buck regulator utilizing a current mode, constant frequency
architecture. It operates from an input voltage range of
2.25V to 5.5V and provides a regulated output voltage
equal to 0.5 • VDDQIN while sourcing and sinking up to
6A of load current. An internal amplifier provides a VTTR
output voltage equal to 0.5 • VDDQIN with an output cur-
rent capability of ±10mA.
The operating frequency is externally programmable up to
4MHz, allowing the use of small surface mount inductors.
For switching-noise-sensitive applications, the LTC3617
can be synchronized to an external clock up to 4MHz.
Forced continuous mode operation in the LTC3617 reduces
noise and RF interference. Adjustable external compensa-
tion allows the transient response to be optimized over a
wide range of loads and output capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external catch diode, minimizing
external component count and board space. The LTC3617
is offered in a leadless 24-pin 3mm
×
5mm thermally
enhanced QFN package.
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents, including 6580258, 5481178, 6498466, 6611131.
±6A
Output Current
2.25V to 5.5V Input Voltage Range
±10mV Output Voltage Accuracy
Optimized for Low Output Voltages Down to 0.5V
High Efficiency
Integrated Buffer for VTTR = VDDQIN • 0.5
Shutdown Current: <1µA
Adjustable Switching Frequency: Up to 4MHz
Optional Internal Compensation
Internal Soft-Start
Power Good Status Output
Input Overvoltage Protected
Thermally Enhanced 24-Pin 3mm
×
5mm
QFN Package
applications
n
n
n
DDR Termination
Supports DDR, DDR2 and DDR3 Standards
Tracking Supplies
typical application
V
IN
2.5V
SV
IN
RUN
VDDQIN
RT
LTC3617
PGOOD
ITH
SYNC
PV
IN
VTTR
0.15µH
SW
SGND
PGND
V
FB
3617 TA01a
Efficiency and Power Loss
vs Load Current
100
22µF
×4
90
V
REF
1.25V
0.1µF ±10mA
VTT
1.25V
47µF ±6A
×2
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
LOAD CURRENT (A)
10
3617 TA01b
10
1
POWER LOSS (W)
3617fa
0.1
0.01
1
LTC3617
absolute MaxiMuM ratings
(Note 1)
pin conFiguration
TOP VIEW
VDDQIN
PGOOD
20 SYNC
19 RUN
18 SV
IN
25
PGND
17 PV
IN
16 SW
15 SW
14 SW
13 SW
9
NC
10 11 12
PV
IN
PV
IN
NC
V
FB
ITH
PV
IN
, SV
IN
Voltages ..................................... –0.3V to 6V
SW Voltage ................................. –0.3V to (PV
IN
+ 0.3V)
ITH, RT, SYNC Voltages .............. –0.3V to (SV
IN
+ 0.3V)
VTTR, RUN, V
FB
Voltages ........... –0.3V to (SV
IN
+ 0.3V)
VDDQIN, PGOOD Voltages ........................... –0.3V to 6V
Operating Junction Temperature Range
(Notes 2, 8) ............................................ –40°C to 125°C
Storage Temperature.............................. –65°C to 150°C
24 23 22 21
RT 1
SGND 2
VTTR 3
PV
IN
4
SW 5
SW 6
SW 7
SW 8
UDD PACKAGE
24-LEAD (3mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 25) IS PGND, MUST BE SOLDERED TO PCB
orDer inForMation
LEAD FREE FINISH
LTC3617EUDD#PBF
LTC3617IUDD#PBF
TAPE AND REEL
LTC3617EUDD#TRPBF
LTC3617IUDD#TRPBF
PART MARKING*
LFXC
LFXC
PACKAGE DESCRIPTION
24-Lead (3mm
×
5mm) Plastic QFN
24-Lead (3mm
×
5mm) 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. *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/
The
l
denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at T
A
= 25°C. PV
IN
= SV
IN
= 3.3V, RT = SV
IN
unless otherwise specified (Notes 1, 2, 8).
SYMBOL
V
IN
V
UVLO
V
OVLO
VTTR
PARAMETER
Input Voltage Operating Range
Undervoltage Lockout Threshold
Overvoltage Lockout Threshold
VTTR Output Voltage with Line and Load
Regulation
VTTR Maximum Output Current
V
FB
I
FB
Feedback Voltage Accuracy
Feedback Input Current
VDDQIN = 1.5V (Note 3)
V
FB
= 0.75V
l
l
electrical characteristics
CONDITIONS
l
MIN
2.25
1.7
l
l
TYP
MAX
5.5
2.2
UNITS
V
V
V
V
mV
V
mA
mV
nA
SV
IN
Ramping Down
SV
IN
Ramping Up
SV
IN
Ramping Up
Hysteresis
VDDQIN = 1.5V, Load = ±10mA
6.5
250
7
l
0.49 • VDDQIN 0.5 • VDDQIN 0.51 • VDDQIN
±10
VTTR – 10
VTTR
VTTR + 10
±30
3617fa
2
LTC3617
electrical characteristics
SYMBOL
PARAMETER
∆V
FB(LINEREG)
Feedback Voltage Line Regulation
∆V
FB(LOADREG)
Feedback Voltage Load Regulation
I
Q
R
DS(ON)
I
LIM
g
m(EA)
I
EAO
t
SS
f
OSC
f
SYNC
V
SYNC
I
SW(LKG)
PGOOD
Input DC Supply Current
Active Mode
Shutdown
Top Switch On-Resistance
Bottom Switch On-Resistance
Top Switch Positive Peak Current Limit
Top Switch Negative Peak Current Limit
Error Amplifier Transconductance
Internal Soft-Start Time
Oscillator Frequency
Internal Oscillator Frequency
Synchronization Frequency Range
SYNC Input Threshold High Voltage
SYNC Input Threshold Low Voltage
Switch Leakage Current
Power Good Voltage Windows
SV
IN
= PV
IN
= 5.5V, V
RUN
= 0V
VDDQIN = 1.5V, Entering Window
V
FB
Ramping Up
V
FB
Ramping Down
VDDQIN = 1.5V, Leaving Window
V
FB
Ramping Up
V
FB
Ramping Down
t
PGOOD
R
PGOOD
V
RUN
Power Good Blanking Time
Power Good Pull-Down On-Resistance
RUN voltage
Input High
Input Low
l
l
The
l
denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at T
A
= 25°C. PV
IN
= SV
IN
= 3.3V, RT = SV
IN
unless otherwise specified (Notes 1, 2, 8).
CONDITIONS
SV
IN
= PV
IN
= 2.25V to 5.5V,
VDDQIN = 1.5V (Notes 3, 4)
ITH from 0.5V to 0.9V (Notes 3, 4)
V
ITH
= SV
IN
(Note 5)
V
FB
= 0.6V, VDDQIN = 1.5V (Note 6)
SV
IN
= PV
IN
= 5.5V, V
RUN
= 0V
PV
IN
= 3.3V
PV
IN
= 3.3V
Sourcing (Note 7), V
FB
= 0.5V
Sinking (Note 7)
–5µA < I
ITH
< 5µA (Note 4)
V
FB
from 0.075V to 0.675V,
VDDQIN = 1.5V
R
T
= 370k
V
RT
= SV
IN
l
l
l
MIN
TYP
MAX
0.2
0.25
0.25
UNITS
%/V
%
%
µA
µA
mΩ
mΩ
1100
0.1
35
25
8
–12
10
–8
200
±30
0.4
0.8
1.8
0.3
1.2
0.1
–3.5
3.5
–5
5
8
–8
70
8
1
105
17
0.85
1
2.25
1
14
–5
A
A
µS
µA
Error Amplifier Maximum Output Current (Note 4)
2
1.2
2.7
4
0.3
1
ms
MHz
MHz
MHz
V
V
µA
%
%
10
–10
140
33
0.4
%
%
µs
Ω
V
V
Entering and Leaving Window
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 LTC3617 is tested under pulsed load conditions such that
T
J
≈ T
A
. The LTC3617E is 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 LTC3617I is guaranteed to meet specifications over the
full –40°C to 125°C operating junction temperature range. Note that
the maximum ambient temperature is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
resistance 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.
Note 3:
This parameter is tested in a feedback loop which servos V
FB
to
the midpoint for the error amplifier (V
ITH
= 0.75V).
Note 4:
External compensation on ITH pin.
Note 5:
Tying the ITH pin to SV
IN
enables the internal compensation.
Note 6:
Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
Note 7:
In sourcing mode the average output current is flowing out of the
SW pin. In sinking mode the average output current is flowing into the SW
Pin.
Note 8:
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 operating junction
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