LTC1709-8/LTC1709-9
2-Phase, 5-Bit VID,
Current Mode, High Efficiency,
Synchronous Step-Down Switching Regulators
FEATURES
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
s
s
Single Controller Operates Two Output Stages
Antiphase Reducing Required Input Capacitance
and Power Supply Induced Noise
Two 5-Bit Desktop VID Codes:
LTC1709-8 For VRM8.4 (V
OUT
from 1.3V to 3.5V)
LTC1709-9 For VRM9.0 (V
OUT
from 1.1V to 1.85V)
Current Mode Control Ensures Best Current Sharing
True Remote Sensing Differential Amplifier
Power Good Output Indicator
OPTI-LOOP
TM
Compensation Minimizes C
OUT
Programmable Fixed Frequency: 150kHz to 300kHz
±1%
Output Voltage Accuracy
Wide V
IN
Range: 4V to 36V Operation
Adjustable Soft-Start Current Ramping
Internal Current Foldback and Short-Circuit Shutdown
Overvoltage Soft Latch Eliminates Nuisance Trips
Low Shutdown Current: 20µA
Available in 36-Lead Narrow SSOP Package
The LTC
®
1709-8/LTC1709-9 are 2-phase, VID program-
mable, synchronous step-down switching regulator con-
trollers that drive two all N-channel external power MOSFET
stages in a fixed frequency architecture. The 2-phase
controller drives its two output stages out of phase at
frequencies from 150kHz to 300kHz to minimize the RMS
ripple currents in both input and output capacitors. The 2-
phase technique effectively multiplies the fundamental
frequency by two, improving transient response while
operating each channel at an optimum frequency for
efficiency. Thermal design is also simplified.
An internal differential amplifier provides true remote
sensing of the regulated supply’s positive and negative
output terminals as required for high current applications.
The RUN/SS pin provides soft-start and optional timed,
short-circuit shutdown. Current foldback limits MOSFET
dissipation during short-circuit conditions when the
overcurrent latchoff is disabled. OPTI-LOOP compensa-
tion allows the transient response to be optimized for a
wide range of output capacitors and ESR values. The
LTC1709-8/LTC1709-9 implement two different VID
tables compliant with VRM8.4 and VRM9.0 respectively.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
Workstations
Internet Servers
Large Memory Arrays
DC Power Distribution Systems
TYPICAL APPLICATION
+
0.1µF
RUN/SS
3.3k
220pF
I
TH
SGND
PGOOD
5 VID BITS
VID0–VID4
EAIN
ATTENOUT
ATTENIN
V
DIFFOUT
V
OS –
V
OS
+
V
IN
TG1
BOOST1
SW1
S
10µF
35V
×4
1µH
0.47µF
S
LTC1709-8
BG1
PGND
SENSE1
+
SENSE1
–
TG2
BOOST2
SW2
BG2
INTV
CC
SENSE2
+
SENSE2
–
0.47µF
1µH
0.002Ω
V
OUT
1.3V TO 3.5V
40A
10µF
+
Figure 1. High Current 2-Phase Step-Down Converter
U
V
IN
5V TO 28V
0.002Ω
U
U
+
C
OUT
1000µF
4V
×2
17097 F01
1
LTC1709-8/LTC1709-9
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUNN/SS
SENSE1
+
SENSE1
–
EAIN
PLLFLTR
PLLIN
NC
I
TH
SGND
1
2
3
4
5
6
7
8
9
36 NC
35 TG1
34 SW1
33 BOOST1
32 V
IN
31 BG1
30 EXTV
CC
29 INTV
CC
28 PGND
27 BG2
26 BOOST2
25 SW2
24 TG2
23 PGOOD
22 V
BIAS
21 VID4
20 VID3
19 VID2
Input Supply Voltage (V
IN
).........................36V to – 0.3V
Topside Driver Voltages (BOOST1,2) .........42V to – 0.3V
Switch Voltage (SW1, 2) ..............................36V to – 5V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages ........................ (1.1)INTV
CC
to – 0.3V
EAIN, V
OS+
, V
OS–
, EXTV
CC
, INTV
CC
, RUN/SS,
V
BIAS
, ATTENIN, ATTENOUT, PGOOD,
VID0–VID4, Voltages ...................................7V to – 0.3V
Boosted Driver Voltage (BOOST-SW) ..........7V to – 0.3V
PLLFLTR, PLLIN, V
DIFFOUT
Voltages .... INTV
CC
to – 0.3V
I
TH
Voltage ................................................2.7V to – 0.3V
Peak Output Current <1µs(TGL1,2, BG1,2) ................ 3A
INTV
CC
RMS Output Current ................................ 50mA
Operating Ambient Temperature Range
(Note 2) ................................................ – 40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1709EG-8
LTC1709EG-9
V
DIFFOUT
10
V
OS
– 11
V
OS
+ 12
SENSE2
–
13
SENSE2
+
14
ATTENOUT 15
ATTENIN 16
VID0 17
VID1 18
G PACKAGE
36-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 90°C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
EAIN
V
SENSEMAX
I
INEAIN
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Maximum Current Sense Threshold
Feedback Current
Output Voltage Load Regulation
Main Control Loop
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
BIAS
= 5V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
I
TH
Voltage = 1.2V (Note 4)
V
SENSE –
= 5V
(Note 4)
(Note 4)
Measured in Servo Loop,
∆I
TH
Voltage: 1.2V to 0.7V
Measured in Servo Loop,
∆I
TH
Voltage: 1.2V to 2V
V
IN
= 3.6V to 30V (Note 4)
Measured at V
EAIN
V
IN
Ramping Down
I
TH
= 1.2V, Sink/Source 5µA (Note 4)
I
TH
= 1.2V, (g
m
xZ
L
; No Ext Load) (Note 4)
(Note 5)
EXTV
CC
Tied to V
OUT
, V
OUT
= 5V
V
RUN/SS
= 0V
V
RUN/SS
= 1.9V
V
RUN/SS
Rising
– 0.5
1.0
q
q
q
q
q
MIN
0.792
62
TYP
0.800
75
–5
0.1
– 0.1
0.002
MAX
0.808
88
– 50
0.5
– 0.5
0.02
0.88
4
UNITS
V
mV
nA
%
%
%/V
V
V
mmho
V/mV
µA
µA
µA
V
V
REFLNREG
V
OVL
UVLO
g
m
g
mOL
I
Q
Reference Voltage Line Regulation
Output Overvoltage Threshold
Undervoltage Lockout
Transconductance Amplifier g
m
Transconductance Amplifier Gain
Input DC Supply Current
Normal Mode
Shutdown
Soft-Start Charge Current
RUN/SS Pin ON Arming
0.84
3
0.86
3.5
3
1.5
470
20
–1.2
1.5
40
1.9
I
RUN/SS
V
RUN/SS
2
U
W
U
U
W W
W
LTC1709-8/LTC1709-9
ELECTRICAL CHARACTERISTICS
SYMBOL
V
RUN/SSLO
I
SCL
I
SDLHO
I
SENSE
DF
MAX
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
V
BIAS
R
ATTEN
ATTEN
ERR
R
PULLUP
VID
THLOW
VID
THHIGH
VID
LEAK
f
NOM
f
LOW
f
HIGH
R
PLLIN
I
PLLFLTR
PARAMETER
RUN/SS Pin Latchoff Arming
RUN/SS Discharge Current
Shutdown Latch Disable Current
Total Sense Pins Source Current
Maximum Duty Factor
Top Gate Transition Time:
Rise Time
Fall Time
Bottom Gate 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
Switchover Hysteresis
Operating Supply Voltage Range
Resistance Between ATTENIN
and ATTENOUT Pins
Resistive Divider Error
VID0–VID4 Pull-Up Resistance
VID0–VID4 Logic Threshold Low
VID0–VID4 Logic Threshold High
VID0–VID4 Leakage
Nominal Frequency
Lowest Frequency
Highest Frequency
PLLIN Input Resistance
Phase Detector Output Current
Sinking Capability
Sourcing Capability
Controller 2-Controller 1 Phase
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
V
BIAS
< VID0–VID4 < 7V
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥
2.4V
190
120
280
1.6
0.1
220
140
320
50
– 15
15
180
1
250
160
360
LTC1709-8
LTC1709-9
LTC1709-8: VID4 = 0; LTC1709-9
LTC1709-8: VID4 = 1
(Note 8)
q
q
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
BIAS
= 5V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
V
RUN/SS
Rising from 3V
Soft Short Condition V
EAIN
= 0.5V, V
RUN/SS
= 4.5V
V
EAIN
= 0.5V
Each Channel: V
SENSE1
–
, 2
– = V
SENSE1
+
, 2
+ = 0V
In Dropout
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver (Note 6)
C
LOAD
= 3300pF Each Driver (Note 6)
Tested with a Square Wave (Note 7)
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
I
CC
= 20mA, EXTV
CC
Ramping Negative
2.7
20
10
– 0.25
–0.35
40
0.4
0.25
0.25
q
MIN
0.5
– 85
98
TYP
4.1
2
1.6
– 60
99.5
30
40
30
20
90
90
180
MAX
4.5
4
5
UNITS
V
µA
µA
µA
%
90
90
90
90
ns
ns
ns
ns
ns
ns
ns
Internal V
CC
Regulator
4.8
5.0
0.2
80
4.5
4.7
0.2
5.5
5.2
1.0
160
V
%
mV
V
V
V
kΩ
kΩ
%
%
kΩ
V
V
µA
kHz
kHz
kHz
kΩ
µA
µA
Deg
VID Parameters
Oscillator and Phase-Locked Loop
R
RELPHS
3
LTC1709-8/LTC1709-9
ELECTRICAL CHARACTERISTICS
SYMBOL
V
PGL
I
PGOOD
V
PG
PARAMETER
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
PGOOD Output
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
EAIN
with Respect to Set Output Voltage
V
EAIN
Ramping Negative
V
EAIN
Ramping Positive
–6
6
0.995
0V < V
CM
< 5V
Measured at V
OS
+ Input
46
– 7.5
7.5
1
55
80
MIN
TYP
0.1
MAX
0.3
±1
– 9.5
9.5
1.005
UNITS
V
µA
%
%
V/V
dB
kΩ
Differential Amplifier/Op Amp Gain Block
A
DA
CMRR
DA
R
IN
Gain
Common Mode Rejection Ratio
Input Resistance
Note 1:
Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.
Note 2:
The LTC1709EG 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:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC1709EG: T
J
= T
A
+ (P
D
• 85°C/W)
Note 4:
The LTC1709-8/LTC1709-9 are tested in a feedback loop that
servos V
ITH
to a specified voltage and measures the resultant V
EAIN
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 7:
The minimum on-time condition corresponds to the on inductor
peak-to-peak ripple current
≥
40% I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
Note 8:
Each built-in pull-up resistor attached to the VID inputs also has a
series diode to allow input voltages higher than the VIDV
CC
supply without
damage or clamping (see the Applications Information section).
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Output Current
(Figure 12)
100
100
V
EXTVCC
= 5V
80
V
IN
= 5V
80
EFFICIENCY (%)
EFFICIENCY (%)
60
V
IN
= 8V
V
IN
= 12V
V
IN
= 20V
60
40
40
EFFICIENCY (%)
20
0
0.1
V
OUT
= 2V
V
EXTVCC
= 0V
FREQ = 200kHz
1
10
OUTPUT CURRENT (A)
100
170989 G01
4
U W
Efficiency vs Output Current
(Figure 12)
100
Efficiency vs Output Current
(Figure 12)
V
OUT
= 3.3V
V
EXTVCC
= 5V
I
OUT
= 20A
V
EXTVCC
= 0V
90
80
20
V
IN
= 12V
V
OUT
= 2V
FREQ = 200kHz
70
1
10
OUTPUT CURRENT (A)
100
170989 G02
0
0.1
5
10
V
IN
(V)
15
20
170989 G03
LTC1709-8/LTC1709-9
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode (Figure 12)
1000
ON
EXTV
CC
VOLTAGE DROP (mV)
200
250
INTV
CC
AND EXTV
CC
SWITCH VOLTAGE (V)
800
SUPPLY CURRENT (µA)
600
400
200
SHUTDOWN
0
0
5
20
15
10
25
INPUT VOLTAGE (V)
30
35
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)
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)
170989 G10
4
U W
170989 G04
170989 G07
EXTV
CC
Voltage Drop
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
150
100
50
EXTV
CC
SWITCHOVER THRESHOLD
0
0
10
30
20
CURRENT (mA)
40
50
170989 G05
4.70
– 50 – 25
50
25
75
0
TEMPERATURE (°C)
100
125
170989 G06
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
20
40
60
DUTY FACTOR (%)
80
100
170989 G08
0
50
100
0
25
75
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
170989 G09
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
90
80
76
70
60
50
40
30
20
10
0
–10
–20
–30
Current Sense Threshold
vs I
TH
Voltage
68
5
6
60
0
1
3
4
2
COMMON MODE VOLTAGE (V)
5
170989 G11
0
0.5
1
1.5
V
ITH
(V)
2
2.5
170989 G12
5
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