monolithic step-down regulator for inverting output
applications. The regulator features a single resistor-
programmable output voltage and high efficiency over a
wide V
OUT
range.
The inverting regulator operates from an input voltage
range of 3.4V to 60V and provides an adjustable output
from (–28V) to zero volts while delivering up to 4A of
inductor current. The switching frequency is also set
with an external resistor. A user-selectable mode input is
provided to allow the user to trade off ripple noise for ef-
ficiency at light loads; Burst Mode operation provides the
highest efficiency at light loads, while forced continuous
mode provides low output ripple. The MODE/SYNC pin
can also be used to synchronize the switching frequency
to an external clock. Internal level-shift circuits allow the
I/O pins (RUN, MODE/SYNC, PGOOD) to be referenced
to board GND.
The LTC7149 operates with a peak current mode architec-
ture that allows for fast transient response with inherent
cycle-to-cycle current limit protection.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents, including 5481178, 5705919, 5847554, 6580258.
n
n
n
n
n
n
n
n
n
n
Wide V
IN
Range: 3.4V to 60V
Wide V
OUT
Range: 0V to –28V
Single Resistor V
OUT
Programming
Integrated 110m Top N-Channel/50m Bottom
N-Channel MOSFETs
Regulated I
Q
: 440µA, Shutdown I
Q
: 15µA
Board GND Referenced I/O Pins (RUN, PGOOD,
MODE/SYNC)
Accurate Resistor Programmable
Frequency (300kHz to 3MHz) with ±50%
Frequency Sync Range
92% Efficiency with 12 V
IN
and –5V
OUT
±0.8% Output Voltage Accuracy
Peak Current Mode Operation
Burst Mode
®
Operation, Forced Continuous Mode
Programmable Soft-Start
Overtemperature Protection
Available in 28-Lead (4mm x 5mm) QFN and
TSSOP Packages
APPLICATIONS
n
n
n
Industrial Applications
Telecom Power Supplies
Distributed Power Systems
TYPICAL APPLICATION
0.1µF
6.8µH
RUN
V
IN
0.1µF
22µF
GND
ITH
1k
100pF
4.7nF
f
SW
= 500kHz
INTV
CC
ISET
2.2µF
100k
10nF
200k
70
7149 TA01
100
95
150 F
V
OUT
–
–5V
3.3A
EFFICIENCY (%)
90
85
80
75
OUT
Efficiency with V
OUT
= –5V
Efficiency with V
= –5V
V
IN
24V
BOOST
SW
V
OUTSNS
+
22µF × 2
LTC7149
V
OUT
–
SV
OUT
–
MODE/SYNC R
T
V
IN
= 12V
V
IN
= 24V
0
0.5
1
1.5
2 2.5
I
OUT
(A)
3
3.5
4
7149 TA01b
7149fa
For more information
www.linear.com/LTC7149
1
LTC7149
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
Voltage* (Note 3) ................................ 64V to –0.3V
ISET Voltage*............................................. V
IN
to –0.3V
GND Voltage* ............................................. 28V to –0.3V
RUN Voltage* .....................................64V to GND –0.3V
MODE/SYNC, PGOOD Voltage* ..GND + 6V to GND –0.3V
V
OUTSNS
Voltage*....................................... V
IN
to –0.3V
R
T
, PGDFB, ITH, V
INREG
.....INTV
CC
+0.3V to (SV
OUT−
–0.3V)
EXTV
CC
Voltage* ....................................... 28V to –0.3V
Operating Junction
Temperature Range (Notes 4, 6) ........ –40°C to 125°C
Storage Temperature Range .................. –65°C to 125°C
*
All voltage referenced to V
OUT–
, unless otherwise specified.
PIN CONFIGURATION
TOP VIEW
V
OUT
–
V –
V
OUT
–
OUT
TOP VIEW
V
OUT
–
V –
OUT
SW
SW
SW
1
2
3
4
5
6
7
8
9
29
SV
OUT
–
28 SW
27 SW
26 SW
25 SW
24 SW
23 SW
22 SW
21 BOOST
20 INTV
CC
19 EXTV
CC
18 ITH
17 ISET
16 V
OUTSNS
15 R
T
V
OUT
– 1
V
OUT
– 2
V
IN
3
V
IN
4
RUN 5
GND 6
MODE/SYNC 7
PGOOD 8
28 27 26 25 24 23
22 SW
21 SW
20 SW
29
SV
OUT
–
19 SW
18 BOOST
17 INTV
CC
16 EXTV
CC
15 ITH
9 10 11 12 13 14
V
INREG
V
OUTSNS
SV
OUT
–
PGDFB
ISET
R
T
V
OUT
–
V –
OUT
V
OUT
–
V
IN
V
IN
RUN
GND
MODE/SYNC 10
PGOOD 11
PGDFB 12
SV
OUT
– 13
V
INREG
14
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 3.4°C/W
EXPOSED PAD (PIN 29) IS SV
OUT–
, MUST BE SOLDERED TO PCB
FE PACKAGE
28-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 30°C/W,
θ
JC
= 5°C to 10°C/W
EXPOSED PAD (PIN 29) IS SV
OUT–
, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC7149EUFD#PBF
LTC7149IUFD#PBF
LTC7149EFE#PBF
LTC7149IFE#PBF
TAPE AND REEL
LTC7149EUFD#TRPBF
LTC7149IUFD#TRPBF
LTC7149EFE#TRPBF
LTC7149IFE#TRPBF
http://www.linear.com/product/LTC7149#orderinfo
PART MARKING*
7149
7149
LTC7149
LTC7149
PACKAGE DESCRIPTION
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
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.
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//.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
7149fa
For more information
www.linear.com/LTC7149
LTC7149
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
IN
= 24V, V
EXTVCC
= 0V unless otherwise specified.
SYMBOL
V
IN
V
OUT –
I
VIN
I
ISET
PARAMETER
Input Supply Operating Voltage Range
Output Operating Voltage Range
Input Quiescent Current
(Note 3)
Shutdown Mode; V
RUN
= 0V
Burst Mode Operation
FC Mode (Note 5)
V
ISET
+ |V
OUT –
| = 3.3V
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
3.4
–28V
TYP
MAX
60 – |V
OUT –
|
–0.05
UNITS
V
V
µA
µA
mA
µA
µA
%
mV
µS
µA
MΩ
m
m
ns
18
440
1.4
49.6
49.4
–5
400
550
0.1
0.5
1
110
50
60
l
30
600
2.5
50.4
50.6
0.5
5
700
1
1.5
Reference Current
50
50
0.1
∆V
OUT(LOAD+LINE)
Output Voltage Load + Line Regulation
V
EA(OFFSET)
g
m
(EA)
I
LSW
R
SW
R
DS(ON)
t
ON(MIN)
V
RUN
I
RUN
V
MODE/SYNC
I
MODE/SYNC
I
LIM
V
UVLO
V
UVLO(HYS)
V
OVLO
V
OVLO(HYS)
f
OSC
f
SYNC
V
INTVCC
V
EXTVCC
R
VOUTSNS
I
PGDFB
OV
PGDFB
UV
PGDFB
∆V
PGDFB
R
PGOOD
I
PGOOD(LEAK)
Error Amp Input Offset
Error Amplifier Transconductance
Topside NMOS Switch Leakage
Resistance to V
OUT–
Topside NMOS On-Resistance
Bottom Side NMOS On-Resistance
Minimum On-Time
RUN Input Rising
RUN Hysteresis
RUN Input Current
Burst Mode Operation
FC Mode
MODE/SYNC Input Current
Peak Current Limit
V
RUN
= 12V
V
MODE/SYNC
= 0V
V
MODE/SYNC
= 0V
V
ISET
= 3.3V
V
ITH
+ |V
OUT –
| = 0.7V,
V
OUT –
= –3.3V
1.08
1.2
120
0
1.32
10
0.4
V
mV
nA
V
V
µA
A
A
V
mV
V
1.2
–8
l
–5
6
6
2.65
200
6.3
6.6
2.9
5.7
5.4
2.4
V
INTVCC
+ |V
OUT –
| Undervoltage Lockout
V
INTVCC
+ |V
OUT –
| Undervoltage Lockout
Hysteresis
V
IN
Overvoltage Lockout Rising (V
IN
+ |V
OUT –
|)
V
IN
Overvoltage Lockout Hysteresis
Oscillator Frequency
SYNC Capture Range
V
INTVCC
LDO Output Voltage (V
INTVCC
+ |V
OUT –
|)
EXTV
CC
Switchover Voltage
V
OUTSNS
Resistance to SV
OUT–
PGDFB Leakage Current
Output Overvoltage PGOOD Upper Threshold
Output Undervoltage PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Pull-Down Resistance
PGOOD Leakage Current
V
IN
Rising
l
64
RT = 100k
% of Programmed Frequency
V
IN
> 3.6V, V
EXTVCC
+ |V
OUT –
| = 0V
V
IN
> 5.0V, V
EXTVCC
+ |V
OUT –
| > 3.2V
V
EXTVCC
+ |V
OUT –
|
l
l
68
2
4
1.08
150
3.45
3
3.15
100
0
0.645
0.555
10
550
3.65
3.15
3.2
120
100
0.66
0.57
1
V
MHz
%
V
V
V
V
kΩ
nA
V
V
mV
0.92
50
3.25
2.85
3.1
3.25
80
V
PGDFB
= 0.6V
V
PGFB
+ |V
OUT –
| Rising
V
PGFB
+ |V
OUT –
| Falling
0.63
0.54
V
PGOOD
= 3.3V
100
nA
7149fa
For more information
www.linear.com/LTC7149
3
LTC7149
ELECTRICAL CHARACTERISTICS
SYMBOL
t
PGOOD
PARAMETER
PGOOD Delay
CONDITIONS
PGOOD Low to High
PGOOD High to Low
Input Voltage Regulation Voltage (V
INREG
+ |V
OUT–
|)
V
INREG
Leakage Current
MIN
TYP
16
64
MAX
UNITS
Switch
Cycles
Switch
Cycles
2.15
100
V
nA
V
VINREG
I
VINREG
l
1.85
2
0
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:
Minimum On-time considerations need to be taken into account
when regulating to an output voltage close to zero. Refer to minimum on-
time section in Operations for more details.
Note 4:
The LTC7149 is tested under pulsed load conditions such
that T
J
≈ T
A
. The LTC7149E 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
LTC7149I 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 5:
The quiescent current in FC mode does not include switching loss
of the power FETs.
Note 6:
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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