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LTC1735CF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P32
1
LTC1735
1735fc
High Efficiency
Synchronous Step-Down
Switching Regulator
The LTC
®
1735 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using a fixed frequency architecture. Burst
Mode
TM
operation provides high efficiency at low load
currents. The precision 0.8V reference is compatible with
future generation microprocessors. OPTI-LOOP compen-
sation allows the transient response to be optimized over
a wide range of output capacitance and ESR values.
The operating frequency (synchronizable up to 500kHz) is
set by an external capacitor allowing maximum flexibility
in optimizing efficiency. A forced continuous control pin
reduces noise and RF interference and can assist second-
ary winding regulation by disabling Burst Mode operation
when the main output is lightly loaded.
Protection features include internal foldback current lim-
iting, output overvoltage crowbar and optional short-
circuit shutdown. Soft-start is provided by an external
capacitor that can be used to properly sequence supplies.
The operating current level is user-programmable via an
external current sense resistor. Wide input supply range
allows operation from 4V to 30V (36V maximum).
■
Synchronizable/Programmable Fixed Frequency
■
OPTI-LOOP
TM
Compensation Minimizes C
OUT
■
±
1% Output Voltage Accuracy
■
Dual N-Channel MOSFET Synchronous Drive
■
Wide V
IN
Range: 4V to 36V Operation
■
V
OUT
Range: 0.8V to 6V
■
Internal Current Foldback
■
Output Overvoltage Crowbar Protection
■
Latched Short-Circuit Shutdown Timer
with Defeat Option
■
Very Low Dropout Operation: 99% Duty Cycle
■
Forced Continuous Control Pin
■
Optional Programmable Soft-Start
■
Remote Output Voltage Sense
■
Power Good Output (LTC1735F Only)
■
Logic Controlled Micropower Shutdown: I
Q
< 25µA
■
LTC1435 Pin Compatible with
Minor Component Changes
■
Available in 16-Lead Narrow SSOP, SO Packages and
20-Lead TSSOP Package (LTC1735F Only)
Figure 1. High Efficiency Step-Down Converter
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
■
Notebook and Palmtop Computers, PDAs
■
Cellular Telephones and Wireless Modems
■
DC Power Distribution Systems
C
OSC
RUN/SS
TG
BOOST
LTC1735
C
B
0.22µF
100pF
C
C
330pF
R
C
33k
R
SENSE
0.005Ω
V
OUT
1.6V
9A
C
OUT
: PANASONIC EEFUEOG181R
C
IN
: MARCON THCR70E1H226ZT
L1: PANASONIC ETQP6F2R0HFA
R
SENSE
: IRC LRF2010-01-R005J
1000pF
C
SS
0.1µF
C
OSC
47pF
+
4.7µF
+
C
OUT
180µF
4V
×4
SP
C
IN
22µF
50V
M1
FDS6680A
M2
FDS6680A
1735 F01
D
B
CMDSH-3
D1
MBRS340T3
V
IN
5V TO 24V
L1
2µH
C
C2
100pF
R2
20k
1%
R1
20k
1%
SGND
V
OSENSE
SENSE
–
SENSE
+
INTV
CC
BG
PGND
I
TH
SW
V
IN
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
2
LTC1735
1735fc
ABSOLUTE AXI U RATI GS
W
WW
U
Input Supply Voltage (V
IN
).........................36V to –0.3V
Topside Driver Supply Voltage (BOOST)....42V to –0.3V
Switch Voltage (SW) ....................................36V to –5V
EXTV
CC
Voltage ...........................................7V to –0.3V
Boosted Driver Voltage (BOOST – SW) .......7V to –0.3V
SENSE
+
, SENSE
–
Voltages ..........1.1 (INTV
CC
) to –0.3V
FCB Voltage ............................(INTV
CC
+ 0.3V) to –0.3V
I
TH
, V
OSENSE
Voltages ...............................2.7V to –0.3V
RUN/SS, PGOOD (LTC1735F Only)
Voltages.......................................................7V to –0.3V
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
Peak Driver Output Current <10µs (TG, BG) .............. 3A
INTV
CC
Output Current ......................................... 50mA
Operating Ambient Temperature Range
LTC1735C ............................................... 0°C to 85°C
LTC1735I/LTC1735E (Note 8) ............ –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)
PACKAGE/ORDER I FOR ATIO
UUW
ORDER PART
NUMBER
LTC1735CGN
LTC1735CS
LTC1735IGN
LTC1735IS
LTC1735EGN
T
JMAX
= 125°C, θ
JA
= 130°C/W (GN)
T
JMAX
= 125°C, θ
JA
= 110°C/W (S)
TOP VIEW
S PACKAGE
16-LEAD PLASTIC SO
GN PACKAGE
16-LEAD NARROW
PLASTIC SSOP
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
C
OSC
RUN/SS
I
TH
FCB
SGND
V
OSENSE
SENSE
–
SENSE
+
TG
BOOST
SW
V
IN
INTV
CC
BG
PGND
EXTV
CC
GN PART MARKING
1735
1735I
1735E
Consult LTC marketing for parts specified with wider operating temperature ranges.
ORDER PART
NUMBER
LTC1735CF
LTC1735IF
T
JMAX
= 125°C, θ
JA
= 110°C/W
1
2
3
4
5
6
7
8
9
10
TOP VIEW
F PACKAGE
20-LEAD PLASTIC TSSOP
20
19
18
17
16
15
14
13
12
11
NC
C
OSC
RUN/SS
I
TH
FCB
SGND
V
OSENSE
PGOOD
SENSE
–
SENSE
+
NC
TG
BOOST
SW
V
IN
INTV
CC
BG
PGND
EXTV
CC
NC
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loop
I
VOSENSE
Feedback Current (Note 3) –4 –25 nA
V
OSENSE
Feedback Voltage (Note 3) ● 0.792 0.8 0.808 V
∆V
LINEREG
Reference Voltage Line Regulation V
IN
= 3.6V to 30V (Note 3) 0.001 0.02 %/V
∆V
LOADREG
Output Voltage Load Regulation (Note 3)
Measured in Servo Loop; V
ITH
= 0.7V ● 0.1 0.3 %
Measured in Servo Loop; V
ITH
= 2V ● –0.1 –0.3 %
DF Max Maximum Duty Factor In Dropout 98 99.4 %
g
m
Transconductance Amplifier g
m
1.3 mmho
V
FCB
Forced Continuous Threshold ● 0.76 0.8 0.84 V
I
FCB
Forced Continuous Current V
FCB
= 0.85V – 0.17 –0.3 µA
3
LTC1735
1735fc
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
V
OVL
Feedback Overvoltage Lockout ● 0.84 0.86 0.88 V
I
Q
Input DC Supply Current (Note 4)
Normal Mode 450 µA
Shutdown V
RUN/SS
= 0V 15 25 µA
V
RUN/SS
Run Pin Start Threshold V
RUN/SS
, Ramping Positive 1.0 1.5 1.9 V
V
RUN/SS
Run Pin Begin Latchoff Threshold V
RUN/SS
, Ramping Positive 4.1 4.5 V
I
RUN/SS
Soft-Start Charge Current V
RUN/SS
= 0V –0.7 –1.2 µA
I
SCL
RUN/SS Discharge Current Soft Short Condition, V
OSENSE
= 0.5V, 0.5 2 4 µA
V
RUN/SS
= 4.5V
UVLO Undervoltage Lockout Measured at V
IN
Pin (V
IN
Ramping Down) ● 3.5 3.9 V
∆V
SENSE(MAX)
Maximum Current Sense Threshold V
OSENSE
= 0.7V ● 60 75 85 mV
I
SENSE
Sense Pins Total Source Current V
SENSE
–
= V
SENSE
+
= 0V 60 80 µA
t
ON(MIN)
Minimum On-Time Tested with a Square Wave (Note 6) 160 200 ns
TG Transition Time: (Note 7)
TG t
r
Rise Time C
LOAD
= 3300pF 50 90 ns
TG t
f
Fall Time C
LOAD
= 3300pF 50 90 ns
BG Transition Time: (Note 7)
BG t
r
Rise Time C
LOAD
= 3300pF 50 90 ns
BG t
f
Fall Time C
LOAD
= 3300pF 40 80 ns
TG/BG t
1D
Top Gate Off to Synchronous C
LOAD
= 3300pF Each Driver 100 ns
Gate On Delay Time
TG/BG t
2D
Synchronous Gate Off to Top C
LOAD
= 3300pF Each Driver 70 ns
Gate On Delay Time
Internal V
CC
Regulator
V
INTVCC
Internal V
CC
Voltage 6V < V
IN
< 30V, V
EXTVCC
= 4V 5.0 5.2 5.4 V
V
LDO(INT)
Internal V
CC
Load Regulation I
CC
= 0 to 20mA, V
EXTVCC
= 4V 0.2 1 %
V
LDO(EXT)
EXTV
CC
Drop Voltage I
CC
= 20mA, V
EXTVCC
= 5V 130 200 mV
V
EXTVCC
EXTV
CC
Switchover Voltage I
CC
= 20mA, EXTV
CC
Ramping Positive ● 4.5 4.7 V
V
EXTVCC(HYS)
EXTV
CC
Hysteresis 0.2 V
Oscillator
f
OSC
Oscillator Frequency C
OSC
= 43pF (Note 5) 265 300 335 kHz
f
H
/f
OSC
Maximum Sync Frequency Ratio 1.3
f
FCB(SYNC)
FCB Pin Threshold For Sync Ramping Negative 0.9 1.2 V
PGOOD Output (LTC1735F Only)
V
PGL
PGOOD Voltage Low I
PGOOD
= 2mA 110 200 mV
I
PGOOD
PGOOD Leakage Current V
PGOOD
= 5V ±1 µA
V
PG
PGOOD Trip Level V
OSENSE
with Respect to Set Output Voltage
V
OSENSE
Ramping Negative –6.0 –7.5 –9.5 %
V
OSENSE
Ramping Positive 6.0 7.5 9.5 %
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
according to the following formulas:
LTC1735CS, LTC1735IS: T
J
= T
A
+ (P
D
• 110 °C/W)
LTC1735CGN, LTC1735IGN, LTC1735EGN: T
J
= T
A
+ (P
D
• 130°C/W)
LTC1735CF, LTC1735IF: T
J
= T
A
+ (P
D
• 110°C/W)
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LTC1735CF

Mfr. #:
Buy LTC1735CF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators LTC1735 - High Efficiency Synchronous Step-Down Switching Regulator
Lifecycle:
New from this manufacturer.
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