FEATURES
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LTC3826-1
30µA I
Q
, Dual, 2-Phase
Synchronous Step-Down Controller
DESCRIPTION
The LTC
®
3826-1 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 30μA 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
LTC3826-1 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
LTC3826 data sheet.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
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.
Wide Output Voltage Range: 0.8V ≤ V
OUT
≤ 10V
Low Operating I
Q
: 30μA (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
: 4μA
Internal LDO Powers Gate Drive from V
IN
or V
OUT
Small 28-Lead SSOP Package
APPLICATIONS
n
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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
V
IN
4V TO 36V
4.7μF
V
IN
TG1
3.3μH
0.1μF
BOOST1
SW1
BG1
LTC3826-1
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
+
0.1μF
22μF
50V
Efficiency and Power Loss
vs Load Current
100
90
10000
7.2μH
EFFICIENCY (%)
80
70
60
50
40
30
20
V
OUT2
8.5V
3.5A
150μF
10
1000
POWER LOSS (mW)
100
10
0.015Ω
1
TRACK/SS1 SGND TRACK/SS2
0.1μF
0.1μF
FIGURE 13 CIRCUIT
0
0.1
0.00001 0.0001 0.001 0.01
0.1
1
10
OUTPUT CURRENT (A)
38261 TA01b
38261 TA01
38261fb
1
LTC3826-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
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
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,
JA
= 95°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3826EG-1#PBF
LTC3826IG-1#PBF
LEAD BASED FINISH
LTC3826EG-1
LTC3826IG-1
TAPE AND REEL
LTC3826EG-1#TRPBF
LTC3826IG-1#TRPBF
TAPE AND REEL
LTC3826EG-1#TR
LTC3826IG-1#TR
PART MARKING
LTC3826EG-1
LTC3826IG-1
PART MARKING
LTC3826EG-1
LTC3826IG-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/
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
Main Control Loops
V
FB1, 2
Regulated Feedback Voltage
I
VFB1, 2
Feedback Current
V
REFLNREG
Reference Voltage Line Regulation
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
(Note 4) I
TH1, 2
Voltage = 1.2V
(Note 4)
V
IN
= 4V to 30V (Note 4)
l
MIN
0.792
TYP
0.800
–5
0.002
MAX
0.808
–50
0.02
UNITS
V
nA
%/V
38261fb
2
LTC3826-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
LOADREG
PARAMETER
Output Voltage Load Regulation
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.
MIN
l
l
CONDITIONS
(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
g
m1, 2
Transconductance Amplifier g
m
I
TH1, 2
= 1.2V; Sink/Source 5μA (Note 4)
I
Q
Input DC Supply Current
(Note 5)
Sleep Mode (Channel 1 On)
RUN1 = 5V, RUN2 = 0V, V
FB1
= 0.83V (No Load)
Sleep Mode (Channel 2 On)
RUN1 = OV, RUN2 = 5V, V
FB2
= 0.83V (No Load)
Shutdown
V
RUN1, 2
= 0V
Sleep Mode (Both Channels)
RUN1,2 = 5V, V
FB1
= V
FB2
= 0.83V
UVLO
Undervoltage Lockout
V
IN
Ramping Down
V
OVL
Feedback Overvoltage Lockout
Measured at V
FB1, 2
, Relative to Regulated V
FB1, 2
I
SENSE
Sense Pins Total Source Current
(Each Channel) V
SENSE1
–,
2
– = V
SENSE1
+,
2
+ = 0V
DF
MAX
Maximum Duty Factor
In Dropout
I
TRACK/SS1, 2
Soft-Start Charge Current
V
TRACK1, 2
= 0V
V
RUN1, 2
ON
RUN Pin ON Threshold
V
RUN1
, V
RUN2
Rising
V
SENSE(MAX)
Maximum Current Sense Threshold
V
FB1, 2
= 0.7V, V
SENSE1
–,
2
– = 3.3V
TG Transition Time:
(Note 6)
TG1, 2 t
r
Rise Time
C
LOAD
= 3300pF
Fall Time
C
LOAD
= 3300pF
TG1, 2 t
f
BG Transition Time:
(Note 6)
BG1, 2 t
r
Rise Time
C
LOAD
= 3300pF
Fall Time
C
LOAD
= 3300pF
BG1, 2 t
f
TG/BG t
1D
Top Gate Off to Bottom Gate On Delay C
LOAD
= 3300pF Each Driver
Synchronous Switch-On Delay Time
BG/TG t
2D
Bottom Gate Off to Top Gate On Delay C
LOAD
= 3300pF Each Driver
Top Switch-On Delay Time
t
ON(MIN)
Minimum On-Time
(Note 7)
INTV
CC
Linear Regulator
V
INTVCCVIN
Internal V
CC
Voltage
8.5V < V
IN
< 30V, V
EXTVCC
= 0V
V
LDOVIN
INTV
CC
Load Regulation
I
CC
= 0mA to 20mA, V
EXTVCC
= 0V
V
INTVCCEXT
Internal V
CC
Voltage
V
EXTVCC
= 8.5V
V
LDOEXT
INTV
CC
Load Regulation
I
CC
= 0mA to 20mA, V
EXTVCC
= 8.5V
V
EXTVCC
EXTV
CC
Switchover Voltage
EXTV
CC
Ramping Positive
V
LDOHYS
EXTV
CC
Hysteresis
Oscillator and Phase-Locked Loop
f
NOM
Nominal Frequency
V
PLLLPF
= Floating; PLLIN/MODE = DC Voltage
f
LOW
Lowest Frequency
V
PLLLPF
= 0V; PLLIN/MODE = DC Voltage
f
HIGH
Highest Frequency
V
PLLLPF
= INTV
CC
; PLLIN/MODE = DC Voltage
f
SYNCMIN
Minimum Synchronizable Frequency PLLIN/MODE = External Clock; V
PLLLPF
= 0V
f
SYNCMAX
Maximum Synchronizable Frequency PLLIN/MODE = External Clock; V
PLLLPF
= 2V
I
PLLLPF
Phase Detector Output Current
Sinking Capability
f
PLLIN/MODE
< f
OSC
Sourcing Capability
f
PLLIN/MODE
> f
OSC
PGOOD Output
V
PGL
PGOOD Voltage Low
I
PGOOD
= 2mA
I
PGOOD
PGOOD Leakage Current
V
PGOOD
= 5V
V
PG
PGOOD Trip Level
V
FB
with Respect to Set Regulated Voltage
V
FB
Ramping Negative
V
FB
Ramping Positive
TYP
0.1
–0.1
0.5
30
30
4
50
3.7
10
–220
99.4
1
0.7
100
50
50
40
40
70
70
230
MAX
0.5
–0.5
UNITS
%
%
mmho
μA
μA
μA
μA
V
%
μA
%
μA
V
mV
ns
ns
ns
ns
ns
ns
ns
l
8
98
0.75
0.5
85
50
50
10
75
4
12
l
1.35
0.9
115
90
90
90
80
5.0
7.2
4.5
5.25
0.2
7.5
0.2
4.7
0.2
390
250
530
115
800
–5
5
0.1
5.5
1.0
7.8
1.0
V
%
V
%
V
V
kHz
kHz
kHz
kHz
kHz
μA
μA
350
220
475
650
430
280
585
140
0.3
±1
–8
12
V
μA
%
%
38261fb
–12
8
–10
10
3
LTC3826-1
ELECTRICAL CHARACTERISTICS
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 LTC3826E-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 LTC3826I-1 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 formula:
T
J
= T
A
+ (P
D
• 95 °C/W)
Note 4:
The LTC3826-1 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
EFFICIENCY (%)
70
60
50
40
30
20
10
V
IN
= 12V
V
OUT
= 3.3V
1
1
10
100
Burst Mode OPERATION
FORCED CONTINUOUS MODE
PULSE SKIPPING
MODE
10000
100
90
1000
POWER LOSS (mW)
EFFICIENCY (%)
80
70
EFFICIENCY (%)
V
IN
= 12V
V
IN
= 5V
V
OUT
= 3.3V
1
10
38261 G02
Efficiency vs Load Current
98
96
94
92
90
88
86
84
82
Efficiency vs Input Voltage
60
50
40
30
20
10
0
0.1
0.00001 0.0001 0.001 0.01
OUTPUT CURRENT (A)
FIGURE 13 CIRCUIT
0.1
10
0
0.00001 0.0001 0.001 0.01
0.1
OUTPUT CURRENT (A)
FIGURE 13 CIRCUIT
0
5
10
15 20 25 30
INPUT VOLTAGE (V)
35
40
38261 G03
38261 G01
Load Step
(Burst Mode Operation)
V
OUT
100mV/DIV
AC
COUPLED
I
L
2A/DIV
V
OUT
100mV/DIV
AC
COUPLED
I
L
2A/DIV
Load Step
(Forced Continuous Mode)
V
OUT
100mV/DIV
AC
COUPLED
I
L
2A/DIV
Load Step
(Pulse Skipping Mode)
20μs/DIV
FIGURE 13 CIRCUIT
V
OUT
= 3.3V
38261 G04
20μs/DIV
FIGURE 13 CIRCUIT
V
OUT
= 3.3V
38261 G05
20μs/DIV
FIGURE 13 CIRCUIT
V
OUT
= 3.3V
38261 G06
38261fb
4
LTC3826-1
TYPICAL PERFORMANCE CHARACTERISTICS
Inductor Current at Light Load
FORCED
CONTINUOUS
MODE
2A/DIV
Burst Mode
OPERATION
PULSE
SKIPPING
MODE
2μs/DIV
FIGURE 13 CIRCUIT
V
OUT
= 3.3V
I
LOAD
= 100μA
38261 G07
Soft Start-Up
V
OUT2
2V/DIV
Tracking Start-Up
V
OUT2
2V/DIV
V
OUT1
2V/DIV
V
OUT1
2V/DIV
20ms/DIV
FIGURE 13 CIRCUIT
38261 G08
20ms/DIV
FIGURE 13 CIRCUIT
38261 G09
Total Input Supply Current
vs Input Voltage
350
EXTV
CC
AND INTV
CC
VOLTAGE (V)
300
SUPPLY CURRENT (μA)
250
200
150
100
50
0
5
10
NO LOAD
300μA LOAD
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
25
20
15
INPUT VOLTAGE (V)
30
35
38261 G10
EXTV
CC
Switchover and INTV
CC
Voltages vs Temperature
5.5
INTV
CC
Line Regulation
5.4
INTV
CC
INTV
CC
VOLTAGE (V)
5.3
EXTV
CC
RISING
5.2
EXTV
CC
FALLING
5.1
4.0
–45
–25
35
15
–5
55
TEMPERATURE (°C)
75
95
5.0
0
5
10
15 20 25 30
INPUT VOLTAGE (V)
35
40
FIGURE 13 CIRCUIT
38261 G11
38261 G12
Maximum Current Sense Voltage
vs I
TH
Voltage
100
CURRENT SENSE THRESHOLD (mV)
80
60
40
20
0
–20
–40
0
0.2
10% DUTY CYCLE
1.0
0.4 0.6 0.8
I
TH
PIN VOLTAGE (V)
1.2
1.4
PULSE SKIPPING
FORCED CONTINUOUS
Burst Mode OPERATION
(RISING)
Burst Mode OPERATION
(FALLING)
60
30
0
INPUT BIAS CURRENT (μA)
–30
–60
–90
–120
–150
–180
–210
Sense Pins Total Input
Bias Current
MAXIMUM CURRENT SENSE VOLTAGE (mV)
120
100
80
60
40
20
0
0
1 2 3 4 5 6 7 8 9
V
SENSE
COMMON MODE VOLTAGE (V)
10
Maximum Current Sense
Threshold vs Duty Cycle
–240
–270
–300
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
38261 G15
38261 G13
38261 G14
38261fb
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