LTC1735
High Efficiency
Synchronous Step-Down
Switching Regulator
FEATURES DESCRIPTIO
n
Synchronizable/Programmable Fixed Frequency The LTC 1735 is a synchronous step-down switching
TM
n
OPTI-LOOP Compensation Minimizes C regulator controller that drives external N-channel power
OUT
n
1% Output Voltage Accuracy MOSFETs using a fixed frequency architecture. Burst
TM
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Dual N-Channel MOSFET Synchronous Drive Mode operation provides high efficiency at low load
n
Wide V Range: 4V to 36V Operation currents. The precision 0.8V reference is compatible with
IN
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V Range: 0.8V to 6V future generation microprocessors. OPTI-LOOP compen-
OUT
n
Internal Current Foldback sation allows the transient response to be optimized over
n
Output Overvoltage Crowbar Protection a wide range of output capacitance and ESR values.
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Latched Short-Circuit Shutdown Timer
The operating frequency (synchronizable up to 500kHz) is
with Defeat Option
set by an external capacitor allowing maximum flexibility
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Very Low Dropout Operation: 99% Duty Cycle
in optimizing efficiency. A forced continuous control pin
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Forced Continuous Control Pin
reduces noise and RF interference and can assist second-
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Optional Programmable Soft-Start
ary winding regulation by disabling Burst Mode operation
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Remote Output Voltage Sense
when the main output is lightly loaded.
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Power Good Output (LTC1735F Only)
Protection features include internal foldback current lim-
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Logic Controlled Micropower Shutdown: I < 25m A
Q
iting, output overvoltage crowbar and optional short-
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LTC1435 Pin Compatible with
circuit shutdown. Soft-start is provided by an external
Minor Component Changes
capacitor that can be used to properly sequence supplies.
n
Available in 16-Lead Narrow SSOP, SO Packages and
The operating current level is user-programmable via an
20-Lead TSSOP Package (LTC1735F Only)
U external current sense resistor. Wide input supply range
APPLICATIO S allows operation from 4V to 30V (36V maximum).
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Notebook and Palmtop Computers, PDAs Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
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Cellular Telephones and Wireless Modems
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DC Power Distribution Systems
TYPICAL APPLICATIO
V
IN
C
5V TO 24V
OSC C
IN
C
SS
M1
22F
C
0.1F OSC TG
FDS6680A
C 50V
47pF B
RUN/SS 0.22F
C : PANASONIC EEFUEOG181R
OUT
C : MARCON THCR70E1H226ZT
IN
BOOST
L1: PANASONIC ETQP6F2R0HFA
I
TH
C
C R : IRC LRF2010-01-R005J
SENSE
SW
330pF
R C
C C2
LTC1735 L1
R
SENSE
100pF
33k
D 2H
B
0.005 V
OUT
SGND V
IN CMDSH-3
1.6V
R2
100pF
9A
20k
V INTV
OSENSE CC
1%
C
OUT
+
+ 180F
4.7F
D1
R1 M2
4V
SENSE BG
MBRS340T3
20k FDS6680A
4
1% 1000pF
SP
+
SENSE PGND
1735 F01
Figure 1. High Efficiency Step-Down Converter
1735fc
1
U
ULTC1735
ABSOLUTE AXI U RATI GS (Note 1)
Input Supply Voltage (V ).........................36V to 0.3V Peak Driver Output Current <10m s (TG, BG) .............. 3A
IN
Topside Driver Supply Voltage (BOOST)....42V to 0.3V INTV Output Current ......................................... 50mA
CC
Switch Voltage (SW) ....................................36V to 5V Operating Ambient Temperature Range
EXTV Voltage ...........................................7V to 0.3V LTC1735C ............................................... 0 C to 85 C
CC
Boosted Driver Voltage (BOOST SW) .......7V to 0.3V LTC1735I/LTC1735E (Note 8) ............ 40 C to 85 C
+
SENSE , SENSE Voltages .......... 1.1 (INTV ) to 0.3V Junction Temperature (Note 2)............................. 125 C
CC
FCB Voltage ............................(INTV + 0.3V) to 0.3V Storage Temperature Range ................. 65 C to 150 C
CC
I , V Voltages ...............................2.7V to 0.3V Lead Temperature (Soldering, 10 sec).................. 300 C
TH OSENSE
RUN/SS, PGOOD (LTC1735F Only)
Voltages.......................................................7V to 0.3V
UUW
PACKAGE/ORDER I FOR ATIO
ORDER PART ORDER PART
TOP VIEW
TOP VIEW
NUMBER NUMBER
NC 1 20 NC
C 1 16 TG
OSC
C 2 19 TG
OSC
RUN/SS 2 15 BOOST
LTC1735CGN LTC1735CF
RUN/SS 3 18 BOOST
I 3 14 SW
TH
LTC1735CS LTC1735IF
I 4 17 SW
TH
FCB 4 13 V
IN
LTC1735IGN
FCB 5 16 V
IN
SGND 5 12 INTV
CC
LTC1735IS
SGND 6 15 INTV
CC
V 6 11 BG
OSENSE
LTC1735EGN
V 7 14 BG
OSENSE
SENSE 7 10 PGND
PGOOD 8 13 PGND
+
SENSE 8 9 EXTV
CC
GN PART MARKING
SENSE 9 12 EXTV
CC
+
GN PACKAGE S PACKAGE
SENSE 10 11 NC
1735
16-LEAD NARROW 16-LEAD PLASTIC SO
PLASTIC SSOP
1735I F PACKAGE
20-LEAD PLASTIC TSSOP
T = 125 C, q = 130 C/W (GN)
JMAX JA
1735E
T = 125 C, q = 110 C/W (S)
JMAX JA
T = 125 C, q = 110 C/W
JMAX JA
Consult LTC marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25 C. V = 15V, V = 5V unless otherwise noted.
A IN RUN/SS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loop
I Feedback Current (Note 3) 4 25 nA
VOSENSE
V Feedback Voltage (Note 3) l 0.792 0.8 0.808 V
OSENSE
D V Reference Voltage Line Regulation V = 3.6V to 30V (Note 3) 0.001 0.02 %/V
LINEREG IN
D V Output Voltage Load Regulation (Note 3)
LOADREG
Measured in Servo Loop; V = 0.7V l 0.1 0.3 %
ITH
Measured in Servo Loop; V = 2V l 0.1 0.3 %
ITH
DF Max Maximum Duty Factor In Dropout 98 99.4 %
g Transconductance Amplifier g 1.3 mmho
m m
V Forced Continuous Threshold l 0.76 0.8 0.84 V
FCB
I Forced Continuous Current V = 0.85V 0.17 0.3 m A
FCB FCB
1735fc
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