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LTC1778IGN#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24
1
LTC1778/LTC1778-1
1778fb
Wide Operating Range,
No R
SENSE
TM
Step-Down Controller
■
No Sense Resistor Required
■
True Current Mode Control
■
Optimized for High Step-Down Ratios
■
t
ON(MIN)
≤ 100ns
■
Extremely Fast Transient Response
■
Stable with Ceramic C
OUT
■
Dual N-Channel MOSFET Synchronous Drive
■
Power Good Output Voltage Monitor (LTC1778)
■
Adjustable On-Time (LTC1778-1)
■
Wide V
IN
Range: 4V to 36V
■
±1% 0.8V Voltage Reference
■
Adjustable Current Limit
■
Adjustable Switching Frequency
■
Programmable Soft-Start
■
Output Overvoltage Protection
■
Optional Short-Circuit Shutdown Timer
■
Micropower Shutdown: I
Q
< 30µA
■
Available in a 16-Pin Narrow SSOP Package
■
Notebook and Palmtop Computers
■
Distributed Power Systems
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 V
IN
.
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)V
IN
at the output.
Figure 1. High Efficiency Step-Down Converter
Efficiency vs Load Current
+
D
B
CMDSH-3
D1
B340A
L1
1.8µH
C
VCC
4.7µF
C
IN
10µF
50V
×3
V
IN
5V TO 28V
V
OUT
2.5V
10A
+
C
OUT
180µF
4V
×2
M2
Si4874
1778 F01a
M1
Si4884
R
ON
1.4MΩ
C
SS
0.1µF
I
ON
V
IN
TG
SW
BOOST
RUN/SS
I
TH
SGND
INTV
CC
BG
PGND
V
FB
PGOOD
C
B
0.22µF
R
C
20k
LTC1778
C
C
500pF
R2
30.1k
R1
14k
LOAD CURRENT (A)
0.01
EFFICIENCY (%)
80
90
1778 F01b
70
60
0.1
1
10
100
V
IN
= 5V
V
OUT
= 2.5V
V
IN
= 25V
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
, LTC and LT 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
2
LTC1778/LTC1778-1
1778fb
Input Supply Voltage (V
IN
, I
ON
)................. 36V to –0.3V
Boosted Topside Driver Supply Voltage
(BOOST) ................................................... 42V to –0.3V
SW Voltage .................................................. 36V to –5V
EXTV
CC
, (BOOST – SW), RUN/SS,
PGOOD Voltages....................................... 7V to – 0.3V
FCB, V
ON
, V
RNG
Voltages .......... INTV
CC
+ 0.3V to –0.3V
I
TH
, V
FB
Voltages...................................... 2.7V to –0.3V
ORDER PART
NUMBER
LTC1778EGN
LTC1778IGN
T
JMAX
= 125°C, θ
JA
= 130°C/ W
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
GN PART MARKING
1778
1778I
TG, BG, INTV
CC
, EXTV
CC
Peak Currents.................... 2A
TG, BG, INTV
CC
, EXTV
CC
RMS Currents .............. 50mA
Operating Ambient Temperature Range (Note 4)
LTC1778E ........................................... –40°C to 85°C
LTC1778I.......................................... –40°C to 125°C
Junction Temperature (Note 2)............................ 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
GN PACKAGE
16-LEAD PLASTIC SSOP
1
2
3
4
5
6
7
8
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
EXTV
CC
ORDER PART
NUMBER
LTC1778EGN-1
GN PART MARKING
17781
TOP VIEW
GN PACKAGE
16-LEAD PLASTIC SSOP
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
RUN/SS
V
ON
V
RNG
FCB
I
TH
SGND
I
ON
V
FB
BOOST
TG
SW
PGND
BG
INTV
CC
V
IN
EXTV
CC
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loop
I
Q
Input DC Supply Current
Normal 900 2000 µA
Shutdown Supply Current 15 30 µA
V
FB
Feedback Reference Voltage I
TH
= 1.2V (Note 3) LTC1778E ● 0.792 0.800 0.808 V
I
TH
= 1.2V (Note 3) LTC1778I ● 0.792 0.800 0.812 V
∆V
FB(LINEREG)
Feedback Voltage Line Regulation V
IN
= 4V to 30V, I
TH
= 1.2V (Note 3) 0.002 %/V
∆V
FB(LOADREG)
Feedback Voltage Load Regulation I
TH
= 0.5V to 1.9V (Note 3) ● –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
Forced Continuous Threshold ● 0.76 0.8 0.84 V
I
FCB
Forced Continuous Pin Current V
FCB
= 0.8V –1 –2 µA
t
ON
On-Time I
ON
= 30µA, V
ON
= 0V (LTC1778-1) 198 233 268 ns
I
ON
= 15µA, V
ON
= 0V (LTC1778-1) 396 466 536 ns
t
ON(MIN)
Minimum On-Time I
ON
= 180µA 50 100 ns
T
JMAX
= 125°C, θ
JA
= 130°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
(Note 1)
3
LTC1778/LTC1778-1
1778fb
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
as follows:
LTC1778E: T
J
= T
A
+ (P
D
• 130°C/W)
Note 3: The LTC1778 is tested in a feedback loop that adjusts V
FB
to achieve
a specified error amplifier output voltage (I
TH
).
Note 4: The LTC1778E is guaranteed to meet performance specifications from
0°C to 70°C. Specifications over the –40°C to 85°C operating temperature
range are assured by design, characterization and correlation with statistical
process controls. The LTC1778I is guaranteed over the full – 40°C to 125°C
operating temperature range.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t
OFF(MIN)
Minimum Off-Time I
ON
= 30µA 250 400 ns
V
SENSE(MAX)
Maximum Current Sense Threshold V
RNG
= 1V, V
FB
= 0.76V ● 113 133 153 mV
V
PGND
– V
SW
V
RNG
= 0V, V
FB
= 0.76V ● 79 93 107 mV
V
RNG
= INTV
CC
, V
FB
= 0.76V ● 158 186 214 mV
V
SENSE(MIN)
Minimum Current Sense Threshold V
RNG
= 1V, V
FB
= 0.84V – 67 mV
V
PGND
– V
SW
V
RNG
= 0V, V
FB
= 0.84V – 47 mV
V
RNG
= INTV
CC
, V
FB
= 0.84V – 93 mV
∆V
FB(OV)
Output Overvoltage Fault Threshold 5.5 7.5 9.5 %
V
FB(UV)
Output Undervoltage Fault Threshold 520 600 680 mV
V
RUN/SS(ON)
RUN Pin Start Threshold ● 0.8 1.5 2 V
V
RUN/SS(LE)
RUN Pin Latchoff Enable Threshold RUN/SS Pin Rising 4 4.5 V
V
RUN/SS(LT)
RUN Pin Latchoff Threshold RUN/SS Pin Falling 3.5 4.2 V
I
RUN/SS(C)
Soft-Start Charge Current V
RUN/SS
= 0V –0.5 –1.2 –3 µA
I
RUN/SS(D)
Soft-Start Discharge Current V
RUN/SS
= 4.5V, V
FB
= 0V 0.8 1.8 3 µA
V
IN(UVLO)
Undervoltage Lockout V
IN
Falling ● 3.4 3.9 V
V
IN(UVLOR)
Undervoltage Lockout Release V
IN
Rising ● 3.5 4 V
TG R
UP
TG Driver Pull-Up On Resistance TG High 2 3 Ω
TG R
DOWN
TG Driver Pull-Down On Resistance TG Low 2 3 Ω
BG R
UP
BG Driver Pull-Up On Resistance BG High 3 4 Ω
BG R
DOWN
BG Driver Pull-Down On Resistance BG Low 1 2 Ω
TG t
r
TG Rise Time C
LOAD
= 3300pF 20 ns
TG t
f
TG Fall Time C
LOAD
= 3300pF 20 ns
BG t
r
BG Rise Time C
LOAD
= 3300pF 20 ns
BG t
f
BG Fall Time C
LOAD
= 3300pF 20 ns
Internal V
CC
Regulator
V
INTVCC
Internal V
CC
Voltage 6V < V
IN
< 30V, V
EXTVCC
= 4V ● 4.7 5 5.3 V
∆V
LDO(LOADREG)
Internal V
CC
Load Regulation I
CC
= 0mA to 20mA, V
EXTVCC
= 4V –0.1 ±2%
V
EXTVCC
EXTV
CC
Switchover Voltage I
CC
= 20mA, V
EXTVCC
Rising ● 4.5 4.7 V
∆V
EXTVCC
EXTV
CC
Switch Drop Voltage I
CC
= 20mA, V
EXTVCC
= 5V 150 300 mV
∆V
EXTVCC(HYS)
EXTV
CC
Switchover Hysteresis 200 mV
PGOOD Output (LTC1778 Only)
∆V
FBH
PGOOD Upper Threshold V
FB
Rising 5.5 7.5 9.5 %
∆V
FBL
PGOOD Lower Threshold V
FB
Falling –5.5 –7.5 –9.5 %
∆V
FB(HYS)
PGOOD Hysteresis V
FB
Returning 1 2 %
V
PGL
PGOOD Low Voltage I
PGOOD
= 5mA 0.15 0.4 V
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LTC1778IGN#PBF

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Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Synchronous Step down Controller
Lifecycle:
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