LTC3737
Dual 2-Phase, No R
SENSE
TM
,
DC/DC Controller with
Output Tracking
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
s
s
s
Sense Resistor Optional
Out-of-Phase Controllers Reduce Required
Input Capacitance
Programmable Output Voltage Tracking
Constant Frequency Current Mode Architecture
Wide V
IN
Range: 2.75V to 9.8V
Wide V
OUT
Range: 0.6V to V
IN
0.6V
±1.5%
Reference
Low Dropout Operation: 100% Duty Cycle
True PLL for Frequency Locking or Adjustment
(Frequency Range 250kHz to 850kHz)
Selectable Burst Mode
®
or Pulse Skipping Operation
at Light Loads
Internal Soft-Start Circuitry
Selectable Maximum Peak Current Sense Threshold
Power Good Output Voltage Monitor
Output Overvoltage Protection
Micropower Shutdown: I
Q
= 9µA
Tiny 4mm
×
4mm QFN and 24-Lead SSOP Packages
The LTC
®
3737 is a 2-phase dual step-down switching
regulator controller that requires few external compo-
nents. The constant frequency current mode architecture
provides excellent AC and DC load and line regulation.
MOSFET V
DS
sensing eliminates the need for current
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.
Burst Mode operation provides high efficiency operation
at light loads. 100% duty cycle provides low dropout
operation and extends battery operating time.
Switching frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and
capacitors. For noise sensitive applications, the LTC3737
can be externally synchronized from 250kHz to 850kHz.
Other features include a power good output voltage moni-
tor, a tracking input and internal soft-start.
The LTC3737 is available in the low profile thermally
enhanced (4mm
×
4mm) QFN package or a 24-lead SSOP
narrow package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation.
U.S. patent numbers 5481178, 5731694, 5929620, 6144194,6580258, 5994885
APPLICATIO S
s
s
s
s
One or Two Lithium-Ion Powered Devices
Notebook and Palmtop Computers, PDAs
Portable Instruments
Distributed DC Power Systems
TYPICAL APPLICATIO
187k
SW1
59k
15k
V
FB1
I
TH1
220pF
220pF
59k
118k
SENSE1
+
PV
IN1
PGATE1
M1
2.2µH
V
IN
2.75V TO
9.8V
+
D1
47µF
V
OUT1
2.5V
EFFICIENCY (%)
PGOOD
V
IN
LTC3737
PGND
SGND
TRACK
I
TH2
V
FB2
SW2
RUN/SS
PV
IN2
SENSE2
+
M2
3737 F01
10µF
×2
15k
2.2µH
Figure 1. High Efficiency, 2-Phase, 550kHz Dual Step-Down Converter
+
PGATE2
D2
47µF
V
OUT2
1.8V
U
Efficiency vs Load Current
100
95
90
85
80
75
70
65
60
55
50
1
10
100
1000
LOAD CURRENT (mA)
10000
3737 F01b
U
U
V
IN
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
3737f
1
LTC3737
ABSOLUTE
AXI U
RATI GS
Input Supply Voltage (V
IN
), PV
IN1
, PV
IN2
,
SENSE1
+
, SENSE2
+
.................................. – 0.3V to 10V
PGATE1, PGATE2, PLLLPF, RUN/SS, SYNC/MODE,
TRACK, 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
PGOOD ..................................................... – 0.3V to 10V
PGATE1, PGATE2 Peak Output Current (<10µs) ......... 1A
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SW1
(SENSE1
–
)
IPRG1
V
FB1
I
TH1
IPRG2
PLLLPF
SGND
V
IN
TRACK
1
2
3
4
5
6
7
8
9
24 SENSE1
+
23 PV
IN1
22 NC
21 SYNC/MODE
20 PGATE1
19 PGND
18 PGATE2
17 RUN/SS
16 NC
IPRG1
SW1
(SENSE1
–
)
SENSE1
+
PV
IN1
ORDER PART
NUMBER
V
FB1
LTC3737EGN
I
TH1
1
IPRG2 2
PLLLPF 3
SGND 4
V
IN
5
TRACK 6
NC
PGOOD
SW2
(SENSE2
–
)
SENSE2
+
I
TH2
I
TH2
11
PGOOD 12
14 SENSE2
+
SW2
13
(SENSE2
–
)
PV
IN2
V
FB2
V
FB2
10
15 PV
IN2
GN PACKAGE
24-LEAD (NARROW) PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Main Control Loops
Input DC Supply Current
Sleep Mode
Shutdown
UVLO
Undervoltage Lockout Threshold
Shutdown Threshold at RUN/SS
Start-Up Current Source
Regulated Feedback Voltage
Output Voltage Line Regulation
(Note 4)
The
q
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
MIN
TYP
MAX
UNITS
RUN/SS = 0V
V
IN
< UVLO Threshold
V
IN
Falling
V
IN
Rising
RUN/SS = 0V
0°C to 85°C (Note 5)
–40°C to 85°C
2.75V < V
IN
< 9.8V (Note 5)
q
q
q
2
U
U
W
W W
U
W
(Note 1)
Operating Temperature Range (Note 2) ... –40°C to 85°C
Storage Ambient Temperature Range
QFN Package .................................... –65°C to 125°C
SSOP Package .................................. –65°C to 150°C
Junction Temperature (Note 3) ............................ 125°C
Lead Temperature (Soldering, 10sec)
LTC3737EGN ................................................... 300°C
TOP VIEW
ORDER PART
NUMBER
LTC3737EUF
SYNC/
18 MODE
17 PGATE1
24 23 22 21 20 19
25
16 PGND
15 PGATE2
14 RUN/SS
13 NC
7
8
9 10 11 12
UF PART
MARKING
3737
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD IS PGND (PIN 25) MUST BE SOLDERED TO PCB
220
9
3
1.95
2.15
0.45
0.5
0.591
0.588
2.25
2.45
0.65
0.7
0.6
0.6
0.05
325
20
10
2.55
2.75
0.85
1
0.609
0.612
0.2
µA
µA
µA
V
V
V
µA
V
V
mV/V
3737f
LTC3737
ELECTRICAL CHARACTERISTICS
PARAMETER
Output Voltage Load Regulation
V
FB1,2
Input Current
TRACK Input Current
Overvoltage Protect Threshold
Overvoltage Protect Hysteresis
Auxiliary Feedback Threshold
Gate Drive 1, 2 Rise Time
Gate Drive 1, 2 Fall Time
Maximum Current Sense Voltage
(SENSE
+
– SW)(∆V
SENSE(MAX)
)
Soft-Start Time
Oscillator and Phase-Locked Loop
Oscilator Frequency
The
q
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
I
TH
= 0.9V (Note 5)
I
TH
= 1.7V
(Note 5)
TRACK = 0.6V
Measured at V
FB
SYNC/MODE Ramping Negative
C
L
= 3000pF
C
L
= 3000pF
IPRG = Floating (Note 6)
IPRG = 0V (Note 6)
IPRG = V
IN
(Note 6)
Time for V
FB1
to Ramp from 0.05V to 0.55V
Unsynchronized (SYNC/MODE Not Clocked)
V
PLLLPF
= Floating
V
PLLLPF
= 0V
V
PLLLPF
= V
IN
SYNC/MODE Clocked
Minimum Synchronizable Frequency
Maximum Synchronizable Frequency
f
OSC
> f
SYNC/MODE
f
OSC
< f
SYNC/MODE
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
13
16
q
q
q
MIN
TYP
0.12
–0.12
10
10
MAX
0.5
–0.5
50
50
0.7
0.675
UNITS
%
%
nA
nA
V
mV
V
ns
ns
0.66
0.525
0.68
20
0.6
40
40
110
70
185
0.667
125
85
204
0.833
140
100
223
1
mV
mV
mV
ms
q
q
q
q
q
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
7
10
%
%
%
%
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3737E is guaranteed to meet specified performance from
0°C to 70°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 LTC3737 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 2.
3737f
3
LTC3737
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
100
95
90
Burst Mode OPERATION
(SYNC/MODE = V
IN
)
EFFICIENCY (%)
EFFICIENCY (%)
85
80
75
70
65
60
55
50
1
T
A
= 25°C
V
IN
= 3.3V
V
OUT
= 2.5V
FIGURE 13 CIRCUIT
100
1000
10
LOAD CURRENT (mA)
10000
3737 G01
PULSE SKIPPING
(SYNC/MODE = 0V)
Load Step (Pulse Skipping Mode)
V
OUT
AC-COUPLED
100mV/DIV
I
L
2A/DIV
V
IN
= 3.3V
200µs/DIV
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/MODE = 0V
FIGURE 13 CIRCUIT
Regulated Feedback Voltage
vs Temperature
0.609
0.607
MAXIMUM CURRENT SENSE THRESHOLD (mV)
FEEDBACK VOLTAGE (V)
0.605
0.603
0.601
0.599
0.597
0.595
0.593
0.591
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
RUN/SS VOLTAGE (V)
4
U W
3737 G07
Efficiency vs Load Current
100
T
A
= 25°C
95 V
OUT
= 2.5V
90
85
80
75
70
65
60
55
50
1
100
1000
10
LOAD CURRENT (mA)
10000
3737 G02
Load Step (Burst Mode Operation)
V
OUT
AC-COUPLED
100mV/DIV
V
IN
= 3.3V
V
IN
= 5V
V
IN
= 4.2V
I
L
2A/DIV
200µs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/MODE = V
IN
FIGURE 13 CIRCUIT
3737 G03
Tracking Start-Up with Internal
Soft-Start (C
SS
= 0nF)
V
OUT1
2.5V
V
OUT2
1.8V
500mV/
DIV
Tracking Start-Up with External
Soft-Start (C
SS
= 10nF)
V
OUT1
2.5V
V
OUT2
1.8V
500mV/
DIV
3737 G04
V
IN
= 4.2V
250µs/DIV
R
LOAD1
= R
LOAD2
= 1Ω
FIGURE 13 CIRCUIT
3737 G05
V
IN
= 4.2V
2.5ms/DIV
R
LOAD1
= R
LOAD2
= 1Ω
FIGURE 13 CIRCUIT
3737 G06
Maximum Current Sense Threshold
vs Temperature
135
I
PRG
= FLOAT
1.0
0.9
Shutdown (RUN) Threshold
vs Temperature
130
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
125
120
115
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
80
100
0
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
3737 G08
3737 G09
3737f
LTC3737
TYPICAL PERFOR A CE CHARACTERISTICS
Undervoltage Lockout Threshold
vs Temperature
2.50
RUN/SS PULL-UP CURRENT (µA)
1.0
2.45
INPUT (V
IN
) VOLTAGE (V)
NROMALIZED FREQUENCY (%)
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
Oscillator Frequency
vs Input Voltage
5
SHUTDOWN CURRENT (µA)
3
2
1
0
–1
–2
–3
–4
–5
2
3
4
8
6
5
7
INPUT VOLTAGE (V)
9
10
16
14
12
10
8
6
4
2
0
2
3
4
8
6
5
7
INPUT VOLTAGE (V)
9
10
RUN/SS PIN START-UP CURRENT (µA)
NORMALIZED FREQUENCY SHIFT (%)
4
T
A
= 25°C
U W
3737 G10
3737 G13
RUN/SS Pull-Up Current
vs Temperature
10
8
0.9
0.8
0.7
0.6
0.5
0.4
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
Oscillator Frequency
vs Temperature
6
4
2
0
–2
–4
–6
–8
80
100
–10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
3737 G11
3737 G12
Shutdown Quiescent Current
vs Input Voltage
T
A
= 25°C
18 RUN/SS = 0V
20
0.9
RUN/SS Start-Up Current
vs Input Voltage
T
A
= 25°C
0.8 RUN/SS = 0V
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2
3
4
6
7
5
8
INPUT VOLTAGE (V)
9
10
3737 G14
3737 G15
3737f
5
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