nous buck regulator using a phase lockable controlled
on-time, current mode architecture. The output voltage
is programmable from 0.4V to 72% of V
IN
with a single
external resistor or an external voltage reference through
the reference input (REF) pin. The output voltage can be
margined up or down up to ±25% with 0.1% resolution
via a PMBus-compliant serial interface. The serial inter-
face can also be used to read back fault status and both
time-averaged (~4ms) and peak input/output current,
input/output voltage and temperature. System configu-
ration and monitoring is supported by the
LTpowerPlay
®
development system.
The architecture provides extremely fast transient
response and allows operation at the very low on-times
required to regulate low output voltages at high switching
frequencies. The operating frequency is programmable
from 400kHz to 3MHz with an external resistor or for
noise sensitive applications, it can be synchronized to an
external clock over the same range. The operating supply
voltage range is from 2.25V to 5.5V making it suitable
for operation from 2.5V, 3.3V or 5V rails or Lithium-Ion
batteries.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents including 5481178, 5705919, 5929620, 6144194, 6177787, 6580258, 5408150,
7420359. Licensed under U.S. Patent 7000125 and other related patents worldwide.
n
n
n
n
n
n
n
n
n
n
n
n
2.25V to 5.5V Input Voltage Range
±1% Total Output Voltage Accuracy Over
Temperature at V
IN
= 3.3V or 5V
Single Resistor-Programmable Output Voltage
PMBus Compliant Serial Interface:
n
Programmable Output Voltage Margining:
Up to ±25% V
OUT
Range with 0.1% Resolution
n
Read back of Average and Peak Temperature,
Current, and Voltage (25Hz Refresh Rate)
n
Fault Status
Phase-Lockable Fixed Frequency Up to 3MHz
Less Than 1ms Power-Up Time
Integrated 13-Bit ADC
Optional External Reference Input
Pin Selectable Fast-Margining of the Output Voltage
Power Good Flag with Pin Programmable Thresholds
and Filter Delay
Differential Remote Output Voltage Sensing
Master Shutdown Mode: <1μA Supply Current
Clock Out for 2-Phase Operation (12A Output Current)
Available in a Thermally-Enhanced 38-Lead
4mm × 6mm QFN Package
Intelligent Energy Efficient Power Conversion
ASIC/FPGA/Processor Power
Distributed Power Systems
Point of Load Power Conversion
APPLICATIONS
n
n
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TYPICAL APPLICATION
V
IN
2.25V TO 5.5V
PV
IN
V
IN
C
IN
LTC3815
MODE/SYNC
PGLIM
R
T
TRACK/SS
RUN_MSTR
RUN_STBY
PMBUS
SCL, SDA,
ALERT
MARGIN
WP
PGOOD
CLKOUT
CSLEW
REF
ASEL
SW
V
CC_SENSE
V
SS_SENSE
DA
OUT
FB
I
TH
R
C1
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
R
C2
0
C
C2
3815 TA01a
Efficiency and Power Loss
vs Load Current
V
OUT
= 1.8V
EFFICIENCY
1
POWER LOSS (W)
10
L
V
OUT
0.4V TO 0.72*V
IN
6A
C
OUT
POWER LOSS
V
IN
= 2.8V
V
IN
= 3.3V
V
IN
= 5V
10
100
1000
LOAD CURRENT (mA)
0.1
PGFD
0
10000
3815 TA01b
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For more information
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1
Rev B
LTC3815
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 7)
PIN CONFIGURATION
V
CC_SENSE
31 V
SS_SENSE
30 TRACK/SS
29 PGOOD
28 C
SLEW
27 RUN_STBY
39
PGND
26 RUN_MSTR
24 PGFD
24 V
IN
23 SW
22 SW
21 SW
20 NC
13 14 15 16 17 18 19
SW
SW
SW
PV
IN
PV
IN
PV
IN
SW
TOP VIEW
PGLIM
DA
OUT
SGND
REF
V
IN
, P
VIN
....................................................... –0.3V to 6V
V
CC_SENSE
, V
SS_SENSE
, C
SLEW
, R
T
, I
TH
, MODE/SYNC,
REF, TRACK/SS, PGFD, PGLIM, ASEL, DA
OUT
, MARGIN,
RUN_STBY, FB .............................. –0.3V to (V
IN
+ 0.3V)
RUN_MSTR, PGOOD,
ALERT,
SCL,
SDA Voltage ............................................. –0.3V to 6V
WP ............................................................ –0.3V to 2.5V
Operating Junction Temperature Range
(Notes 2, 3) ............................................ –40°C to 125°C
Storage Temperature Range .................. –65°C to 125°C
38 37 36 35 34 33 32
R
T
1
ASEL 2
MARGIN 3
WP 4
ALERT
5
CLKOUT 6
SDA 7
SCL 8
MODE/SYNC 9
SW 10
SW 11
NC 12
UFE PACKAGE
38-LEAD (4mm
×
6mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 38°C/W
EXPOSED PAD (PIN 39) IS PGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3815EUFE#PBF
LTC3815IUFE#PBF
TAPE AND REEL
LTC3815EUFE#TRPBF
LTC3815IUFE#TRPBF
PART MARKING*
3815
3815
PACKAGE DESCRIPTION
38-Lead (4mm × 6mm) Plastic QFN
38-Lead (4mm × 6mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult ADI Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications.
Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
I
TH
FB
2
Rev B
For more information
www.analog.com
LTC3815
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
OUT
I
Q
PARAMETER
Input Supply Range
Output Voltage Programming Range
V
IN
Supply Current
Normal Mode
Standby
Shutdown
V
IN
Undervoltage Reset
Hysterisis
Reference Current
Reference Current Line Regulation
Regulation Accuracy
ΔV
OUT,OFFSET
= (V
CC_SEN
– V
SS_SEN
) – V
REF
Maximum Margining Range
Set Point Accuracy
Resolution
LSD Step Size
NL_V
OUT
A
EA
f
BW
R
IN
t
SS
I
CSLEW
I
LIM
I
RUN_STBY
V
RUN_MSTR
V
RUN_STBY
I
ASEL
I
PGFD
I
SS
V
IH,MARGIN
V
IL,MARGIN
I
WP
SR
MARGIN
t
INIT
DAC Nonlinearity
Error Amplifier Open Loop Gain
Error Amp Gain Bandwidth Product
Differential Amplier Input Resistance
Internal Soft-Start Time/V
REF
C
SLEW
Pull-Up Current
SW Valley Current Limit
Regulator On Source Current
Regulator On Threshold (Master Shutdown)
Regulator On Hysterisis
Regulator Power-Down Threshold
Regulator On Threshold (Standby Mode)
ASEL Programming Current
PGFD Programming Current
SS Current
MARGIN High Voltage
MARGIN Low Voltage
WP Pin Pull-Up Current
Reference Slew Rate During Margin Change
WP = 0V
C
SLEW
= 1nF
C
SLEW
= OPEN
C
SLEW
= SV
IN
Delay from Power Applied Until
V
OUT
Ramp Up
R
T
= 25.5k
R
T
= SV
IN
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, V
IN
= 3.3V unless otherwise noted. (Note 2)
CONDITIONS
l
l
MIN
2.25
0.4
TYP
MAX
5.5
72% of V
IN
UNITS
V
V
mA
µA
µA
V
V
µA
µA
%/V
%
%
%
Bits
%
V
RUN_MSTR
> 1V (Note 4)
V
RUN_STBY
= 0V, V
RUN_MSIR
> 1V
V
RUN_MSTR
= 0V, V
SDA
= V
SCL
≥ V
IN
V
IN
Rising
V
IN
Falling
(Note 10)
V
IN
= 2.5V to 5.5V (Note 10)
V
REF
= 1.5V (Notes 5, 10)
MFR_VOUT_COMMAND = –25% to
25%, V
REF
= 1.5V (Note 5)
l
l
l
5
120
1
2.05
99.2
99.5
–0.5
–25
–0.5
9
0.1
2.15
0.2
100
100
0.05
8
200
2.25
100.8
100.5
0.2
0.5
25
0.5
V
UVLO
I
REF
ΔI
REF,LINE
ΔV
OUT,OFFSET
ΔV
OUT,MARGIN
l
±1
I
TH
= 1V (Note 5)
(Note 6)
Measured at V
CC_SEN
Pin
External C
SS
= Float
V
CSLEW
= 0V
Sourcing (Note 8)
Sinking
V
RUN_STBY
= 0V
Rising Edge
Falling Edge
I
Q
< 10μA
0.9
l
LSB
dB
MHz
kΩ
ms/V
µA
80
20
160
1
–10
5.5
6.5
–6
–2.5
1
0.1
0.65
1
10
10
1.1
7.5
A
A
µA
V
V
V
V
µA
µA
0.7
1.2
V
SS
= 0V
4
1.2
5
6
0.4
µA
V
V
µA
%/ms
%/ms
%/µs
10
0.1
23
10
1
2
Initialization Time
ms
Oscillator and Power Switch
f
OSC
V
SYNC
Oscillator Frequency
SYNC Level High
SYNC Level Low
0.85
0.85
1.2
1.0
1.0
1.15
1.15
0.3
MHz
MHz
V
V
For more information
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3
Rev B
LTC3815
ELECTRICAL CHARACTERISTICS
SYMBOL
V
MODE
t
ON(MIN)
t
OFF(MIN)
R
TOP
R
BOTTOM
PARAMETER
Discontinuous Mode Threshold
Minimum On-Time
Minimum Off-Time
Top Power PMOS On Resistance
Bottom Power NMOS On Resistance
Relative Phase of CLKOUT
Default PGOOD Threshold
MODE/SYNC = 0V
V
PGLIM
= V
IN
, V
OUT
>1V
V
PGLIM
/V
REF
= 0.19, V
OUT
≥ 1V
V
PGLIM
/V
REF
= 0.38
I
OUT
= 3mA
PGFD = 0V
PGFD = 0.65V
PGFD = V
IN
150
1.0
17
±8
±6
±13
The
l
denotes the specifications which apply over the specified operating
junction temperature range, V
IN
= 3.3V unless otherwise noted. (Note 2)
CONDITIONS
MIN
TYP
1
75
100
35
20
180
±10
±10
±30
0.1
190
1.6
24
13
0.5
(Note 9)
l
MAX
UNITS
V
ns
ns
mΩ
mΩ
Deg
θ
CLKOUT
PGOOD
V
PGOOD,DEFAULT
±12
±9
±17
±5
0.3
250
2.2
32.5
%
%
%
µA
V
µs
ms
ms
Bits
mV
V
V
PGOOD,PROGRAM
Program PGOOD Threshold
I
LEAK
V
OL
t
PGFD
PGOOD Leakage Current
PGOOD Output Low Voltage
PGOOD Filter Delay
Output Voltage Readback
N
V
F/S
V
OUT_TUE
t
CONVERT
N
V
F/S
V
IN_TUE
t
CONVERT
N
V
F/S
I
OUT_TUE
t
CONVERT
N
V
F/S
I
IN_TUE
t
CONVERT
Resolution
LSB Step Size
Full Scale Output Voltage
Total Unadjusted Error
Conversion Time
Resolution
LSB Step Size
Full Scale Input Voltage
Total Unadjusted Error
Conversion Time
Resolution
LSB Step Size
Full Scale Output Current
Total Unadjusted Error
Conversion Time
Resolution
LSB Step Size
Full Scale Input Current
Total Unadjusted Error
Conversion Time
40
40
13
10
±82
±3
(Note 9)
l
16.4
±0.75
±0.5
40
13
4
131
±1.5
40
13
10
±82
±3
%
%
ms
Bits
mV
V
%
ms
Bits
mA
A
%
ms
Bits
mA
A
%
ms
Input Voltage Readback
Output Current Readback
Input Current Readback
4
Rev B
For more information
www.analog.com
LTC3815
ELECTRICAL CHARACTERISTICS
SYMBOL
N
V
F/S
T
TUE
t
CONVERT
V
IH,
SDA, SCL
V
IL,
SDA, SCL
I
IH,
SDA, SCL
V
OL, SDA
V
OL, ALERT
f
SCL
t
BUF
t
HD_SDA
t
SU_SDA
t
SU_STO
t
HD_DAT(OUT)
t
HD_DAT(IN)
t
SU_DAT
t
LOW
t
HIGH
t
TIMEOUT_SMB
PARAMETER
Resolution
LSB Step Size
Full Scale Temperature
Total Unadjusted Error
Conversion Time
Input High Voltage
Input Low Voltage
Input Leakage Current
Output Low Voltage (SDA)
Output Low Voltage (ALERT)
Serial Bus Operating Frequency
Bus Free Time Between Stop and Start
Condition
Hold Time After (Repeated) Start Condition
Repeated Start Condition Setup Time
Stop Condition Setup Time
Data Hold Time
Input Data Hold Time
Data Set-Up Time
Clock Low Period
Clock High Period
Stuck PMBus Timer
Measured from Last PMBus Start
Event
0V ≤ V
PIN
≤ 5.5V
I
SDA
= 3mA
I
ALERT
= 1mA
10
1.3
0.6
0.6
0.6
300
0
100
1.3
0.6
30
10000
900
–5
2.1
0.8
5
0.4
0.4
400
Temperature Readback
9
1
±256
±3
40
Bits
°C
°C
°C
ms
V
V
µA
V
V
kHz
µs
µs
µs
µs
ns
ns
ns
µs
µs
ms
The
l
denotes the specifications which apply over the specified operating
junction temperature range, V
IN
= 3.3V unless otherwise noted. (Note 2)
CONDITIONS
MIN
TYP
MAX
UNITS
PMBus Interface Parameters
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3815 is tested under pulsed load conditions such that T
J
≈ T
A
.
The LTC3815E is guaranteed to meet specifications from 0°C to 85°C
junction temperature. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3815I is guaranteed
over the –40°C to 125°C operating junction temperature range. Note that
the maximum ambient temperature consistent with these specifications
is determined by specific operating conditions in conjunction with board
layout, the rated package thermal impedance and other environmental
factors.
Note 3:
The junction temperature (T
J
, in °C) is calculated from the ambient
temperature (T
A
, in °C) and power dissipation (PD, in Watts) according to
the formula:
where
θ
JA
(in °C/W) is the package thermal impedance.
T
J
= T
A
+ (PD •
θ
JA
)
Note 4 :
The dynamic input supply current is higher due to power
MOSFET gate charging (Q
G
× f
OSC
). See applications Information for more
information.
Note 5:
The LTC3815 is tested in a feedback loop that servos V
FB
to a
referenced voltage with the I
TH
pin forced to a voltage between 0.6V
and 1V.
Note 6:
Guaranteed by design, not subject to test.
Note 7:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum junction temperature
may impair device reliability or permanently damage the device.
Note 8:
The LTC3815 uses valley current mode control so the current
limits specified correspond to the valley of the inductor current waveform.
Maximum load current is higher and equals the valley current limit I
LIM
plus one half of the inductor ripple current.
Note 9:
The maximum input and output voltage is 5.5V.
Note 10:
Total output accuracy is the sum of the tolerances of I
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