LTC3736
Dual 2-Phase, No R
SENSE
TM
,
Synchronous Controller
with Output Tracking
FEATURES
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
DESCRIPTIO
No Current Sense Resistors Required
Out-of-Phase Controllers Reduce Required
Input Capacitance
Tracking Function
Wide V
IN
Range: 2.75V to 9.8V
Constant Frequency Current Mode Operation
0.6V
±1.5%
Voltage Reference
Low Dropout Operation: 100% Duty Cycle
True PLL for Frequency Locking or Adjustment
Selectable Burst Mode
®
/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
The LTC
®
3736 is a 2-phase dual synchronous step-down
switching regulator controller with tracking that drives
external complementary power MOSFETs using few exter-
nal components. The constant frequency current mode
architecture 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
minimized by operating the two controllers out of phase.
Burst Mode 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
switching frequency can be externally synchronized from
250kHz to 850kHz. Burst Mode operation is inhibited dur-
ing synchronization or when the SYNC/FCB pin is pulled low
in order to reduce noise and RF interference. Automatic soft-
start is internally controlled.
The LTC3736 is available in the tiny thermally enhanced
(4mm
×
4mm) QFN package or 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. All other trademarks are the property of their respective
owners. Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258,
6304066, 6611131, 6498466.
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
SW1
LTC3736
BG1
V
OUT1
2.5V
187k
PGND
V
FB1
220pF
59k
15k
I
TH1
SGND
BG2
PGND
V
FB2
I
TH2
220pF
15k
59k
3736 TA01a
10µF
×2
EFFICIENCY (%)
TG2
SW2
2.2µH
118k
V
OUT2
1.8V
47µF
47µF
U
Efficiency vs Load Current
100
95
90
85
80
75
70
65
60
55
50
1
FIGURE 16 CIRCUIT
V
OUT
= 2.5V
100
1000
10
LOAD CURRENT (mA)
10000
3736 TA01b
U
U
V
IN
= 3.3V
V
IN
= 4.2V
V
IN
= 5V
3736fa
1
LTC3736
ABSOLUTE
AXI U
RATI GS
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
PGOOD ..................................................... – 0.3V to 10V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SENSE1
+
IPRG1
PGND
SW1
V
FB1
BG1
ORDER PART
NUMBER
SW1
24 23 22 21 20 19
I
TH1
1
IPRG2 2
PLLLPF 3
SGND 4
V
IN
5
TRACK 6
7
V
FB2
LTC3736EUF
18 SYNC/FCB
17 TG1
25
16 PGND
15 TG2
14 RUN/SS
13 BG2
UF PART MARKING
3736
8
I
TH2
9 10 11 12
PGOOD
SENSE2
+
PGND
SW2
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
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
●
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 –200mV
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)
●
●
●
2
U
U
W
W W
U
W
(Note 1)
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) ..................................................... 300°C
TOP VIEW
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
ORDER PART
NUMBER
LTC3736EGN
IPRG1
V
FB1
I
TH1
IPRG2
PLLLPF
SGND
V
IN
TRACK
V
FB2
10
I
TH2
11
PGOOD 12
GN PACKAGE
24-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/ W
300
9
3
1.95
2.15
0.45
0.4
0.591
0.588
2.25
2.45
0.65
0.7
0.6
0.6
0.05
425
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
3736fa
LTC3736
ELECTRICAL CHARACTERISTICS
PARAMETER
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
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
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
ns
ns
0.66
0.525
0.68
20
0.6
40
40
50
40
110
70
185
0.667
125
85
204
0.833
140
100
223
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:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3736E 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 LTC3736 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.
3736fa
3
LTC3736
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency and Power Loss
vs Load Current
100
95
90
85
1
FIGURE 15 CIRCUIT
10
V
OUT
AC-COUPLED
100mV/DIV
V
OUT
AC-COUPLED
100mV/DIV
EFFICIENCY (%)
80
75
70
65
60
55
50
1
V
IN
= 5V
SYNC/FCB = V
IN
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
V
OUT
= 1.2V
0.1
10
100
1000
LOAD CURRENT (mA)
Load Step (Pulse Skipping Mode)
V
OUT
AC-COUPLED
100mV/DIV
I
L
2A/DIV
V
IN
= 3.3V
100µs/DIV
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = 550kHz EXTERNAL CLOCK
FIGURE 17 CIRCUIT
Tracking Start-Up with Internal
Soft-Start (C
SS
= 0µF)
V
OUT1
2.5V
V
OUT2
1.8V
500mV/
DIV
NORMALIZED FREQUENCY SHIFT (%)
V
IN
= 5V
200µs/DIV
R
LOAD1
= R
LOAD2
= 1Ω
FIGURE 15 CIRCUIT
3736 G06
4
U W
3736 G01
T
A
= 25°C unless otherwise noted.
Load Step
(Forced Continuous Mode)
Load Step (Burst Mode Operation)
0.01
100µs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = V
IN
FIGURE 17 CIRCUIT
3736 G02
0.001
10000
POWER LOSS (W)
I
L
2A/DIV
I
L
2A/DIV
V
IN
= 3.3V
100µs/DIV
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/FCB = 0V
FIGURE 17 CIRCUIT
3736 G03
Inductor Current at Light Load
Burst Mode
OPERATION
SYNC/FCB = V
IN
FORCED
CONTINUOUS
MODE
SYNC/FCB = 0V
PULSE
SKIPPING MODE
SYNC/FCB = 550kHz
I
L
1A/DIV
3736 G04
4µs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 200mA
FIGURE 17 CIRCUIT
3736 G05
Tracking Start-Up with External
Soft-Start (C
SS
= 0.15µF)
5
V
OUT1
2.5V
V
OUT2
1.8V
500mV/
DIV
Oscillator Frequency
vs Input Voltage
4
3
2
1
0
–1
–2
–3
–4
–5
2
3
4
8
6
5
7
INPUT VOLTAGE (V)
9
10
V
IN
= 5V
40ms/DIV
R
LOAD1
= R
LOAD2
= 1Ω
FIGURE 15 CIRCUIT
3736 G07
3736 G08
3736fa
LTC3736
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Current Sense Voltage
vs I
TH
Pin Voltage
100
80
CURRENT LIMIT (%)
60
40
20
0
–20
Burst Mode OPERATION
(I
TH
RISING)
Burst Mode OPERATION
(I
TH
FALLING)
FORCED CONTINUOUS
MODE
PULSE SKIPPING
MODE
100
95
90
85
EFFICIENCY (%)
FEEDBACK VOLTAGE (V)
0.5
1
1.5
I
TH
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
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
2
3736 G09
3736 G12
T
A
= 25°C unless otherwise noted.
Regulated Feedback Voltage
vs Temperature
0.609
0.607
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
Efficiency vs Load Current
Burst Mode
OPERATION
(SYNC/FCB = V
IN
)
80
75
70
65
60
55
50
1
FORCED
CONTINUOUS
(SYNC/FCB = 0V)
PULSE SKIPPING
MODE
(SYNC/FCB = 550kHz)
FIGURE 15 CIRCUIT
V
IN
= 5V
V
OUT
= 2.5V
10
100
1000
LOAD CURRENT (mA)
10000
3736 G10
3736 G11
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)
Maximum Current Sense Threshold
vs Temperature
135
I
PRG
= FLOAT
130
125
120
80
100
115
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
80
100
3736 G13
3736 G14
Undervoltage Lockout Threshold
vs Temperature
2.50
2.45
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
3736 G15
3736 G16
3736fa
5
京公网安备 11010802033920号
EEWORLD
