regulator controller that drives an all N-channel synchro-
nous power MOSFET stage. A constant-frequency current
mode architecture allows a phase-lockable frequency of
up to 650kHz.
The 80μA no-load quiescent current extends operating
life in battery powered systems. OPTI-LOOP compensa-
tion allows the transient response to be optimized over
a wide range of output capacitance and ESR values. The
LTC3835 features a precision 0.8V reference and a power
good output indicator. The 4V to 36V input supply range
encompasses a wide range of battery chemistries.
The TRACK/SS pin ramps the output voltage during start-
up. Current foldback limits MOSFET heat dissipation during
short-circuit conditions.
Comparison of LTC3835 and LTC3835-1
PART #
CLKOUT/
PHASMD
YES
NO
EXTV
CC
YES
NO
PGOOD
YES
NO
PACKAGES
FE20/4
×
5 QFN
GN16/3
×
5 DFN
Wide Output Voltage Range: 0.8V ≤ V
IN
≤ 10V
Low Operating Quiescent Current: 80μA
OPTI-LOOP
®
Compensation Minimizes C
OUT
±1% Output Voltage Accuracy
Wide V
IN
Range: 4V to 36V Operation
Phase-Lockable Fixed Frequency 140kHz to 650kHz
Dual N-Channel MOSFET Synchronous Drive
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Output Voltage Soft-Start or Tracking
Output Current Foldback Limiting
Power Good Output Voltage Monitor
Clock Output for PolyPhase
®
Applications
Output Overvoltage Protection
Low Shutdown I
Q
: 10μA
Internal LDO Powers Gate Drive from V
IN
or V
OUT
Selectable Continuous, Pulse-Skipping or
Burst Mode
®
Operation at Light Loads
Small 20-Lead TSSOP or 4mm
×
5mm QFN Package
APPLICATIONS
n
n
n
n
LTC3835
LTC3835-1
Automotive Systems
Telecom Systems
Battery-Operated Digital Devices
Distributed DC Power Systems
L,
LT, LTC, LTM, Burst Mode, PolyPhase and OPTI-LOOP are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents including 5408150, 5481178, 5705919, 5929620,
6304066, 6498466, 6580258, 6611131.
TYPICAL APPLICATION
High Efficiency Synchronous Step-Down Converter
CLKOUT
PLLLPF
0.01μF
RUN
PGOOD
TRACK/SS
I
TH
330pF
33k
100pF
SGND
20k
PLLIN/MODE
V
FB
62.5k
SENSE
–
Efficiency and Power Loss
vs Load Current
V
IN
4V TO
36V
V
IN
TG
0.22μF
BOOST
SW
10μF
100
90
80
EFFICIENCY (%)
EFFICIENCY
V
IN
= 12V; V
OUT
= 3.3V
100000
10000
POWER LOSS (mW)
1000
100
POWER LOSS
10
1
0.1
0.1
1
10 100 1000 10000
LOAD CURRENT (mA)
3835 TA01b
3.3μH
0.012Ω
LTC3835
V
OUT
3.3V
5A
150μF
70
60
50
40
30
20
10
INTV
CC
EXTV
CC
BG
4.7μF
SENSE
+
PGND
0
0.001 0.01
3835 TA01
3835fc
1
LTC3835
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (V
IN
) ......................... 36V to –0.3V
Top Side Driver Voltage (BOOST) ............... 42V to –0.3V
Switch Voltage (SW) ..................................... 36V to –5V
INTV
CC
, (BOOST-SW), CLKOUT, PGOOD ... 8.5V to –0.3V
RUN, TRACK/SS ......................................... 7V to –0.3V
SENSE
+
, SENSE
–
Voltages ........................ 11V to –0.3V
PLLIN/MODE, PHASMD, PLLLPF ......... INTV
CC
to –0.3V
EXTV
CC
...................................................... 10V to –0.3V
I
TH
, V
FB
Voltages ...................................... 2.7V to –0.3V
Peak Output Current <10μs (TG,BG) ...........................3A
INTV
CC
Peak Output Current ................................. 50mA
Operating Temperature Range (Note 2).... –40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range
FE Package ........................................ –65°C to 150°C
Storage Temperature Range
UFD Package ..................................... –65°C to 125°C
Lead Temperature (FE Package, Soldering, 10 sec)... 300°C
PIN CONFIGURATION
TOP VIEW
PHASMD
CLKOUT
TOP VIEW
CLKOUT
PLLLPF
I
TH
TRACKS/SS
V
FB
SGND
PGND
BG
INTV
CC
1
2
3
4
5
6
7
8
9
21
20 PHASMD
19 PLLIN/MODE
18 PGOOD
17 SENSE
+
16
SENSE
–
I
TH
1
TRACK/SS 2
V
FB
3
SGND 4
PGND 5
BG 6
7
INTV
CC
8
EXTV
CC
9 10
V
IN
SW
21
PLLLPF
PLLIN/MODE
16 PGOOD
15 SENSE
+
14 SENSE
–
13 RUN
12 BOOST
11 TG
20 19 18 17
15 RUN
14 BOOST
13 TG
12 SW
11 V
IN
EXTV
CC
10
FE PACKAGE
20-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 35°C/W
EXPOSED PAD (PIN 21) IS SGND MUST BE SOLDERED TO PCB
UFD PACKAGE
20-PIN (4mm 5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 21) IS SGND MUST BE SOLDERED TO PCB
3835fc
2
LTC3835
ORDER INFORMATION
LEAD FREE FINISH
LTC3835EFE#PBF
LTC3835IFE#PBF
LTC3835EUFD#PBF
LTC3835IUFD#PBF
LEAD BASED FINISH
LTC3835EFE
LTC3835IFE
LTC3835EUFD
LTC3835IUFD
TAPE AND REEL
LTC3835EFE#TRPBF
LTC3835IFE#TRPBF
LTC3835EUFD#TRPBF
LTC3835IUFD#TRPBF
TAPE AND REEL
LTC3835EFE#TR
LTC3835IFE#TR
LTC3835EUFD#TR
LTC3835IUFD#TR
(Note 2)
PART MARKING*
LTC3835EFE
LTC3835IFE
3835
3835
PART MARKING*
LTC3835EFE
LTC3835IFE
3835
3835
PACKAGE DESCRIPTION
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
20-Pin (4mm
×
5mm) Plastic DFN
20-Pin (4mm
×
5mm) Plastic DFN
PACKAGE DESCRIPTION
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
20-Pin (4mm
×
5mm) Plastic DFN
20-Pin (4mm
×
5mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
FB
I
VFB
V
REFLNREG
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Main Control Loops
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, V
RUN
= 5V unless otherwise noted.
CONDITIONS
(Note 4); I
TH
Voltage = 1.2V
(Note 4)
V
IN
= 4V to 30V (Note 4)
(Note 4)
Measured in Servo Loop;
ΔI
TH
Voltage = 1.2V to 0.7V
Measured in Servo Loop;
ΔI
TH
Voltage = 1.2V to 2V
I
TH
= 1.2V; Sink/Source 5μA (Note 4)
(Note 5)
RUN = 5V, V
FB
= 0.83V (No Load)
V
RUN
= 0V
V
IN
Ramping Down
Measured at V
FB
Relative to Regulated V
FB
V
SENSE
– = V
SENSE
+ = 0V
In Dropout
V
TRACK
= 0V
V
RUN
Rising
V
FB
= 0.7V, V
SENSE
– = 3.3V
V
FB
= 0.7V, V
SENSE
– = 3.3V
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
l
l
l
l
l
MIN
0.792
TYP
0.800
–5
0.002
0.1
–0.1
1.55
80
10
3.5
MAX
0.808
–50
0.02
0.5
–0.5
UNITS
V
nA
%/V
%
%
mmho
g
m
I
Q
Transconductance Amplifier g
m
Input DC Supply Current
Sleep Mode
Shutdown
Undervoltage Lockout
Feedback Overvoltage Lockout
Sense Pins Total Source Current
Maximum Duty Factor
Soft-Start Charge Current
RUN Pin ON Threshold
Maximum Current Sense Threshold
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
125
20
4
12
μA
μA
V
%
μA
%
UVLO
V
OVL
I
SENSE
DF
MAX
I
TRACK/SS
V
RUN
ON
V
SENSE(MAX)
8
98
0.75
0.5
90
80
10
–660
99.4
1.0
0.7
100
100
50
50
40
40
1.35
0.9
110
115
90
90
90
80
μA
V
mV
mV
ns
ns
ns
ns
TG t
r
TG t
f
BG t
r
BG t
f
3835fc
3
LTC3835
ELECTRICAL CHARACTERISTICS
SYMBOL
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCCVIN
V
LDOVIN
V
INTVCCEXT
V
LDOEXT
V
EXTVCC
V
LDOHYS
f
NOM
f
LOW
f
HIGH
f
SYNCMIN
f
SYNCMAX
I
PLLLPF
PARAMETER
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, V
RUN
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
70
70
180
5
7.2
4.5
5.25
0.2
7.5
0.2
4.7
0.2
V
PLLLPF
= No Connect
V
PLLLPF
= 0V
V
PLLLPF
= INTV
CC
PLLIN/MODE = External Clock; V
PLLLPF
= 0V
PLLIN/MODE = External Clock; V
PLLLPF
= 2V
f
PLLIN/MODE
< f
OSC
f
PLLIN/MODE
> f
OSC
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
FB
with Respect to Set Regulated Voltage
V
FB
Ramping Negative
V
FB
Ramping Positive
-12
8
–10
10
650
360
220
475
400
250
530
115
800
–5
5
0.1
0.3
±1
–8
12
440
280
580
140
5.5
1.0
7.8
1.0
MAX
UNITS
ns
ns
ns
V
%
V
%
V
V
kHz
kHz
kHz
kHz
kHz
μA
μA
V
μA
%
%
Top Gate Off to Bottom Gate On Delay C
LOAD
= 3300pF
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay C
LOAD
= 3300pF
Top Switch-On Delay Time
Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Hysteresis
Nominal Frequency
Lowest Frequency
Highest Frequency
Minimum Synchronizable Frequency
Maximum Synchronizable Frequency
Phase Detector Output Current
Sinking Capability
Sourcing Capability
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level
(Note 7)
8.5V < V
IN
< 30V, V
EXTVCC
= 0V
I
CC
= 0mA to 20mA, V
EXTVCC
= 0V
V
EXTVCC
= 8.5V
I
CC
= 0mA to 20mA, V
EXTVCC
= 8.5V
EXTV
CC
Ramping Positive
INTV
CC
Linear Regulator
Oscillator and Phase-Locked Loop
PGOOD Output
V
PGL
I
PGOOD
V
PG
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3835E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3835I is guaranteed to meet
performance specifications over the full –40°C to 85°C operating
temperature range.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC3835FE: T
J
= T
A
+ (P
D
• 35°C/W)
LTC3835UFD: T
J
= T
A
+ (P
D
• 37°C/W)
Note 4:
The LTC3835 is tested in a feedback loop that servos V
ITH
to a
specified voltage and measures the resultant V
FB
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6:
Rise and fall times are measured using 10% and 90% levels.
Delay times are measured using 50% levels.
Note 7:
The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥40% of I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
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