chronous step-down switching regulator controllers that
employ a constant frequency voltage mode architecture.
They maintain excellent current balance between channels
when paralleled with their internal current sharing loop.
Lossless DCR or a low value R
SENSE
is used for output
current sensing. Multiple LTC7851/LTC7851-1 devices can
be used for high phase count operation.
A very low offset, high bandwidth error amplifier, combined
with remote output voltage sensing, provides excellent
transient response and output regulation. The LTC7851/
LTC7851-1 operates with a V
CC
supply voltage from 3V to
5.5V and is designed for step-down conversion with V
IN
from 3V to 27V* and produces an output voltage from
0.6V to V
CC
– 0.5V.
The LTC7851-1 is identical to the LTC7851 except it has
a lower current sense amplifier gain, making it ideal for
DrMOS devices with internal current sense.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents, including 6144194, 5055767.
n
n
n
n
n
Operates with Power Blocks, DrMOS or External
Gate Drivers and MOSFETs
Voltage Mode Control with Accurate Current Sharing
±0.75% 0.6V Voltage Reference
Quad Differential Output Voltage Sense Amplifiers
Multiphase Capability
Phase-Lockable Fixed Frequency 250kHz to 2.25MHz
Lossless Current Sensing Using Inductor DCR or
Precision Current Sensing with Sense Resistor or
DrMOS with Integrated Current Sensing
V
CC
Range: 3V to 5.5V
V
OUT
Range: 0.6V to V
CC
– 0.5V
Power Good Output Voltage Monitor
Output Voltage Tracking Capability with Soft-Start
Available in 58-Lead 5mm × 9mm QFN Package
High Current Distributed Power Systems
DSP, FPGA and ASIC Supplies
Datacom, Telecom and Computing Systems
APPLICATIONS
n
n
n
*See Note 5.
TYPICAL APPLICATION
V
IN
7V TO 14V
0.25µH
Dual-Output Converter: 1V/90A and 1.5V/30A with DrMOS
VINSNS
0.25µH
DrMOS
PWM3
LTC7851
ISNS3P
ISNS3N
V
CC
ISNS2P
ISNS2N
FB2,3
PGOOD1
PWM1
TRACK/SS1
TRACK/SS2
TRACK/SS3
PWM2
DrMOS
3.57k
0.22µF
3.57k
0.22µF
V
CC
5V
V
OUT2
1.5V/30A
V
CC
100k
0.25µH
DrMOS
3.57k
0.22µF
100µF
x6
V
OUT1
1.0V/90A
1µF
0.25µH
100k
100µF
x2
15k
DrMOS
3.57k
0.22µF
PGOOD4
PWM4
RUN1
RUN2
RUN3
+
330µF
x3
+
10k
330µF
x9
PINS NOT USED
IN THIS CIRCUIT:
CLKIN
CLKOUT
VSNSP2
VSNSP3
VSNSN2
VSNSN3
PGOOD2
PGOOD3
RUN4
I
AVG4
TRACK/SS4
10k
3.3nF
332
6.04k
10k
2.2nF
100pF
30.9k
42.2k
ISNS4P
ISNS1P
ISNS4N
ISNS1N
VSNSP4
VSNSP1
VSNSN4
VSNSN1
VSNSOUT4 VSNSOUT1,2,3
COMP4
FB4
FREQ
I
LIM4
COMP1,2,3
FB1
I
AVG1,2,3
I
LIM1,2,3
SGND
4.02k
10k
100pF
42.2k
100pF
2.2nF
3.3nF
332
15k
7851 TA01
Document Feedback
For more information
www.analog.com
1
Rev A
LTC7851/LTC7851-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TRACK/SS1
TOP VIEW
PGOOD1
48 I
LIM1
47 I
AVG1
46 ISNS1P
45 ISNS1N
44 ISNS2N
43 ISNS2P
42 I
AVG2
41 I
LIM2
59
SGND
40 TRACK/SS2
39 VINSNS
38 PGOOD2
37 TRACK/SS3
36 I
LIM3
35 I
AVG3
34 ISNS3P
33 ISNS3N
32 ISNS4N
31 ISNS4P
30 I
AVG4
20 21 22 23 24 25 26 27 28 29
COMP4
PWM4
TRACK/SS4
PWM3
RUN4
PGOOD4
PGOOD3
RUN3
I
LIM4
FB4
CLKOUT
PWM1
PWM2
CLKIN
RUN1
RUN2
FREQ
V
CC
Voltage .............................................. –0.3V to 6.5V
VINSNS Voltage ........................................ –0.3V to 30V
RUN1, RUN2, RUN3,
RUN4 Voltage ............................–0.3V to (V
CC
+0.3V)
ISNS1P, ISNS1N,
ISNS2P, ISNS2N ....................... –0.3V to (V
CC
+ 0.1V)
ISNS3P, ISNS3N,
ISNS4P, ISNS4N ....................... –0.3V to (V
CC
+ 0.1V)
All Other Pin Voltages ...................–0.3V to (V
CC
+ 0.3V)
Operating Junction Temperature Range ... –40° to 125°C
Storage Temperature Range .................. –65°C to 150°C
COMP1 1
VSNSP1 2
VSNSN1 3
VSNSOUT1 4
SGND 5
VSNSOUT2 6
VSNSN2 7
VSNSP2 8
COMP2 9
FB2 10
V
CC
11
FB3 12
COMP3 13
VSNSP3 14
VSNSN3 15
VSNSOUT3 16
VSNSOUT4 17
VSNSN4 18
VSNSP4 19
UHH PACKAGE
58-LEAD (5mm × 9mm) PLASTIC QFN
LEAD PITCH 0.4mm
θ
JA
= 49°C/W,
θ
JC
= 15.5°C/W
EXPOSED PAD (PIN 59) IS SGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC7851EUHH#PBF
LTC7851IUHH#PBF
LTC7851EUHH-1#PBF
LTC7851IUHH-1#PBF
TAPE AND REEL
LTC7851EUHH#TRPBF
LTC7851IUHH#TRPBF
LTC7851EUHH-1#TRPBF
LTC7851IUHH-1#TRPBF
PART MARKING
7851
7851
78511
78511
PACKAGE DESCRIPTION
58-LEAD (5mm × 9mm) Plastic QFN
58-LEAD (5mm × 9mm) Plastic QFN
58-LEAD (5mm × 9mm) Plastic QFN
58-LEAD (5mm × 9mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–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.
FB1
58 57 56 55 54 53 52 51 50 49
2
Rev A
For more information
www.analog.com
LTC7851/LTC7851-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
INSNS
V
CC
V
OUT
I
Q
PARAMETER
V
IN
Sense Range
V
CC
Voltage Range
V
OUT
Voltage Range
Input Voltage Supply Current
Normal Operation
Shutdown Mode
UVLO
RUN Input Threshold
RUN Input Pull-Up Current
Undervoltage Lockout Threshold
Soft-Start Pin Output Current
Internal Soft-Start Time
Regulated Feedback Voltage
–20°C to 85°C
–40°C to 125°C
V
ILIM
= 0.8V
V
FB
Falling
V
FB
Rising
V
FB
Falling
V
FB
Rising
V
PGOOD
= 5V
V
PGOOD
High to Low
V
FB
= 600mV
Sourcing
Sinking
(Note 4)
(Note 4)
Measured in a Servo Loop with EA in Loop
0°C to 85°C
Measured in a Servo Loop with EA in Loop
–40°C to 125°C
V
SNSP
= 600mV
(Note 4)
VSNSOUT = 600mV
VSNSOUT = 600mV
594
l
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
CC
= 5V, V
RUN1,2,3,4
= 5V, V
FREQ
= V
CLKIN
= 0V,
V
FB
= 0.6V, f
OSC
= 600kHz, unless otherwise specified.
CONDITIONS
V
CC
= 5V (Note 5)
Limited by ISNSP/N Common Mode
Voltage Range (Note 3)
V
RUN1,2,3,4
= 5V
V
RUN1,2,3,4
= 0V
V
CC
< V
UVLO
V
RUN
Rising
V
RUN
Hysteresis
V
RUN
= 2.4V
V
CC
Rising
V
CC
Hysteresis
V
SS
= 0V
l
l
l
l
MIN
3
3
0.6
TYP
MAX
27
5.5
V
CC
– 0.5
UNITS
V
V
V
60
16
1.95
2.25
250
1.5
100
1.5
595.5
594
18.5
2.5
1.5
600
600
0.05
20
645
660
540
555
15
30
–100
1
4
75
45
40
600
600
110
100
2.45
mA
µA
mA
V
mV
µA
V
mV
µA
ms
mV
mV
%/V
µA
mV
mV
mV
mV
Ω
µA
µs
V
RUN
I
RUN
V
UVLO
I
SS
t
SS
V
FB
½V
FB
/½V
CC
I
LIMIT
Power Good
V
FB(OV)
V
FB(UV)
V
PGOOD(ON)
I
PGOOD(OFF)
t
PGOOD
Error Amplifier
I
FB
I
OUT
A
V(OL)
SR
f
0dB
V
DA
3
3.5
604.5
606
0.2
21.5
Regulated Feedback Voltage Line Dependence 3.0V < V
CC
< 5.5V
I
LIM
Pin Output Current
PGOOD/V
FB
Overvoltage Threshold
PGOOD/V
FB
Undervoltage Threshold
PGOOD Pull-Down Resistance
PGOOD Leakage Current
PGOOD Delay
FB Pin Input Current
COMP Pin Output Current
Open Loop Voltage Gain
Slew Rate
COMP Unity-Gain Bandwidth
V
SNSP
Accuracy
650
530
670
550
60
2
100
nA
mA
mA
dB
V/µs
MHz
Differential Amplifier
606
608
100
40
100
500
mV
mV
nA
MHz
µA
µA
592
–100
I
DIFF
+
f
Odb
I
OUT(SINK)
I
OUT(SOURCE)
Input Bias Current
DA Unity-Gain Bandwidth
Maximum Sinking Current
Maximum Sourcing Current
For more information
www.analog.com
3
Rev A
LTC7851/LTC7851-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
ISENSE(MAX)
A
V(ISENSE)
V
CM(ISENSE)
I
ISENSE
V
IAVG
V
OS
PARAMETER
Maximum Differential Current Sense Voltage
(V
ISNSP
– V
ISNSN
)
Voltage Gain
Input Common Mode Range
SENSE Pin Input Current
Zero Current I
AVG
Pin Voltage
Current Sense Input Referred Offset
V
CM
= 1.5V
V
ISNSP
= V
ISNSN
LTC7851
LTC7851-1
Oscillator and Phase-Locked Loop
f
OSC
Oscillator Frequency
V
CLKIN
= 0V
V
CLKIN
= 5V
V
FREQ
= 0V
V
FREQ
= 5V
R
FREQ
< 24.9k
R
FREQ
= 30.9k
R
FREQ
= 36.5k
R
FREQ
= 48.7k
R
FREQ
= 64.9k
R
FREQ
= 82.5k
R
FREQ
= 88.7k
3
0.25
18.5
100
100
20
V
CLKIN
Falling
V
CLKIN
Rising
V
CLKIN
= 0V
V
FREQ
Falling
V
FREQ
Rising
I
LOAD
= –500µA
I
LOAD
= 500µA
0.8
2
1.5
2.5
0.2
V
CC
– 0.2
180
90
270
45
I
LOAD
= 500µA
I
LOAD
= –500µA
l
l
l
l
l
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
CC
= 5V, V
RUN1,2,3,4
= 5V, V
FREQ
= V
CLKIN
= 0V,
V
FB
= 0.6V, f
OSC
= 600kHz, unless otherwise specified.
CONDITIONS
LTC7851
LTC7851-1
LTC7851
LTC7851-1
–0.3
100
500
–1
–3
1
3
MIN
50
150
20
4
V
CC
– 0.5
TYP
MAX
UNITS
mV
mV
V/V
V/V
V
nA
mV
mV
mV
Current Sense Amplifier
520
0.85
600
1
180
370
570
970
1.4
1.9
2.1
680
1.15
kHz
MHz
kHz
kHz
kHz
kHz
MHz
MHz
MHz
MHz
MHz
µA
ns
ns
kΩ
V
V
V
V
V
V
Deg
Deg
Deg
Deg
V
Maximum Frequency
Minimum Frequency
I
FREQ
t
CLKIN(HI)
t
CLKIN(LO)
R
CLKIN
V
CLKIN
V
FREQ
V
OL(CLKOUT)
V
OH(CLKOUT)
FREQ Pin Output Current
CLKIN Pulse Width High
CLKIN Pulse Width Low
CLKIN Pull Up Resistance
CLKIN Input Threshold
FREQ Input Threshold
V
FREQ
= 0.8V
V
CLKIN
= 0V to 5V
V
CLKIN
= 0V to 5V
20
21.5
CLKOUT Low Output Voltage
CLKOUT High Output Voltage
Channel 2 to Channel 1 Phase Relationship
Channel 3 to Channel 1 Phase Relationship
Channel 4 to Channel 1 Phase Relationship
CLKOUT to Channel 1 Phase Relationship
PWM Output High Voltage
PWM Output Low Voltage
PWM Output Current in Hi-Z State
PWM Maximum Duty Cycle
θ
2
–
θ
1
θ
3 –
θ
1
θ
4 –
θ
1
θ
CLKOUT
–
θ
1
PWM Output
PWM
V
CC
– 0.5
0.5
±5
91.5
V
µA
%
Rev A
4
For more information
www.analog.com
LTC7851/LTC7851-1
ELECTRICAL CHARACTERISTICS
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 LTC7851/LTC7851-1 are tested under pulsed load conditions
such that T
J
≈ T
A
. The LTC7851E/LTC7851E-1 are guaranteed to meet
performance specifications from 0°C to 85°C. Specifications over the
–40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LTC7851I/LTC7851I-1 are 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. 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
• 49˚C/W)
Note 3:
The maximum V
OUT
range is limited by the current sense pins
(ISNSP/ISNSN) common mode voltage range. See the Current Sensing in
the Applications Information section.
Note 4:
Guaranteed by design.
Note 5:
The Absolute Maximum Voltage Rating for the VINSNS voltage
limits the Maximum V
IN
Voltage. For operation with a V
IN
range higher
than 27V, the VINSNS pin must be connected through a resistor divider
from V
IN
to limit the maximum VINSNS voltage to less than 27V.
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