This makes it
quite flexible, but also requires some tuning to optimize
the loop response. To make the loop response more
observable the DC2578 board contains a load pulser that
can step a controlled load current on the 8V intermediate
bus, causing the LTC3886 to exhibit its step response.
Enable this load pulser by setting the LOAD PULSE jumper
(Figure 12) to the ON position. An LTC6992-2 Timerblox
IC generates a repetitive pulse train that periodically
pulses the gates of three MOSFETs loading the IBV_8V
bus, forcing 1A total load current pulses from IBV_8V to
GND.
As we will see later, the load pulser makes it easy to
observe the load transient response on the IBV_8V turret while adjusting the loop stability parameters in the
LTC3886. The LTC3886 data sheet contains a helpful section called PROGRAMMABLE LOOP COMPENSATION that
explains the circuit and how to estimate loop bandwidth
and phase margin by measuring the voltage at the at the
ITH pin. On the DC2578A board this is the voltage across
C17 near the LTC3886 in the center of the board. A similar
transient, like Figure 13, can be more easily observed at
the voltage on the IBV_8V turret in the center of the board.
Also, see Application Note 170.
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DEMO MANUAL DC2578A
DC2578A BUTTONS AND FUNCTIONS
THE I2C/SMBUS/PMBUS
The I2C bus is accessible through the connectors on the
left hand side of the board. There are three: the black
14-pin LINDUINO header, the white 12-pin DC1613 header,
and the SCL, SDA and ALRT pins. Each of the connectors
is buffered to provide bus isolation and acceleration for
the heavily loaded SCL and SDA lines.
Use the white DC1613 header to connect a DC1613 dongle
and LTpowerPlay to the board. This is the most common
use model. The DC1613 dongle provides a connection
from a Windows PC running LTpowerPlay that can control
and monitor all of the features of the parts on the I2C bus.
See the LTpowerPlay section below for more details.
Use the black Linduino connector to attach a DC2026
Linduino and demonstrate the firmware control capabilities of that platform. The Linduino section below gives
more details.
Use the SCL, SDA and ALRT header pins to attach other
I2C bus masters. These pins are also useful for probing
the I2C bus with an oscilloscope or Beagle bus sniffer. One
additional, very useful use is to attach a scope probe to
the ALRT line, and trigger on a falling edge. This provides
a very simple trigger when a fault happens on the board,
showing the events taking place directly before and after
the fault condition.
Figure 14. LTpowerPlay Graphical User Interface
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DEMO MANUAL DC2578A
USING LTpowerPlay TO EXPLORE
The LTpowerPlay GUI is the best way to view and interact
with the DC2578 system in real time. The ICs on the board
have a rich set of features that are accessible through the
I2C/SMBus/PMBus interface, and LTpowerPlay taps into
all of these resources, making them visible, clear, and
controllable in one place.
You can use LTpowerPlay to evaluate the DC2578A demo
board (one of many demo boards available), or connect it
to a complete production system through an I2C/SMBus/
PMBus bus. It also works in off-line mode to plan and
prepare register settings with no board connection at all.
Use any of these modes to build a multichip configuration
file, then save it to disk so it can be uploaded to a board
later. It is a powerful debug tool for use during board
bring-up or for diagnosing problems. It can show status
and faults in all of the ADI ICs on the bus, as well as record
and play back events as they happen, and it can provide
live remote support with a helpful support representative.
LTpowerPlay keeps itself up-to-date with the latest drivers
and documentation through an auto-update feature. You
can download LTpowerPlay here:
http://www.linear.com/ltpowerplay
LTpowerPlay talks to the I2C/SMBus/PMBus through the
DC1613 dongle, which converts from the USB port on
the PC (see Figure 3). Make the connections by plugging in the DC1613 to a USB port on the PC and plug the
12-pin ribbon cable to the DC2578A board at the white
header labeled DC1613 on the left side of the board. When
LTpowerPlay launches it finds the dongle, then probes the
DC2578A board to find the PMBus parts there. For this
demonstration system LTpowerPlay automatically loads
all of the ICs in the system tree, and the hardware configuration in each one (Figure 14).
LTpowerPlay BASICS
LTpowerPlay is a powerful tool for visualizing what is
going on in a system in real time. Here are some of the
many features that are available. This is a subset of all
available capabilities in LTpowerPlay. Use the Help menu
to find more information.
INITIALIZING THE DC2578A BOARD
Begin with the 12V power supply and the DC1613 dongle
connected.
When LTpowerPlay first starts and finds the DC2578A
board connected to the DC1613 dongle it populates
the system tree with all of the I2C ICs on the board: the
LTC4281, the LTC3886, the LTC3887, and the LTC2975.
It then communicates with each IC at its default address,
and loads the register contents from each one into the
GUI. Under normal conditions all of the ICs will be powered, and will communicate with LTpowerPlay. In situations where one or more of the ICs is not powered,
LTpowerPlay displays demo board default values from a
default file1. See Figure 15. Under normal circumstances
this is all that is necessary, and the user doesn’t need to
do any further initialization.
USING A PROJECT FILE
If you make changes to register settings in LTpowerPlay
and wish to preserve these settings in a file for later,
simply save a project file using the File  Save and File
 Open menu items. A project file contains all of the
information about the system tree, device addresses, and
register configurations.
Save a project file containing the current state of the registers represented in LTpowerPlay using the File  Save...
menu and entering an appropriate file location and name.
The default configuration file for the DC2578A board is
located here in the LTpowerPlay installation directory:
C:\Program Files (x86)\Linear Technology\LTpowerPlay\
demos\democircuits\DC2578A\DC2578A_Defaults.proj
The simplest method to access this default programming file is using the demo menu, by selecting Demo 
DC2578A_Defaults. This demo menu loads the file, downloads the register values into the ICs on the board, and
commands each IC to store the settings into EEPROM.
1. For complete instructions on programming the DC2578A see Appendix A on Programming at
the end of this manual.
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DEMO MANUAL DC2578A
USING LTpowerPlay TO EXPLORE
The procedure for loading any new project file into the
operating memory of the ICs on the DC2578A board is
as follows:
which can include a problem with a channel (like CH5 in
Figure 16), a stored fault log, or simply commanded off
with power not good, as with CH0 and CH1 in the figure.
1) File  Open...
In Figure 17 we see the system tree when the hot swap
is communicating over the bus, but not supplying downstream power. All other ICs are off, so not communicating.
This is indicated by the red circle icons indicating a device
that is not communicating on the bus.
2) Select the desired file (it may be in your work area or
in the LTpowerPlay installation directory).
3) Press the GO ONLINE button to begin communicating
with the I2C bus.
4) Press the PC  RAM button to download the register
settings to the ICs on the board.
Figure 16. System Tree with Color Coding
Figure 15. System Tree
THE SYSTEM TREE
The main visualization of the overall system is the system
tree, which shows the status of each IC in the design at
a glance. Each power supply device and each channel is
represented in the tree. Each device’s type and I2C address
is shown, and each channel is labeled with an appropriate
name representing its function on the DC2578A board.
Select an IC or channel in the system tree by clicking it.
Colors and icons are important in the system tree. Each
little square icon is divided into a lower half labeled O
for OUTPUT ENABLE, and an upper half labeled S for
STATUS. Green means good, and red means fault. Gray
means inactive (OFF). Yellow means status warning,
Figure 17. System Tree with Limited Communication
The system can also be sub-divided by group. In the tab
above the system tree is a set of group names that represent the parts of the power hierarchy for this board. Select
a group by clicking its name (Figure 18). A selected group
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DEMO MANUAL DC2578A
USING LTpowerPlay TO EXPLORE
limits the devices shown in the system tree, and also the
operations that are performed (such as group operation
commands). It is useful to sub-divide the system because
the complexity of a multi-tiered power supply makes operating on sub-blocks necessary.
Figure 18. System Tree with Point-of-Load Group
Figure 19. Configuration Registers Tab
CONFIGURATION REGISTERS
The configuration registers for each IC are accessible
in the Config tab (Figure 19). Registers for the selected
device or channel in the system tree are displayed here.
Note the buttons along the top, which select groups
of registers by category, such as Setup, Voltage, Fault
Responses, etc.
Change a register value by clicking to select the register
and typing the new value. Write the changed register value
to the IC register using the shortcut key: F12. Write ALL
register values from LTpowerPlay to all ICs using the PC
 RAM button in the button bar.
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DEMO MANUAL DC2578A
USING LTpowerPlay TO EXPLORE
TELEMETRY, STATUS AND FAULT REGISTERS
The telemetry tab displays all of the status and fault registers in the selected channel (Figure 20). Available telemetry depends upon which IC and which channel is selected
in the system tree. All of this information is updated in
real time while LTpowerPlay is actively scanning the I2C
bus and the ICs are on line and communicating. Available
telemetry from the PSM parts includes input voltage and
current, output voltage and current, power, temperature,
fault conditions, and historical values.
Figure 21. Telemetry Plot
TELEMETRY PLOT
Figure 20. Telemetry Registers Tab
The telemetry plot shows a graphical timeline of the
selected sampled telemetry for all available ICs in the
system, similar to a slow-motion oscilloscope trace
(Figure 21). For the PMBus devices, which share a common set of commands (like READ_VOUT), all available
similar telemetry for all PMBus ICs in the system is represented on one plot. The LTC4281 is the only device
of its kind on the bus, and it does not support PMBus
commands, so when it is selected only a single register
is represented on the plot.
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DEMO MANUAL DC2578A
USING LTpowerPlay TO EXPLORE
IDEALIZED WAVEFORMS
FAULT WARN LIST
The idealized On/Off waveforms tab shows idealized timing information for all channels in the system, based upon
how the ICs are programmed to sequence up and down.
The data is representative of the on and off delays, the
ramp times (where applicable), and the voltage levels for
each channel. This is a very easy way to visualize the real
sequencing behavior of the whole system (Figure 22).
The FAULT_WARN_LIST tab collects a complete set of
fault and warning indicators for all of the PMBus ICs in the
system (or in the currently selected group in the system
tree). It is a virtual register representation at the level of
each IC, displaying all of these virtual registers collected
into one easy to read location under the FAULT_WARN_
LIST aggregation tab.
Simply select the FAULT_WARN_LIST register in the
status summary section of the telemetry tab of any chip
in the system. This virtual register in the telemetry tab
shows fault and warning status for the currently selected
chip. Concurrently, the aggregation tab displays all of the
FAULT_WARN_LIST registers for all chips in the system
tree. This is a powerful way to quickly determine where
there are faults and warnings in the system without needing to click through many registers (Figure 23).
Figure 22. Idealized Waveforms Tab
Figure 23. LTPowerPlay FAULT_WARN_LIST
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DEMO MANUAL DC2578A
SEQUENCING
The DC2578A board is somewhat unique among demo
systems in that it contains a complete hierarchy of
power-handling capabilities. Because of this structure, it
requires special sequencing that simpler boards do not.
This uniqueness is a virtue because it demonstrates how
powerful all of the Analog Devices power management
ICs are when they work together seamlessly. We will
revisit the sequencing operations here, focusing on the
LTpowerPlay features that affect it.
All of the ICs on the demo board are programmed to
autonomously start delivering power down stream as
soon as they can. The LTC4281 detects a good input
voltage and turns on the pass FET. The LTC3886 detects
its input voltage and generates the two intermediate bus
voltages. The LTC3887 and LTC2975 both detect that
their input voltages are good and enable their outputs
cooperatively in the programmed sequence. Any chip in
the system that is not powered may show in LTpowerPlay
as a red circle because it does not communicate on the
I2C bus (Figure 24). This flow of power is required by the
design, so it is not programmable. There are, however,
many programmable features at each step in the process.
LTC4281 HOT SWAP POWER-UP
The LTC4281 is primarily an input control device. It measures input voltage, current, and FET health, and reports
all of its status and telemetry on the I2C bus. During
sequencing it limits the current allowed to flow through
the FET by measuring it and actively controlling the FET
gate when current is too large. The maximum allowed current is programmed as the voltage across the sense resistor, set in the ILIM_ADJUST register. During power-up the
inrush current is limited to 30% of the ILIM_ADJUST current while V(SOURCE) is below 1.3V (the voltage across
the FET is large).
To control the allowable current, change the value of the
ILIM_ADJUST register. We can see the effect of changing
the value of the ILIM_ADJUST current on the power-up
behavior in Figure 25. Here three different ILIM_ADJUST
values were used, resulting in three different ramp-up
times. The value of the FOLDBACK_MODE setting also
affects the ramp behavior to limit current more aggressively for larger input voltages.
Once power is up, the LTC4281 actively enforces the
ILIM_ADJUST current limit by actively regulating the FET
gate when current exceeds the limit. This current clamp
can prevent down-stream devices from pulling too much
current, and in the event of overcurrent, the voltage will
droop as the FET current limits.
Figure 25. Hot Swap Ramp with Three Different Current
Limit Settings
Figure 24. Partially-Sequenced System Tree
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DEMO MANUAL DC2578A
SEQUENCING
Control the LTC4281 directly on the DC2578A board by
pressing the 4281 DISABLE pushbutton. This turns off
the device and powers down the entire board. This is
also an effective reset for all of the ICs when their power
is removed. This is equivalent to toggling the FET_ON
bit in the CONTROL register of the LTC4281 (Figure 26).
Figure 26. I2C Command of the LTC4281 FET
LTC3886 IBC SEQUENCING
This timing is programmed by several registers in the
LTC3886. The VIN_ON and VIN_OFF configuration registers command the voltages at which the LTC3886 recognizes its input as high enough to begin operation (Figure
27).
Once the sequencer begins operating, it honors the
TON_DELAY and TON_RISE configuration registers. In
the scope shot in Figure 28 we see that both the IBV_8V
and IBV_5V buses rise approximately 155ms after the
12V hot swap voltage rises. The delay from the hot swap
rising includes approximately 55ms boot time of the
LTC3886, but the remaining 100ms is commanded by the
TON_DELAY register. The two intermediate buses must
sequence up and down together to properly coordinate
the timing of the down-stream point-of-load devices.
Notice that the TON_RISE value is set to 8ms rise time.
This is because a fast rise time represents a larger inrush
current, and can exceed the current limit in the LTC4281
hot swap, causing a fault. The programmed values on
this board are for demonstration, and can be scaled up
appropriately for any larger system.
During sequencing the LTC3886 manages the ramp rates
and relative timing between the IBV_8V and IBV_5V intermediate buses. It waits until it receives 12V power from
the hot swap, then begins to sequence up the two intermediate buses.
Figure 28. Intermediate Bus Sequencing
Figure 27. LTC3886 VIN_ON and VIN_OFF Settings
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DEMO MANUAL DC2578A
SEQUENCING
sentative. Remember, however, that while the system is
powering up, you may observe additional delays due to
boot up time in the ICs.
Figure 29. LTC3886 Sequence Timing
LTC2975 AND LTC3887 POL SEQUENCING
Even though these two POL controllers are on different
intermediate buses they can still coordinate their timing
and fault responses, managing sequencing from a common TIME = 0 based upon their shared SHARE_CLK line,
and communicating fault information through their shared
FAULT line. These two sequencers have TON_DELAY values that both begin when the two ICs release SHARE_CLK
to begin clocking. This happens when both the LTC3887
and the LTC2975 observe VIN values above their respective VIN_ON settings.
Setting the relative sequence timing of the six POL power
supplies is simple. PMBus commands are common
between devices, so TON_DELAY, TOFF_DELAY, TON_
RISE, TON_MAX, TOFF_MAX, and others, are defined
similarly, and can be programmed into each IC so that
they all cooperate during sequencing. On the DC2578A
board the LTC2975 and LTC3887 are programmed to
stagger their sequence up events every 100ms, starting
with CH2, and CH3, then CH0, and proceeding left to right
(Figure 30). The sequence is completely configurable, as
is the independent down sequence.
Notice that the idealized waveforms tab maintains a visual
representation of the relative sequence timing between
all of the channels as they are configured. This view is
accurate to the extent that the register values are repre-
Figure 30. LTC2975 Sequence-Up Timing
MARGINING (GROUP OP)
LTpowerPlay can address several ICs simultaneously
using grouped PMBus commands. This is convenient in
cases like margining the power supplies or simultaneous sequencing. Select the group OP button to activate
the group OP window (Figure 31). The buttons in this
window allow you to conveniently command sequencing
or margining operations for all of the ICs currently visible in the system tree. If you have selected a sub-group
in the system tree, such as the POINT-OF-LOAD group,
only that sub-group will receive the group commands.
This is important in cases when power is not applied to
the entire power tree, so some ICs will not respond to
bus commands.
Selecting the POINT-OF-LOAD group in the system tree
tab limits the operation to the LTC2975 and LTC3887
devices. Clicking the Margin High group operation
causes all of the POL supplies to ramp to their predefined
VOUT_MARGIN_HIGH voltages, as defined in each channel’s configuration (Figure 32). The DC2578A board configuration sets margin excursions to ±5%. Clicking the
On group operation button returns the voltages to their
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DEMO MANUAL DC2578A
SEQUENCING
nominal settings (Figure 33). The servo mechanisms in
the LTC3886, LTC3887, and LTC2975 accurately control
the voltages to within 0.5% of their target values.
Figure 31. LTpowerPlay Group OP Menu
Figure 33. LTPowerPlay Telemetry Plot During Margining
LTC3886 TRANSIENT RESPONSE
The LTC3886 has programmable loop compensation
through two registers that allow the user to adjust the
control loop gm and resistance to move the loop gain
and pole locations without changing any hardware. The
LTC3886 PWM_COMP register contains settings for both
of these values.
gm
RTH
ITH_R
CTH
+
VREF
–
FB
ITH
CTHP
Figure 34. LTC3886 Programmable gm and RTH
Figure 32. LTPowerPlay VOUT MARGIN
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DEMO MANUAL DC2578A
SEQUENCING
The DC2578A has an onboard load pulse circuit for stimulating the IBV_8V channel of the LTC3886 by pulsing a 1A
load current to GND repeatedly. This causes the IBV_8V
channel to respond with its step response that can be
easily observed on an oscilloscope. To observe and adjust
the transient response:
Fault Log tool. Access this tool by clicking the FL button
in the tool bar. If any PMBus IC in the tree has a stored
fault log, the FL button will have a red spot to indicate the
presence of fault information.
1) Move the LOAD PULSE jumper to ON.
2) Connect a scope probe to the IBV_8V turret.
3) Set the probe to 100mv/div, 100µs/div, AC coupled.
4) Modify the values of EA_GM and R_TH in the MFR_
PWM_COMP register of the LTC3886 control.
5) Observe that you can drive the loop between instability and well-damped response simply by adjusting
these registers (Figure 35).
6) Move the LOAD PULSE jumper to OFF when finished.
In Figure 35 we see the voltage step response at IBV_8V
for a tuned loop (yellow) and a detuned loop (gray).
This button brings up the Fault Log tool, which makes it
easy to read and decode the fault log for the IC selected in
the System Tree (Figure 36). If there is a stored fault log
(indicated in the EEPROM Log Status section), retrieve it
by pressing the Read NVM Log button. The decoded contents of the EEPROM fault log appear in the window. This
represents the stored ADC readings and status indicators
leading up to the time of the fault, in an easy-to-read text
format. Clear the EEPROM fault log and re-arm the system
by pressing the Clear/Re-arm EEPROM Log button. This
will also clear the latched fault state of the RAM registers
in the selected IC.
Note that the Fault Log tool is for the LTC3886, LTC3887,
and LTC2975 PMBus ICs on the board, which conform
to a standard fault log protocol. Accessing the EEPROM
fault log in the LTC4281 is handled by directly reading the
EEPROM fault and ALERT registers. Refer to the LTC4281
data sheet for full details.
Figure 35. LTC3886 Adjustable Loop Step Response
FAULT LOGS
All of the ICs on this board offer a EEPROM black box
fault log capability that can store the state of the system
at the time that a fault is detected. LTpowerPlay makes it
easy to read these fault logs for the PMBus parts with its
Figure 36. LTpowerPlay PMBus Fault Log Tool
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DEMO MANUAL DC2578A
LINDUINO AND FIRMWARE CODE
The DC2578A is supported by the Linduino microcontroller platform, which is an Arduino-compatible microcontroller, programmed in C and C++. The Linduino code
library provides a thorough set of sample code demonstrating the best practices for communicating with and
controlling the ADI ICs on the board. If you have the latest
Linduino development environment and the sketchbook
code installed, then you will be able to use the Linduino to
talk to the DC2578A on the I2C/SMBus/PMBus, controlling all of the functions and features of the LTC4281, the
LTC3886, the LTC2975, and the LTC3887 on the board.
The Linduino code gives practical examples of how to
use the extensive PMBus and SMBus libraries to access
the devices.
See the Linduino web site, and the DC2026 demo manual
for instructions on getting started with the Linduino platform:
http://www.linear.com/solutions/linduino
http://cds.linear.com/docs/en/demo-board-manual/
dc2026cfe.pdf
http://cds.linear.com/docs/en/application-note/an153fb.
pdf
Once you have a working Linduino and the latest
LTSketchbook code library, simply select the DC2578A.
ino sketch from the sketchbook and upload it to your
Linduino.
File  Sketchbook  User Contributed  DC2578A 
DC2578A
Figure 37. Linduino Sketch for the DC2578A
The Linduino code exists to give examples for programming an embedded system to communicate with the
Analog Devices PSM ICs on this and other demonstration
boards. Find the code in your locally-installed LTSketchbook here:
.../LTSketchbook/User Contributed/DC2578A/
.../LTSketchbook/libraries/LT_PMBUS/
.../LTSketchbook/libraries/LT_SMBUS/
You may control many of the features of the DC2578A
demo board by selecting the appropriate menu items in
the serial monitor window. Type the menu number and hit
ENTER. The Linduino will send the necessary commands
over the bus to the demo board (Figure 37).
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DEMO MANUAL DC2578A
APPENDIX A: PROGRAMMING
There are many ways to program the very flexible ICs on
the DC2578A and there are relatively few ways to get it
right, with everything programmed for best performance.
In some cases you can get the system into a state of
partial power that makes it tough to program, since some
of the devices are not powered. This appendix presents
the best way to bring the system back to a known-good
program state.
3) Note the group labels at the top of the system tree
tab: All, HOT SWAP, INTERMEDIATE BUS, and POINTOF-LOAD groups should be available. Select the HOT
SWAP group. Note that if you create your own project
file you may need to create your own groups using the
Edit Groups... tool.
Because this board has several layers of power supplies,
flowing power from the board input through the hot swap,
then through the intermediate buses, and finally to the two
cooperating POL managers/controllers, there are many
ways to disable power supplies down stream. Disabling
down-stream power supplies will prevent one or more
of the ICs from communicating on the I2C bus, which
will prevent LTpowerPlay from being able to successfully
program that device.
The easiest programming technique in LTpowerPlay is
to select the demo menu and allow the tool to attempt to
program all of the devices on the board at once. Selecting
Demo  DC2578A_Defaults instructs the tool to write the
RAM contents of all ICs on the board, then burn those
RAM values into the EEPROMs for persistent storage.
Unfortunately, if one or more of the ICs is not powered,
then the process will not succeed. The result may be an
incompletely programmed board.
Figure 38. System Tree with Hot Swap Group Selected
4) Press the Write to RAM button on the tool bar. This will
write correct values to the hot swap IC, instructing it
to enable its output.
The most general solution to successfully programming
in this environment is an iterative approach in which each
up-stream device is programmed in order, followed by
devices further down stream. The process looks like this:
5) Select the INTERMEDIATE BUS group next. Press Write
to RAM. This programs the LTC3886, activating the
IBV_8V and IBV_5V rails which power the LTC3887
and LTC2875.
1) Load the desired project file from disk. The DC2578A_
Defaults project file is a safe option:
C:\Program Files (x86)\Linear Technology\LTpowerPlay\
demos\democircuits\DC2578A\DC2578A_Defaults.proj
6) Select the POINT-OF-LOAD group. Press Write to RAM.
This programs the LTC3887 and LTC2975 ICs. At this
point all of the rails should be active, and all of the ICs
should be correctly programmed.
2) Press the GO ONLINE button to activate communication with the board.
7) Store RAM contents to EEPROM by pressing the Write
to EEPROM button.
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DEMO MANUAL DC2578A
APPENDIX A: PROGRAMMING
8) Verify the contents of all ICs by selecting the All group
and pressing the VERIFY button in the toolbar.
There are additional resources on the web to help with
advanced programming topics. These documents include
I2C/SMBus/PMBus addressing for Analog Devices
devices:
http://cds.linear.com/docs/en/application-note/an152f.pdf
If the Verification process indicates problems, repeat the
process for the offending ICs. Since every part of the system should now have power it is not necessary to use the
sub-groups during programming, but it may be helpful to
isolate specific elements of the system.
Programming directly through in-flight update:
http://cds.linear.com/docs/en/application-note/an166f.pdf
EEPROM structure in Analog Devices PSM devices:
http://cds.linear.com/docs/en/application-note/AN145f.
pdf
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DEMO MANUAL DC2578A
APPENDIX B: SCHEMATICS
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APPENDIX B: SCHEMATICS
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APPENDIX B: SCHEMATICS
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APPENDIX B: SCHEMATICS
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APPENDIX B: SCHEMATICS
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APPENDIX B: SCHEMATICS
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APPENDIX B: SCHEMATICS
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APPENDIX B: SCHEMATICS
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DEMO MANUAL DC2578A
APPENDIX B: SCHEMATICS
dc2578af
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Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
31
DEMO MANUAL DC2578A
ESD Caution
ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection
circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.
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LT 1117 • PRINTED IN USA
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