FEATURES
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LTC3827-1
Low I
Q
, Dual, 2-Phase
Synchronous Step-Down Controller
DESCRIPTION
The LTC
®
3827-1 is a high performance dual step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant frequency
current mode architecture allows a phase-lockable fre-
quency of up to 650kHz. Power loss and noise due to the
ESR of the input capacitor ESR are minimized by operating
the two controller output stages out of phase.
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
LTC3827-1 features a precision 0.8V reference and a power
good output indicator. A wide 4V to 36V input supply range
encompasses all battery chemistries.
Independent TRACK/SS pins for each controller ramp the
output voltage during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit conditions.
The PLLIN/MODE pin selects among Burst Mode opera-
tion, pulse-skipping mode, or continuous inductor cur-
rent mode at light loads. For a leadless package version
(5mm × 5mm QFN) with additional features, see the
LTC3827 data sheet.
L,
LT, LTC, LTM, Burst Mode 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 5481178, 5929620, 6177787, 6144194, 5408150,
6580258, 6304066, 5705919.
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Wide Output Voltage Range: 0.8V ≤ V
OUT
≤ 10V
Low Operating I
Q
: 80μA (One Channel On)
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
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
Selectable Continuous, Pulse-Skipping or
Low Ripple
Burst Mode
®
Operation at Light Loads
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
Output Overvoltage Protection
Low Shutdown I
Q
: 8μA
Internal LDO Powers Gate Drive from V
IN
or V
OUT
Small 28-Lead SSOP Package
APPLICATIONS
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Automotive Systems
Battery-Operated Digital Devices
Distributed DC Power Systems
TYPICAL APPLICATION
High Efficiency Dual 8.5V/3.3V Step-Down Converter
+
4.7μF
V
IN
TG1
3.3μH
0.1μF
BOOST1
SW1
BG1
LTC3827-1
SENSE1
+
0.015Ω
V
OUT1
3.3V
5A
SENSE1
–
V
FB1
62.5k
150μF
220pF
20k
15k
I
TH1
SENSE2
–
V
FB2
I
TH2
220pF
15k
20k
192.5k
INTV
CC
TG2
BOOST2
SW2
BG2
PGND
SENSE2
+
0.015Ω
V
OUT2
8.5V
3.5A
150μF
0.1μF
EFFICIENCY (%)
7.2μH
V
IN
4V TO 36V
1μF
22μF
50V
100
90
80
70
60
50
40
30
20
10
0
0.001 0.01
0.1
0.1
1
10 100 1000 10000
LOAD CURRENT (mA)
38271 TA01b
Efficiency and Power Loss
vs Load Current
100000
EFFICIENCY
V
IN
= 12V; V
OUT
= 3.3V
10000
POWER LOSS (mW)
1000
100
POWER LOSS
10
1
TRACK/SS1 SGND TRACK/SS2
0.1μF
0.1μF
FIGURE 13 CIRCUIT
38271 TA01
38271fe
1
LTC3827-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
I
TH1
V
FB1
SENSE1
+
SENSE1
–
PLLLPF
PLLIN/MODE
SGND
RUN1
RUN2
SENSE2
–
1
2
3
4
5
6
7
8
9
10
28 TRACK/SS1
27 PGOOD1
26 TG1
25 SW1
24 BOOST1
23 BG1
22 V
IN
21 PGND
20 EXTV
CC
19 INTV
CC
18 BG2
17 BOOST2
16 SW2
15 TG2
Input Supply Voltage (V
IN
) .........................36V to – 0.3V
Topside Driver Voltages
BOOST1, BOOST2.................................. 42V to –0.3V
Switch Voltage (SW1, SW2) ......................... 36V to –5V
(BOOST1-SW1), (BOOST2-SW2) ............. 8.5V to –0.3V
RUN1, RUN2 ............................................... 7V to –0.3V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages ..................................... 11V to –0.3V
PLLIN/MODE, PLLLPF, TRACK/SS1, TRACK/SS2
Voltages ............................................... INTV
CC
to –0.3V
EXTV
CC
...................................................... 10V to –0.3V
I
TH1,
I
TH2
, V
FB1
, V
FB2
Voltages .................. 2.7V to –0.3V
PGOOD1 Voltage ....................................... 8.5V to –0.3V
Peak Output Current <10μs (TG1, TG2, BG1, BG2) .....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................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
SENSE2
+
11
V
FB2
12
I
TH2
13
TRACK/SS2 14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3827EG-1#PBF
LTC3827IG-1#PBF
LEAD BASED FINISH
LTC3827EG-1
LTC3827IG-1
TAPE AND REEL
LTC3827EG-1#TRPBF
LTC3827IG-1#TRPBF
TAPE AND REEL
LTC3827EG-1#TR
LTC3827IG-1#TR
PART MARKING
3827EG-1
3827IG-1
PART MARKING
3827EG-1
3827IG-1
PACKAGE DESCRIPTION
28-Lead Plastic SSOP
28-Lead Plastic SSOP
PACKAGE DESCRIPTION
28-Lead Plastic SSOP
28-Lead Plastic SSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
38271fe
2
LTC3827-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
FB1, 2
I
VFB1, 2
V
REFLNREG
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Main Control Loops
(Note 4) I
TH1, 2
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
TH1, 2
= 1.2V; Sink/Source 5μA (Note 4)
(Note 5)
RUN1 = 5V, RUN2 = 0V, V
FB1
= 0.83V (No Load)
RUN1 = 0V, RUN2 = 5V, V
FB2
= 0.83V (No Load)
V
RUN1, 2
= 0V
RUN1,2 = 5V, V
FB1
= V
FB2
= 0.83V
V
IN
Ramping Down
Measured at V
FB1, 2
, Relative to Regulated V
FB1, 2
(Each Channel) V
SENSE1
–
, 2
– = V
SENSE1
+
, 2
+ = 0V
In Dropout
V
TRACK1, 2
= 0V
V
RUN1,
V
RUN2
Rising
V
FB1, 2
= 0.7V, V
SENSE1–, 2–
= 3.3V
V
FB1, 2
= 0.7V, V
SENSE1–, 2–
= 3.3V
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
●
●
●
●
●
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/SS1, 2
= 5V unless otherwise noted.
CONDITIONS
MIN
0.792
TYP
0.800
–5
0.002
0.1
– 0.1
1.55
80
80
8
115
3.5
8
98
0.75
0.5
90
80
10
–660
99.4
1.0
0.7
100
100
50
50
40
40
70
70
180
5.0
7.2
4.5
5.25
0.2
7.5
0.2
4.7
0.2
V
PLLLPF
= Floating; PLLIN/MODE = DC Voltage
360
400
440
5.5
1.0
7.8
1.0
1.35
0.9
110
115
90
90
90
80
125
125
20
160
4
12
MAX
0.808
–50
0.02
0.5
–0.5
UNITS
V
nA
%/V
%
%
mmho
μA
μA
μA
μA
V
%
μA
%
μA
V
mV
mV
ns
ns
ns
ns
ns
ns
ns
V
%
V
%
V
V
kHz
g
m1, 2
I
Q
Transconductance Amplifier g
m
Input DC Supply Current
Sleep Mode (Channel 1 On)
Sleep Mode (Channel 2 On)
Shutdown
Sleep Mode (Both Channels)
Undervoltage Lockout
Feedback Overvoltage Lockout
Sense Pins Total Source Current
Maximum Duty Factor
RUN Pin ON Threshold
Maximum Current Sense Threshold
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
UVLO
V
OVL
I
SENSE
DF
MAX
V
RUN1, 2
ON
V
SENSE(MAX)
I
TRACK/SS1, 2
Soft-Start Charge Current
TG1, 2 t
r
TG1, 2 t
f
BG1, 2 t
r
BG1, 2 t
f
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
Top Gate Off to Bottom Gate On Delay C
LOAD
= 3300pF Each Driver
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay C
LOAD
= 3300pF Each Driver
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
(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
38271fe
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LTC3827-1
ELECTRICAL CHARACTERISTICS
SYMBOL
f
LOW
f
HIGH
f
SYNCMIN
f
SYNCMAX
I
PLLLPF
PARAMETER
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
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/SS1, 2
= 5V unless otherwise noted.
CONDITIONS
V
PLLLPF
= 0V; PLLIN/MODE = DC Voltage
V
PLLLPF
= INTV
CC
; PLLIN/MODE = DC Voltage
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
MIN
220
475
TYP
250
530
115
800
–5
5
0.1
0.3
±1
–8
12
MAX
280
580
140
UNITS
kHz
kHz
kHz
kHz
μA
μA
V
μA
%
%
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 LTC3827E-1 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 LTC3827I-1 is guaranteed to meet
performance specifications over the –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 formula:
T
J
= T
A
+ (P
D
• 95 °C/W)
Note 4:
The LTC3827-1 is tested in a feedback loop that servos V
ITH1, 2
to
a specified voltage and measures the resultant V
FB1, 2.
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).
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency and Power Loss
vs Output Current
100
90
80
70
EFFICIENCY (%)
60
50
40
30 V
IN
= 12V
V
OUT
= 3.3V
20
10
0
0.001 0.01
0.1
0.1
1
10 100 1000 10000
LOAD CURRENT (mA)
38271 G01
Efficiency vs Load Current
10000
100
90
80
70
60
50
40
0.001 0.01
V
IN
= 12V
V
IN
= 5V
V
OUT
= 3.3V
98
96
94
POWER LOSS (mW)
EFFICIENCY (%)
EFFICIENCY (%)
0.1
1
10 100 1000 10000
LOAD CURRENT (mA)
38271 G02
Efficiency vs Input Voltage
Burst Mode OPERATION
FORCED CONTINUOUS MODE
PULSE SKIPPING MODE
1000
100
92
90
88
86
84
V
OUT
= 3.3V
82
0
5
10
15 20 25 30
INPUT VOLTAGE (V)
35
40
38271 G03
10
1
38271fe
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LTC3827-1
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step
(Burst Mode Operation)
Load Step
(Forced Continuous Mode)
Load Step
(Pulse Skip Mode)
V
OUT
100mV/DIV
AC
COUPLED
V
OUT
100mV/DIV
AC
COUPLED
V
OUT
100mV/DIV
AC
COUPLED
I
L
2A/DIV
I
L
2A/DIV
I
L
2A/DIV
20μs/DIV
FIGURE 13 CIRCUIT
V
OUT
= 3.3V
38271 G04
20μs/DIV
FIGURE 13 CIRCUIT
V
OUT
= 3.3V
38271 G05
20μs/DIV
FIGURE 13 CIRCUIT
V
OUT
= 3.3V
38271 G06
Inductor Current at Light Load
Soft Start-Up
V
OUT2
2V/DIV
Tracking Start-Up
V
OUT2
2V/DIV
FORCED
CONTINUOUS
MODE
2A/DIV
BURST MODE
PULSE
SKIPPING
MODE
4μs/DIV
FIGURE 13 CIRCUIT
V
OUT
= 3.3V
I
LOAD
= 300μA
38271 G07
V
OUT1
2V/DIV
V
OUT1
2V/DIV
20ms/DIV
FIGURE 13 CIRCUIT
38271 G08
20ms/DIV
FIGURE 13 CIRCUIT
38271 G09
Total Input Supply Current
vs Input Voltage
350
300
SUPPLY CURRENT (μA)
250
300μA LOAD
200
150
100
50
0
25
20
15
INPUT VOLTAGE (V)
35
NO LOAD
EXTV
CC
AND INTV
CC
VOLTAGES (V)
6.0
5.8
5.6
EXTV
CC
Switchover and INTV
CC
Voltages vs Temperature
5.50
5.45
5.40
INTV
CC
VOLTAGE (V)
INTV
CC
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
–25
35
15
–5
55
TEMPERATURE (°C)
75
95
INTV
CC
Line Regulation
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
–45
EXTV
CC
RISING
EXTV
CC
FALLING
5
10
30
0
5
10
15 20 25 30
INPUT VOLTAGE (V)
35
40
FIGURE 13 CIRCUIT
38271 G10
38271 G11
38271 G12
38271fe
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