LTC1702
Dual 550kHz Synchronous
2-Phase Switching Regulator Controller
FEATURES
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DESCRIPTIO
Two Independent Controllers in One Package
Two Sides Run Out-of-Phase to Minimize C
IN
All N-Channel External MOSFET Architecture
No External Current Sense Resistors
Excellent Output Regulation: 1% Total Output
Accuracy
550kHz Switching Frequency Minimizes External
Component Size
1A to 25A Output Current per Channel
High Efficiency over Wide Load Current Range
Quiescent Current Drops Below 100µA in Shutdown
Small 24-Pin Narrow SSOP Package
APPLICATIO S
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Microprocessor Core and I/O Supplies
Multiple Logic Supply Generator
Distributed Power Applications
High Efficiency Power Conversion
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode
is a registered trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents including 5481178,
5847554, 6304066, 6307356, 6580258.
The LTC
®
1702 is a dual switching regulator controller opti-
mized for high efficiency with low input voltages. It includes
two complete, on-chip, independent switching regulator
controllers each designed to drive a pair of external N-channel
MOSFET devices in a voltage mode feedback, synchronous
buck configuration. The LTC1702 uses a constant-frequency,
true PWM design switching at 550kHz, minimizing external
component size and cost and maximizing load transient
performance. The synchronous buck architecture automati-
cally shifts to discontinuous and then to Burst Mode
TM
operation as the output load decreases, ensuring maximum
efficiency over a wide range of load currents.
The LTC1702 features an onboard reference trimmed to
0.5% and can provide better than 1% regulation at the
converter outputs. Open-drain logic outputs indicate whether
either output has risen to within 5% of the final output voltage
and an optional latching FAULT mode protects the load if the
output rises 15% above the intended voltage. Each channel
can be enabled independently; with both channels disabled,
the LTC1702 shuts down and supply current drops below
100µA.
TYPICAL APPLICATIO
C
OUT1
, C
OUT2
: PANASONIC EEFUE0G181R
C
IN
: KEMET TS10X337M010AS
D1, D2: MOTOROLA MBR0520LT1
D3, D4: MOTOROLA MBRS320T3
L1, L2: SUMIDA CEP125-1R0
Q1 TO Q8: FAIRCHILD FDS6670A
1µF
Dual Output High Power 3.3V/2.5V Logic Supply
V
IN
= 5V
±10%
D1
27k
10µF
Q5
21
20
19
18
17
16
15
14
13
27pF
1µF
68k
3300pF
10k
1702 TA01
D2
1µF
1
1µF
2
3
Q1
Q2
4
5
PV
CC
BOOST1
BG1
TG1
SW1
I
MAX1
PGOOD1
FCB
RUN/SS
COMP1
SGND
FB1
LTC1702
I
MAX2
BOOST2
BG2
TG2
SW2
PGND
PGOOD2
FAULT
RUN/SS2
COMP2
FB2
V
CC
10Ω
24
23
22
10µF
+
V
OUT1
2.5V
AT 15A
1µF
L1
1µH
27k
+
C
OUT1
180µF
×4
D3
1.2k
10k
1%
Q3
Q4
6
7
8
820pF
9
1µF
10
4.75k
1%
V
IN
10k
PWRGD1
47k
680pF
27pF
11
12
U
C
IN
330µF
×3
1µF
Q6
L2
1µH
V
OUT2
3.3V/15A
Q7
Q8
D4
1.6k
15.8k
1%
U
U
+
680pF
C
OUT2
180µF
×4
1µF
4.99k
1%
V
IN
PWRGD2
FAULT
1702fa
1
LTC1702
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
Supply Voltage
V
CC
........................................................................ 7V
BOOSTn
...............................................................
15V
BOOSTn – SWn .................................................... 7V
Input Voltage
SWn .......................................................... – 1V to 8V
All Other Inputs ......................... – 0.3V to V
CC
+ 0.3V
Peak Output Current < 10µs
TGn, BGn ............................................................... 5A
Operating Temperature Range
LTC1702C ............................................... 0°C to 70°C
LTC1702I ........................................... – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
PV
CC
BOOST1
BG1
TG1
SW1
I
MAX1
PGOOD1
FCB
RUN/SS1
1
2
3
4
5
6
7
8
9
24 I
MAX2
23 BOOST2
22 BG2
21 TG2
20 SW2
19 PGND
18 PGOOD2
17 FAULT
16 RUN/SS2
15 COMP2
14 FB2
13 V
CC
COMP1
10
SGND
11
FB1
12
GN PACKAGE
24-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 100°C/ W
ORDER PART NUMBER
LTC1702CGN
LTC1702IGN
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/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC
PV
CC
BV
CC
I
CC
IPV
CC
I
BOOST
V
FB
∆V
FB
I
FB
∆V
OUT
V
FCB
∆V
FCB
I
FCB
V
RUN
I
SS
PARAMETER
V
CC
Supply Voltage
PV
CC
Supply Voltage
BOOST Pin Voltage
V
CC
Supply Current
PV
CC
Supply Current
BOOST Pin Current
Feedback Voltage
Feedback Voltage Line Regulation
Feedback Current
Output Voltage Load Regulation
FCB Threshold
FCB Feedback Hysteresis
FCB Pin Current
RUN/SS Pin RUN Threshold
Soft-Start Source Current
Main Control Loop
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. V
CC
= 5V unless otherwise specified. (Note 3)
CONDITIONS
●
MIN
3
3
2.7
TYP
MAX
7
7
7
UNITS
V
V
V
mA
µA
mA
µA
mA
µA
V
V
%/V
µA
%
V
mV
µA
V
µA
1702fa
(Note 2)
V
BOOST
– V
SW
(Note 2)
Test Circuit 1, C
L
= 0pF
RUN/SS1 = RUN/SS2 = 0V (Note 5)
Test Circuit 1, C
L
= 0pF (Note 4)
RUN/SS1 = RUN/SS2 = 0V (Note 5)
Test Circuit 1, C
L
= 0pF (Note 4)
RUN/SS1 = RUN/SS2 = 0V
Test Circuit 1, C
L
= 0pF, LTC1702C
Test Circuit 1, C
L
= 0pF, LTC1702I
V
CC
= 3V to 7V
(Note 6)
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
2.2
30
2.2
6
1.3
0.1
0.792
0.790
0.800
0.800
±0.005
±0.001
0.1
0.75
0.8
20
±0.001
0.45
–2
0.55
– 3.5
8
100
6
100
3
10
0.808
0.810
±0.05
±1
±0.2
0.85
±1
0.65
–6
RUN/SSn = 0V
2
U
W
U
U
W W
W
LTC1702
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. V
CC
= 5V unless otherwise specified. (Note 3)
SYMBOL
f
OSC
Φ
OSC2
DC
MIN1
DC
MIN2
DC
MAX
t
NOV
t
r
, t
f
A
VFB
GBW
I
ERR
V
MIN
V
MAX
A
VILIM
I
IMAX
Status Outputs
V
PGOOD
V
OLPG
I
PGOOD
t
PGOOD
V
FAULT
V
OLF
I
FAULT
t
FAULT
PGOOD Trip Point
PGOOD Output Low Voltage
PGOOD Output Leakage
PGOOD Delay Time
FAULT Trip Point
FAULT Output Low Voltage
FAULT Output Current
FAULT Delay Time
V
FB
< V
PGOOD
to PGOOD
I
FAULT
= 1mA
V
FAULT
= 0V
V
FB
> V
FAULT
to FAULT
(Note 7)
(Note 7)
●
●
ELECTRICAL CHARACTERISTICS
PARAMETER
Oscillator Frequency
Converter 2 Oscillator Phase
Minimum Duty Cycle
Minimum Duty Cycle
Maximum Duty Cycle
Driver Nonoverlap
Driver Rise/Fall Time
FB DC Gain
FB Gain Bandwidth
FB Sink/Source Current
MIN Comparator Threshold
MAX Comparator Threshold
I
LIM
Gain
I
MAX
Source Current
CONDITIONS
Test Circuit 1, C
L
= 0pF
Relative to Converter 1 (Note 6)
V
FB
< V
MAX
V
FB
> V
MAX
Test Circuit 1, C
L
= 2000pF (Note 7)
Test Circuit 1, C
L
= 2000pF (Note 7)
●
●
●
●
●
●
●
●
●
●
MIN
475
7
0
87
TYP
550
180
10
90
40
12
MAX
750
UNITS
kHz
DEG
%
%
Switching Characteristics
93
100
80
%
ns
ns
dB
MHz
mA
Feedback Amplifier
74
±3
815
85
25
±10
760
840
40
I
MAX
= 0V, LTC1702C
I
MAX
= 0V, LTC1702I
V
FB
Relative to Regulated V
OUT
PGOOD = 1mA
●
●
●
●
●
785
mV
mV
dB
Current Limit Loop
–7
–7
– 10
–10
–10
–5
0.03
±0.1
100
+ 10
+ 15
0.03
– 10
25
+ 20
0.1
–13
–14
–2
0.1
±1
µA
µA
%
V
µA
µs
%
V
µA
µs
V
FB
Relative to Regulated V
OUT
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:
PV
CC
and BV
CC
(V
BOOST
– V
SW
) must be greater than V
GS(ON)
of
the external MOSFETs used to ensure proper operation.
Note 3:
All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.
Note 4:
Supply current in normal operation is dominated by the current
needed to charge and discharge the external MOSFET gates. This current
will vary with supply voltage and the external MOSFETs used.
Note 5:
Supply current in shutdown is dominated by external MOSFET
leakage and may be significantly higher than the quiescent current drawn
by the LTC1702, especially at elevated temperature.
Note 6:
This parameter is guaranteed by correlation and is not tested
directly.
Note 7:
Rise and fall times are measured using 10% and 90% levels. Delay
and nonoverlap times are measured using 50% levels.
1702fa
3
LTC1702
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
100
V
IN
= 5V
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.6V
EFFICIENCY (%)
90
DRIVER SUPPLY CURRENT (mA)
80
70
0
5
10
LOAD CURRENT (A)
15
1702 G01
Supply Current vs Temperature
2.6
2.4
TEST CIRCUIT 1
C
L
= 0pF
PV
CC
V
CC
2.5
2.0
NORMALIZED FREQUENCY (%)
SUPPLY CURRENT (mA)
2.2
2.0
1.8
1.6
1.4
1.2
1.0
– 50 – 25
0
BOOST1, BOOST2
0
–0.5
–1.0
–1.5
–2.0
R
ON
(Ω)
50
75
25
TEMPERATURE (°C)
RUN/SS Source Current
vs Temperature
5.0
4.5
SOURCE CURRENT (µA)
V
CC
= 5V
4.0
3.5
3.0
2.5
2.0
–50 –25
NONOVERLAP (ns)
50
40
30
20
10
RISE/FALL TIME (ns)
50
25
75
0
TEMPERATURE (°C)
4
U W
100
1702 G04
Transient Response
V
IN
= 5V
V
OUT
= 1.8V
I
LOAD
= 0A-10A-0A
±2.2%
MAX DEVIATION
35
MOSFET Driver Supply Current
vs Gate Capacitance
TEST CIRCUIT 1
ONE DRIVER LOADED
30 MULTIPLY BY # OF ACTIVE
DRIVERS TO OBTAIN TOTAL
25 DRIVER SUPPLY CURRENT
20mV/
DIV
20
15
10
5
0
10µs/DIV
1702 G02
0
2000
6000
8000
GATE CAPACITANCE (pF)
4000
10000
1702 G03
Normalized Frequency
vs Temperature
V
CC
= 5V
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
50
25
0
75
TEMPERATURE (°C)
100
125
Driver R
ON
vs Temperature
V
PVCC
= 5V
V
BOOST
– V
SW
= 5V
1.5
1.0
0.5
125
–2.5
–50 –25
0.4
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1702 G05
1702 G06
Nonoverlap Time vs Temperature
70
60
15
Driver Rise/Fall vs Temperature
TEST CIRCUIT 1
C
L
= 2000pF
14
TEST CIRCUIT 1
C
L
= 2000pF
TG FALLING EDGE
BG RISING EDGE
13
BG FALLING EDGE
TG RISING EDGE
12
11
100
125
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
12
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1702 G07
1702 G08
1702 G09
1702fa
LTC1702
PIN FUNCTIONS
PV
CC
(Pin 1):
Driver Power Supply Input. PV
CC
provides
power to the two BGn output drivers. PV
CC
must be
connected to a voltage high enough to fully turn on the
external MOSFETs QB1 and QB2. PV
CC
should generally
be connected directly to V
IN
. PV
CC
requires at least a 1µF
bypass capacitor directly to PGND.
BOOST1 (Pin 2):
Controller 1 Top Gate Driver Supply. The
BOOST1 pin supplies power to the floating TG1 driver.
BOOST1 should be bypassed to SW1 with a 1µF capacitor.
An additional Schottky diode from V
IN
to BOOST1 pin will
create a complete floating charge-pumped supply at
BOOST1. No other external supplies are required.
BG1 (Pin 3):
Controller 1 Bottom Gate Drive. The BG1 pin
drives the gate of the bottom N-channel synchronous
switch MOSFET, QB1. BG1 is designed to drive up to
10,000pF of gate capacitance directly. If RUN/SS1 goes
low, BG1 will go low, turning off QB1. If FAULT mode is
tripped, BG1 will go high and stay high, keeping QB1 on
until the power is cycled.
TG1 (Pin 4):
Controller 1 Top Gate Drive. The TG1 pin
drives the gate of the top N-channel MOSFET, QT1. The
TG1 driver draws power from the BOOST1 pin and returns
to the SW1 pin, providing true floating drive to QT1. TG1
is designed to drive up to 10,000pF of gate capacitance
directly. In shutdown or fault modes, TG1 will go low.
SW1 (Pin 5):
Controller 1 Switching Node. SW1 should be
connected to the switching node of converter 1. The TG1
driver ground returns to SW1, providing floating gate
drive to the top N-channel MOSFET switch, QT1. The
voltage at SW1 is compared to I
MAX1
by the current limit
comparator while the bottom MOSFET, QB1, is on.
I
MAX1
(Pin 6):
Controller 1 Current Limit Set. The I
MAX1
pin sets the current limit comparator threshold for
controller 1. If the voltage drop across the bottom MOSFET,
QB1, exceeds the magnitude of the voltage at I
MAX1
,
controller 1 will go into current limit. The I
MAX1
pin has an
internal 10µA current source pull-up, allowing the current
threshold to be set with a single external resistor to PGND.
See the Current Limit Programming section for more
information on choosing R
IMAX
.
PGOOD1 (Pin 7):
Controller 1 Power Good. PGOOD1 is an
open-drain logic output. PGOOD1 will pull low whenever
FB1 falls 5% below its programmed value. When RUN/SS1
is low (side 1 shut down), PGOOD1 will go high.
FCB (Pin 8):
Force Continuous Bar. The FCB pin forces
both converters to maintain continuous synchronous
operation regardless of load when the voltage at FCB
drops below 0.8V. FCB is normally tied to V
CC
. To force
continuous operation, tie FCB to SGND. FCB can also be
connected to a feedback resistor divider from a secondary
winding on one converter’s inductor to generate a third
regulated output voltage. Do not leave FCB floating.
RUN/SS1 (Pin 9):
Controller 1 Run/Soft-start. Pulling
RUN/SS1 to SGND will disable controller 1 and turn off
both of its external MOSFET switches. Pulling both
RUN/SS pins down will shut down the entire LTC1702,
dropping the quiescent supply current below 100µA. A
capacitor from RUN/SS1 to SGND will control the turn-on
time and rate of rise of the controller 1 output voltage at
power-up. An internal 3.5µA current source pull-up at
RUN/SS1 pin sets the turn-on time at approximately
500ms/µF.
COMP1 (Pin 10):
Controller 1 Loop Compensation. The
COMP1 pin is connected directly to the output of the first
controller’s error amplifier and the input to the PWM
comparator. An RC network is used at the COMP1 pin to
compensate the feedback loop for optimum transient
response.
SGND (Pin 11):
Signal Ground. All internal low power
circuitry returns to the SGND pin. Connect to a low
impedance ground, separated from the PGND node. All
feedback, compensation and soft-start connections should
return to SGND. SGND and PGND should connect only at
a single point, near the PGND pin and the negative plate of
the C
IN
bypass capacitor.
FB1 (Pin 12):
Controller 1 Feedback Input. FB1 should be
connected through a resistor network to V
OUT1
to set the
output voltage. The loop compensation network for con-
troller 1 also connects to FB1.
V
CC
(Pin 13):
Power Supply Input. All internal circuits
except the output drivers are powered from this pin. V
CC
should be connected to a low noise power supply voltage
between 3V and 7V and should be bypassed to SGND with
at least a 1µF capacitor in close proximity to the LTC1702.
1702fa
U
U
U
5
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