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LTC3878IGN#PBF

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LTC3878
1
3878fa
Typical applicaTion
FeaTures
applicaTions
DescripTion
Fast, Wide Operating Range
No R
SENSE
Step-Down
DC/DC Controller
n
Distributed Power Systems
n
Embedded Computing
n
Communications Infrastructure
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. No R
SENSE
is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected
by U.S. Patents, including 5481178, 6100678, 6580258, 5847554, 6304066.
n
Wide V
IN
Range: 4V to 38V
n
±1% 0.8V Voltage Reference
n
Extremely Fast Transient Response
n
t
ON(MIN)
: 43ns
n
No R
SENSE
™ Valley Current Mode Control
n
Stable with Low ESR Ceramic C
OUT
n
Supports Smooth Start-Up Into Pre-Biased Output
n
Optimized for High Step-Down Ratios
n
Pin Compatible with the LTC1778 (No EXTV
CC
Pin)
n
Power Good Output Voltage Monitor
n
Dual N-Channel MOSFET Synchronous Drive
n
Adjustable Switching Frequency
n
Programmable Current Limit with Foldback
n
Output Overvoltage Protection
n
Small 16-Pin Narrow SSOP Package
The LTC
®
3878 is a synchronous step-down switching
DC/DC controller optimized for high switching frequency
and fast transient response. The constant on-time valley
current mode architecture allows for a wide input range,
including very low duty factor operation. No external sense
resistor or slope compensation is required. The LTC3878
is pin compatible with the LTC1778 in applications that do
not use EXTV
CC
while offering better efficiency. Consult
with the factory to verify compatibility.
Operating frequency is set by an external resistor and
compensated for variations in V
IN
to offer excellent line
stability. Discontinuous mode operation provides high
efficiency during light load conditions. A forced continu
-
ous control
pin allows the user to reduce noise and RF
interference. Safety features include output overvoltage
protection and programmable current limit with foldback.
Soft-start capability for supply sequencing is accomplished
through an external timing capacitor. The current limit is
user programmable.
The LTC3878 allows operation from 4V to 38V at the input
and from 0.8V to 90% V
IN
at the output. The LTC3878 is
available in a small 16-pin narrow SSOP package.
High Efficiency Step-Down Converter
Efficiency vs Load Current
I
ON
V
IN
RUN/SS
I
TH
SGND
PGOOD
TG
BG
PGND
V
RNG
V
FB
SW
BOOST
INTV
CC
FCB
0.22µF
0.1µF
220pF RJK0305
RJK0330
0.56µH
432k
12.1k
LTC3878
3878 TA01a
5.11k
10k
V
OUT
1.2V
15A
V
IN
4.5V TO 28V
4.7µF
330µF
s2
10µF
LOAD CURRENT (A)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
0.01 1 10 100
3878 G07
0
0.1
CONTINUOUS
MODE
DISCONTINUOUS
MODE
V
IN
= 12V
V
OUT
= 1.2V
SW FREQ = 400kHz
FIGURE 7 CIRCUIT
LTC3878
2
3878fa
absoluTe MaxiMuM raTings
Input Supply Voltage (V
IN
) ......................... –0.3V to 40V
I
ON
Voltage ................................................. –0.3V to 40V
BOOST Voltage .......................................... –0.3V to 46V
SW Voltage ................................................... –5V to 40V
INTV
CC
, (BOOST-SW), RUN/SS,
PGOOD Voltages .......................................... –0.3V to 6V
FCB, V
RNG
Voltages .................... –0.3V to INTV
CC
+ 0.3V
V
FB
, I
TH
Voltages ....................................... –0.3V to 2.7V
Operating Temperature Range (Note 4).... –40°C
to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage
Temperature Range ................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ..................
300°C
(Note 1)
GN PACKAGE
16-LEAD PLASTIC SSOP NARROW
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
RUN/SS
PGOOD
V
RNG
FCB
I
TH
SGND
I
ON
V
FB
BOOST
TG
SW
PGND
BG
INTV
CC
V
IN
NC
T
JMAX
= 125°C, θ
JA
= 110°C/W
pin conFiguraTion
elecTrical characTerisTics
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loop
Input Operating Voltage Range 4 38 V
I
Q
Input DC Supply Current
Normal
Shutdown
Supply Current
1500
18
2000
35
µA
µA
V
FBREF
Feedback Reference Voltage I
TH
= 1.2V (Note 3)
l
0.792 0.8 0.808 V
Feedback Voltage Line Regulation V
IN
= 4V to 38V, I
TH
= 1.2V (Note 3) 0.002 %/V
Feedback Voltage Load Regulation I
TH
= 0.5V to 1.9V (Note 3)
l
–0.05 –0.3 %
I
FB
Feedback Input Current V
FB
= 0.8V –5 ±50 nA
g
m(EA)
Error Amplifier Transconductance I
TH
= 1.2V (Note 3) 1.4 1.7 2 mS
V
FCB
FCB Threshold 0.76 0.8 0.84 V
FCB Pin Current V
FCB
= 0.8V 0 ±1 µA
t
ON
On-Time I
ON
= 30µA
I
ON
= 15µA
198
396
233
466
268
536
ns
ns
t
ON(MIN)
Minimum On-Time I
ON
= 180µA 43 75 ns
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V unless otherwise noted.
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3878EGN#PBF LTC3878EGN#TRPBF 3878 16-Lead
Plastic SSOP –40°C to 85°C (Note 4)
LTC3878IGN#PBF LTC3878IGN#TRPBF 3878 16-Lead
Plastic SSOP –40°C to 85°C (Note 4)
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/
LTC3878
3
3878fa
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: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
as follows:
T
J
= T
A
+ (P
D
• 110°C/W)
Note 3: The LTC3878 is tested in a feedback loop that adjusts V
FB
to
achieve a specified error amplifier output voltage (I
TH
).
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t
OFF(MIN)
Minimum Off-Time I
ON
= 30µA 220 300 ns
V
SENSE(MAX)
Valley Current Sense Threshold
V
PGND
– V
SW
Peak Current = Valley + Ripple
V
RNG
= 1V, V
FB
= 0.76V
V
RNG
= 0V, V
FB
= 0.76V
V
RNG
= INTV
CC
, V
FB
= 0.76V
l
l
l
108
74
152
133
93
186
165
119
224
mV
mV
mV
V
SENSE(MIN)
Minimum Current Sense Threshold
V
PGND
– V
SW
Forced Continuous Operation
V
RNG
= 1V, V
FB
= 0.84V
V
RNG
= 0V, V
FB
= 0.84V
V
RNG
= INTV
CC
, V
FB
= 0.84V
–67
–47
–93
mV
mV
mV
V
RUN/SS
RUN/SS Pin On Threshold V
RUN/SS
Rising 1.4 1.5 1.6 V
Soft-Start Charging Current V
RUN/SS
= 0V –1.2 µA
INTV
CC(UVLO)
INTV
CC
Undervoltage Lockout Falling
l
3.3 3.9 V
INTV
CC(UVLOR)
INTV
CC
Undervoltage Lockout Release Rising
l
3.6 4 V
TG Driver Pull-Up On-Resistance TG High 2.5 Ω
TG
Driver Pull-Down On-Resistance TG Low 1.2 Ω
BG
Driver Pull-Up On-Resistance BG High 2.5 Ω
BG
Driver Pull-Down On-Resistance BG Low 0.7 Ω
TG
Rise Time C
LOAD
= 3300pF (Note 5) 20 ns
TG Fall Time C
LOAD
= 3300pF (Note 5) 20 ns
BG Rise Time C
LOAD
= 3300pF (Note 5) 20 ns
BG Fall Time C
LOAD
= 3300pF (Note 5) 20 ns
TG/BG t
1D
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
C
LOAD
= 3300pf Each Driver (Note 5) 15 ns
TG/BG t
2D
Bottom Gate Off to Top Gate On Delay
Synchronous Switch-On Delay Time
C
LOAD
= 3300pf Each Driver (Note 5) 15 ns
Internal V
CC
Regulator
Internal V
CC
Voltage 6V < V
IN
< 38V 5.15 5.3 5.45 V
Internal V
CC
Load Regulation I
CC
= 0mA to 20mA –0.1 ±2 %
PGOOD Output
PGOOD Upper Threshold V
FB
Rising 5.5 7.5 9.5 %
PGOOD Lower Threshold V
FB
Falling –5.5 –7.5 –9.5 %
PGOOD Hysteresis V
FB
Returning 2 3.5 %
PGOOD Low Voltage I
PGOOD
= 5mA 0.15 0.4 V
PGOOD Turn-On Delay 12 µs
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V unless otherwise noted.
Note 4: The LTC3878E is guaranteed to meet specifications from
0°C to 85°C. Specifications over the –40°C to 85°C operating temperature
range are assured by design, characterization and correlation with
statistical process controls. The LTC3878I is guaranteed to meet
specifications over the full –40°C to 85°C operating temperature range.
Note 5: Rise and fall time are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
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LTC3878IGN#PBF

Mfr. #:
Buy LTC3878IGN#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Wide Operating Range No Rsense Step-Down Controller
Lifecycle:
New from this manufacturer.
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