LTC1778/LTC1778-1
Wide Operating Range,
TM
No R Step-Down Controller
SENSE
FEATURES
DESCRIPTIO
No Sense Resistor Required The LTC 1778 is a synchronous step-down switching
True Current Mode Control regulator controller optimized for CPU power. The con-
Optimized for High Step-Down Ratios troller uses a valley current control architecture to deliver
t 100ns very low duty cycles with excellent transient response
ON(MIN)
Extremely Fast Transient Response without requiring a sense resistor. Operating frequency is
Stable with Ceramic C selected by an external resistor and is compensated for
OUT
Dual N-Channel MOSFET Synchronous Drive variations in V .
IN
Power Good Output Voltage Monitor (LTC1778)
Discontinuous mode operation provides high efficiency
Adjustable On-Time (LTC1778-1)
operation at light loads. A forced continuous control pin
Wide V Range: 4V to 36V
IN
reduces noise and RF interference, and can assist second-
1% 0.8V Voltage Reference
ary winding regulation by disabling discontinuous opera-
Adjustable Current Limit
tion when the main output is lightly loaded.
Adjustable Switching Frequency
Fault protection is provided by internal foldback current
Programmable Soft-Start
limiting, an output overvoltage comparator and optional
Output Overvoltage Protection
short-circuit shutdown timer. Soft-start capability for sup-
Optional Short-Circuit Shutdown Timer
ply sequencing is accomplished using an external timing
Micropower Shutdown: I < 30A
Q
capacitor. The regulator current limit level is user program-
Available in a 16-Pin Narrow SSOP Package
mable. Wide supply range allows operation from 4V to 36V
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APPLICATIO S at the input and from 0.8V up to (0.9)V at the output.
IN
, LTC and LT are registered trademarks of Linear Technology Corporation.
Notebook and Palmtop Computers No R is a trademark of Linear Technology Corporation.
SENSE
All other trademarks are the property of their respective owners.
Distributed Power Systems
Protected by U.S. Patents, including 5481178, 6100678, 6580258, 5847554, 6304066
TYPICAL APPLICATIO
R
ON
Efficiency vs Load Current
1.4M
I
ON
100
C
SS
V = 2.5V
V OUT
IN
0.1F V
IN
V = 5V
5V TO 28V IN
C
IN
M1
RUN/SS TG 10F
Si4884 L1
90
50V
C
C 1.8H
SW V
3 OUT
500pF
C 0.22F 2.5V
V = 25V
B IN
I C
BOOST OUT 10A
TH +
D
B 180F
R
C 80
LTC1778
CMDSH-3
4V
20k
SGND INTV 2
CC
M2
D1
BG
Si4874
B340A
+
70
C
VCC
4.7F R2
PGOOD PGND
30.1k
60
V
FB
0.01 0.1 1 10
R1
LOAD CURRENT (A)
14k
1778 F01b
1778 F01a
Figure 1. High Efficiency Step-Down Converter
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EFFICIENCY (%)
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ULTC1778/LTC1778-1
ABSOLUTE AXI U RATI GS (Note 1)
Input Supply Voltage (V , I )................. 36V to 0.3V TG, BG, INTV , EXTV Peak Currents.................... 2A
CC CC
IN ON
Boosted Topside Driver Supply Voltage TG, BG, INTV , EXTV RMS Currents .............. 50mA
CC CC
(BOOST) ................................................... 42V to 0.3V Operating Ambient Temperature Range (Note 4)
SW Voltage .................................................. 36V to 5V LTC1778E ........................................... 40C to 85C
EXTV , (BOOST SW), RUN/SS, LTC1778I.......................................... 40C to 125C
CC
PGOOD Voltages....................................... 7V to 0.3V Junction Temperature (Note 2)............................ 125C
FCB, V , V Voltages .......... INTV + 0.3V to 0.3V Storage Temperature Range ................. 65C to 150C
ON RNG CC
I , V Voltages...................................... 2.7V to 0.3V Lead Temperature (Soldering, 10 sec).................. 300C
TH FB
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W
PACKAGE/ORDER I FOR ATIO
TOP VIEW TOP VIEW
ORDER PART ORDER PART
RUN/SS 1 NUMBER RUN/SS 1 NUMBER
16 BOOST 16 BOOST
PGOOD 2 15 V 2 15
TG TG
ON
LTC1778EGN LTC1778EGN-1
V 3 14 V 3 14
SW SW
RNG RNG
LTC1778IGN
FCB 4 13 FCB 4 13
PGND PGND
I 5 12 I 5 12
BG BG
TH TH
SGND 6 11 SGND 6 11
INTV INTV
CC CC
GN PART MARKING GN PART MARKING
I 7 10 I 7 10
V V
ON IN ON IN
V 8 9 V 8 9
EXTV EXTV
FB CC FB CC
1778 17781
GN PACKAGE GN PACKAGE
1778I
16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SSOP
T = 125C, = 130C/ W T = 125C, = 130C/ W
JMAX JA JMAX JA
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The denotes specifications which apply over the full operating
temperature range, otherwise specifications are T = 25C. V = 15V unless otherwise noted.
A IN
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loop
I Input DC Supply Current
Q
Normal 900 2000 A
Shutdown Supply Current 15 30 A
V Feedback Reference Voltage I = 1.2V (Note 3) LTC1778E 0.792 0.800 0.808 V
FB TH
I = 1.2V (Note 3) LTC1778I 0.792 0.800 0.812 V
TH
V Feedback Voltage Line Regulation V = 4V to 30V, I = 1.2V (Note 3) 0.002 %/V
FB(LINEREG) IN TH
V Feedback Voltage Load Regulation I = 0.5V to 1.9V (Note 3) 0.05 0.3 %
FB(LOADREG) TH
I Feedback Input Current V = 0.8V 5 50 nA
FB FB
g Error Amplifier Transconductance I = 1.2V (Note 3) 1.4 1.7 2 mS
m(EA) TH
V Forced Continuous Threshold 0.76 0.8 0.84 V
FCB
I Forced Continuous Pin Current V = 0.8V 1 2 A
FCB FCB
t On-Time I = 30A, V = 0V (LTC1778-1) 198 233 268 ns
ON ON ON
I = 15A, V = 0V (LTC1778-1) 396 466 536 ns
ON ON
t Minimum On-Time I = 180A 50 100 ns
ON(MIN) ON
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