FEATURES
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LTC3812-5
60V Current Mode
Synchronous Switching
Regulator Controller
DESCRIPTION
The LTC3812-5 is a synchronous step-down switching
regulator controller that can directly step down voltages
from up to 60V input, making it ideal for telecom and
automotive applications. The LTC3812-5 uses a constant
on-time valley current control architecture to deliver very
low duty cycles with accurate cycle-by-cycle current limit
without requiring a sense resistor.
A precise internal reference provides 0.5% DC accuracy.
A high bandwidth (25MHz) error amplifier provides very
fast line and load transient response. Large 1Ω gate driv-
ers allow the LTC3812-5 to drive large power MOSFETs
for higher current applications. The operating frequency
is selected by an external resistor and is compensated for
variations in V
IN
. A shutdown pin allows the LTC3812-5 to
be turned off reducing the supply current to <230μA.
Integrated bias control generates gate drive power from
the input supply during start-up and when an output short-
circuit occurs, with the addition of a small external SOT23
MOSFET. When in regulation, power is derived from the
output for higher efficiency.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5481178, 5847554, 6304066, 6476589, 6580258,
6677210, 6774611.
High Voltage Operation: Up to 60V
Large 1Ω Gate Drivers
No Current Sense Resistor Required
Dual N-Channel MOSFET Synchronous Drive
Extremely Fast Transient Response
±0.5% 0.8V Voltage Reference
Programmable Soft-Start
Generates 5.5V Driver Supply
Selectable Pulse-Skipping Mode Operation
Power Good Output Voltage Monitor
Adjustable On-Time/Frequency: t
ON(MIN)
< 100ns
Adjustable Cycle-by-Cycle Current Limit
Undervoltage Lockout On Driver Supply
Output Overvoltage Protection
Thermally Enhanced 16-Pin TSSOP Package
APPLICATIONS
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48V Telecom and Base Station Power Supplies
Networking Equipment, Servers
Automotive and Industrial Control Systems
TYPICAL APPLICATION
High Efficiency High Voltage Step-Down Converter
R
ON
110k
I
ON
100k
PGOOD
PGOOD
V
RNG
FCB
RUN/SS
1000pF
47pF
200k
V
FB
5pF
1.89k
SGND
PGND
I
TH
BOOST
TG
SW
EXTV
CC
INTV
CC
BG
1μF
M2
Si7850DP
D1
MBR1100
10k
M1
Si7850DP
L1
4.7μH
LTC3812-5
0.1μF
NDRV
100k
M3
ZXMN-
10A07F
Efficiency vs Load Current
100
V
IN
= 12V
95
EFFICIENCY (%)
V
IN
= 42V
V
IN
= 24V
+
V
IN
6V TO 60V
C
IN
22μF
90
V
OUT
5V
5A
85
80
+
0
C
OUT
270μF
1
2
3
4
LOAD CURRENT (A)
5
6
38125 TA01b
38125 TA01
38125fc
1
LTC3812-5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
I
ON
V
RNG
PGOOD
FCB
I
TH
V
FB
RUN/SS
SGND
1
2
3
4
5
6
7
8
17
16 BOOST
15 TG
14 SW
13 PGND
12 BG
11 INTV
CC
10 EXTV
CC
9
NDRV
Supply Voltages
INTV
CC
................................................... –0.3V to 14V
(INTV
CC
– PGND), (BOOST – SW) ......... –0.3V to 14V
BOOST (Continuous) ............................. –0.3V to 85V
BOOST (≤400ms) .................................. –0.3V to 95V
EXTV
CC
.................................................. –0.3V to 15V
(EXTV
CC
– INTV
CC
).................................. –12V to 12V
(NDRV – INTV
CC
) Voltage........................... –0.3V to 10V
SW Voltage (Continuous).............................. –1V to 70V
SW Voltage (400ms) ..................................... –1V to 80V
I
ON
Voltage (Continuous) ........................... –0.3V to 70V
I
ON
Voltage (400ms) .................................. –0.3V to 80V
RUN/SS Voltage ........................................... –0.3V to 5V
PGOOD Voltage ............................................ –0.3V to 7V
V
RNG
, FCB Voltages .................................... –0.3V to 14V
FB Voltage ................................................. –0.3V to 2.7V
TG, BG, INTV
CC
, EXTV
CC
RMS Currents .................50mA
Operating Junction Temperature Range
(Notes 2, 3, 7) ........................................ –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 38°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3812EFE-5#PBF
LTC3812IFE-5#PBF
TAPE AND REEL
LTC3812EFE-5#TRPBF
LTC3812IFE-5#TRPBF
PART MARKING*
3812EFE-5
3812IFE-5
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
38125fc
2
LTC3812-5
The
l
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C (Note 2), INTV
CC
= V
BOOST
= V
RNG
= V
EXTVCC
= V
NDRV
= 5V, V
FCB
= V
SW
=
0V, unless otherwise specified.
SYMBOL
Main Control Loop
INTV
CC
I
Q
I
BOOST
V
FB
INTV
CC
Supply Voltage
INTV
CC
Supply Current
INTV
CC
Shutdown Current
BOOST Supply Current
Feedback Voltage
RUN/SS > 1.5V (Notes 4, 5)
RUN/SS = 0V
RUN/SS > 1.5V (Note 5)
RUN/SS = 0V
(Note 4)
0°C to 85°C
–40°C to 85°C
–40°C to 125°C
5V < INTV
CC
< 14V (Note 4)
V
RNG
= 2V, V
FB
= 0.76V
V
RNG
= 0V, V
FB
= 0.76V
V
RNG
= INTV
CC
, V
FB
= 0.76V
V
RNG
= 2V, V
FB
= 0.84V
V
RNG
= 0V, V
FB
= 0.84V
V
RNG
= INTV
CC
, V
FB
= 0.84V
V
FB
= 0.8V
65
(Note 6)
V
FCB
Rising
FCB = 5V
1.2
RUN/SS = 0V
INTV
CC
Rising, I
NDRV
= 100μA
INTV
CC
Rising, NDRV = INTV
CC
= EXTV
CC
INTV
CC
Rising, NDRV = INTV
CC
, EXTV
CC
= 0
INTV
CC
Falling
I
ON
= 100μA
I
ON
= 300μA
I
ON
= 2500μA
250
V
BG
= 0V
V
TG
– V
SW
= 0V
0.7
0.7
1
1
1
1
V
FB
Rising
V
FB
Falling
V
FB
Returning
I
PGOOD
= 5mA
7.5
–7.5
10
–10
1.5
0.3
1.5
12.5
–12.5
3
0.6
1.5
l
l
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
4.35
TYP
MAX
14
UNITS
V
mA
μA
μA
μA
V
V
V
V
%/V
mV
mV
mV
mV
mV
mV
3
224
240
0
0.796
0.794
0.792
0.792
0.800
0.800
0.800
0.800
0.002
256
70
170
320
95
215
–300
–85
–200
20
100
25
0.75
0.8
0
1.5
1.4
4.2
4.2
9.0
3.7
1.85
605
0.7
4.05
4.05
8.70
6
600
400
5
0.804
0.806
0.806
0.808
0.02
384
120
260
∆V
FB,LINE
V
SENSE(MAX)
Feedback Voltage Line Regulation
Maximum Current Sense Threshold
V
SENSE(MIN)
Minimum Current Sense Threshold
I
VFB
A
VOL
(EA)
f
U
V
FCB
I
FCB
V
RUN/SS
I
RUN/SS
V
VCCUV
Feedback Current
Error Amplifier DC Open-Loop Gain
Error Amp Unity Gain Crossover
Frequency
FCB Threshold
FCB Current
Shutdown Threshold
RUN/SS Source Current
INTV
CC
Undervoltage Lockout
Linear Regulator Mode
External Supply Mode
Trickle-Charge Mode
150
nA
dB
MHz
0.85
1
2
2.5
4.35
4.35
9.30
V
μA
V
μA
V
V
V
V
μs
ns
ns
ns
A
Ω
A
Ω
%
%
%
V
38125fc
Oscillator
t
ON
t
ON(MIN)
t
OFF(MIN)
Driver
I
BG,PEAK
R
BG,SINK
I
TG,PEAK
R
TG,SINK
PGOOD Output
∆V
FBOV
∆V
FB,HYST
V
PGOOD
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysterisis
PGOOD Low Voltage
BG Driver Peak Source Current
BG Driver Pull-Down R
DS(ON)
TG Driver Peak Source Current
TG Driver Pull-Down R
DS(ON)
On-Time
Minimum On-Time
Minimum Off-Time
1.55
515
2.15
695
100
350
3
LTC3812-5
The
l
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C (Note 2), INTV
CC
= V
BOOST
= V
RNG
= V
EXTVCC
= V
NDRV
= 5V, V
FCB
= V
SW
=
0V, unless otherwise specified.
SYMBOL
I
PGOOD
PG Delay
V
CC
Regulators
V
EXTVCC
EXTV
CC
Switchover Voltage
EXTV
CC
Rising
EXTV
CC
Hysterisis
INTV
CC
Voltage from EXTV
CC
V
EXTVCC
- V
INTVCC
at Dropout
INTV
CC
Load Regulation from EXTV
CC
INTV
CC
Voltage from NDRV Regulator
INTV
CC
Load Regulation from NDRV
Current into NDRV Pin
Linear Regulator Timeout Enable
Threshold
Maximum Supply Voltage
Maximum Current into NDRV/INTV
CC
Trickle Charger Shunt Regulator
Trickle Charger Shunt Regulator,
INTV
CC
≤ 16.7V (Note 8)
10
6V < V
EXTVCC
< 15V
I
CC
= 20mA, V
EXTVCC
= 5V
I
CC
= 0mA to 20mA, V
EXTVCC
= 10V
Linear Regulator in Operation
I
CC
= 0mA to 20mA, V
EXTVCC
= 0
V
NDRV
– V
INTVCC
= 3V
20
210
5.2
l
ELECTRICAL CHARACTERISTICS
PARAMETER
PGOOD Leakage Current
PGOOD Delay
CONDITIONS
V
PGOOD
= 5V
V
FB
Falling
MIN
TYP
0
120
MAX
2
UNITS
μA
μs
4.5
0.1
5.2
4.7
0.25
5.5
75
0.01
5.5
0.01
40
270
15
0.4
5.8
150
V
V
V
mV
%
V
INTVCC,1
∆V
EXTVCC,1
∆V
LOADREG,1
V
INTVCC,2
∆V
LOADREG,2
I
NDRV
I
NDRVTO
V
CCSR
I
CCSR
5.8
V
%
60
350
μA
μA
V
mA
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 LTC3812-5 is tested under pulsed load conditions such that
T
J
≈
T
A
.The LTC3812E-5 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3812I-5 is guaranteed
to meet performance specifications over the full –40°C to 125°C operating
junction temperature range.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC3812-5: T
J
= T
A
+ (P
D
• 38°C/W)
PARAMETER
Maximum V
IN
MOSFET Gate Drive
INTV
CC
UV
+
INTV
CC
UV
–
LTC3810
100V
6.35V to 14V
6.2V
6V
Note 4:
The LTC3812-5 is tested in a feedback loop that servos V
FB
to the
reference voltage with the I
TH
pin forced to a voltage between 1V and 2V.
Note 5:
The dynamic input supply current is higher due to the power
MOSFET gate charging being delivered at the switching frequency
(Q
G
• f
OSC
).
Note 6:
Guaranteed by design. Not subject to test.
Note 7:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 8:
I
CC
is the sum of current into NDRV and INTV
CC
.
LTC3810-5
60V
4.5V to 14V
4.2V
4V
LTC3812-5
60V
4.5V to 14V
4.2V
4V
38125fc
4
LTC3812-5
TYPICAL PERFORMANCE CHARACTERISTICS
Load Transient Response
V
IN
20V/DIV
V
OUT
50mV/DIV
I
OUT
5A/DIV
INTV
CC
,
V
OUT
2V/DIV
I
L
2A/DIV
10μs/DIV
FRONT PAGE CIRCUIT
V
IN
= 25V
0A TO 5A LOAD STEP
38125 G01
Start-Up
V
OUT
5V/DIV
INTV
CC
V
OUT
SS/TRACK
2V/DIV
I
L
5A/DIV
Short-Circuit/Fault Timeout
Operation
2ms/DIV
FRONT PAGE CIRCUIT
V
IN
= 30V
I
LOAD
= 0.5A
FCB = 0V
38125 G02
5ms/DIV
FRONT PAGE CIRCUIT
V
IN
= 25V
R
SHORT
= 0.1Ω
38125 G03
Short-Circuit/Foldback Operation
V
OUT
5V/DIV
I
L
5A/DIV
V
OUT
100mV/DIV
Pulse-Skipping Mode Operation
100
Efficiency vs Input Voltage
FRONT PAGE CIRCUIT
f = 250kHz
I
LOAD
= 5A
FORCED
CONTINUOUS
I
LOAD
= 0.5A
FORCED
CONTINUOUS
I
LOAD
= 0.5A
PULSE-SKIPPING
I
L
2A/DIV
EFFICIENCY (%)
I
TH
0.5A/DIV
95
90
200μs/DIV
FRONT PAGE CIRCUIT
V
IN
= 25V
38125 G04
20μs/DIV
FRONT PAGE CIRCUIT
V
IN
= 25V
I
OUT
= 100mA
FCB = INTV
CC
38125 G05
85
80
0
10
20
30
40
INPUT VOLTAGE (V)
50
60
38125 G06
Efficiency vs Load Current
100
V
IN
= 24V
EFFICIENCY (%)
95
FREQUENCY (kHz)
300
290
280
270
260
250
240
230
220
210
5
6
38125 G07
Frequency vs Input Voltage
350
FRONT PAGE CIRCUIT
FCB = 0V
LOAD = 5A
FREQUENCY (kHz)
300
250
200
Frequency vs Load Current
FRONT PAGE CIRCUIT
FORCED
CONTINUOUS
V
IN
= 42V
PULSE SKIPPING
150
100
50
0
LOAD = 0A
90
V
OUT
= 12V
FCB = INTV
CC
f = 250kHz
85
0
1
2
3
4
LOAD CURRENT (A)
200
0
10
30
40
20
INPUT VOLTAGE (V)
50
60
0
1
2
3
4
5
38125 G09
LOAD CURRENT (A)
LT1108 • TPC12
38125fc
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