LTC3836
Dual 2-Phase,
No R
SENSE
TM
Low V
IN
Synchronous Controller
FEATURES
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DESCRIPTION
The LTC
®
3836 is a 2-phase dual output synchronous
step-down switching regulator controller with tracking
that drives external N-channel power MOSFETs using few
external components. The constant-frequency current
mode architecture with MOSFET V
DS
sensing eliminates
the need for sense resistors and improves efficiency.
The power loss and noise due to the ESR of the input
capacitance are minimized by operating the two control-
lers out-of-phase. Pulse-skipping operation provides high
efficiency at light loads. The 97% duty cycle capability
provides low dropout operation, extending operating time
in battery-powered systems.
The operating frequency is selectable from 300kHz to
750kHz, allowing the use of small surface mount induc-
tors and capacitors. For noise sensitive applications, the
LTC3836 operating frequency can be externally synchro-
nized from 250kHz to 850kHz.
The LTC3836 features an internal 1ms soft-start that can
be extended with an external capacitor. A tracking input al-
lows the second output to track the first during start-up.
The LTC3836 is available in the tiny thermally enhanced
(4mm
×
5mm) QFN and 28-lead narrow SSOP packages.
No Current Sense Resistors Required
Out-of-Phase Controllers Reduce Required Input
Capacitance
All N-Channel Synchronous Drive
V
IN
Range: 2.75V to 4.5V
Constant-Frequency Current Mode Operation
0.6V
±1.5%
Voltage Reference
Low Dropout Operation: 97% Duty Cycle
True PLL for Frequency Locking or Adjustment
Selectable Pulse-Skipping/Continuous Operation
Tracking Function
Internal Soft-Start Circuitry
Power Good Output Voltage Monitor
Output Overvoltage Protection
Micropower Shutdown: I
Q
= 6.5μA
Tiny Low Profile (4mm
×
5mm) QFN and Narrow
SSOP Packages
APPLICATIONS
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General Purpose 3.3V to 1.X Supplies
Single Lithium-Ion Powered Devices
Distributed DC Power Systems
L,
LT, LTC, LTM, Linear Technology, Burst Mode, OPTI-LOOP and the Linear logo are
registered trademarks and No R
SENSE
is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents including
5481178, 5929620, 6144194, 6304066, 6498466, 6580258, 6611131.
TYPICAL APPLICATION
High Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
V
IN
BOOST1 BOOST2
SENSE1
+
SENSE2
+
TG1
0.47μH
SW1
LTC3836
BG1
V
OUT1
1.8V AT
15A
118k
820pF
100μF
×
2
59k
15k
V
FB1
I
TH1
SGND
BG2
PGND
V
FB2
I
TH2
59k
820pF
59k
15k
V
OUT2
1.2V AT
15A
100μF
×
2
3836 TA01
Efficiency/Power Loss vs Load Current
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
10
CIRCUIT OF FIGURE 15
100
1000
10000
LOAD CURRENT (mA)
1
100000
3836 TA01b
22μF
×
3
V
IN
3.3V
3.3V-1.8V
EFFICIENCY
3.3V-1.2V
EFFICIENCY
10000
1000
POWER LOSS (mW)
TG2
SW2
0.47μH
100
3.3V-1.2V
POWER LOSS
3.3V-1.8V
POWER LOSS
10
3836fb
1
LTC3836
ABSOLUTE MAXIMUM RATINGS
(Note 1)
BOOST1, BOOST2 Voltages ....................... –0.3V to 10V
Input Supply Voltage (V
IN
) ........................ –0.3V to 4.5V
PLLLPF RUN/SS, SYNC/FCB,
,
SENSE1
+
, SENSE2
+
,
IPRG1, IPRG2 Voltages..................–0.3V to (V
IN
+ 0.3V)
V
FB1
, V
FB2
, I
TH1
, I
TH2
,
TRACK/SS2 Voltages ................................ –0.3V to 2.4V
SW1, SW2 Voltages ............................... –2V to V
IN
+ 1V
PGOOD....................................................... –0.3V to 10V
Operating Temperature Range (Note 2).... –40°C to 85°C
Storage Temperature Range................... –65°C to 125°C
Junction Temperature (Note 3) ............................. 125°C
PIN CONFIGURATION
TOP VIEW
SW1
N/C
IPRG1
V
FB1
I
TH1
IPRG2
PLLLPF
SGND
V
IN
1
2
3
4
5
6
7
8
9
28
SENSE1
+
N/C
TOP VIEW
SENSE1
+
BOOST1
BOOST2
IPRG1
PGND
22 BG1
21 SYNC/FCB
20 TG1
29
19 PGND
18 TG2
17 RUN/SS
16 N/C
15 BG2
9 10 11 12 13 14
ITH2
PGOOD
SW2
SENSE2
+
PGND
SW1
27 BOOST1
26 PGND
25 BG1
24 SYNC/FCB
23 TG1
22 PGND
21 TG2
20 RUN/SS
19 BG2
18 N/C
17 PGND
16 BOOST2
+
15 SENSE2
28 27 26 25 24 23
VFB1 1
ITH1 2
IPRG2 3
PLLLPF 4
SGND 5
V
IN
6
TRACK/SS2 7
VFB2 8
TRACK/SS2 10
V
FB2
11
I
TH2
12
PGOOD 13
SW2 14
GN PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 90°C/W
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3836EGN#PBF
LTC3836EUFD#PBF
TAPE AND REEL
LTC3836EGN#TRPBF
LTC3836EUFD#TRPBF
PART MARKING
LTC3836EGN
3836
PACKAGE DESCRIPTION
28-Lead Plastic SSOP
28-Lead (4mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°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/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V unless otherwise specified.
PARAMETER
Main Control Loops
Input DC Supply Current
Normal Mode
Shutdown
UVLO
(Note 4)
RUN/SS = V
IN
RUN/SS = 0V
V
IN
= UVLO Threshold –200mV
450
6.5
4
700
15
10
μA
μA
μA
3836fb
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP
MAX
UNITS
2
LTC3836
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V unless otherwise specified.
PARAMETER
Undervoltage Lockout Threshold
Shutdown Threshold at RUN/SS
Start-Up Current Source
Regulated Feedback Voltage
Output Voltage Line Regulation
Output Voltage Load Regulation
V
FB1,2
Input Current
TRACK/SS2 Input Current
Overvoltage Protect Threshold
Overvoltage Protect Hysteresis
Auxiliary Feedback Threshold
Top Gate (TG) Drive 1, 2 Rise Time
Top Gate (TG) Drive 1, 2 Fall Time
Bottom Gate (BG) Drive 1, 2 Rise Time
Bottom Gate (BG) Drive 1, 2 Fall Time
SYNC/FCB Ramping Positive
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
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ELECTRICAL CHARACTERISTICS
CONDITIONS
V
IN
Falling
V
IN
Rising
RUN/SS = 0V
MIN
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TYP
2.25
2.45
0.65
0.65
0.6
0.05
0.12
–0.12
10
MAX
2.55
2.75
0.85
1
0.609
0.2
0.5
–0.5
50
2.2
0.7
0.675
UNITS
V
V
V
μA
V
mV/V
%
%
nA
μA
V
mV
V
ns
ns
ns
ns
1.95
2.15
0.45
0.4
–40°C to 85°C (Note 5)
2.75V < V
IN
< 4.5V (Note 5)
I
TH
= 0.9V (Note 5)
I
TH
= 1.7V
(Note 5)
TRACK/SS2 = 0V
Measured at V
FB
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0.591
1
0.66
0.525
1.5
0.68
20
0.6
40
40
50
40
Maximum Current Sense Voltage (∆V
SENSE(MAX)
) IPRG = Floating
(SENSE
+
– SW)
IPRG = 0V
IPRG = V
IN
Maximum Duty Cycle
Soft-Start Time
Oscillator and Phase-Locked Loop
Oscillator Frequency
Unsynchronized (SYNC/FCB Not Clocked)
PLLLPF = Floating
PLLLPF = 0V
PLLLPF = V
IN
SYNC/FCB Clocked
Minimum Synchronizable Frequency
Maximum Synchronizable Frequency
f
OSC
> f
SYNC/FCB
f
OSC
> f
SYNC/FCB
I
PGOOD
Sinking 1mA
V
FB
with Respect to Set Output Voltage
V
FB
< 0.6V, Ramping Positive
V
FB
< 0.6V, Ramping Negative
V
FB
> 0.6V, Ramping Negative
V
FB
> 0.6V, Ramping Positive
In Dropout
Time for V
FB1
to Ramp from 0.05V to 0.55V
110
70
185
0.6
122
82
202
97
0.8
135
95
220
1
mV
mV
mV
%
ms
480
260
650
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550
300
750
200
1150
–4
4
140
600
340
825
250
kHz
kHz
kHz
kHz
kHz
μA
μA
mV
Phase-Locked Loop Lock Range
850
Phase Detector Output Current
Sinking
Sourcing
PGOOD Output
PGOOD Voltage Low
PGOOD Trip Level
–13
–16
7
10
–10.0
–13.3
10.0
13.3
–7
–10
13
16
%
%
%
%
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 LTC3836 is guaranteed to meet specified performance from
0°C to 85°C. Specifications over the –40°C to 85°C operating range are
assured by design, characterization and correlation with statistical process
controls.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power dissi-
pation P
D
according to the following formula: T
J
= T
A
+ (P
D
•
θ
JA
°C/W)
Note 4:
Dynamic supply current is higher due to gate charge being
delivered at the switching frequency.
Note 5:
The LTC3836 is tested in a feedback loop that servos I
TH
to a
specified voltage and measures the resultant V
FB
voltage.
Note 6:
Peak current sense voltage is reduced dependent on duty cycle to
a percentage of value as shown in Figure 1.
3836fb
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LTC3836
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
1
SYNC/FCB = V
IN
SYNC/FCB = 0V
100
1000
10
LOAD CURRENT (mA)
10000
3836 G01
T
A
= 25°C unless otherwise noted.
Load Step
(Pulse-Skipping Mode)
V
OUT
AC COUPLED
100mV/DIV
Load Step
(Forced Continuous Mode)
V
OUT
AC COUPLED
100mV/DIV
PULSE-SKIPPING
MODE
FORCED
CONTINUOUS
MODE
INDUCTOR
CURRENT
5A/DIV
3836 G02
INDUCTOR
CURRENT
5A/DIV
3836 G03
100μs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
CONTINUOUS MODE: 400mA TO 4A
CIRCUIT OF FIGURE 15
100μs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
PULSE-SKIPPING MODE: 400MA TO 4A
CIRCUIT OF FIGURE 15
V
IN
= 3.3V
V
OUT
= 1.5V
CIRCUIT OF FIGURE 15
Light Load
(Pulse-Skipping Mode)
Light Load
(Forced Continuous Mode)
Tracking Start-Up with Internal
Soft-Start (C
RUN/SS
= 0μF)
V
OUT1
1.8V
V
SW
2V/DIV
V
OUT
20mV/DIV
AC COUPLED
INDUCTOR
CURRENT
5A/DIV
V
IN
= 3.6V
2μs/DIV
V
OUT
= 1.8V
I
LOAD
= 300mA
CIRCUIT OF FIGURE 15
3836 G04
V
SW
2V/DIV
V
OUT
20mV/DIV
AC COUPLED
INDUCTOR
CURRENT
5A/DIV
2μs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 300mA
CIRCUIT OF FIGURE 15
3836 G05
V
OUT2
1.2V
500mV/DIV
250μs/DIV
V
IN
= 3.6V
R
LOAD1
= R
LOAD2
= 1Ω
CIRCUIT OF FIGURE 15
3836 G06
Tracking Start-Up with External
Soft-Start (C
RUN/SS
= 0.01μF)
V
OUT1
1.8V
Sequential Start-Up
5
V
OUT1
1.8V
NORMALIZED FREQUENCY SHIFT (%)
4
3
2
1
0
–1
–2
–3
–4
Oscillator Frequency
vs Input Voltage
V
OUT2
1.2V
500mV/DIV
500mV/DIV
V
OUT2
1.2V
2.50ms/DIV
V
IN
= 3.6V
R
LOAD1
= R
LOAD2
= 1Ω
CIRCUIT OF FIGURE 15
3836 G07
V
IN
= 3.3V
4ms/DIV
R
LOAD1
= R
LOAD2
= 1Ω
V
OUT1
: INTERNAL SOFT-START
V
OUT2
: C
TRACK/SS
= 0.047μF
CIRCUIT OF FIGURE 15
3836 G10
–5
2.5
3.0
4.0
3.5
INPUT VOLTAGE (V)
4.5
3836 G08
3836fb
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LTC3836
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Current Sense Voltage
vs I
TH
Pin Voltage
100
80
CURRENT LIMIT (%)
60
40
20
0
–20
FORCED CONTINUOUS
MODE
PULSE-SKIPPING
MODE
0.606
0.605
0.604
FEEDBACK VOLTAGE (V)
RUN/SS VOLTAGE (V)
0.603
0.602
0.601
0.600
0.599
0.598
0.597
0.596
0.595
0.5
1
1.5
I
TH
VOLTAGE (V)
2
3836 G09
T
A
= 25°C unless otherwise noted.
Shutdown (RUN/SS) Threshold
vs Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
80
100
0
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
Regulated Feedback Voltage
vs Temperature
0.594
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
3836 G11
3836 G12
RUN/SS Pull-Up Current
vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
1.0
RUN/SS PULL-UP CURRENT (μA)
0.9
0.8
0.7
0.6
0.5
0.4
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
135
Maximum Current Sense
Threshold vs Temperature
I
PRG
= FLOAT
NROMALIZED FREQUENCY (%)
10
8
130
6
4
2
0
–2
–4
–6
–8
115
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
80
100
Oscillator Frequency
vs Temperature
125
120
80
100
–10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
3836 G13
3836 G14
3836 G15
Undervoltage Lockout Threshold
vs Temperature
2.50
2.45
INPUT (V
IN
) VOLTAGE (V)
2.40
2.35
2.30
V
IN
FALLING
2.25
2.20
2.15
2.10
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
V
IN
RISING
18
16
SHUTDOWN CURRENT (μA)
14
12
10
8
6
4
2
Shutdown Quiescent Current
vs Input Voltage
0.9
RUN/SS PIN PULL-UP CURRENT (μA)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
RUN/SS Start-Up Current
vs Input Voltage
RUN/SS = 0V
0
2.5
3.0
3.5
4.0
INPUT VOLTAGE (V)
4.5
3836 G17
0
2.5
3.0
3.5
4.0
INPUT VOLTAGE (V)
4.5
3836 G18
3836 G16
3836fb
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