down regulators using a current mode, constant-frequency
architecture. The DC supply current is only 130µA (Burst
Mode operation at no-load) while maintaining the output
voltages, dropping to zero current in shutdown. The 2.25V
to 5.5V input supply range makes the parts ideally suited
for single Li-Ion applications. 100% duty cycle capability
provides low dropout operation, which extends operating
time in battery-operated systems.
The operating frequency is externally programmable up to
4MHz, allowing the use of small surface mount inductors.
0°, 90°, or 180° (LTC3615) or 140°/180° (LTC3615-1) of
phase shift between the two channels can be selected to
minimize input current ripple and output voltage ripple in a
dual 3A or single 6A output configuration. Programmable
slew rate limiting reduces EMI, and external synchroniza-
tion can be applied up to 4MHz.
The internal synchronous switches increase efficiency
and eliminate the need for external catch diodes, saving
external components and board space.
The LTC3615/LTC3615-1 are offered in leadless 24-pin
4mm
×
4mm QFN and thermally enhanced 24-pin TSSOP
packages.
L,
LT, LTC, LTM, Linear Technology, Burst Mode 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, 5994885, 6304066, 6498466, 6580258,
6611131.
n
n
n
n
n
n
High Efficiency: Up to 94%
Dual Outputs with 2
×
3A Output Current Capability
Low Output Ripple Burst Mode
®
Operation: I
Q
= 130µA
2.25V to 5.5V Input Voltage Range
±1% Output Voltage Accuracy
Output Voltages Down to 0.6V
Programmable Slew Rate at Switch Pins
Low Dropout Operation: 100% Duty Cycle
Shutdown Current ≤1µA
Adjustable Switching Frequency Up to 4MHz
Internal or External Compensation
Selectable Pulse-Skipping/Forced Continuous/
Burst Mode Operation with Adjustable Burst Clamp
Optional Active Voltage Positioning (AVP) with
Internal Compensation
Selectable 0°/90°/180° (LTC3615) or selectable
140°/180° (LTC3615-1) Phase Shift Between Channels
Fixed Internal and Programmable External Soft-Start
Accurate Start-Up Tracking Capability
DDR Memory Mode I
OUT
= ±1.5A
Available in 4mm × 4mm QFN-24 and TSSOP-24 Packages
applicaTions
n
n
n
n
n
Point-of-Load Supplies
Distributed Power Supplies
Portable Computer Systems
DDR Memory Termination
Handheld Devices
Typical applicaTion
V
IN
100µF
SV
IN
PV
IN1
RUN1
TRACK/SS1
PGOOD1
LTC3615
ITH1
SRLIM
R
T
/SYNC
MODE
PHASE
RUN2
TRACK/SS2
PGOOD2
ITH2 SGND
PV
IN2
SW1
0.47µH
422k
FB1
210k
SW2
0.47µH
665k
FB2
PGND
3615 TA01a
Efficiency and Power Loss vs Load Current
100
90
V
OUT1
1.8V/3A
47µF
80
EFFICIENCY (%)
70
60
50
40
30
20
10 2.25MHz
V
OUT
= 2.5V
0
0.001
0.01
0.1
1
OUTPUT CURRENT (A)
V
IN
= 3.3V
V
IN
= 4V
V
IN
= 5V
0.001
0.01
0.1
1
POWER LOSS (W)
10
V
OUT2
2.5V/3A
47µF
210k
0.0001
3615 TA01b
3615fb
For more information
www.linear.com/LTC3615
1
LTC3615/LTC3615-1
absoluTe MaxiMuM raTings
(Notes 1, 11)
PV
IN1
, PV
IN2
Voltages .................... –0.3V to SV
IN
+ 0.3V
SV
IN
Voltage ................................................ –0.3V to 6V
SW1 Voltage .............................–0.3V to (PV
IN1
+ 0.3V)
SW2 Voltage ..............................–0.3V to (PV
IN2
+ 0.3V)
PGOOD1, PGOOD2 Voltages ........................ –0.3V to 6V
All Other Pins .............................. –0.3V to (SV
IN
+ 0.3V)
Operating Junction Temperature
Range (Notes 2, 11) ............................... –55°C to 150°C
Storage Temperature.............................. –65°C to 150°C
Lead Soldering Temperature (eTSSOP) ................. 300°C
Reflow Peak Body Temperature (QFN) .................. 260°C
pin conFiguraTion
PV
IN1
PV
IN1
SW1
FB2
ITH2
TRACK/SS2
SGND
PV
IN2
PV
IN2
SW2
SW2
2
3
4
5
6
7
8
9
25
PGND
23 FB1
22 ITH1
21 TRACK/SS1
20 SV
IN
19 PV
IN1
18 PV
IN1
17 SW1
16 SW1
15 PGOOD1
14 SRLIM
13 PGOOD2
ITH1 1
FB1 2
MODE 3
PHASE 4
FB2 5
ITH2 6
7
TRACK/SS2
8
SGND
9 10 11 12
SW2
PV
IN2
PV
IN2
SW2
25
PGND
24 23 22 21 20 19
18 PGOOD1
17 SRLIM
16 PGOOD2
15 R
T
/SYNC
14 RUN1
13 RUN2
SW1
SV
IN
PHASE
1
24 MODE
TRACK/SS1
TOP VIEW
TOP VIEW
RUN2 10
RUN1 11
R
T
/SYNC 12
FE PACKAGE
24-LEAD PLASTIC eTSSOP
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 150°C,
θ
JA
= 33°C/W
EXPOSED PAD (PIN 25) IS PGND, MUST BE SOLDERED TO PCB
T
JMAX
= 150°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 25) IS PGND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3615EFE#PBF
LTC3615EFE#TRPBF
LTC3615FE
24-Lead Plastic TSSOP
–40°C to 125°C
LTC3615IFE#PBF
LTC3615IFE#TRPBF
LTC3615FE
24-Lead Plastic TSSOP
–40°C to 125°C
LTC3615HFE#PBF
LTC3615HFE#TRPBF
LTC3615FE
24-Lead Plastic TSSOP
–40°C to 150°C
LTC3615MPFE#PBF
LTC3615MPFE#TRPBF
LTC3615FE
24-Lead Plastic TSSOP
–55°C to 150°C
24-Lead (4mm
×
4mm) Plastic QFN
–40°C to 125°C
LTC3615EUF#PBF
LTC3615EUF#TRPBF
3615
LTC3615IUF#PBF
LTC3615IUF#TRPBF
3615
24-Lead (4mm
×
4mm) Plastic QFN
–40°C to 125°C
LTC3615HUF#PBF
LTC3615HUF#TRPBF
3615
24-Lead (4mm
×
4mm) Plastic QFN
–40°C to 150°C
LTC3615MPUF#PBF
LTC3615MPUF#TRPBF
3615
24-Lead (4mm
×
4mm) Plastic QFN
–55°C to 150°C
LTC3615EFE-1#PBF
LTC3615EFE-1#TRPBF
LTC3615FE-1
24-Lead Plastic TSSOP
–40°C to 125°C
LTC3615IFE-1#PBF
LTC3615IFE-1#TRPBF
LTC3615FE-1
24-Lead Plastic TSSOP
–40°C to 125°C
LTC3615HFE-1#PBF
LTC3615HFE-1#TRPBF
LTC3615FE-1
24-Lead Plastic TSSOP
–40°C to 150°C
LTC3615MPFE-1#PBF
LTC3615MPFE-1#TRPBF
LTC3615FE-1
24-Lead Plastic TSSOP
–55°C to 150°C
LTC3615EUF-1#PBF
LTC3615EUF-1#TRPBF
36151
24-Lead (4mm
×
4mm) Plastic QFN
–40°C to 125°C
LTC3615IUF-1#PBF
LTC3615IUF-1#TRPBF
36151
24-Lead (4mm
×
4mm) Plastic QFN
–40°C to 125°C
36151
24-Lead (4mm
×
4mm) Plastic QFN
–40°C to 150°C
LTC3615HUF-1#TRPBF
LTC3615HUF-1#PBF
LTC3615MPUF-1#PBF
LTC3615MPUF-1#TRPBF
36151
24-Lead (4mm
×
4mm) Plastic QFN
–55°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard 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/
3615fb
2
For more information
www.linear.com/LTC3615
LTC3615/LTC3615-1
elecTrical characTerisTics
SYMBOL
V
IN
V
UVLO
V
FB
PARAMETER
Operating Voltage Range
Undervoltage Lockout Threshold
Feedback Voltage Internal Reference
SV
IN
Ramping Down
SV
IN
Ramping Up
(Note 3) V
TRACK
= SV
IN
, V
SRLIM
= 0V
0°C < T
J
< 85°C
–40°C < T
J
< 125°C
–55°C < T
J
< 150°C
(Note 3) V
TRACK
= 0.3V, V
SRLIM
= SV
IN
(Note 3) V
TRACK
= 0.5V, V
SRLIM
= SV
IN
V
FBx
= 0.6V
SV
IN
= PV
INx
= 2.25V to 5.5V (Note 4)
V
ITHx
from 0.5V to 0.9V (Note 4)
V
ITHx
= SV
IN
, V
FBx
= 0.6V (Note 5)
V
FB1
= 0.5V, V
MODE
= SV
IN
, V
RUN2
= 0V (Note 6)
V
FBx
= 0.5V, V
MODE
= SV
IN
, V
RUNx
= SV
IN
(Note
6)
Sleep Mode
V
FB1
= 0.7V, V
RUN1
= SV
IN
, V
RUN2
= 0V,
V
MODE
= 0V, V
ITH1
= SV
IN
(Note 5)
V
FBx
= 0.7V, V
RUN1
= SV
IN
, V
RUN2
= 0V,
V
MODE
= 0V (Note 4)
V
FBx
= 0.7V, V
RUNx
= SV
IN
, V
MODE
=0V,
V
ITHx
= SV
IN
(Note 5)
V
FBx
= 0.7V, V
RUNx
= SV
IN
, V
MODE
=0V,
I
TH
= (Note 4)
Shutdown
R
DS(ON)
I
LIM
Top Switch On-Resistance
Bottom Switch On-Resistance
Top Switch Current Limit
SV
IN
= PV
IN
= 5.5V, V
RUNx
= 0V
PV
INx
= 3.3V (Note 10)
PV
INx
= 3.3V (Note 10)
Sourcing (Note 8), V
FB
= 0.5V
Duty Cycle <35%
Duty Cycle = 100%
Sinking (Note 8), V
FB
= 0.7V,
Forced Continuous Mode
SV
IN
= PV
IN
= 5.5V, V
RUNx
= 0V
–5µA < I
TH
< 5µA
(Note 4)
V
FBx
from 0.06V to 0.54V, TRACK/SSx = SV
IN
0.65
4.5
3.6
–2.5
1100
1900
95
145
130
240
0.1
75
55
6
–3.5
0.01
240
±30
1.1
1.7
200
70
R
RT/SYNC
= 178k
V
RT/SYNC
= SV
IN
f
SYNC
V
RT/SYNC
Synchronization Frequency
SYNC Level High
SYNC Level Low
t
LOW
, t
HIGH
> 30ns
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), SV
IN
= PV
INx
= 3.3V, R
T
= 178k, R
SRLIM
= 40.2k, unless
otherwise specified.
CONDITIONS
l
l
MIN
2.25
1.7
TYP
MAX
5.5
2.25
UNITS
V
V
V
V
V
V
V
V
nA
%/ V
%
%
µA
µA
l
l
0.592
0.590
0.588
0.289
0.489
0.6
0.608
0.610
0.612
0.311
0.511
±30
0.2
0.2
2
Feedback Voltage External Reference
(Note 7)
I
FB
∆V
LINEREG
∆V
LOADREG
I
S
Feedback Input Current
Line Regulation
Load Regulation
Active Mode
0.3
0.5
0
130
220
200
360
1
µA
µA
µA
µA
µA
mΩ
mΩ
7.5
–5
1
A
A
A
µA
µmho
µA
ms
Ω
µs
Bottom Switch Current Limit
I
SW(LKG)
g
m(EA)
I
EA
t
SOFT-START
R
DIS
t
DIS
f
OSC
Switch Leakage Current
Error Amplifier Transconductance
Error Amplifier Output Current
Internal Soft-Start Time
TRACK/SS Pull-Down Resistance at
Start-Up
Soft-Start Discharge Time at Start-Up
Internal Oscillator Frequency
1.85
1.8
0.4
1.2
2.25
2.25
2.65
2.7
4
0.3
MHz
MHz
MHz
V
V
3615fb
For more information
www.linear.com/LTC3615
3
LTC3615/LTC3615-1
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2), SV
IN
= PV
INx
= 3.3V, R
T
= 178k, R
SRLIM
= 40.2k, unless
otherwise specified.
SYMBOL
j
SW1–SW2
PARAMETER
Output Phase Shift Between SW1
and SW2 (LTC3615)
CONDITIONS
V
PHASE
< 0.15 •
SV
IN
0.35 •
SV
IN
< V
PHASE
< 0.65 •
SV
IN
V
PHASE
> 0.85 •
SV
IN
V
PHASE
< 0.65 •
SV
IN
V
PHASE
> 0.85 •
SV
IN
(Note 9)
SV
IN
– 0.3
0.3
SV
IN
– 0.3
1.1
0.5
TRACK/SSx = SV
IN
, Entering Window
V
FBx
Ramping Up
V
FBx
Ramping Down
TRACK/SSx = SV
IN
, Leaving Window
V
FBx
Ramping Up
V
FBx
Ramping Down
t
PGOOD
R
PGOOD
V
RUN
Power Good Blanking Time
Enable Pin
Entering/Leaving Window
Input High
Input Low
Pull-Down Resistance
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 LTC3615/LTC3615-1 are tested under pulsed load conditions
such that T
J
≈
T
A
. The LTC3615E/LTC3615E-1 are guaranteed to meet
performance specifications over the 0°C to 85°C operating junction
temperature range. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3615I/LTC3615I-1
are guaranteed to meet specifications over the –40°C to 125°C operating
junction temperature range. The LTC3615H/LTC3615H-1 are guaranteed
to meet specifications over the –40°C to 150°C operating temperature
range. The LTC3615MP/LTC3615MP-1 are tested and guaranteed to meet
specifications over the full –55°C to 150°C operating junction temperature
range. High junction temperatures degrade operating lifetime; operating
lifetime is derated for junction temperatures greater than 125°C. 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. The junction temperature (T
J
, in °C) is calculated from the ambient
temperature
(T
A
, in °C) and power dissipation (P
D
, in watts) according to the formula:
T
J
= T
A
+ (P
D
•
θ
JA
)
where
θ
JA
(in °C/W) is the package thermal impedance.
l
l
elecTrical characTerisTics
MIN
TYP
0
90
180
140
180
MAX
UNITS
Deg
Deg
Deg
Deg
Deg
V
V
V
V
V
%
%
Output Phase Shift Between SW1
and SW2 (LTC3615-1)
V
SRLIM
V
MODE
(Note 9)
Voltage at SRLIM to Enable DDR
Mode
Internal Burst Mode Operation
Pulse-Skipping Mode
Forced Continuous Mode
External Burst Mode Operation
PGOOD
Power Good Voltage Windows
SV
IN
• 0.58
0.85
–6
6
9
–9
11
–11
140
30
0.4
4
–3.5
3.5
%
%
µs
Ω
V
V
MΩ
70
8
1
105
12
Power Good Pull-Down On-Resistance I = 10mA
Note 3:
This parameter is tested in a feedback loop which servos V
FB1,2
to
the midpoint for the error amplifier (V
ITH1,2
= 0.75V).
Note 4:
External compensation on ITH pin.
Note 5:
Tying the ITH pin to SV
IN
enables internal compensation and AVP
mode for the selected channel.
Note 6:
Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
Note 7:
See description of the TRACK/SS pin in the Pin Functions section.
Note 8:
When sourcing current, the average output current is defined
as flowing out of the SW pin. When sinking current, the average output
current is defined as flowing into the SW pin. Sinking mode requires the
use of forced continuous mode.
Note 9:
See description of the MODE pin in the Pin Functions section.
Note 10:
Guaranteed by design and correlation to wafer level
measurements for QFN packages.
Note 11:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 150°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability or permanently damage the
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