1
LTC1702A
1702af
Dual 550kHz Synchronous
2-Phase Switching Regulator Controller
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
100
A.
s
Pin Compatible with the LTC1702 with Improved
Current Limit Control
s
Two Sides Run Out-of-Phase to Minimize C
IN
s
No External Current Sense Resistors
s
Excellent Output Regulation: 1% Total Output
Accuracy
s
Two Independent Controllers in One Package
s
All N-Channel External MOSFET Architecture
s
550kHz Switching Frequency Minimizes External
Component Size
s
1A to 25A Output Current per Channel
s
High Efficiency over Wide Load Current Range
s
Less Than 100
A Shutdown Current
s
Small 24-Pin Narrow SSOP Package
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
s
Microprocessor, DSP Core and I/O Supplies
s
Multiple Logic Supply Generator
s
Distributed Power Applications
s
High Efficiency Power Conversion
Dual Output High Power 3.3V/2.5V Logic Supply
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
LTC1702A
PV
CC
BOOST1
BG1
TG1
SW1
I
MAX1
PGOOD1
FCB
RUN/SS
COMP1
SGND
FB1
I
MAX2
BOOST2
BG2
TG2
SW2
PGND
PGOOD2
FAULT
RUN/SS2
COMP2
FB2
V
CC
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
1
F
10
1
F
1
F
11.8k
11.8k
1.6k
68k
1702 TA01
V
IN
1.2k
10k
1%
C
OUT1
180
F
4
820pF
27pF
680pF
47k
1
F
V
OUT1
2.5V
AT 15A
1
F
4.75k
1%
Q2
Q1
Q4
Q3
D3
D2
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
D1
PWRGD1
L1
1
H
+
10
F
10
F
1
F
V
IN
= 5V
10%
1
F
C
IN
330
F
3
+
Q7
Q5
Q8
Q6
D4
680pF
27pF
3300pF
15.8k
1%
4.99k
1%
10k
L2
1
H
C
OUT2
180
F
4
1
F
V
OUT2
3.3V
AT 15A
PWRGD2
FAULT
+
V
IN
10k
2
LTC1702A
1702af
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
(Note 1)
Supply Voltage
V
CC ...........................................................................................
7V
BOOST
n ............................................................... 15V
BOOST
n SWn .................................................... 7V
Input Voltage
SW
n .......................................................... 1V to 8V
All Other Inputs ......................... 0.3V to V
CC
+ 0.3V
Peak Output Current < 10
s
TG
n, 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
PACKAGE/ORDER I
N
FOR
M
ATIO
N
W
U
U
ORDER PART
NUMBER
1
2
3
4
5
6
7
8
9
10
11
12
TOP VIEW
GN PACKAGE
24-LEAD NARROW PLASTIC SSOP
24
23
22
21
20
19
18
17
16
15
14
13
PV
CC
BOOST1
BG1
TG1
SW1
I
MAX1
PGOOD1
FCB
RUN/SS1
COMP1
SGND
FB1
I
MAX2
BOOST2
BG2
TG2
SW2
PGND
PGOOD2
FAULT
RUN/SS2
COMP2
FB2
V
CC
T
JMAX
= 125
C,
JA
= 100
C/ W
LTC1702ACGN
LTC1702AIGN
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Main Control Loop
V
CC
V
CC
Supply Voltage
q
3
7
V
PV
CC
PV
CC
Supply Voltage
(Note 2)
q
3
7
V
BV
CC
BOOST Pin Voltage
V
BOOST
V
SW
(Note 2)
q
2.7
7
V
I
CC
V
CC
Supply Current
Test Circuit 1, C
L
= 0pF
q
2.2
8
mA
RUN/SS1 = RUN/SS2 = 0V (Note 5)
q
30
100
A
IPV
CC
PV
CC
Supply Current
Test Circuit 1, C
L
= 0pF (Note 4)
q
2.2
6
mA
RUN/SS1 = RUN/SS2 = 0V (Note 5)
q
6
100
A
I
BOOST
BOOST Pin Current
Test Circuit 1, C
L
= 0pF (Note 4)
q
1.3
3
mA
RUN/SS1 = RUN/SS2 = 0V
q
0.1
10
A
V
FB
Feedback Voltage
Test Circuit 1, C
L
= 0pF, LTC1702AC
q
0.792
0.800
0.808
V
Test Circuit 1, C
L
= 0pF, LTC1702AI
q
0.790
0.800
0.810
V
V
FB
Feedback Voltage Line Regulation
V
CC
= 3V to 7V
q
0.005
0.05
%/V
I
FB
Feedback Current
q
0.001
1
A
V
OUT
Output Voltage Load Regulation
(Note 6)
q
0.1
0.2
%
V
FCB
FCB Threshold
q
0.75
0.8
0.85
V
V
FCB
FCB Feedback Hysteresis
20
mV
I
FCB
FCB Pin Current
q
0.001
1
A
V
RUN
RUN/SS Pin RUN Threshold
q
0.45
0.55
0.65
V
I
SS
Soft-Start Source Current
RUN/SS
n = 0V
2
3.5
6
A
Maximum Soft-Start Sink Current
V
IMAX
= 0V, V
SW
= 0.5V
1
mA
I
MAX
I
MAX
Source Current
V
IMAX
= 0V
q
12
10
8
A
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25
C.
V
CC
= 5V unless otherwise specified. (Note 3)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LTC1702A
1702af
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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.
The
q
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
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Switching Characteristics
f
OSC
Oscillator Frequency
Test Circuit 1, C
L
= 0pF
q
475
550
750
kHz
OSC2
Converter 2 Oscillator Phase
Relative to Converter 1 (Note 6)
180
DEG
DC
MIN
Minimum Duty Cycle
q
0
%
DC
MAX
Maximum Duty Cycle
q
87
90
93
%
t
NOV
Driver Nonoverlap
Test Circuit 1, C
L
= 2000pF (Note 7)
q
40
100
ns
t
r
, t
f
Driver Rise/Fall Time
Test Circuit 1, C
L
= 2000pF (Note 7)
q
12
80
ns
Feedback Amplifier
A
VFB
FB DC Gain
q
74
85
dB
GBW
FB Gain Bandwidth
25
MHz
I
ERR
FB Sink/Source Current
q
3
10
mA
Status Outputs
V
PGOOD
PGOOD Trip Point
V
FB
Relative to Regulated V
OUT
q
10
5
2
%
V
OLPG
PGOOD Output Low Voltage
PGOOD = 1mA
q
0.03
0.1
V
I
PGOOD
PGOOD Output Leakage
q
0.1
1
A
t
PGOOD
PGOOD Delay Time
V
FB
< V
PGOOD
to PGOOD (Note 7)
100
s
V
FAULT
FAULT Trip Point
V
FB
Relative to Regulated V
OUT
q
10
15
20
%
V
OLF
FAULT Output Low Voltage
I
FAULT
= 1mA
q
0.03
0.1
V
I
FAULT
FAULT Output Current
V
FAULT
= 0V
10
A
t
FAULT
FAULT Delay Time
V
FB
> V
FAULT
to FAULT (Note 7)
25
s
4
LTC1702A
1702af
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Efficiency vs Load Current
TEMPERATURE (
C)
50
SUPPLY CURRENT (mA)
2.4
PV
CC
V
CC
25
1702A G04
1.8
1.4
25
0
50
1.2
1.0
2.6
2.2
2.0
1.6
75
100
125
BOOST1, BOOST2
TEST CIRCUIT 1
C
L
= 0pF
Transient Response
TEMPERATURE (
C)
50
2.5
NORMALIZED OSCILLATOR FREQUENCY (%)
2.0
1.0
0.5
0
2.5
1.0
0
50
75
1702A G05
1.5
1.5
2.0
0.5
25
25
100
125
V
CC
= 5V
TEMPERATURE (
C)
50
0.4
R
ON
(
)
0.5
0.7
0.8
0.9
1.4
1.1
0
50
75
1702A G06
0.6
1.2
1.3
1.0
25
25
100
125
V
PVCC
= 5V
V
BOOST
V
SW
= 5V
MOSFET Driver Supply Current
vs Gate Capacitance
Supply Current vs Temperature
Normalized Oscillator Frequency
vs Temperature
Driver R
ON
vs Temperature
RUN/SS Source Current
vs Temperature
TEMPERATURE (
C)
50
SOURCE CURRENT (
A)
4.0
4.5
5.0
25
75
1702A G07
3.5
3.0
25
0
50
100
125
2.5
2.0
V
CC
= 5V
Nonoverlap Time vs Temperature
Driver Rise/Fall vs Temperature
LOAD CURRENT (A)
0
70
EFFICIENCY (%)
80
90
100
5
10
1702A G01
15
V
IN
= 5V
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.6V
V
IN
= 5V
V
OUT
= 1.8V
I
LOAD
= 0A-10A-0A
2.2% MAX DEVIATION
1702A G02
GATE CAPACITANCE (pF)
0
25
30
35
6000
8000
1702A G03
20
15
2000
4000
10000
10
5
0
DRIVER SUPPLY CURRENT (mA)
TEST CIRCUIT 1
ONE DRIVER LOADED
MULTIPLY BY # OF ACTIVE
DRIVERS TO OBTAIN TOTAL
DRIVER SUPPLY CURRENT
TEMPERATURE (
C)
50
40
50
70
25
75
1702A G08
30
20
25
0
50
100
125
10
0
60
NONOVERLAP (ns)
TEST CIRCUIT 1
C
L
= 2000pF
BG FALLING EDGE
TG RISING EDGE
TG FALLING EDGE
BG RISING EDGE
TEMPERATURE (
C)
50
25
12
RISE/FALL TIME (ns)
12
15
0
50
75
1702A G09
11
14
13
25
100
125
TEST CIRCUIT 1
C
L
= 2000pF
20mV/
DIV
10
s/DIV
5
LTC1702A
1702af
PI
N
FU
N
CTIO
N
S
U
U
U
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 10
A 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 100
A. 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 3.5
A current source pull-up at
RUN/SS1 pin sets the turn-on time at approximately
500ms/
F.
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.
PV
CC
(Pin 1): Driver Power Supply Input. PV
CC
provides
power to the two BG
n 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 1
F
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 1
F 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 5
to
10
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
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