LTC3701
2-Phase, Low Input Voltage,
Dual Step-Down DC/DC Controller
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
Out-of-Phase Controllers Reduce Required
Input Capacitance
True PLL for Frequency Locking or Frequency
Adjustment
Operating Frequency Range: 300kHz to 750kHz
Wide V
IN
Range: 2.5V to 10V
Constant Frequency Current Mode Architecture
Low Dropout: 100% Duty Cycle
Power Good Output Voltage Monitor
Internal Soft-Start Circuitry
Selectable Burst Mode
®
/Pulse Skipping Operation
at Light Loads
Output Overvoltage Protection
Low Quiescent Current: 460µA
0.8V
±2%
Voltage Reference
Small 16-Lead Narrow SSOP Package
The LTC
®
3701 is a 2-phase dual constant frequency cur-
rent mode step-down DC/DC controller providing excellent
load and line regulation. Power loss and noise due to ESR
of the input capacitor are minimized by operating the two
controller output stages out-of-phase.
The LTC3701 provides a 0.8V
±2%
voltage reference and
consumes only 460µA of quiescent current. To further
maximize the life of a battery source, the external
P-channel MOSFET is turned on continuously in dropout
(100% duty cycle).
Switching frequency is internally set at 550kHz, allowing
the use of small inductors and capacitors. For noise sen-
sitive applications, the LTC3701 can be externally syn-
chronized using its phase-locked loop. The frequency can
also be externally set from 300kHz to 750kHz by applying
a voltage to the PLLLPF pin. Burst Mode operation is inhib-
ited during synchronization or when the EXTCLK/MODE
pin is pulled low to reduce noise and RF interference.
The LTC3701 contains independent internal soft-start
circuitry for each controller. Other features include a
power good output voltage monitor and output overvolt-
age and short-circuit protection.
The LTC3701 is available in a small footprint 16-lead nar-
row SSOP package.
APPLICATIO S
s
s
s
s
s
One or Two Lithium-Ion Powered Applications
Notebook and Handheld Computers
Personal Digital Assistants
Portable Instruments
Distributed DC Power Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
169k
1
78.7k
10k
220pF
3
2
SENSE1
–
V
FB1
V
IN
2.5V TO 9.8V
16
SENSE1
+
V
IN
15
0.03Ω
M1
L1
4.7µH
D1
M2
0.03Ω
L2
4.7µH
100k
D1, D2: IR10BQ015 L1, L2: LQN6C-4R7 M1, M2: FDC638P
3701 F01a
Figure 1. High Efficiency 2-Phase 550kHz Dual Step-Down Converter
+
80.6k
10k
220pF
14
I
TH
/RUN1
PGATE1
13
4
LTC3701
SGND
PGND
12
6
I
TH
/RUN2
PGATE2
11
5
PGOOD
V
FB2
10
7
PLLLPF EXTCLK/MODE
9
8
SENSE2
+
SENSE2
–
+
47µF
EFFICIENCY (%)
V
OUT1
2.5V
2A
10µF
D2
47µF
V
OUT2
1.8V
2A
U
Efficiency vs Load Current
100
V
IN
= 4.2V
90
80
V
IN
= 6V
70
60
50
40
1
V
OUT
= 2.5V
100
1000
10
LOAD CURRENT (mA)
10000
3701 F01b
U
U
V
IN
= 3.3V
V
IN
= 8.4V
3701fa
1
LTC3701
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SENSE1
–
I
TH
/RUN1
V
FB1
SGND
V
FB2
I
TH
/RUN2
PLLLPF
SENSE2
–
1
2
3
4
5
6
7
8
16 SENSE1
+
15 V
IN
14 PGATE1
13 PGND
12 PGATE2
11 PGOOD
10 EXTCLK/MODE
9
SENSE2
+
Input Supply Voltage (V
IN
)........................ – 0.3V to 10V
SENSE1
–
, SENSE2
–
, PGATE1, PGATE2,
PLLLPF, SENSE1
+
, SENSE2
+
,
EXTCLK/MODE Voltages .............. – 0.3V to (V
IN
+ 0.3V)
V
FB1
, V
FB2
, I
TH
/RUN1,
I
TH
/RUN2 Voltages .................................. – 0.3V to 2.4V
PGOOD Voltage ........................................ – 0.3V to 10V
PGATE1, PGATE2 Peak Output Current (<10µs) ....... 1A
Operating Ambient Temperature Range
(Note 2) ...................................................–40°C to 85°C
Storage Ambient Temperature Range ... – 65°C to 150°C
Junction Temperature (Note 3) ............................ 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC3701EGN
GN PART
MARKING
3701
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 150°C,
θ
JA
= 140°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Main Control Loops
Input DC Supply Current
Normal Operation
Sleep Mode
Shutdown
UVLO
Undervoltage Lockout Threshold
Shutdown Threshold at I
TH
/RUN1, 2
Start-Up Current Source on I
TH
/RUN1, 2
Regulated Feedback Voltage
Output Voltage Line Regulation
Output Voltage Load Regulation
V
FB1, 2
Input Current
Output Overvoltage Protect Threshold
Output Overvoltage Protect Hysteresis
Gate Drive 1, 2 Rise Time
Gate Drive 1, 2 Fall Time
Maximum Current Sense Voltage (SENSE
+
– SENSE
–
)
Soft-Start
Current Sense Voltage Step
Time to Maximum Sense Voltage
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 4.2V unless otherwise noted.
CONDITIONS
(Note 4)
2.5V < V
IN
< 9.8V
2.5V < V
IN
< 9.8V
2.5V < V
IN
< 9.8V, I
TH
/RUN1 = I
TH
/RUN2 = 0V
V
IN
< UVLO Threshold
V
IN
Falling
V
IN
Rising
V
ITH
/RUN1, 2 = 0V
0°C to 70°C (Note 5), I
TH
/RUN = 1.3V
–40°C to 85°C (Note 5)
2.5V < V
IN
< 9.8V (Note 5)
I
TH
/RUN = 0.9V (Note 5)
I
TH
/RUN = 1.6V
(Note 5)
Measured at V
FB
C
L
= 3000pF
C
L
= 3000pF
(Note 6)
95
0.835
q
q
q
MIN
TYP
MAX
UNITS
460
305
9
18
1.55
1.70
0.2
0.25
0.784
0.774
2.00
2.12
0.35
0.5
0.8
0.8
0.05
0.2
– 0.2
10
0.88
20
40
40
120
30
2048
780
470
28
30
2.50
2.55
0.5
0.85
0.816
0.826
0.20
0.8
– 0.8
50
0.930
145
mV
Cycles
2
U
µA
µA
µA
µA
V
V
V
µA
V
V
mV/V
%
%
nA
V
mV
ns
ns
mV
3701fa
W
U
U
W W
W
LTC3701
ELECTRICAL CHARACTERISTICS
PARAMETER
Oscillator and Phase-Locked Loop
Oscillator Frequency
V
PLLLPF
= 1.2V or Floating
V
PLLLPF
= 0V
V
PLLLPF
≥
2.4V
f
EXTCLK/MODE
< f
OSC
f
EXTCLK/MODE
> f
OSC
I
PGOOD
= 500µA
V
FB
with Respect to Set Output Voltage
V
FB
Ramping Positive
V
FB
Ramping Negative
–15
2.5
500
230
690
550
280
775
–5
5
70
–8
8
150
–2.5
15
600
320
890
kHz
kHz
kHz
µA
µA
mV
%
%
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 4.2V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
Phase Detector Output Current
Sinking
Sourcing
PGOOD Output
PGOOD Voltage Low
PGOOD Trip Level
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3701E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
TJ 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 LTC3701 is tested in a feedback loop that servos I
TH/RUN
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 given in Figure 2.
TYPICAL PERFOR A CE CHARACTERISTICS
Reference Voltage vs Temperature
0.810
0.805
V
IN
= 4.2V
REFERENCE VOLTAGE (V)
FREQUENCY (kHz)
0.800
0.795
0.790
0.785
0.780
0.775
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
I
TH
/RUN VOLTAGE (V)
U W
80
Shutdown Threshold
vs Temperature
0.50
0.48 V
IN
= 4.2V
0.46
0.44
0.42
0.40
0.38
0.36
0.34
0.32
0.30
0.28
0.26
0.24
0.22
0.20
20
40 60
–60 –40 –20 0
TEMPERATURE (°C)
1000
900
800
700
600
500
400
300
200
100
80 100
3701 G02
Oscillator Frequency
vs Temperature
V
IN
= 4.2V
PLLLPF = 2.4V
PLLLPF = FLOAT
PLLLPF = 0V
100
0
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
3701 G01
3701 G03
3701fa
3
LTC3701
TYPICAL PERFOR A CE CHARACTERISTICS
Undervoltage Lockout Trip
Voltage (Falling) vs Temperature
2.15
2.10
2.20
2.18
2.16
MAXIMUM CURRENT SENSE THRESHOLD (mV)
INPUT VOLTAGE (V)
2.05
2.00
1.95
1.90
1.85
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
INPUT VOLTAGE (V)
Input and Shutdown Currents vs
Input Voltage
600
500
INPUT CURRENT (µA)
400
300
200
100
0
FIGURE 1 CIRCUIT
LOAD CURRENT = 0A
SHUTDOWN
(I
TH
/RUN
1,2
= 0V)
2
3
4
9
5
7
8
6
INPUT VOLTAGE (V)
10
11
PULSE SKIPPING MODE OPERATION
(EXTCLK/MODE = 0V)
100
BURST MODE OPERATION
(EXTCLK/MODE = V
IN
)
EFFICIENCY (%)
PGOOD R
ON
vs Input Voltage
500
450
400
PGOOD R
DS(ON)
(Ω)
350
300
250
200
150
100
50
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
4
U W
80
3701 G04
Undervoltage Lockout Trip
Voltage (Rising) vs Temperature
125
Maximum Current Sense
Threshold vs Temperature
120
2.14
2.12
2.10
2.08
2.06
2.04
2.02
115
110
105
100
2.00
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
100
20
40 60
–60 –40 –20 0
TEMPERATURE (°C)
80 100
3701 G06
3701 G05
Efficiency vs Load Current (Pulse
Skipping Mode)
FIGURE 1 CIRCUIT
EXTCLK/MODE = GND
90 V
OUT
= 2.5V
80
70
V
IN
= 6V
60
50
40
V
IN
= 4.2V
V
IN
= 3.3V
V
IN
= 8.4V
1
100
100O
10
LOAD CURRENT (mA)
1OOOO
3701 G08
3701 G07
2-Phase Operation
SW1
5V/DIV
SW2
5V/DIV
INPUT
CURRENT
1A/DIV
FIGURE 1 CIRCUIT
500ns/DIV
I
PGOOD
= 500µA
3701 G09
3701fa
LTC3701
PI FU CTIO S
SENSE1
–
, SENSE2
–
(Pins 1, 8):
The (–) Inputs to the
Differential Current Comparators.
I
TH
/RUN1, I
TH
/RUN2 (Pins 2, 6):
These pins each serve
two functions. Each pin serves as the error amplifier
compensation point as well as the run control input for the
respective controller. Forcing one pin below 0.35V causes
the functions associated with that controller to be shut
down. Forcing both I
TH/RUN
pins below 0.35V causes the
device to be shut down. Nominal operating voltage range
on these pins is from 0.7V to 1.9V.
V
FB1
, V
FB2
(Pins 3, 5):
Each receives the remotely sensed
feedback voltage for each controller from an external
resistive divider across the output.
SGND (Pin 4):
Signal Ground.
PLLLPF (Pin 7):
Serves as the lowpass filter point for the
PLL and as the voltage control input to the internal
oscillator. Normally, a series RC is connected between this
pin and ground when synchronizing to an external clock.
Nominal voltage range is from 0V to 2.4V. Frequency can
be set by forcing this pin with a voltage. Tying this pin to
GND selects 300kHz. Tying to V
IN
or a voltage
≥
2.4V
selects 750kHz. Floating this pin selects 550kHz opera-
tion.
SENSE2
+
(PV
IN2
), SENSE1
+
(PV
IN1
) (Pins 9, 16):
The (+)
Inputs to the Differential Current Comparators. These pins
also power the gate drivers.
EXTCLK/MODE (Pin 10):
External Clock Input. Applying a
clock to this pin causes the internal oscillator to phase-
lock to the external clock (nominal lock frequency range
between 300kHz and 750kHz). This also disables Burst
Mode operation but allows pulse-skipping at low load
currents.
Forcing this pin high enables Burst Mode operation.
Forcing this pin low enables pulse-skipping mode. In
these cases, the frequency of the internal oscillator is set
by the voltage on the PLLLPF pin. If the PLLLPF voltage is
not set externally, the frequency internally defaults to
550kHz.
PGOOD (Pin 11):
Power Good Output Voltage Monitor
Open-Drain Logic Output. This pin is pulled to ground
when the voltage on either feedback pin (V
FB1
, V
FB2
) is not
within
±8%
of its nominal set point. PGOOD is pulled low
when channel 1 or both channels are shut down. When
channel 2 is shut down and channel 1 enabled, the
PGOOD output indicates the state of V
FB1
only.
PGATE2, PGATE1 (Pins 12, 14):
Gate Drivers for the
External P-Channel MOSFETs. These pins swing from 0 to
SENSE
+
(PV
IN
).
PGND (Pin 13):
Ground Pin for Gate Drivers.
V
IN
(Pin 15):
Chip Signal Power Supply Input. This pin
powers the entire chip except for the gate drivers.
U
U
U
3701fa
5
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
