3711f.pm6
1
LTC3711
3711f
5-Bit Adjustable,
Wide Operating Range,
No R
SENSE
TM
Step-Down Controller
s
5-Bit Programmable Output Voltage: 0.925V to 2V
s
No Sense Resistor Required
s
True Current Mode Control
s
2% to 90% Duty Cycle at 200kHz
s
t
ON(MIN)
< 100ns
s
Supports Active Voltage Positioning
s
Extremely Fast Transient Response
s
Stable with Ceramic C
OUT
s
Dual N-Channel MOSFET Synchronous Drive
s
Power Good Output Voltage Monitor
s
Wide V
IN
Range: 4V to 36V
s
1% 0.8V Reference
s
Adjustable Current Limit
s
Adjustable Switching Frequency
s
Programmable Soft-Start
s
Output Overvoltage Protection
s
Optional Short-Circuit Shutdown Timer
s
Micropower Shutdown: I
Q
< 30
A
s
Available in 24-Lead Narrow SSOP Package
s
Power Supplies for Mobile Pentium
Processors
s
Notebook and Palmtop Computers, PDAs
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.
+
D
B
CMDSH-3
D1
UPS840
C
IN
: UNITED CHEMICON
THCR70EIH226ZT
C
OUT
: CORNELL DUBILIER
ESRE271M02B
L1: SUMIDA CEP125-IROMC
L1
1
H
C
VCC
4.7
F
C
IN
22
F
50V
3
V
IN
5V TO 24V
V
OUT
1.5V
15A
+
C
OUT
270
F
2V
4
M2
IRF7811A
2
3711 F01a
M1
IRF7811A
R
ON
330k
C
SS
0.1
F
I
ON
PGOOD
V
IN
TG
SW
BOOST
RUN/SS
I
TH
SGND
INTV
CC
BG
PGND
5-BIT VID
V
OSENSE
VID0
VID1
VID2
VID3
VID4
C
B
0.33
F
R
C
20k
LTC3711
C
C
500pF
Figure 1. High Efficiency Step-Down Converter
LOAD CURRENT (A)
0.01
EFFICIENCY (%)
80
90
3711 F01b
70
60
0.1
1
10
100
V
OUT
= 1.5V
EXTV
CC
= 5V
V
IN
= 5V
V
IN
= 15V
Efficiency vs Load Current
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
2
LTC3711
3711f
(Note 1)
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
T
JMAX
= 125
C,
JA
= 130
C/ W
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.
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
1
2
3
4
5
6
7
8
9
10
11
12
TOP VIEW
GN PACKAGE
24-LEAD PLASTIC SSOP
24
23
22
21
20
19
18
17
16
15
14
13
VID2
RUN/SS
V
ON
PGOOD
V
RNG
FCB
I
TH
SGND
I
ON
V
FB
V
OSENSE
VID3
VID1
VID0
BOOST
TG
SW
SENSE
+
PGND
BG
INTV
CC
V
IN
EXTV
CC
VID4
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Main Control Loop
I
Q
Input DC Supply Current
Normal
900
2000
A
Shutdown Supply Current
15
30
A
V
FB
Feedback Reference Voltage
I
TH
= 1.2V (Note 4)
q
0.792
0.800
0.808
V
V
FB(LINEREG)
Feedback Voltage Line Regulation
V
IN
= 4V to 30V, I
TH
= 1.2V (Note 4)
0.002
%/V
V
FB(LOADREG)
Feedback Voltage Load Regulation
I
TH
= 0.5V to 1.9V (Note 4)
q
0.05
0.3
%
I
FB
Feedback Input Current
V
FB
= 0.8V
5
50
nA
g
m(EA)
Error Amplifier Transconductance
I
TH
= 1.2V (Note 4)
q
1.4
1.7
2
mS
V
FCB
Forced Continuous Threshold
q
0.76
0.8
0.84
V
I
FCB
Forced Continuous Pin Current
V
FCB
= 0.8V
1
2
A
t
ON
On-Time
I
ON
= 60
A, V
ON
= 1.5V
212
250
288
ns
I
ON
= 30
A, V
ON
= 1.5V
425
500
575
ns
t
ON(MIN)
Minimum On-Time
I
ON
= 180
A, V
ON
= 0V
50
100
ns
t
OFF(MIN)
Minimum Off-Time
I
ON
= 60
A, V
ON
= 1.5V
250
400
ns
V
SENSE(MAX)
Maximum Current Sense Threshold
V
RNG
= 1V, V
FB
= 0.76V
113
133
153
mV
V
PGND
V
SENSE
+
V
RNG
= 0V, V
FB
= 0.76V
q
79
93
107
mV
V
RNG
= INTV
CC
, V
FB
= 0.76V
158
186
214
mV
V
SENSE(MIN)
Minimum Current Sense Threshold
V
RNG
= 1V, V
FB
= 0.84V
67
mV
V
PGND
V
SENSE
+
V
RNG
= 0V, V
FB
= 0.84V
47
mV
V
RNG
= INTV
CC
, V
FB
= 0.84V
93
mV
V
FB(OV)
Output Overvoltage Fault Threshold
5.5
7.5
9.5
%
V
FB(UV)
Output Undervoltage Fault Threshold
520
600
680
mV
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LTC3711
3711f
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.
ELECTRICAL CHARACTERISTICS
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.
V
RUN/SS(ON)
RUN Pin Start Threshold
q
0.8
1.5
2
V
V
RUN/SS(LE)
RUN Pin Latchoff Enable Threshold
RUN/SS Pin Rising
4
4.5
V
V
RUN/SS(LT)
RUN Pin Latchoff Threshold
RUN/SS Pin Falling
3.5
4.2
V
I
RUN/SS(C)
Soft-Start Charge Current
V
RUN/SS
= 0V
0.5
1.2
3
A
I
RUN/SS(D)
Soft-Start Discharge Current
V
RUN/SS
= 4.5V, V
FB
= 0V
0.8
1.8
3
A
V
IN(UVLO)
Undervoltage Lockout
V
IN
Falling
q
3.4
3.9
V
V
IN(UVLOR)
Undervoltage Lockout Release
V
IN
Rising
q
3.5
4
V
TG R
UP
TG Driver Pull-Up On Resistance
TG High
2
3
TG R
DOWN
TG Driver Pull-Down On Resistance
TG Low
2
3
BG R
UP
BG Driver Pull-Up On Resistance
BG High
3
4
BG R
DOWN
BG Driver Pull-Down On Resistance
BG Low
1
2
TG t
r
TG Rise Time
C
LOAD
= 3300pF
20
ns
TG t
f
TG Fall Time
C
LOAD
= 3300pF
20
ns
BG t
r
BG Rise Time
C
LOAD
= 3300pF
20
ns
BG t
f
BG Fall Time
C
LOAD
= 3300pF
20
ns
Internal V
CC
Regulator
V
INTVCC
Internal V
CC
Voltage
6V < V
IN
< 30V, V
EXTVCC
= 4V
q
4.7
5
5.3
V
V
LDO(LOADREG)
Internal V
CC
Load Regulation
I
CC
= 0mA to 20mA, V
EXTVCC
= 4V
0.1
2
%
V
EXTVCC
EXTV
CC
Switchover Voltage
I
CC
= 20mA, V
EXTVCC
Rising
q
4.5
4.7
V
V
EXTVCC
EXTV
CC
Switch Drop Voltage
I
CC
= 20mA, V
EXTVCC
= 5V
150
300
mV
V
EXTVCC(HYS)
EXTV
CC
Switchover Hysteresis
200
mV
PGOOD Output
V
FBH
PGOOD Upper Threshold
V
FB
Rising
5.5
7.5
9.5
%
V
FBL
PGOOD Lower Threshold
V
FB
Falling
5.5
7.5
9.5
%
V
FB(HYS)
PGOOD Hysteresis
V
FB
Returning
1
2
%
V
PGL
PGOOD Low Voltage
I
PGOOD
= 5mA
0.15
0.4
V
VID DAC
V
VID(T)
VID0-VID4 Logic Threshold Voltage
0.4
1.2
2
V
I
VID(PULLUP)
VID0-VID4 Pull-Up Current
V
VID0
to V
VID4
= 0V
2.5
A
V
VID(PULLUP)
VID0-VID4 Pull-Up Voltage
V
VID0
to V
VID4
Open
4.5
V
I
VID(LEAK)
VID0-VID4 Leakage Current
V
VID0
to V
VID4
= 5V, V
RUN/SS
= 0V
0.01
1
A
R
VID
Resistance from V
OSENSE
to V
FB
6
10
14
K
V
OSENSE
DAC Output Accuracy
V
OSENSE
Programmed from
0.25
0
0.25
%
0.925V to 2V (Note 5)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
4
LTC3711
3711f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Transient Response
V
OUT
50mV/DIV
I
L
10A/DIV
20
s/DIV
3711 G01
LOAD STEP = 0A TO 15A
V
IN
= 15V
V
OUT
= 1.5V
FCB = 0V
FIGURE 9 CIRCUIT
Transient Response
(Discontinuous Mode)
20
s/DIV
3711 G02
LOAD STEP = 1A TO 15A
V
IN
= 15V
V
OUT
= 1.5V
FCB = INTV
CC
FIGURE 9 CIRCUIT
V
OUT
50mV/DIV
I
L
10A/DIV
50ms/DIV
3711 G03
V
IN
= 15V
V
OUT
= 1.5V
R
LOAD
= 0.1
FIGURE 9 CIRCUIT
V
OUT
1V/DIV
I
L
10A/DIV
RUN/SS
2V/DIV
LOAD CURRENT (A)
0.001
EFFICIENCY (%)
10
3711 G04
0.01
0.1
1
100
90
80
70
60
50
DISCONTINUOUS
MODE
CONTINUOUS
MODE
V
IN
= 15V
V
OUT
= 1.5V
EXTV
CC
= 5V
FIGURE 9 CIRCUIT
INPUT VOLTAGE (V)
0
EFFICIENCY (%)
3711 G05
100
95
90
85
80
75
70
5
10
15
20
25
30
I
LOAD
= 15A
I
LOAD
= 1.5A
FIGURE 9 CIRCUIT
FCB = 5V
EXTV
CC
= 5V
INPUT VOLTAGE (V)
5
FREQUENCY (kHz)
3711 G07
350
325
300
275
250
225
200
10
15
20
25
I
OUT
= 0A
I
OUT
= 15A
FIGURE 9 CIRCUIT
FCB = 0V
LOAD CURRENT (A)
0
I
TH
VOLTAGE (V)
3711 G09
2.5
2.0
1.5
1.0
0.5
0
5
10
15
20
25
FIGURE 9 CIRCUIT
FCB = 0V
Start-Up
Efficiency vs Load Current
Efficiency vs Input Voltage
Frequency vs Load Current
Frequency vs Input Voltage
I
TH
Voltage vs Load Current
LOAD CURRENT (A)
0
FREQUENCY (kHz)
3711 G06
350
300
250
200
150
100
50
0
2
4
6
8
10
DISCONTINUOUS MODE
CONTINUOUS MODE
FIGURE 9 CIRCUIT
Current Sense Threshold
vs I
TH
Voltage
I
TH
VOLTAGE (V)
0
200
CURRENT SENSE THRESHOLD (mV)
100
0
100
200
300
0.5
1.0
1.5
2.0
3711 G10
2.5
3.0
V
RNG
=
1V
0.7V
0.5V
1.4V
2V
5
LTC3711
3711f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Maximum Current Sense
Threshold vs Temperature
Maximum Current Sense
Threshold vs V
RNG
Voltage
Feedback Reference Voltage
vs Temperature
V
RNG
VOLTAGE (V)
0.5
0
MAXIMUM CURRENT SENSE THRESHOLD (mV)
50
100
150
200
300
0.75
1.0
1.25
1.5
3711 G15
1.75
2.0
250
TEMPERATURE (
C)
50
25
100
MAXIMUM CURRENT SENSE THRESHOLD (mV)
120
150
0
50
75
3711 G17
110
140
130
25
100
125
V
RNG
= 1V
TEMPERATURE (
C)
50
0.78
FEEDBACK REFERENCE VOLTAGE (V)
0.79
0.80
0.81
0.82
25
0
25
50
3711 G18
75
100
125
Current Limit Foldback
V
FB
(V)
0
0
MAXIMUM CURRENT SENSE THRESHOLD (mV)
25
50
75
100
125
150
V
RNG
= 1V
0.2
0.4
0.6
0.8
3711 G14
On-Time vs I
ON
Current
I
ON
CURRENT (
A)
1
10
ON-TIME (ns)
100
1k
10k
10
100
3711 G11
V
VON
= 0V
V
ON
VOLTAGE (V)
0
ON-TIME (ns) 400
600
3711 G12
200
0
1
2
3
1000
I
ION
= 30
A
800
TEMPERATURE (
C)
50
ON-TIME (ns)
200
250
300
25
75
3711 G13
150
100
25
0
50
100
125
50
0
I
ION
= 30
A
V
VON
= 0V
On-Time vs V
ON
Voltage
On-Time vs Temperature
RUN/SS VOLTAGE (V)
1.5
0
MAXIMUM CURRENT SENSE THRESHOLD (mV)
25
50
75
100
125
150
V
RNG
= 1V
2
2.5
3
3.5
3711 G16
Maximum Current Sense
Threshold vs RUN/SS Voltage
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