LTC7124
17V, Dual 3.5A Synchronous Step-Down
Regulator with Ultralow Quiescent Current
FEATURES
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DESCRIPTION
The
LTC
®
7124
is a dual channel, 3.5A per output, high
efficiency monolithic step-down regulator capable of
operating from input supplies up to 17V. The program-
mable switching frequency ranges from 500kHz to 4MHz
with a ±25% external clock synchronization capability
around the programmed frequency. The regulator features
ultralow quiescent current for high efficiency over a wide
V
OUT
range.
The step-down regulator operates from an input voltage
range of 3.1V to 17V and provides an adjustable output
range from 0.6V to 99% of V
IN
while delivering up to 3.5A
of output current per channel. A user selectable mode input
is provided to allow the user to trade off output ripple for
light load efficiency; Burst Mode
®
operation provides the
highest efficiency at light loads, while forced continuous
operation provides the lowest output ripple. The LTC7124
includes spread spectrum modulation for low radiated and
conductive noise. The LTC7124 is offered in a thermally
enhanced, low profile 24-lead 3mm × 5mm QFN package
L,
LT, LTC, LTM, Burst Mode, Linear Technology, the Linear logo, LTpowerCAD and LTspice
are registered trademarks of Analog Devices, Inc. All other trademarks are the property of their
respective owners. Protected by U.S. Patents, including 5481178, 6580258, 6498466, 6611131,
6177787, 5705919, 5847554.
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Wide V
IN
Range: 3.1V to 17V
Wide V
OUT
Range: 0.6V to 99% V
IN
Dual Step-Down Outputs: 3.5A Per Channel
Integrated 80mΩ/40mΩ N-Channel MOSFETs
Provide Up to 95% Efficiency
No-Load I
Q
< 8μA with Both Channels Enabled;
I
Q
< 5.5μA with Only One Channel Enabled
Programmable Frequency (500kHz to 4MHz) with
±25% Frequency Synchronization Range
Configurable for a 2-Phase Single Output at Up to 7A
±1.0% Output Voltage Accuracy
Current Mode Operation for Excellent Line and Load
Transient Response
Internal or Programmable External Loop Compensation
Available in a 3mm × 5mm QFN-24 Package
APPLICATIONS
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Battery-Powered Systems
Point-of-Load Supplies
Portable Instruments
Handheld Scanners
TYPICAL APPLICATION
1.8V/3.3V 1MHz Step-Down Regulator
V
IN
10.8V TO 13.2V
C
IN
47µF
x2
100
V
IN2
RUN1
INTV
CC
RUN2
MODE/SYNC
ITH1
ITH2
RT
LTC7124
BOOST1
BOOST2
V
IN1
90
C
INTVCC
2.2µF
EFFICIENCY (%)
R
RT
100k
80
70
60
50
40
30
20
10
0
C
OUT2
100µF
0
0.5
V
IN
= 12V
V
OUT
= 5.0V
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
1
1.5
2
2.5
LOAD CURRENT (A)
3
0.4
0.8
1.2
POWER LOSS (W)
Efficiency & Power Loss
vs Load Current at 1MHz
1.6
C
BOOST1
0.1µF
V
OUT1
1.8V AT 3.5A
L
1
1.2µH
C
FF1
22pF
C
OUT1
100µF
R1
619k
R2
309k
C
BOOST2
0.1µF
L
2
1.8µH
SW1
SW2
R3
619k
R4
137k
C
FF2
16pF
V
OUT2
3.3V AT 3.5A
FB1
ILIM
GND
FB2
7124 TA01
0
3.5
7124 TA01a
7124fa
For more information
www.linear.com/LTC7124
1
LTC7124
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
PGOOD1
PGOOD2
RUN1
20
SW1
19
SW1
18
BOOST1
17
MODE/SYNC
16
INTV
CC
15
BOOST2
14
SW2
13
SW2
9 10 11 12
FB2
ITH2
RUN2
25
26
GND GND
ITH1
FB1
GND
1
GND
2
V
IN1
3
I
LIM
4
RT
5
V
IN2
6
GND
7
GND
8
V
IN1
, V
IN2
(Note 2) ..................................... –0.3V to 17V
RUN1, RUN2 .............................................. –0.3V to 17V
MODE/SYNC ................................–0.3V to INTV
CC
+0.3V
I
LIM
, RT ........................................–0.3V to INTV
CC
+0.3V
ITH1, ITH2....................................–0.3V to INTV
CC
+0.3V
PGOOD1, PGOOD2 ....................................... –0.3V to 6V
FB1, FB2 ....................................................... –0.3V to 6V
Operating Junction Temperature Range
(Note 3).............................................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
24 23 22 21
UDD PACKAGE
VARIATION: AA
24-LEAD (3mm
×
5mm) PLASTIC QFN
T
JMAX
= 150°C,
θ
JA
= 22°C/W
EXPOSED PAD (PINS 25 & 26) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC7124EUDD#PBF
LTC7124IUDD#PBF
TAPE AND REEL
LTC7124EUDD#TRPBF
LTC7124IUDD#TRPBF
http://www.linear.com/product/LTC7124#orderinfo
PART MARKING
LGVF
LGVF
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.
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/
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
= V
IN2
= 12V, unless otherwise noted. (Note 3)
SYMBOL
V
IN
V
OUT
I
Q
PARAMETER
Operating Voltage
Output Voltage
Input Quiescent Current
(Note 6)
Active Mode, Single Channel (Note 4)
Active Mode, Dual Channels (Note 4)
Burst Mode, I
OUT1
= I
OUT2
= 0A
Burst Mode, Single Channel, I
OUT
= 0A
Shutdown Mode; V
RUN1
= V
RUN2
= 0V
(Note 5)
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
3.1
0.6
TYP
MAX
17
0.99 • V
IN
UNITS
V
V
mA
mA
µA
µA
µA
V
V
1.5
2
8
5.5
0.1
0.596
0.594
0.6
0.6
2.75
3
16
11
1
0.604
0.606
V
FB
Regulated Feedback Voltage
2
7124fa
For more information
www.linear.com/LTC7124
LTC7124
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN1
= V
IN2
= 12V, unless otherwise noted. (Note 3)
SYMBOL
ΔV
LOAD&LINE
REG
ELECTRICAL CHARACTERISTICS
PARAMETER
Output Voltage Load and Line Regulation
Feedback Pin Input Current
Error Amplifier Transconductance
Minimum On Time
Top NMOS Switch Leakage
Bottom NMOS Switch Leakage
Top NMOS On Resistance
Bottom NMOS On Resistance
RUN Input High
RUN Input Low
RUN Input Current
V
MODE/SYNC
V
ILIM
I
LIM
Pulse Skip Mode
Burst Mode Operation
Forced Continuous Mode
I
LIM
Input Threshold
Peak Current Limit
CONDITIONS
V
IN
= 3.1 to 17V (Note 5)
ITH = 0.3V to 0.9V
ITH = 0.6V
(Note 7)
MIN
TYP
0.3
MAX
0.5
10
UNITS
%
nA
µS
ns
µA
µA
mΩ
mΩ
I
FB
g
m(EA)
t
ON-MIN
I
SW
R
DS(ON)
V
RUN
300
500
50
0.1
0.1
80
40
700
±1
±1
1.0
V
RUN
= 12V
INTV
CC
–0.4
1.0
Input Low
Input High
I
LIM
= 0V (Both Channels)
I
LIM
= INTV
CC
(Both Channels)
I
LIM
= Floating, Channel 1
I
LIM
= Floating, Channel 2
V
IN1
> 4V
V
IN1
Ramping Up
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0.3
0
±100
0.3
INTV
CC
–1.2
0.2
5.0
2.6
5.0
2.6
1100
3.6
5.6
3.0
5.6
3.0
V
V
nA
V
V
V
V
V
A
A
A
A
µs
V
INTV
CC
–0.3
4.4
2.2
4.4
2.2
t
SS
V
INTVCC
Internal Soft Start Time
V
INTVCC
LDO Output Voltage
V
INTVCC
Undervoltage Lockout
V
INTVCC
Undervoltage Lockout Hysteresis
V
IN
Overvoltage Lockout Rising
V
IN
Overvoltage Lockout Hysteresis
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2.75
17.9
0.92
75
±5
2.9
300
18.4
500
1
±7.5
650
25
32
3.05
18.9
1.08
125
±10
1000
V
mV
V
mV
MHz
%
%
Ω
µs
µs
f
OSC
f
SYNC
R
PGOOD
t
PGOOD
R
T
Programmable Oscillator Frequency
SYNC Capture Range
Power Good Range
Power Good Resistance
PGOOD Delay
R
RT
= 100k
% of Programmed Frequency
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PGOOD Low to High, R
RT
= 100k
PGOOD High to Low, R
RT
= 100k
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:
Transient Absolute Maximum Voltages should not be applied for
more than 4% of the switching duty cycle.
Note 3:
The LTC7124 is tested under pulsed load conditions such that
T
J
≈ T
A
. The LTC7124E is guaranteed to meet specified performance 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 LTC7124I 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.
T
J
is calculated from the ambient T
A
and power dissipation P
D
according
to the following formula: T
J
= T
A
+ (P
D
•
θ
JA
)
Note 4:
The Quiescent Current in active mode does not include switching
loss of the power FETs.
Note 5:
The LTC7124 is tested in a proprietary test mode that connects
V
FB
to the output of error amplifier.
Note 6:
The maximum V
OUT
is limited by the automatic boost refresh that
occurs in high duty cycle and dropout cases. The maximum V
OUT
value
listed here is guaranteed by design.
Note 7:
The minimum on-time is determined by the speed of the top
switch driver and peak current comparator. The typical value listed here is
guaranteed by design.
7124fa
For more information
www.linear.com/LTC7124
3
LTC7124
otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current in
Burst Mode at 1MHz
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.001
*L = 1µH
V
OUT
= 1.2V*
V
OUT
= 2.5V
V
OUT
= 3.3V
V
OUT
= 5.0V
0.01
0.1
1
LOAD CURRENT (A)
10
7124 G01
T
A
= 25°C, V
IN
= 12V, L = 2.2µH, f = 1MHz unless
Efficiency vs Load Current in
Forced Continuous Mode at
2.25MHz
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
10
7124 G02
Efficiency vs Load Current in
Forced Continuous Mode at 1MHz
100
90
80
70
60
50
40
30
20
10
0
0.001
*L = 1µH
V
OUT
= 1.2V*
V
OUT
= 2.5V
V
OUT
= 3.3V
V
OUT
= 5.0V
0.01
0.1
1
LOAD CURRENT (A)
L = 1µH
V
OUT
= 2.5V
V
OUT
= 3.3V
V
OUT
= 5.0V
0.01
0.1
1
LOAD CURRENT (A)
10
7124 G03
0
0.001
Efficiency vs Load Current
for Varying Input Supply
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.001
V
IN
= 4V
V
IN
= 8V
V
IN
= 12V
V
IN
= 17V
0.01
0.1
1
LOAD CURRENT (A)
10
7124 G04
V
IN1
Supply Current
vs Temperature
20
0.5
I
Q
SHUTDOWN
I
Q
BURST MODE, SINGLE
I
Q
BURST MODE, DUAL
∆V
OUT
ERROR (%)
18
V
IN1
SUPPLY CURRENT (uA)
16
14
12
10
8
6
4
2
0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
–0.5
Line Regulation, No Load
V
OUT
= 2.5V
FORCED CONTINUOUS MODE
V
OUT
= 1.8V
L = 1.0µH
0.3
0.1
–0.1
–0.3
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
INPUT VOLTAGE (V)
7124 G06
7124 G05
Load Regulation
5
V
OUT
= 3.3V
FORCED CONTINUOUS MODE
1.25
1.20
1.15
FREQUENCY (MHz)
RT Frequency vs Temperature
R
RT
= 100k
2.75
2.65
2.55
FREQUENCY (MHz)
2.45
2.35
2.25
2.15
2.05
1.95
1.85
–25
0
25
50
75
TEMPERATURE (°C)
100
125
Spread Spectrum Center
Frequency vs Temperature
RT TIED TO INTV
CC
3
1.10
1.05
1.00
0.95
0.90
0.85
0.80
∆V
OUT
(%)
1
–1
–3
–5
0
1
2
3
LOAD CURRENT (A)
4
7124 G07
0.75
–50
1.75
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
7124 G08
7124 G09
4
7124fa
For more information
www.linear.com/LTC7124
LTC7124
otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
Peak Current Limit
vs Temperature
5.2
V
OUT
AC–COUPLED
200mV/DIV
I
LOAD
5A/DIV
T
A
= 25°C, V
IN
= 12V, L = 2.2µH, f = 1MHz unless
Load Step
with External Compensation
V
OUT
AC–COUPLED
200mV/DIV
Load Step
with Internal Compensation
PEAK CURRENT LIMIT (A)
5.1
5.0
I
LOAD
5A/DIV
I
L
2A/DIV
40µs/DIV
V
IN
= 12V
V
OUT
= 2.5V
I
LOAD
= 100mA to 3.5A
L = 1.8µH
ITH = INTV
CC
C
OUT
= 100µF
7124 G11
4.8
I
L
2A/DIV
4.7
10µs/DIV
V
IN
= 12V
V
OUT
= 2.5V
I
LOAD
= 150mA to 3.5A
L = 1.2µH
C
ITH
= 150pF R
ITH
= 30kΩ
,
C
OUT
= 100µF
7124 G14
4.6
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
7124 G10
Reference Voltage
vs Temperature
601.5
601.0
REFERENCE VOLTAGE (mV)
600.5
R
DS,ON
(mΩ)
600.0
599.5
599.0
598.5
598.0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
150
125
100
75
50
25
R
DS(ON)
vs Temperature
TOP SWITCH
BOTTOM SWITCH
100
R
DS(ON)
vs Input Supply Voltage
TOP SWITCH
BOTTOM SWITCH
80
R
DS, ON
(mΩ)
60
40
20
0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
INPUT VOLTAGE (V)
7124 G15
7124 G13
7124 G14
Switch Leakage Current
16
14
12
SW LEAKAGE (µA)
10
8
6
4
2
0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
TOP SWITCH
BOTTOM SWITCH
RUN
2V/DIV
I
L
1A/DIV
V
OUT
2V/DIV
PGOOD
2V/DIV
Start–Up With Load
in Burst Mode Operation
RUN
2V/DIV
V
OUT
2V/DIV
PGOOD
2V/DIV
I
L
1A/DIV
500µs/DIV
R
LOAD
= 5Ω
V
OUT
= 5V
7124 G17
Start–Up into Pre–Biased Output
in Burst Mode Operation
500µs/DIV
V
OUT
= 5V
7124 G18
7124 G16
7124fa
For more information
www.linear.com/LTC7124
5
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