High Performance Single Phase DC/DC Controller with Digital Power Management

design ideas
High Performance Single Phase DC/DC Controller with
Digital Power Management
Yi Sun
LTC3883 is a single phase
synchronous step-down
DC/DC controller featuring
a PMBus interface for digital
control and monitoring,
and integrated MOSFET
gate drivers. It can function
either standalone or in a
digitally managed system
with other Linear Technology
PMBus enabled parts.
5mΩ
VIN
6V TO 24V
10µF
100Ω
1µF
100Ω
10nF
3Ω
10nF
VIN
10k
10k
PMBus
INTERFACE
10k
10k
10k
10k
•±0.5% output voltage accuracy over the
operation temperature range of –40°C to
125°C.
• PMBus, which provides programmable
voltage, current limits, sequencing,
margining, OV/UV thresholds, frequency
synchronization and fault logging.
•Telemetry read back including VIN, IIN,
VOUT, IOUT, temperature and faults.
•External voltage divider to set the chip
address, switching frequency and the
output voltage.
•Input current sensing and inductor
DCR auto calibration.
1.8V/30A SINGLE PHASE DIGITAL
POWER SUPPLY WITH I IN SENSE
Figure 1 shows a 7V to 14V input,
1.8V/30A output application that features
inductor DCR current sensing. To improve
the accuracy of DCR current sense, the
LTC3883 senses inductor temperature and
10k
5k
VDD33
PGOOD
SDA
M2
ALERT
RUN
1.4k
1µF
VDD25
20k
24.9k
10k
20k
12.7k
9.09k
23.2k
17.8k
FREQ_CFG
SCL
VOUT_CFG
1.4k
VTRIM_CFG
0.22µF
SHARE_CLK ASEL
GPIO
SYNC
WP
VDD25
VDD33
1.0µF
0.56µH
BG
PGND
10µF
M1
0.1µF
SW
VIN_SNS
The LTC3883 features:
•4.5V to 24V input voltage range and
0.5V to 5.5V output voltage range.
TG
LTC3883
BOOST
IIN_SNS
22µF
50V
1µF
D1
INTVCC
ISENSE+
ISENSE–
VSENSE+
VSENSE–
+
TSNS
GND
ITH
2200pF
1.0µF
100pF
D1: CENTRAL CMDSH-3TR
L: COILCRAFT XAL7070-551ME
VOUT
1.8V
30A
COUT
1520µF
MMBT3906
4.99k
M1: INFINEON BSC050N03LSG COUT: 4× 330µF SANYO 2R5TPE330M9,
2× 100µF AVX 12106D107KAT2A
M2: INFINEON BSC011N03LSI
Figure 1. 1.8V/30A single phase digital power supply with IIN sense
compensates for the TC of the DCR. This
method ensures the accuracy of the readback current and overcurrent limit. The
LTC3883’s control loop uses peak current
mode control, which offers fast transient
response. Figure 2 shows the typical
waveforms of a 10A load step transient.
Figure 2. Transient performance
of a 10A load step
VOUT
100mV/DIV
(AC-COUPLED)
IOUT
10A/DIV
(AC-COUPLED)
120mV
30A
20A
IL
10A/DIV
(AC-COUPLED)
20µs/DIV
January 2013 : LT Journal of Analog Innovation | 37
The LTC3883 uses a proprietary inductor DCR autocalibration function, which enables output current read back
accuracy within 3%, regardless of inductor DCR tolerance.
LTPOWERPLAY DEVELOPMENT
IIN
VIN
+
CIN
VIN VIN_SNS IIN_SNS
TG
LTC3883
Figure 3. DCR auto calibration
INDUCTOR DCR AUTO CALIBRATION
The problem with the conventional inductor DCR current sensing is that the tolerance of the DCR can be as large as ±10%,
greatly limiting the current read back accuracy. To solve this problem, the LTC3883
uses a proprietary inductor DCR autocalibration function. Figure 3 shows
the simplified diagram of this circuit.
The LTC3883 accurately measures the input
current, IIN, the duty cycle, D and calibrates
the real DCR value based on the relation:
LTpowerPlay
LTpowerPlay™ software is available for free at
www.llinear.com/ltpowerplay
SW
BG
ISENSE+
ISENSE–
The LTC3883 features input current sensing via a resistor in series with the input
side of the buck converter—a 5mΩ sense
resistor as shown in Figure 1. The sense
voltage is translated into a power stage
input current by the LTC3883’s 16-bit
internal ADC. An internal sense resistor
senses chip’s supply current at VIN, so it
can provide both the chip and the power
stage’s input current measurements.
M1
M2
IOUT
DCR
+
+ –
COUT
VCS
DCRCALIBRATED = VCS •
+
D
IIN
With this auto-calibration method,
the output current read back accuracy can be within 3%, regardless of inductor DCR tolerance.
1.2V/60A 3-PHASE DIGITAL
POWER SUPPLY
VOUT
–
All digital power management functions can be controlled by LTpowerPlay,
PC-based software compatible with all
of Lintear Technology’s digital power
products. With LTpowerPlay, designers can easily program and control the
entire power system without writing
a line of code. It is easy to configure
any chip on the bus, verify the system’s
status, read the telemetry, check fault
status, control supply sequencing.
CONCLUSION
The LTC3883 combines a best-in-class
analog DC/DC controller with complete
digital power management functions and
precision data converters for unprecedented performance and control. Multiple
LTC3883s can be used with other Linear
Technology PMBus products to optimize
multirail digital power systems. Powerful
LTpowerPlay software simplifies the development of complex power systems. The
LTC3883 can be used for telecom, computing, data storage, and other applications. n
The LTC3883 has an analog current
control loop, which makes it ideal for
PolyPhase® operation. Figure 4 shows
an example of a 3-phase single output
circuit, with one LTC3883 and one LTC3880
for a 7V to 14V input, 1.2V/60A output
application. The LTC3880 is a 2-phase
synchronous buck controller with digital
Figure 5. Transient performance of a 30A load
power system management. The interstep for 3-phase power supply
connection between these two chips is
straightforward and easy. Note how
VOUT
50mV/DIV
the input current sense resistor of
(AC-COUPLED)
the LTC3883 is used to sense the total
input current for all three phases.
Figure 5 shows the dynamic current sharing for a load step transient. All the three phases can
share the current evenly.
IL0
10A/DIV
IL0
10A/DIV
IL0
10A/DIV
20µs/DIV
38 | January 2013 : LT Journal of Analog Innovation
60mV
design ideas
5mΩ
VIN
6V TO 14V
10µF
INTVCC
100Ω
1µF
TG
LTC3883
BOOST
IIN_SNS
100Ω
Figure 4. 1.0V/60A 3-phase digital
power supply with IIN sense
VIN_SNS
10nF
22µF
50V
1µF
D1
M1A
0.1µF
M1
L0
0.56µH
SW
10nF
M1B
BG
PGND
3Ω
10k
10µF
1k
PGOOD
10k
PMBus
INTERFACE
VDD25
VIN
10k
10k
SDA
VOUT_CFG
SCL
VTRIM_CFG
ALERT
10k
GPIO
5k
SYNC
WP
ASEL
0.22µF
ISENSE–
VSENSE+
TSNS
ITH
GND
D2
VIN
TG0
TG1
LTC3880
22µF
1µF
M2A
0.1µF
M2
L2
0.56µH
SW1
BG0
M2B
BG1
PGND
VDD33
1µF
COUT1
530µF
10nF
BOOST1
SW0
M3B
VOUT
1V
60A
MMBT3906
2200pF
D3
INTVCC
BOOST0
1µF
+
VSENSE
4.99k
0.1µF
1k
1k
ISENSE+
1.0µF
M3A
17.8k
–
VDD25
VDD33
1.0µF
M3
L1
0.56µH
11.3k
SHARE_CLK
10k
10µF
20k
FREQ_CFG
RUN
10k
1µF
24.9k
1k
SYNC
1µF
SDA
SCL
VDD25
ALERT
VOUT1_CFG
GPIO1
SHARE_CLK
VTRIM0_CFG
RUN0
RUN1
VTRIM1_CFG
0.22µF
TSNS0
ISENSE0+
TSNS1
ISENSE1+
ISENSE0–
ISENSE1–
ITH0
MMBT3906
11.3k
15.8k
17.8k
0.22µF
1k
ITH1
GND
100pF
10µF
D1-D3: CENTRAL CMDSH-3TR
L0-L2: COILCRAFT XAL7070-301ME
1µF
VSENSE1
VSENSE0–
COUT2
530µF
20k
FREQ_CFG
VSENSE0+
+
10k
ASEL
WP
1k
24.9k
VOUT0_CFG
GPIO0
MMBT3906
10nF
+
COUT3
530µF
M1, M2, M3: FAIRCHILD FDMS3620S
COUT1, COUT2, COUT3: 330μH SANYO 4TPF330ML, 2× 100µF AVX 12106D107KAT2A
January 2013 : LT Journal of Analog Innovation | 39