LTC3711
5-Bit Adjustable,
Wide Operating Range,
No R
SENSE
TM
Step-Down Controller
FEATURES
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DESCRIPTIO
5-Bit Programmable Output Voltage: 0.925V to 2V
No Sense Resistor Required
True Current Mode Control
2% to 90% Duty Cycle at 200kHz
t
ON(MIN)
< 100ns
Supports Active Voltage Positioning
Extremely Fast Transient Response
Stable with Ceramic C
OUT
Dual N-Channel MOSFET Synchronous Drive
Power Good Output Voltage Monitor
Wide V
IN
Range: 4V to 36V
±1%
0.8V Reference
Adjustable Current Limit
Adjustable Switching Frequency
Programmable Soft-Start
Output Overvoltage Protection
Optional Short-Circuit Shutdown Timer
Micropower Shutdown: I
Q
< 30µA
Available in 24-Lead Narrow SSOP Package
The LTC
®
3711 is a synchronous step-down switching
regulator controller for CPU power. An output voltage
between 0.925V and 2.000V is selected by a 5-bit code
(Intel mobile VID specification). The controller uses a
valley current control architecture to deliver very low duty
cycles without requiring a sense resistor. Operating fre-
quency is selected by an external resistor and is compen-
sated for variations in V
IN
and V
OUT
.
Discontinuous mode operation provides high efficiency
operation at light loads. A forced continuous control pin
reduces noise and RF interference and can assist second-
ary winding regulation by disabling discontinuous mode
operation when the main output is lightly loaded.
Fault protection is provided by internal foldback current
limiting, an output overvoltage comparator and optional
short-circuit shutdown timer. Soft-start capability for sup-
ply sequencing is accomplished using an external timing
capacitor. The regulator current limit level is user pro-
grammable. Wide supply range allows operation from 4V
to 36V at the input.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
APPLICATIO S
s
s
Power Supplies for Mobile Pentium
®
Processors
Notebook and Palmtop Computers, PDAs
TYPICAL APPLICATIO
R
ON
330k
PGOOD
C
SS
0.1µF
RUN/SS
C
C
500pF
R
C
20k
I
TH
SGND
I
ON
V
IN
TG
SW
BOOST
INTV
CC
VID4
VID3
5-BIT VID
VID2
VID1
VID0
V
OSENSE
PGND
BG
C
B
0.33µF
M1
IRF7811A
L1
1µH
EFFICIENCY (%)
C
IN
22µF
50V
×3
V
IN
5V TO 24V
LTC3711
D
B
CMDSH-3
M2
IRF7811A
×2
D1
UPS840
+
C
OUT
270µF
2V
×4
V
OUT
1.5V
15A
+
C
VCC
4.7µF
C
IN
: UNITED CHEMICON
THCR70EIH226ZT
C
OUT
: CORNELL DUBILIER
ESRE271M02B
L1: SUMIDA CEP125-IROMC
3711 F01a
Figure 1. High Efficiency Step-Down Converter
U
Efficiency vs Load Current
100
V
OUT
= 1.5V
EXTV
CC
= 5V
90
V
IN
= 15V
80
V
IN
= 5V
70
60
0.01
1
0.1
LOAD CURRENT (A)
10
3711 F01b
U
U
3711f
1
LTC3711
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
VID2
RUN/SS
V
ON
PGOOD
V
RNG
FCB
I
TH
SGND
I
ON
1
2
3
4
5
6
7
8
9
24 VID1
23 VID0
22 BOOST
21 TG
20 SW
19 SENSE
+
18 PGND
17 BG
16 INTV
CC
15 V
IN
14 EXTV
CC
13 VID4
Input Supply Voltage
V
IN
, I
ON
..................................................36V to – 0.3V
Boosted Topside Driver Supply Voltage
BOOST .................................................. 42V to – 0.3V
SW, SENSE
+
Voltages ................................. 36V to – 5V
EXTV
CC
, (BOOST – SW), RUN/SS,
VID0-VID4, PGOOD Voltages ..................... 7V to – 0.3V
FCB, V
ON
, V
RNG
Voltages .......... INTV
CC
+ 0.3V to – 0.3V
I
TH
, V
FB
, V
OSENSE
Voltages ....................... 2.7V to – 0.3V
TG, BG, INTV
CC
, EXTV
CC
Peak Currents .................... 2A
TG, BG, INTV
CC
, EXTV
CC
RMS Currents .............. 50mA
Operating Ambient Temperature Range
LTC3711EGN (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
LTC3711EGN
V
FB
10
V
OSENSE
11
VID3 12
GN PACKAGE
24-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
PARAMETER
Input DC Supply Current
Normal
Shutdown Supply Current
Feedback Reference Voltage
Feedback Voltage Line Regulation
Feedback Voltage Load Regulation
Feedback Input Current
Error Amplifier Transconductance
Forced Continuous Threshold
Forced Continuous Pin Current
On-Time
Minimum On-Time
Minimum Off-Time
Maximum Current Sense Threshold
V
PGND
– V
SENSE+
Minimum Current Sense Threshold
V
PGND
– V
SENSE+
Output Overvoltage Fault Threshold
Output Undervoltage Fault Threshold
Main Control Loop
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
900
15
I
TH
= 1.2V (Note 4)
V
IN
= 4V to 30V, I
TH
= 1.2V (Note 4)
I
TH
= 0.5V to 1.9V (Note 4)
V
FB
= 0.8V
I
TH
= 1.2V (Note 4)
V
FCB
= 0.8V
I
ON
= 60µA, V
ON
= 1.5V
I
ON
= 30µA, V
ON
= 1.5V
I
ON
= 180µA, V
ON
= 0V
I
ON
= 60µA, V
ON
= 1.5V
V
RNG
= 1V, V
FB
= 0.76V
V
RNG
= 0V, V
FB
= 0.76V
V
RNG
= INTV
CC
, V
FB
= 0.76V
V
RNG
= 1V, V
FB
= 0.84V
V
RNG
= 0V, V
FB
= 0.84V
V
RNG
= INTV
CC
, V
FB
= 0.84V
5.5
520
q
q
q
q
q
2000
30
0.808
– 0.3
±50
2
0.84
–2
288
575
100
400
153
107
214
V
FB
∆V
FB(LINEREG)
∆V
FB(LOADREG)
I
FB
g
m(EA)
V
FCB
I
FCB
t
ON
t
ON(MIN)
t
OFF(MIN)
V
SENSE(MAX)
0.792
0.800
0.002
– 0.05
–5
1.4
0.76
212
425
1.7
0.8
–1
250
500
50
250
113
79
158
133
93
186
– 67
– 47
– 93
7.5
600
V
SENSE(MIN)
∆V
FB(OV)
V
FB(UV)
9.5
680
2
U
µA
µA
V
%/V
%
nA
mS
V
µA
ns
ns
ns
ns
mV
mV
mV
mV
mV
mV
%
mV
3711f
W
U
U
W W
W
LTC3711
ELECTRICAL CHARACTERISTICS
SYMBOL
V
RUN/SS(ON)
V
RUN/SS(LE)
V
RUN/SS(LT)
I
RUN/SS(C)
I
RUN/SS(D)
V
IN(UVLO)
V
IN(UVLOR)
TG R
UP
TG R
DOWN
BG R
UP
BG R
DOWN
TG t
r
TG t
f
BG t
r
BG t
f
V
INTVCC
∆V
LDO(LOADREG)
V
EXTVCC
∆V
EXTVCC
∆V
EXTVCC(HYS)
PGOOD Output
∆V
FBH
∆V
FBL
∆V
FB(HYS)
V
PGL
VID DAC
V
VID(T)
I
VID(PULLUP)
V
VID(PULLUP)
I
VID(LEAK)
R
VID
∆V
OSENSE
VID0-VID4 Logic Threshold Voltage
VID0-VID4 Pull-Up Current
VID0-VID4 Pull-Up Voltage
VID0-VID4 Leakage Current
Resistance from V
OSENSE
to V
FB
DAC Output Accuracy
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Low Voltage
PARAMETER
RUN Pin Start Threshold
RUN Pin Latchoff Enable Threshold
RUN Pin Latchoff Threshold
Soft-Start Charge Current
Soft-Start Discharge Current
Undervoltage Lockout
Undervoltage Lockout Release
TG Driver Pull-Up On Resistance
TG Driver Pull-Down On Resistance
BG Driver Pull-Up On Resistance
BG Driver Pull-Down On Resistance
TG Rise Time
TG Fall Time
BG Rise Time
BG Fall Time
Internal V
CC
Voltage
Internal V
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Switch Drop Voltage
EXTV
CC
Switchover Hysteresis
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V unless otherwise noted.
CONDITIONS
q
MIN
0.8
TYP
1.5
4
3.5
MAX
2
4.5
4.2
–3
3
3.9
4
3
3
4
2
UNITS
V
V
V
µA
µA
V
V
Ω
Ω
Ω
Ω
ns
ns
ns
ns
RUN/SS Pin Rising
RUN/SS Pin Falling
V
RUN/SS
= 0V
V
RUN/SS
= 4.5V, V
FB
= 0V
V
IN
Falling
V
IN
Rising
TG High
TG Low
BG High
BG Low
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
CC
= 0mA to 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
Rising
I
CC
= 20mA, V
EXTVCC
= 5V
q
q
q
q
– 0.5
0.8
– 1.2
1.8
3.4
3.5
2
2
3
1
20
20
20
20
Internal V
CC
Regulator
4.7
4.5
5
– 0.1
4.7
150
200
V
FB
Rising
V
FB
Falling
V
FB
Returning
I
PGOOD
= 5mA
0.4
V
VID0
to V
VID4
= 0V
V
VID0
to V
VID4
Open
V
VID0
to V
VID4
= 5V, V
RUN/SS
= 0V
6
V
OSENSE
Programmed from
0.925V to 2V (Note 5)
– 0.25
5.5
– 5.5
7.5
– 7.5
1
0.15
1.2
– 2.5
4.5
0.01
10
0
1
14
0.25
9.5
– 9.5
2
0.4
2
300
5.3
±2
V
%
V
mV
mV
%
%
%
V
V
µA
V
µA
KΩ
%
Note 1:
Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2:
The LTC3711E 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
as follows:
LTC3711EGN: T
J
= T
A
+ (P
D
• 130°C/W)
Note 4:
The LTC3711 is tested in a feedback loop that adjusts V
FB
to achieve
a specified error amplifier output voltage (I
TH
).
Note 5:
The LTC3711 VID DAC is tested in a feedback loop that adjusts
V
OSENSE
to achieve a specified feedback voltage (V
FB
= 0.8V) for each DAC VID
code.
3711f
3
LTC3711
TYPICAL PERFOR A CE CHARACTERISTICS
Transient Response
V
OUT
50mV/DIV
V
OUT
50mV/DIV
I
L
10A/DIV
20µs/DIV
LOAD STEP = 0A TO 15A
V
IN
= 15V
V
OUT
= 1.5V
FCB = 0V
FIGURE 9 CIRCUIT
Efficiency vs Load Current
100
DISCONTINUOUS
MODE
100
95
90
EFFICIENCY (%)
EFFICIENCY (%)
90
I
LOAD
= 1.5A
85
I
LOAD
= 15A
80
75
70
80
FREQUENCY (kHz)
70
CONTINUOUS
MODE
V
IN
= 15V
V
OUT
= 1.5V
EXTV
CC
= 5V
FIGURE 9 CIRCUIT
0.1
1
0.01
LOAD CURRENT (A)
10
3711 G04
60
50
0.001
Frequency vs Input Voltage
350
325
FIGURE 9 CIRCUIT
FCB = 0V
2.0
I
OUT
= 15A
2.5
CURRENT SENSE THRESHOLD (mV)
FREQUENCY (kHz)
I
TH
VOLTAGE (V)
300
275
I
OUT
= 0A
250
225
200
5
10
15
20
INPUT VOLTAGE (V)
4
U W
3711 G07
Transient Response
(Discontinuous Mode)
Start-Up
RUN/SS
2V/DIV
V
OUT
1V/DIV
I
L
10A/DIV
I
L
10A/DIV
3711 G01
20µs/DIV
LOAD STEP = 1A TO 15A
V
IN
= 15V
V
OUT
= 1.5V
FCB = INTV
CC
FIGURE 9 CIRCUIT
3711 G02
50ms/DIV
V
IN
= 15V
V
OUT
= 1.5V
R
LOAD
= 0.1Ω
FIGURE 9 CIRCUIT
3711 G03
Efficiency vs Input Voltage
FIGURE 9 CIRCUIT
FCB = 5V
EXTV
CC
= 5V
350
300
250
200
Frequency vs Load Current
CONTINUOUS MODE
DISCONTINUOUS MODE
150
100
50
FIGURE 9 CIRCUIT
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
3711 G05
0
2
4
6
LOAD CURRENT (A)
8
10
3711 G06
I
TH
Voltage vs Load Current
300
FIGURE 9 CIRCUIT
FCB = 0V
Current Sense Threshold
vs I
TH
Voltage
V
RNG
=
2V
1.4V
1V
100
0.7V
0.5V
200
1.5
1.0
0
0.5
–100
25
0
0
5
10
15
LOAD CURRENT (A)
20
25
3711 G09
–200
0
0.5
1.0
1.5
2.0
I
TH
VOLTAGE (V)
2.5
3.0
3711 G10
3711f
LTC3711
TYPICAL PERFOR A CE CHARACTERISTICS
On-Time vs I
ON
Current
10k
V
VON
= 0V
1000
ON-TIME (ns)
1k
ON-TIME (ns)
600
ON-TIME (ns)
100
10
1
10
I
ON
CURRENT (µA)
100
3711 G11
Current Limit Foldback
MAXIMUM CURRENT SENSE THRESHOLD (mV)
MAXIMUM CURRENT SENSE THRESHOLD (mV)
MAXIMUM CURRENT SENSE THRESHOLD (mV)
150
125
100
75
50
25
0
V
RNG
= 1V
0
0.2
0.4
V
FB
(V)
0.6
Maximum Current Sense
Threshold vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
150
V
RNG
= 1V
140
FEEDBACK REFERENCE VOLTAGE (V)
130
120
110
100
–50
–25
50
25
0
75
TEMPERATURE (°C)
U W
3711 G14
On-Time vs V
ON
Voltage
I
ION
= 30µA
300
250
200
150
100
On-Time vs Temperature
I
ION
= 30µA
V
VON
= 0V
800
400
200
50
0
–50 –25
0
0
2
1
V
ON
VOLTAGE (V)
3
3711 G12
50
25
75
0
TEMPERATURE (°C)
100
125
3711 G13
Maximum Current Sense
Threshold vs V
RNG
Voltage
300
250
200
150
100
50
0
150
125
100
75
50
25
0
Maximum Current Sense
Threshold vs RUN/SS Voltage
V
RNG
= 1V
0.8
0.5
0.75
1.0
1.25
1.5
V
RNG
VOLTAGE (V)
1.75
2.0
1.5
2
2.5
3
RUN/SS VOLTAGE (V)
3.5
3711 G16
3711 G15
Feedback Reference Voltage
vs Temperature
0.82
0.81
0.80
0.79
100
125
0.78
–50 –25
75
0
25
50
TEMPERATURE (°C)
100
125
3711 G17
3711 G18
3711f
5
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