LTC3877
Dual Phase Step-Down
Synchronous Controller with VID Output Voltage
Programming and Low Value DCR Sensing
FeaTures
DescripTion
n
n
n
n
n
n
n
n
n
n
n
n
n
n
6-Bit Parallel VID (Voltage Identification) Inputs Set
Output Voltage from 0.6V to 1.23V in 10mV Steps
Output Voltage Range: 0.6V to 5V (Without VID)
Ultra Low Value DCR/R
SENSE
Current Sensing
±1% Maximum Total Regulation Voltage Accuracy
Over Temperature
Dual Differential Remote Sensing Amplifiers
t
ON(MIN)
= 40ns, Capable of Very Low Duty Cycles at
High Frequency
Phase-Lockable Frequency from 250kHz to 1MHz
Current Mismatch Between Channels: 5% Max
Adjustable Soft-Start Current Ramping or Tracking
Multi-IC Operation Up To 12 Phases
Wide V
IN
Range: 4.5V to 38V
Dual Power Good Output Voltage Monitors
Output Overvoltage Protection
Foldback Output Current Limiting and Soft Recovery
The
LTC
®
3877
is a VID-programmable, constant frequency
current mode step-down controller using an advanced and
proprietary architecture. This new architecture enhances
the signal-to-noise ratio of the current sense signal, al-
lowing the use of very low DC resistance power inductors
to maximize efficiency in high current applications. This
feature also dramatically reduces the current sensing error,
so that current sharing is greatly improved in multi-phase
low DCR applications. In addition, the controller achieves a
minimum on-time of just 40ns, permitting the use of high
switching frequency at high step-down ratios.
The LTC3877 features dual high speed remote sense dif-
ferential amplifiers, programmable current sense limits
and DCR temperature compensation to limit the maximum
output current precisely over temperature. The LTC3877
also features a precise 0.6V reference with guaranteed
accuracy of ±0.5%. The LTC3877 is available in a low
profile 44-lead 7mm
×
7mm QFN package.
L,
LT, LTC, LTM, Burst Mode, OPTI-LOOP, PolyPhase, Linear Technology and the Linear
logo are registered trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents including 5481178, 5705919,
5929620, 6100678, 6144194, 6177787, 6304066, 6580258.
applicaTions
n
n
FPGAs and Processor Power
Servers and Computing
Typical applicaTion
V
IN
6V TO 20V
High Efficiency Dual Phase Single Output, 400kHz, 0.9V/60A Step-Down Converter
+
270µF
10µF
×4
34.8k V
IN
RUN
10k
I
LIM
TG1
INTV
CC
CHL_SEL FROM
µP
VID_EN
VID
1,2,3,4
MODE/PLLIN
LTC3877
TG2
BOOST2
SW2
BG2
GND
220nF
3.57k
220nF
SNSA1
+
SNS1
–
SNSD1
+
V
FB2+
V
FB1
SNSA2
+
SNS2
–
SNSD2
+
V
OSNS1+
V
OSNS1–
I
TH1
I
TH2
220nF
220nF 3.57k
100µF
×2
V
OUT
0.9V
60A
715
EFFICIENCY (%)
0.1µF
INTV
CC
4.7µF
100
95
90
85
80
75
70
Efficiency and Power Loss
vs Load Current
12V V
IN
400kHz
CCM
EFFICIENCY
10
9
8
7
6
5
POWER LOSS
4
PINS NOT SHOWN
IN THIS CIRCUIT:
CLKOUT
EXTV
CC
PGOOD1
PGOOD2
PHASMD
ITEMP
0.25µH
(0.32m DCR)
0.1µF
BOOST1
SW1
BG1
715
0.25µH
(0.32m DCR)
0
10
3
V
OUT
= 1.2V
2
V
OUT
= 0.9V
V
OUT
= 1.2V 1
V
OUT
= 0.9V
0
20
30
40
50
60
LOAD CURRENT (A)
3877 TA01b
V
OUT
100µF
×2
330µF
×3
20k
86.6k
10k
+
DIFFOUT
V
FB2–
FREQ
TK/SS1 TK/SS2 VID
0,5
0.1µF
+
1.5nF
8.45k
330µF
×3
3877 TA01
For more information
www.linear.com/LTC3877
1
3877f
LTC3877
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
44 SNS1
–
43 SNSD1
+
42 ITEMP
41 VID0
40 VID1
39 VID2
38 VID3
37 VID4
36 VID5
35 VID_EN
34 CHL_SEL
SNSA1
+
1
TK/SS1 2
V
OSNS1+
3
V
OSNS1–
4
DIFFOUT 5
V
FB1
6
I
TH1
7
I
TH2
8
TK/SS2 9
V
FB2+
10
V
FB2–
11
45
SGND/PGND
33 SW1
32 TG1
31 BOOST1
30 BG1
29 V
IN
28 INTV
CC
27 EXTV
CC
26 BG2
25 BOOST2
24 TG2
23 SW2
UK PACKAGE
44-LEAD (7mm
×
7mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W,
θ
JC
= 3.0°C/W
EXPOSED PAD (PIN 45) IS SGND/PGND, MUST BE SOLDERED TO PCB
Input Supply Voltage (V
IN
) ......................... –0.3V to 40V
Topside Driver Voltages
(BOOST1, BOOST2) ............................... –0.3V to 46V
Switch Voltages (SW1, SW2) ........................ –5V to 40V
SNSA1
+
, SNSD1
+
, SNS1
–
, SNSA2
+
, SNSD2
+
,
SNS2
–
Voltages ................................ –0.3V to INTV
CC
(BOOST1-SW1), (BOOST2-SW2) Voltages ... –0.3V to 6V
RUN Voltage................................................... –0.3 to 9V
PGOOD1, PGOOD2,
EXTV
CC
Voltages ..................................... –0.3V to 6V
MODE/PLLIN, FREQ, PHASMD Voltages ... –0.3V to INTV
CC
CHL_SEL, VID(s), VID_EN Voltages ...... –0.3V to INTV
CC
TK/SS1, TK/SS2 Voltages ..................... –0.3V to INTV
CC
I
TH1
, I
TH2
, ITEMP, I
LIM
Voltages ............ –0.3V to INTV
CC
V
FB1
, V
OSNS1+
, V
OSNS1–
, V
FB2+
,
V
FB2–
Voltages .................................. –0.3V to INTV
CC
INTV
CC
Peak Output Current ................................100mA
Operating Junction Temperature Range
(Note2, Note 3) .................................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 125°C
orDer inForMaTion
LEAD FREE FINISH
LTC3877EUK#PBF
LTC3877IUK#PBF
TAPE AND REEL
LTC3877EUK#TRPBF
LTC3877IUK#TRPBF
PART MARKING
LTC3877UK
LTC3877UK
PACKAGE DESCRIPTION
44-Lead (7mm
×
7mm) Plastic QFN
44-Lead (7mm
×
7mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
SNSA2
+
12
SNS2
–
13
SNSD2
+
14
I
LIM
15
RUN 16
FREQ 17
MODE/PLLIN 18
PHASMD 19
PGOOD1 20
PGOOD2 21
CLKOUT 22
2
3877f
For more information
www.linear.com/LTC3877
LTC3877
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 3). V
IN
= 15V, V
RUN
= 5V unless otherwise specified.
SYMBOL
V
IN
V
OUT
V
OUT_VID
PARAMETER
Input Voltage Range
Output Voltage Range When VID
Control Disabled
Output Voltage When VID Control
Enabled (Diff Amp and Error Amp
Included)
V
INTVCC
= 5.5V,
With Low DCR Sensing (Note 10)
Without Low DCR Sensing (Note 9)
(Note 4) I
TH1
Voltage = 1.2V
VID0,1,2,3,4,5 = 0V
VID0 = 1V, VID1,2,3,4,5 = 0V
VID0,5 = 0V, VID1,2,3,4 = 1V
VID1,2,3,4 = 0V, VID0,5 = 1V
VID0,1,2,3,4,5 = 1V
(Note 5)
V
IN
= 15V, V
RUN
= 5V, No Switching, EXTV
CC
Float
V
RUN
= 0V
V
INTVCC
Ramping Down
(Note 4), I
TH2
Voltage = 1.2V (–40°C to 85°C)
(Note 4), I
TH2
Voltage = 1.2V (–40°C to 125°C)
(Note 4)
(Note 4)
In Dropout, f
OSC
= 625kHz
Measured at V
FB1
, V
FB2+
V
IN
= 4.5V to 38V (Note 4)
(Note 4)
In Servo Loop; ∆I
TH
Voltage = 1.2V to 0.7V
In Servo Loop; ∆I
TH
Voltage = 1.2V to 1.6V
I
TH1,2
Voltage = 1.2V; Sink/Source 5μA (Note 4)
V
ITEMP
= 0.5V
V
TK/SS
= 5V (Note 8)
V
TK/SS
= 0V
V
RUN
Rising
l
l
l
l
l
l
l
l
l
l
elecTrical characTerisTics
Main Control Loops
CONDITIONS
MIN
4.5
0.6
0.6
594
604
891
921
1.218
TYP
MAX
38
3.5
5
UNITS
V
V
V
mV
mV
mV
mV
V
mA
µA
V
V
mV
mV
nA
nA
%
mV
%/V
%
%
mmho
μA
µs
µA
V
mV
µA
600
610
900
930
1.23
7.3
33
606
616
909
939
1.242
10
50
4.1
603
604.5
20
100
690
0.01
0.1
–0.1
31
1.5
1.35
I
Q
UVLO
UVLO
HYS
V
FB2+
I
FB1
I
FB2+
DF
MAX
V
OVL
V
REFLNREG
V
LOADREG
g
m1,2
I
TEMP
t
SSINT
I
TK/SS1,2
V
RUN
V
RUN
HYS
I
RUN
HYS
Current Sensing
I
SNSA+
I
SNSD+
A
VT_SNS
Input DC Supply Current
Normal Operation
Shutdown
Undervoltage Lockout Threshold
UVLO Hysteresis
Regulated V
OUT
Feedback Voltage
Including Diffamp Error (Channel 2)
Channel 1 Feedback Current
Channel 2 Feedback Current
Maximum Duty Cycle
Feedback Overvoltage Lockout
Reference Voltage Line Regulation
Output Voltage Load Regulation
3.6
597
595.5
3.8
0.5
600
600
2
40
l
94
650
96
670
0.002
0.01
–0.01
2.5
EA Transconductance
DCR Temp. Compensation Current
Internal Soft Start Time
Soft Start Charge Current
RUN Pin ON Threshold
RUN Pin ON Hysteresis
RUN Pin Current Hysteresis
AC Sense Pin Bias Current
DC Sense Pin Bias Current
Total Sense Gain to Current Comp
29
1.0
1.1
30
600
1.25
1.22
80
4.5
V
SNSAn+
= 1V
V
SNSDn+
= 1V
l
l
55
30
5
120
50
nA
nA
V/V
For more information
www.linear.com/LTC3877
3
3877f
LTC3877
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 3). V
IN
= 15V, V
RUN
= 5V unless otherwise specified.
SYMBOL
V
SENSE(MAX)DC
PARAMETER
Maximum Current Sense Threshold
with Low DCR Sensing (Note 10)
CONDITIONS
V
SNS–(s)
= 0.9V, I
LIM
= 0V
V
SNS–(s)
= 0.9V, I
LIM
= 1/4 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= 1/2 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= 3/4 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= INTV
CC
–40°C to 125°C
V
SNS–(s)
= 0.9V, I
LIM
= 0V
V
SNS–(s)
= 0.9V, I
LIM
= 1/4 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= 1/2 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= 3/4 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= INTV
CC
V
SENSE(MAX)NODC
Maximum Current Sense Threshold
without Low DCR Sensing (Note 11)
V
SNS–(s)
= 0.9V, I
LIM
= 0V
V
SNS–(s)
= 0.9V, I
LIM
= 1/4 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= 1/2 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= 3/4 INTV
CC
V
SNS–(s)
= 0.9V, I
LIM
= INTV
CC
l
l
l
l
l
l
l
l
l
l
elecTrical characTerisTics
MIN
9
14
19
23.5
28.5
8.5
13.5
17.5
22
26.5
45
70
95
117.5
142.5
TYP
10
15
20
25
30
10
15
20
25
30
50
75
100
125
150
MAX
11
16
21
26.5
31.5
11.5
16.5
22.5
28
33.5
55
80
105
132.5
157.5
5
UNITS
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
%
mA
V
MHz
V/µs
kΩ
V
I
MISMATCH
I
CL
V
OUT(MAX)
GBW
Slew Rate
VID Parameters
R
TOP
V
IH
V
IL
Rpd
Gate Drivers
TG R
UP1,2
TG R
DOWN1,2
BG R
UP1,2
BG R
DOWN1,2
TG
1,2
t
r
TG
1,2
t
f
BG
1,2
t
r
BG
1,2
t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
Channel-to-Channel Current Mismatch I
LIM
= Float
Maximum Output Current
Maximum Output Voltage
Gain Bandwidth Product
Differential Amplifier Slew Rate
VID Top Resistance
Input High Threshold Voltage
Input Low Threshold Voltage
Pin Pull-down Resistor
TG Pull-Up R
DS(ON)
TG Pull-Down R
DS(ON)
BG Pull-Up R
DS(ON)
BG Pull-Down R
DS(ON)
TG Transition Time
Rise Time
Fall Time
BG Transition Time
Rise Time
Fall Time
Top Gate Off to Bottom Gate On
Delay
Bottom Gate Off to Top Gate On
Delay
Minimum On-Time
TG High
TG Low
BG High
BG Low
(Notes 6, 8)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Notes 6, 8)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
(Note 7)
100
2.6
1.5
2.4
1.1
25
25
25
25
30
30
40
I
DIFFOUT
= 300μA
(Note 8)
(Note 8)
(Note 8)
0.7
3
3
5
INTV
CC
– 1.5V
4.5
2V
3.33
Differential Amplifier 1
Digital Inputs VID
0,1,2,3,4,5
, VID_EN, CHL_SEL
0.3
V
kΩ
Ω
Ω
Ω
Ω
ns
ns
ns
ns
ns
ns
ns
4
3877f
For more information
www.linear.com/LTC3877
LTC3877
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 3). V
IN
= 15V, V
RUN
= 5V unless otherwise specified.
SYMBOL
V
INTVCC
V
LDO
INT
V
EXTVCC
V
LDO
EXT
V
LDOHYS
f
NOM
f
RANGE
V
SYNC
R
MODE/PLLIN
I
FREQ
V
CLKOUT
Φ
2
–
Φ
1
Φ
CLKOUT
–
Φ
1
PARAMETER
Internal LDO Output Voltage
INTV
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Voltage Drop
EXTV
CC
Hysteresis
Nominal Frequency
PLL SYNC Range
MODE/PLLIN Sync Input Threshold
MODE/PLLIN Input Resistance
Frequency Setting Current
High Output Voltage
Low Output Voltage
Channel 2 to Channel 1 Phase Delay
V
FREQ
= 1.2V
V
INTVCC
= 5.5V
V
PHSMD
= 0V
V
PHSMD
= Float
V
PHSMD
= INTV
CC
V
PHSMD
= 0V
V
PHSMD
= Float
V
PHSMD
= INTV
CC
I
PGOOD
= 2mA
V
PGOOD
= 5.5V
V
FB1
, V
FB2+
with Respect to Set Output Voltage
V
FB1
, V
FB2+
Ramping Up
V
FB1
, V
FB2+
Ramping Down
Measure from VID Transition Edge
10
–10
50
235
9
4
V
SYNC
Rising
V
SYNC
Falling
V
FREQ
= 1.22V
l
elecTrical characTerisTics
INTV
CC
Linear Regulator
CONDITIONS
6V < V
IN
< 38V
I
CC
= 0 to 20mA
EXTV
CC
Rising
I
CC
= 20mA, V
EXTVCC
= 5.5V
l
MIN
5.3
4.5
TYP
5.5
0.5
4.7
40
300
MAX
5.7
2.0
100
UNITS
V
%
V
mV
mV
Oscillator and Phase-Locked Loop
575
250
1.6
1
250
10
5.5
0
180
180
240
60
90
120
0.1
0.3
2
11
0.2
625
675
1000
kHz
kHz
V
V
kΩ
μA
V
V
Deg
Deg
Deg
Deg
Deg
Deg
V
µA
%
%
µs
µs
CLKOUT to Channel 1 Phase Delay
Power Good Output
V
PGL
I
PGOOD
V
PG
T
DELAY
T
BLANK
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level
V
PGOOD
High to Low Delay Time
PGOOD Bad Blanking Time
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:
T
J
is calculated from the ambient temperature T
A
and power
dissipation PD according to the following formula: T
J
= T
A
+ (P
D
• 34°C/W).
Note 3:
The LTC3877 is tested under pulsed load conditions such that
T
J
≈ T
A
. The LTC3877E 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
LTC3877I is guaranteed over the full –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 4:
The LTC3877 is tested in a feedback loop that servos V
ITH1,2
to a
specified voltage and measures the resultant V
OSNS1+,
V
FB2+
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 7:
The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥40% of I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
Note 8:
Guaranteed by design.
Note 9:
Both VID_EN and SNSD
+
pins to GND. In order to obtain 5V at the
output of Channel 1, the V
OSNS1+
pin must be connected to the mid-point
of an external resistor divider, and the V
FB1
pin must be shorted to the
DIFFOUT pin.
Note 10:
SNSD
+
pin to V
OUT
.
Note 11:
SNSD
+
pin to GND.
For more information
www.linear.com/LTC3877
5
3877f
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