LTC3736-2
Dual 2-Phase, No R
SENSE
TM
,
Synchronous Controller
with Output Tracking
DESCRIPTIO
The LTC
®
3736-2 is a 2-phase dual synchronous step-down
switching regulator controller with tracking that drives ex-
ternal complementary power MOSFETs using few external
components. The constant frequency current mode archi-
tecture with MOSFET V
DS
sensing eliminates the need for
sense resistors and improves efficiency. Power loss and
noise due to the ESR of the input capacitance are mini-
mized by operating the two controllers out of phase.
Pulse-skipping operation provides high efficiency at light
loads. 100% duty cycle capability provides low dropout
operation, extending operating time in battery-powered
systems.
The switching frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and ca-
pacitors. For noise sensitive applications, the LTC3736-2
switching frequency can be externally synchronized from
250kHz to 850kHz. An internal soft-start, which can be
lengthened externally, smoothly ramps the output voltage
during start-up.
The LTC3736-2 is available in the tiny thermally enhanced
(4mm
×
4mm) QFN and 24-lead narrow SSOP packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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, 6580258, 6304066, 6611131, 6498466.
FEATURES
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
No Current Sense Resistors Required
Out-of-Phase Controllers Reduce Required
Input Capacitance
Tracking Function
Wide V
IN
Range: 2.75V to 9.8V
0.6V
±1%
Voltage Reference
High Current Limit
Constant Frequency Current Mode Operation
Low Dropout Operation: 100% Duty Cycle
True PLL for Frequency Locking or Adjustment
Selectable Pulse-Skipping/Forced Continuous
Operation
Auxiliary Winding Regulation
Internal Soft-Start Circuitry
Power-Good Output Voltage Monitor
Output Overvoltage Protection
Micropower Shutdown: I
Q
= 9µA
Tiny Low Profile (4mm
×
4mm) QFN and Narrow
SSOP Packages
APPLICATIO S
■
■
■
■
One or Two Lithium-Ion Powered Devices
Notebook and Palmtop Computers, PDAs
Portable Instruments
Distributed DC Power Systems
TYPICAL APPLICATIO
High Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
V
IN
2.75V TO 9.8V
V
IN
SENSE1 SENSE2
TG1
2.2µH
+
+
Efficiency and Power Loss
vs Load Current (Figure 15 Circuit)
100
95
90
85
V
OUT
= 2.5V
10
10µF
×2
EFFICIENCY (%)
TG2
2.2µH
SW1
SW2
LTC3736-2
BG1
BG2
PGND
V
FB2
I
TH2
SGND
15k
220pF
15k
PGND
V
FB1
220pF
59k
I
TH1
V
OUT1
2.5V
187k
118k
V
OUT2
1.8V
47µF
47µF
59k
37362 TA01a
U
80
75
70
65
60
55
50
U
U
EFFICIENCY
1
POWER LOSS (W)
0.1
POWER LOSS
0.01
1
10
100
1000
LOAD CURRENT (mA)
0.001
10000
37362 TA01b
37362fa
1
LTC3736-2
ABSOLUTE
(Note 1)
AXI U
RATI GS
PGOOD ..................................................... – 0.3V to 10V
TG1, TG2, BG1, BG2 Peak Output Current (<10µs) ..... 1A
Operating Temperature Range (Note 2) ... –40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
Junction Temperature (Note 3) ............................ 125°C
Lead Temperature (Soldering, 10 sec)
(LTC3736EGN-2) .................................................. 300°C
Input Supply Voltage (V
IN
) ........................ – 0.3V to 10V
PLLLPF, RUN/SS, SYNC/FCB,
TRACK, SENSE1
+
, SENSE2
+
,
IPRG1, IPRG2 Voltages ................. – 0.3V to (V
IN
+ 0.3V)
V
FB1
, V
FB2
, I
TH1
, I
TH2
Voltages .................. – 0.3V to 2.4V
SW1, SW2 Voltages ............ –2V to V
IN
+ 1V or 10V Max
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SW1
IPRG1
V
FB1
I
TH1
IPRG2
PLLLPF
SGND
V
IN
TRACK
1
2
3
4
5
6
7
8
9
24 SENSE1
+
23 PGND
22 BG1
21 SYNC/FCB
20 TG1
19 PGND
18 TG2
17 RUN/SS
16 BG2
15 PGND
14 SENSE2
+
13 SW2
SENSE1
+
IPRG1
PGND
SW1
V
FB1
24 23 22 21 20 19
I
TH1
1
IPRG2 2
PLLLPF 3
SGND 4
V
IN
5
TRACK 6
7
8
9 10 11 12
25
18 SYNC/FCB
17 TG1
16 PGND
15 TG2
14 RUN/SS
13 BG2
PGOOD
SW2
I
TH2
11
PGOOD 12
GN PACKAGE
24-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/ W
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 25) IS PGND
MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3736EGN-2
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
ORDER PART NUMBER
LTC3736EUF-2
SENSE2
+
UF PART MARKING
37362
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Main Control Loops
Input DC Supply Current
Normal Mode
Shutdown
UVLO
Undervoltage Lockout Threshold
The
●
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 4.2V unless otherwise specified.
CONDITIONS
(Note 4)
RUN/SS = V
IN
RUN/SS = 0V
V
IN
= UVLO Threshold –200mV
V
IN
Falling
V
IN
Rising
●
●
MIN
PGND
V
FB2
I
TH2
V
FB2
10
BG1
2
U
U
W
W W
U
W
TOP VIEW
TYP
MAX
UNITS
475
9
3
1.95
2.15
2.25
2.45
750
20
10
2.55
2.75
µA
µA
µA
V
V
37362fa
LTC3736-2
ELECTRICAL CHARACTERISTICS
PARAMETER
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 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
Maximum Current Sense Voltage (∆V
SENSE(MAX)
)
(SENSE
+
– SW)
Soft-Start Time
Oscillator and Phase-Locked Loop
Oscillator Frequency
The
●
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 4.2V unless otherwise specified.
CONDITIONS
RUN/SS = 0V
0°C to 85°C (Note 5)
–40°C to 85°C
2.75V < V
IN
< 9.8V (Note 5)
I
TH
= 0.9V (Note 5)
I
TH
= 1.7V
(Note 5)
TRACK = 0.6V
Measured at V
FB
SYNC/FCB Ramping Positive
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
IPRG = Floating
IPRG = 0V
IPRG = V
IN
Time for V
FB1
to Ramp from 0.05V to 0.55V
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
–13
–16
7
10
●
●
●
●
●
●
MIN
0.45
0.4
0.594
0.591
TYP
0.65
0.7
0.6
0.6
0.05
0.12
–0.12
10
10
MAX
0.85
1
0.606
0.609
0.2
0.5
–0.5
50
50
0.7
0.675
UNITS
V
µA
V
V
mV/V
%
%
nA
nA
V
mV
V
ns
ns
ns
ns
0.66
0.525
0.68
20
0.6
40
40
50
40
220
150
320
0.667
240
167
345
0.833
260
185
370
1
mV
mV
mV
ms
480
260
650
550
300
750
200
1150
–4
4
125
–10.0
–13.3
10.0
13.3
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
–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 LTC3736E-2 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
dissipation 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 LTC3736-2 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.
37362fa
3
LTC3736-2
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency and Power Loss
vs Load Current
100
95
90
85
V
OUT
= 2.5V
10
EFFICIENCY
EFFICIENCY (%)
80
75
70
65
60
55
50
1
V
IN
= 3.3V
V
IN
= 5V
10
100
1000
LOAD CURRENT (mA)
0.01
POWER LOSS
0.1
Load Step (Pulse-Skipping Mode)
V
OUT
AC-COUPLED
100mV/DIV
I
L
2A/DIV
100µs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = V
IN
FIGURE 15 CIRCUIT
Tracking Start-Up with Internal
Soft-Start (C
SS
= 0µF)
V
OUT1
2.5V
V
OUT2
1.8V
500mV/
DIV
500mV/
DIV
V
OUT1
2.5V
V
OUT2
1.8V
NORMALIZED FREQUENCY SHIFT (%)
V
IN
= 5V
200µs/DIV
R
LOAD1
= R
LOAD2
= 1Ω
FIGURE 15 CIRCUIT
4
U W
37362 G06
T
A
= 25°C unless otherwise noted.
Load Step
(Forced Continuous Mode)
1
V
OUT
AC-COUPLED
100mV/DIV
POWER LOSS (W)
I
L
2A/DIV
0.001
10000
V
IN
= 3.3V
100µs/DIV
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = 0V
FIGURE 15 CIRCUIT
37362 G03
37362 G01
Light Load
(Pulse-Skipping Mode)
Light Load
(Forced Continuous Mode)
SW
5V/DIV
V
OUT
50mV/DIV
AC COUPLED
I
L
2A/DIV
SW
5V/DIV
V
OUT
50mV/DIV
AC COUPLED
I
L
2A/DIV
37362 G04
V
IN
= 5V
2.5µs/DIV
V
OUT
= 2.5V
I
LOAD
= 300mA
SYNC/FBC = V
IN
FIGURE 15 CIRCUIT
37362 G02
2.5µs/DIV
V
IN
= 5V
V
OUT
= 2.5V
I
LOAD
= 300mA
SYNC/FCB = 0V
FIGURE 15 CIRCUIT
37362 G05
Tracking Start-Up with External
Soft-Start (C
SS
= 0.10µF)
5
4
3
2
1
0
–1
–2
–3
–4
–5
Oscillator Frequency
vs Input Voltage
V
IN
= 5V
40ms/DIV
R
LOAD1
= R
LOAD2
= 1Ω
FIGURE 15 CIRCUIT
37362 G07
2
3
4
8
6
5
7
INPUT VOLTAGE (V)
9
10
37368 G08
37362fa
LTC3736-2
TYPICAL PERFOR A CE 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
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
55
50
0.5
1
1.5
I
TH
VOLTAGE (V)
2
37362 G09
FEEDBACK VOLTAGE (V)
Shutdown (RUN) Threshold
vs Temperature
1.0
0.9
MAXIMUM CURRENT SENSE THRESHOLD (mV)
RUN/SS PULL-UP CURRENT (µA)
0.8
RUN/SS VOLTAGE (V)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
Oscillator Frequency
vs Temperature
10
8
2.50
2.45
NROMALIZED FREQUENCY (%)
INPUT (V
IN
) VOLTAGE (V)
6
4
2
0
–2
–4
–6
–8
–10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
U W
37362 G12
T
A
= 25°C unless otherwise noted.
Efficiency vs Load Current
FIGURE 15 CIRCUIT
V
IN
= 3.3V
V
OUT
= 2.5V
Regulated Feedback Voltage
vs Temperature
0.606
0.605
0.604
0.603
0.602
0.601
0.600
0.599
0.598
0.597
0.596
0.595
10000
37362 G10
PULSE-SKIPPING
MODE
(SYNC/FCB = V
IN
)
FORCED
CONTINUOUS
(SYNC/FCB = 0V)
1
100
1000
10
LOAD CURRENT (mA)
0.594
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
37362 G14
RUN/SS Pull-Up Current
vs Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
180
175
170
165
160
155
Maximum Current Sense Threshold
vs Temperature
I
PRG
= GND
80
100
150
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
80
100
37362 G13
37362 G11
Undervoltage Lockout Threshold
vs Temperature
V
IN
RISING
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
37362 G15
37362 G16
37362fa
5
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