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Linear Technology Electronic Components Datasheet

LTC1778 Datasheet

Wide Operating Range/ No RSENSE Step-Down Controller

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LTC1778 pdf
LTC1778/LTC1778-1
Wide Operating Range,
No RSENSETM Step-Down Controller
FEATURES
s No Sense Resistor Required
s True Current Mode Control
s Optimized for High Step-Down Ratios
s tON(MIN) 100ns
s Extremely Fast Transient Response
s Stable with Ceramic COUT
s Dual N-Channel MOSFET Synchronous Drive
s Power Good Output Voltage Monitor (LTC1778)
s Adjustable On-Time (LTC1778-1)
s Wide VIN Range: 4V to 36V
s ±1% 0.8V Voltage Reference
s Adjustable Current Limit
s Adjustable Switching Frequency
s Programmable Soft-Start
s Output Overvoltage Protection
s Optional Short-Circuit Shutdown Timer
s Micropower Shutdown: IQ < 30µA
s Available in a 16-Pin Narrow SSOP Package
U
APPLICATIO S
s Notebook and Palmtop Computers
s Distributed Power Systems
DESCRIPTIO
The LTC®1778 is a synchronous step-down switching
regulator controller optimized for CPU power. The con-
troller uses a valley current control architecture to deliver
very low duty cycles with excellent transient response
without requiring a sense resistor. Operating frequency is
selected by an external resistor and is compensated for
variations in VIN.
Discontinuous mode operation provides high efficiency
operation at light loads. A forced continuous control pin
reduces noise and RF interference, and can assist second-
ary winding regulation by disabling discontinuous opera-
tion when the main output is lightly loaded.
Fault protection is provided by internal foldback current
limiting, an output overvoltage comparator and optional
short-circuit shutdown timer. Soft-start capability for sup-
ply sequencing is accomplished using an external timing
capacitor. The regulator current limit level is user program-
mable. Wide supply range allows operation from 4V to 36V
at the input and from 0.8V up to (0.9)VIN at the output.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No RSENSE is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
CSS
0.1µF
CC
500pF
RC
20k
RUN/SS
ION
VIN
TG
SW
ITH BOOST
LTC1778
SGND INTVCC
BG
PGOOD PGND
RON
1.4M
CB 0.22µF
DB
CMDSH-3
+ CVCC
4.7µF
M1
Si4884 L1
1.8µH
M2
Si4874
D1
B340A
CIN
10µF
VIN
5V TO 28V
50V
×3 VOUT
2.5V
+ COUT 10A
180µF
4V
×2
R2
30.1k
VFB
R1
14k
1778 F01a
Figure 1. High Efficiency Step-Down Converter
Efficiency vs Load Current
100
VOUT = 2.5V
VIN = 5V
90
VIN = 25V
80
70
60
0.01
0.1 1
LOAD CURRENT (A)
10
1778 F01b
1778fa
1


Linear Technology Electronic Components Datasheet

LTC1778 Datasheet

Wide Operating Range/ No RSENSE Step-Down Controller

No Preview Available !

LTC1778 pdf
LTC1778/LTC1778-1
ABSOLUTE AXI U RATI GS (Note 1)
Input Supply Voltage (VIN, ION)................. 36V to – 0.3V
Boosted Topside Driver Supply Voltage
(BOOST) ................................................... 42V to – 0.3V
SW Voltage .................................................. 36V to – 5V
EXTVCC, (BOOST – SW), RUN/SS,
PGOOD Voltages ....................................... 7V to – 0.3V
FCB, VON, VRNG Voltages .......... INTVCC + 0.3V to – 0.3V
ITH, VFB Voltages...................................... 2.7V to – 0.3V
TG, BG, INTVCC, EXTVCC Peak Currents .................... 2A
TG, BG, INTVCC, EXTVCC RMS Currents .............. 50mA
Operating Ambient 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
UW U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS 1
PGOOD 2
VRNG 3
FCB 4
ITH 5
SGND 6
ION 7
VFB 8
16 BOOST
15 TG
14 SW
13 PGND
12 BG
11 INTVCC
10 VIN
9 EXTVCC
GN PACKAGE
16-LEAD PLASTIC SSOP
TJMAX = 125°C, θJA = 130°C/ W
ORDER PART
NUMBER
LTC1778EGN
GN PART MARKING
1778
Consult LTC Marketing for parts specified with wider operating temperature ranges.
TOP VIEW
RUN/SS 1
VON 2
VRNG 3
FCB 4
ITH 5
SGND 6
ION 7
VFB 8
16 BOOST
15 TG
14 SW
13 PGND
12 BG
11 INTVCC
10 VIN
9 EXTVCC
GN PACKAGE
16-LEAD PLASTIC SSOP
TJMAX = 125°C, θJA = 130°C/ W
ORDER PART
NUMBER
LTC1778EGN-1
GN PART MARKING
17781
ELECTRICAL CHARACTERISTICS The q denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. VIN = 15V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN TYP MAX
Main Control Loop
IQ Input DC Supply Current
Normal
Shutdown Supply Current
900 2000
15 30
VFB
VFB(LINEREG)
VFB(LOADREG)
IFB
gm(EA)
VFCB
IFCB
tON
Feedback Reference Voltage
Feedback Voltage Line Regulation
Feedback Voltage Load Regulation
Feedback Input Current
Error Amplifier Transconductance
Forced Continuous Threshold
Forced Continuous Pin Current
On-Time
tON(MIN)
Minimum On-Time
ITH = 1.2V (Note 3)
VIN = 4V to 30V, ITH = 1.2V (Note 3)
ITH = 0.5V to 1.9V (Note 3)
VFB = 0.8V
ITH = 1.2V (Note 3)
VFCB = 0.8V
ION = 30µA, VON = 0V (LTC1778-1)
ION = 15µA, VON = 0V (LTC1778-1)
ION = 180µA
q 0.792
q
q 1.4
q 0.76
198
396
0.800
0.002
– 0.05
–5
1.7
0.8
–1
233
466
50
0.808
– 0.3
±50
2
0.84
–2
268
536
100
2
UNITS
µA
µA
V
%/V
%
nA
mS
V
µA
ns
ns
ns
1778fa


Part Number LTC1778
Description Wide Operating Range/ No RSENSE Step-Down Controller
Maker Linear Technology
Total Page 24 Pages
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