LTC1628-SYNC
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulator
FEATURES
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DESCRIPTIO
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
OPTI-LOOP
®
Compensation Minimizes C
OUT
Dual N-Channel MOSFET Synchronous Drive
±1%
Output Voltage Accuracy
Power Good Output Voltage Monitor
Phase-Lockable Fixed Frequency 150kHz to 300kHz
Wide V
IN
Range: 3.5V to 36V Operation
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Soft-Start Current Ramping
Foldback Output Current Limiting
Latched Short-Circuit Shutdown with Defeat Option
Output Overvoltage Protection
Remote Output Voltage Sense
Low Shutdown I
Q
: 20µA
5V and 3.3V Standby Regulators
Selectable Constant Frequency or Burst Mode
®
Operation
Small 28-Lead SSOP Package
The LTC
®
1628-SYNC is a high performance dual step-
down switching regulator controller that drives all
N-channel synchronous power MOSFET stages. A con-
stant frequency current mode architecture allows phase-
lockable frequency of up to 300kHz. Power loss and noise
due to the ESR of the input capacitors are minimized by
operating the two controller output stages out of phase.
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance and
ESR values. The precision 0.8V reference and power good
output indicator are compatible with future microproces-
sor generations, and a wide 3.5V to 30V (36V maximum)
input supply range encompasses all battery chemistries.
A RUN/SS pin for each controller provides both soft-start
and optional timed, short-circuit shutdown. Current
foldback limits MOSFET dissipation during short-circuit
conditions when overcurrent latchoff is disabled. Output
overvoltage protection circuitry latches on the bottom
MOSFET until V
OUT
returns to normal. The FCB mode pin
can select among Burst Mode, constant frequency mode
and continuous inductor current mode or regulate a
secondary winding.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 5929620, 6177787, 6144194, 6100678, 5408150, 6580258, 6304066,
5705919.
APPLICATIO S
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Notebook and Palmtop Computers, PDAs
Telecom Systems
Battery-Operated Digital Devices
DC Power Distribution Systems
TYPICAL APPLICATIO
L1
6.3µH
+
4.7µF
M1
C
B1
, 0.1µF
D1
M2
f
IN
R
SENSE1
0.01Ω
V
OUT1
5V
5A
D3
V
IN
PGOOD INTV
CC
TG1
BOOST1
SW1
BG1
LTC1628-SYNC
TG2
BOOST2
SW2
BG2
PGND
SENSE2
+
1000pF
SENSE1
–
V
OSENSE1
R2
105k
1%
SENSE2
–
V
OSENSE2
I
TH2
C
SS2
0.1µF
C
C2
220pF
R
C2
15k
D4
1µF
CERAMIC
M3
C
B2
, 0.1µF
PLLIN
SENSE1
+
1000pF
+
C
OUT1
47µF
6V
SP
R1
20k
1%
C
C1
220pF
R
C1
15k
I
TH1
C
SS1
0.1µF
RUN/SS1 SGND RUN/SS2
M1, M2, M3, M4: FDS6680A
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
U
V
IN
5.2V TO 28V
C
IN
22µF
50V
CERAMIC
L2
6.3µH
M4
D2
R
SENSE2
0.01Ω
V
OUT2
3.3V
5A
C
OUT
56µF
6V
SP
R3
20k
1%
R4
63.4k
1%
U
U
+
1628 F01
1628syncfa
1
LTC1628-SYNC
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS1
SENSE1
+
SENSE1
–
V
OSENSE1
PLLFLTR
PLLIN
FCB
I
TH1
SGND
1
2
3
4
5
6
7
8
9
28 PGOOD
27 TG1
26 SW1
25 BOOST1
24 V
IN
23 BG1
22 EXTV
CC
21 INTV
CC
20 PGND
19 BG2
18 BOOST2
17 SW2
16 TG2
15 RUN/SS2
Input Supply Voltage (V
IN
).........................36V to – 0.3V
Top Side Driver Voltages
(BOOST1, BOOST2) ...................................42V to – 0.3V
Switch Voltage (SW1, SW2) .........................36V to – 5V
INTV
CC,
EXTV
CC
, RUN/SS1, RUN/SS2, (BOOST1-SW1),
(BOOST2-SW2), PGOOD .............................7V to – 0.3V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages ........................ (1.1)INTV
CC
to – 0.3V
PLLIN, PLLFLTR, FCB, Voltage ............ INTV
CC
to – 0.3V
I
TH1,
I
TH2
, V
OSENSE1
, V
OSENSE2
Voltages ...2.7V to – 0.3V
Peak Output Current <10µs (TG1, TG2, BG1, BG2) ... 3A
INTV
CC
Peak Output Current ................................ 50mA
Operating Temperature Range
LTC1628CG-SYNC ................................... 0°C to 85°C
LTC1628IG-SYNC ............................... – 40°C to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
3.3V
OUT
10
I
TH2
11
V
OSENSE2
12
SENSE2
–
SENSE2
+
13
14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W
*PGOOD ON THE LTC1628-SYNC
ORDER PART NUMBER
LTC1628CG-SYNC
LTC1628IG-SYNC
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.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS1, 2
= 5V unless otherwise noted.
SYMBOL
V
OSENSE1, 2
I
VOSENSE1, 2
V
REFLNREG
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
CONDITIONS
(Note 3); I
TH1, 2
Voltage = 1.2V
(Note 3)
V
IN
= 3.6V to 30V (Note 3)
(Note 3)
Measured in Servo Loop;
∆I
TH
Voltage = 1.2V to 0.7V
Measured in Servo Loop;
∆I
TH
Voltage = 1.2V to 2.0V
I
TH1, 2
= 1.2V; Sink/Source 5uA; (Note 3)
I
TH1, 2
= 1.2V; (Note 3)
(Note 4)
V
IN
= 15V; EXTV
CC
Tied to V
OUT1
; V
OUT1
= 5V
V
RUN/SS1, 2
= 0V, V
STBYMD
= Open;
●
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
0.792
TYP
0.800
–5
0.002
0.1
– 0.1
1.3
3
350
20
MAX
0.808
– 50
0.02
0.5
– 0.5
UNITS
V
nA
%/V
%
%
mmho
MHz
µA
µA
V
µA
V
Main Control Loops
g
m1, 2
g
mGBW1, 2
I
Q
Transconductance Amplifier g
m
Transconductance Amplifier GBW
Input DC Supply Current
Normal Mode
Shutdown
Forced Continuous Threshold
Forced Continuous Pin Current
Burst Inhibit (Constant Frequency)
Threshold
35
0.84
– 0.1
4.8
V
FCB
I
FCB
V
BINHIBIT
0.76
– 0.30
0.800
– 0.18
4.3
V
FCB
= 0.85V
Measured at FCB Pin
1628syncfa
2
U
W
U
U
W W
W
LTC1628-SYNC
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS1, 2
= 5V unless otherwise noted.
SYMBOL
UVLO
V
OVL
I
SENSE
DF
MAX
I
RUN/SS1, 2
PARAMETER
Undervoltage Lockout
Feedback Overvoltage Lockout
Sense Pins Total Source Current
Maximum Duty Factor
Soft-Start Charge Current
CONDITIONS
V
IN
Ramping Down
Measured at V
OSENSE1, 2
(Each Channel); V
SENSE1
–
, 2
– = V
SENSE1
+
, 2
+ = 0V
In Dropout
V
RUN/SS1, 2
= 1.9V
V
RUN/SS1,
V
RUN/SS2
Rising
V
RUN/SS1,
V
RUN/SS2
Rising from 3V
Soft Short Condition V
OSENSE1, 2
= 0.5V;
V
RUN/SS1, 2
= 4.5V
V
OSENSE1, 2
= 0.5V
V
OSENSE1, 2
= 0.7V,V
SENSE1–, 2
–
= 5V
V
OSENSE1, 2
= 0.7V,V
SENSE1–, 2
–
= 5V
(Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
Tested with a Square Wave (Note 6)
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
CC
= 0 to 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
= 5V
I
CC
= 20mA, EXTV
CC
Ramping Positive
●
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
0.84
– 85
98
0.5
1.0
TYP
3.5
0.86
– 60
99.4
1.2
1.5
4.1
MAX
4
0.88
UNITS
V
V
µA
%
µA
V
RUN/SS1, 2
ON RUN/SS Pin ON Threshold
V
RUN/SS1, 2
LT RUN/SS Pin Latchoff Arming
Threshold
I
SCL1, 2
I
SDLHO
V
SENSE(MAX)
RUN/SS Discharge Current
Shutdown Latch Disable Current
Maximum Current Sense Threshold
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Voltage Drop
EXTV
CC
Switchover Voltage
EXTV
CC
Hysteresis
Nominal Frequency
Lowest Frequency
Highest Frequency
PLLIN Input Resistance
Phase Detector Output Current
Sinking Capability
Sourcing Capability
3.3V Regulator Output Voltage
3.3V Regulator Load Regulation
3.3V Regulator Line Regulation
Leakage Current of 3.3V Regulator
in Shutdown
1.9
4.5
4
5
85
88
90
90
90
80
V
V
µA
µA
mV
mV
ns
ns
ns
ns
ns
ns
ns
0.5
2
1.6
65
62
75
75
50
50
40
40
90
90
180
TG1, 2 t
r
TG1, 2 t
f
BG1, 2 t
r
BG1, 2 t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCC
V
LDO
INT
V
LDO
EXT
V
EXTVCC
V
LDOHYS
f
NOM
f
LOW
f
HIGH
R
PLLIN
I
PLLFLTR
INTV
CC
Linear Regulator
4.8
5.0
0.2
80
4.5
4.7
0.2
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥
2.4V
190
120
280
220
140
310
50
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
No Load
I
3.3
= 0 to 10mA
6V < V
IN
< 30V
V
RUN/SS1, 2
= 0V, V
IN
= 30V
●
●
5.2
1.0
160
V
%
mV
V
V
Oscillator and Phase-Locked Loop
250
160
360
kHz
kHz
kHz
kΩ
µA
µA
3.45
2
0.2
50
V
%
%
µA
–15
15
3.25
3.35
0.5
0.05
10
3.3V Linear Regulator
V
3.3OUT
V
3.3IL
V
3.3VL
I
3.3LEAK
1628syncfa
3
LTC1628-SYNC
ELECTRICAL CHARACTERISTICS
SYMBOL
PGOOD Output
V
PGL
I
PGOOD
V
PG
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
OSENSE
with Respect to Set Output Voltage
V
OSENSE
Ramping Negative
V
OSENSE
Ramping Positive
–6
6
–7.5
7.5
0.1
0.3
±1
– 9.5
9.5
V
µA
%
%
PARAMETER
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS1, 2
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1628-SYNC: T
J
= T
A
+ (P
D
• 95
°C/W)
Note 3:
The LTC1628-SYNC is tested in a feedback loop that servos
V
ITH1,2
to a specified voltage and measures the resultant V
OSENSE1, 2.
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 5:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 6:
The minimum on-time condition is specified for an inductor
peak-to-peak ripple current
≥
40% of I
MAX
(see minimum on-time
considerations in the Applications Information section).
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Output Current
and Mode (Figure 14)
100
90
80
EFFICIENCY (%)
Burst Mode
OPERATION
60
50
40
30
20
10
0
0.001
EFFICIENCY (%)
EFFICIENCY (%)
70
FORCED
CONTINUOUS
MODE
CONSTANT
FREQUENCY
(BURST DISABLE)
V
IN
= 15V
V
OUT
= 5V
0.1
0.01
1
OUTPUT CURRENT (A)
10
1628 G01
Supply Current vs Input Voltage
and Mode (Figure 14)
1000
INTV
CC
AND EXTV
CC
SWITCH VOLTAGE (V)
EXTV
CC
VOLTAGE DROP (mV)
800
SUPPLY CURRENT (µA)
600
BOTH
CONTROLLERS ON
400
200
STANDBY
SHUTDOWN
0
0
5
20
15
10
25
INPUT VOLTAGE (V)
30
35
4
U W
1628 G04
Efficiency vs Output Current
(Figure 14)
100
V
IN
= 7V
90
V
IN
= 10V
V
IN
= 15V
V
IN
= 20V
70
Efficiency vs Input Voltage
(Figure 14)
100
V
OUT
= 5V
I
OUT
= 3A
90
80
80
70
60
V
OUT
= 5V
0.1
0.01
1
OUTPUT CURRENT (A)
10
1628 G02
60
50
0.001
50
5
25
15
INPUT VOLTAGE (V)
35
1628 G03
EXTV
CC
Voltage Drop
250
5.05
5.00
4.95
4.90
4.85
4.80
4.75
INTV
CC
and EXTV
CC
Switch
Voltage vs Temperature
INTV
CC
VOLTAGE
200
150
100
50
EXTV
CC
SWITCHOVER THRESHOLD
0
0
10
30
20
CURRENT (mA)
40
50
1628 G05
4.70
– 50 – 25
50
25
75
0
TEMPERATURE (°C)
100
125
1628 G06
1628syncfa
LTC1628-SYNC
TYPICAL PERFOR A CE CHARACTERISTICS
Internal 5V LDO Line Regulation
5.1
5.0
I
LOAD
= 1mA
INTV
CC
VOLTAGE (V)
4.9
4.8
4.7
4.6
4.5
4.4
0
5
20
15
25
10
INPUT VOLTAGE (V)
30
35
V
SENSE
(mV)
V
SENSE
(mV)
0
20
40
60
DUTY FACTOR (%)
80
100
1628 G08
Maximum Current Sense Threshold
vs V
RUN/SS
(Soft-Start)
80
V
SENSE(CM)
= 1.6V
80
60
V
SENSE
(mV)
V
SENSE
(mV)
72
V
SENSE
(mV)
40
20
64
0
0
1
2
3
V
RUN/SS
(V)
1628 G10
4
Load Regulation
0.0
FCB = 0V
V
IN
= 15V
FIGURE 1
2.5
NORMALIZED V
OUT
(%)
–0.1
–0.2
V
ITH
(V)
1.5
I
SENSE
(µA)
–0.3
0.5
–0.4
0
1
3
2
LOAD CURRENT (A)
U W
1628 G07
Maximum Current Sense Threshold
vs Duty Factor
75
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
80
70
60
50
50
40
30
20
10
25
0
0
50
0
100
25
75
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
1628 G09
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
90
80
76
70
60
50
40
30
20
10
0
–10
–20
60
–30
Current Sense Threshold
vs I
TH
Voltage
68
5
6
0
1
3
4
2
COMMON MODE VOLTAGE (V)
5
1628 G11
0
0.5
1
1.5
V
ITH
(V)
2
2.5
1628 G12
V
ITH
vs V
RUN/SS
V
OSENSE
= 0.7V
100
SENSE Pins Total Source Current
2.0
50
0
1.0
–50
4
5
1628 G13
0
0
1
2
3
V
RUN/SS
(V)
4
5
6
1628 G14
–100
0
2
4
6
1628 G15
V
SENSE
COMMON MODE VOLTAGE (V)
1628syncfa
5
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