FEATURES
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LTC1702A
Dual 550kHz Synchronous
2-Phase Switching Regulator Controller
DESCRIPTIO
The LTC
®
1702A is a dual switching regulator controller
optimized for high efficiency with low input voltages. It
includes two complete, on-chip, independent switching regu-
lator controllers each designed to drive a pair of external N-
channel MOSFETs in a voltage mode feedback, synchronous
buck configuration. The LTC1702A uses a constant-fre-
quency, true PWM design switching at 550kHz, minimizing
external component size and cost and maximizing load
transient performance. The synchronous buck architecture
automatically shifts to discontinuous and then to Burst
Mode
®
operation as the output load decreases, ensuring
maximum efficiency over a wide range of load currents.
The LTC1702A 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 LTC1702A shuts down and supply current drops below
100µA.
Pin Compatible with the LTC1702 with Improved
Current Limit Control
Two Sides Run Out-of-Phase to Minimize C
IN
No External Current Sense Resistors
Excellent Output Regulation: 1% Total Output
Accuracy
Two Independent Controllers in One Package
All N-Channel External MOSFET Architecture
550kHz Switching Frequency Minimizes External
Component Size
1A to 25A Output Current per Channel
High Efficiency over Wide Load Current Range
Less Than 100µA Shutdown Current
Small 24-Pin Narrow SSOP Package
APPLICATIO S
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Microprocessor, DSP Core and I/O Supplies
Multiple Logic Supply Generator
Distributed Power Applications
High Efficiency Power Conversion
, LT, LTC and LTM 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 6144194.
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
D2
1µF
1
1µF
2
3
Q1
Q2
4
5
Q3
Q4
11.8k
6
PV
CC
BOOST1
BG1
TG1
SW1
I
MAX1
I
MAX2
BOOST2
BG2
TG2
SW2
10Ω
24
23
22
10µF
+
11.8k
10µF
Q5
Q6
L2
1µH
Q7
Q8
D4
1.6k
15.8k
1%
V
OUT2
3.3V
AT 15A
1µF
V
OUT1
2.5V
AT 15A
1µF
L1
1µH
D3
1.2k
10k
1%
820pF
21
20
+
C
OUT1
180µF
×4
4.75k
1%
V
IN
10k
PWRGD1
47k
680pF
27pF
19
PGND
LTC1702A
7
18
PGOOD1
PGOOD2
8
17
FCB
FAULT
9
16
RUN/SS
RUN/SS2
1µF
10
15
COMP1
COMP2
11
14
SGND
FB2
12
13
FB1
V
CC
1µF
68k
27pF
3300pF
10k
PWRGD2
FAULT
1702 TA01
U
U
U
C
IN
330µF
×3
+
680pF
C
OUT2
180µF
×4
1µF
4.99k
1%
V
IN
1702afa
1
LTC1702A
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
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
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
LTC1702AC ............................................. 0°C to 70°C
LTC1702AI ........................................ – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
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
LTC1702ACGN
LTC1702AIGN
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
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
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
%
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(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, LTC1702AC
Test Circuit 1, C
L
= 0pF, LTC1702AI
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
8
100
6
100
3
10
0.808
0.810
±0.05
±1
±0.2
2
U
W
U
U
W W
W
LTC1702A
ELECTRICAL CHARACTERISTICS
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
V
FCB
∆V
FCB
I
FCB
V
RUN
I
SS
I
MAX
f
OSC
Φ
OSC2
DC
MIN
DC
MAX
t
NOV
t
r
, t
f
A
VFB
GBW
I
ERR
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)
●
●
PARAMETER
FCB Threshold
FCB Feedback Hysteresis
FCB Pin Current
RUN/SS Pin RUN Threshold
Soft-Start Source Current
Maximum Soft-Start Sink Current
I
MAX
Source Current
Oscillator Frequency
Converter 2 Oscillator Phase
Minimum Duty Cycle
Maximum Duty Cycle
Driver Nonoverlap
Driver Rise/Fall Time
FB DC Gain
FB Gain Bandwidth
FB Sink/Source Current
CONDITIONS
●
●
●
MIN
0.75
TYP
0.8
20
±0.001
MAX
0.85
±1
0.65
–6
–8
750
UNITS
V
mV
µA
V
µA
mA
µA
kHz
DEG
%
0.45
–2
0.55
– 3.5
1
–10
550
180
RUN/SSn = 0V
V
IMAX
= 0V, V
SW
= – 0.5V
V
IMAX
= 0V
Test Circuit 1, C
L
= 0pF
Relative to Converter 1 (Note 6)
●
●
●
●
–12
475
0
87
Switching Characteristics
90
40
12
93
100
80
%
ns
ns
dB
MHz
mA
Test Circuit 1, C
L
= 2000pF (Note 7)
Test Circuit 1, C
L
= 2000pF (Note 7)
●
●
●
●
Feedback Amplifier
74
±3
–10
85
25
±10
–5
0.03
±0.1
100
10
15
0.03
–10
25
20
0.1
–2
0.1
±1
V
FB
Relative to Regulated V
OUT
PGOOD = 1mA
●
●
●
%
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 LTC1702A, 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.
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3
LTC1702A
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
1702A G01
Supply Current vs Temperature
NORMALIZED OSCILLATOR FREQUENCY (%)
2.6
2.4
TEST CIRCUIT 1
C
L
= 0pF
PV
CC
V
CC
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
–2.5
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
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
1702A 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
I
L
20mV/DIV
20
15
10
5
0
10µs/DIV
1702A G02
0
2000
4000
6000
8000
GATE CAPACITANCE (pF)
10000
1702A G03
Normalized Oscillator Frequency
vs Temperature
2.5
2.0
1.5
1.0
0.5
V
CC
= 5V
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
Driver R
ON
vs Temperature
V
PVCC
= 5V
V
BOOST
– V
SW
= 5V
125
0.4
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1702A G05
1702A 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
1702A G07
1702A G08
1702A G09
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LTC1702A
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. A 5Ω to
10Ω resistor in series with this pin can help control ringing
at the switch node. See the EXTERNAL COMPONENTS
SELECTION/MOSFET Series Resistors section for more
information.
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 V
CC
is cycled. BG1 should be directly connected
to the MOSFET gate. Do not use a series resistor. See the
EXTERNAL COMPONENTS SELECTION/MOSFET Series
Resistors section for more information.
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. TG1 should be
directly connected to the MOSFET gate. Do not use a series
resistor. See the EXTERNAL COMPONENTS SELECTION/
MOSFET Series Resistors section for more information.
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 LTC1702A,
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.
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