LTC3770
Fast No R
SENSE
TM
Step-Down
Synchronous Controller with
Margining, Tracking and PLL
FEATURES
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DESCRIPTIO
Wide V
IN
Range: 4V to 32V
±0.67%
0.6V Reference Voltage
Output Voltage Tracking Capability
Programmable Margining
Sense Resistor Optional
True Current Mode Control
2% to 90% Duty Cycle at 200kHz
t
ON(MIN)
≤
100ns
Phase Lock Loop Frequency Synchronization
Powerful Dual N-Channel MOSFET Driver
Adjustable Cycle-by-Cycle Current Limit
Adjustable Switching Frequency
Programmable Soft-Start
Current Foldback Protection (Disabled at Start-Up)
Output Overvoltage Protection
Micropower Shutdown: I
Q
< 30µA
Power Good Output Voltage Monitor
Tracks the Reference Input Pin
Available in (5mm
×
5mm) QFN and 28-Lead
SSOP Packages
The LTC
®
3770 is a synchronous step-down switching
regulator controller with output voltage up/down tracking
capability and voltage margining. Its advanced functions
and high accuracy reference are ideal for powering
high performance server, ASIC and computer memory
systems.
The LTC3770 uses a constant on-time, valley current
mode control architecture to deliver very low duty factors
without requiring a sense resistor. The operating fre-
quency is selected by an external resistor and is compen-
sated for variations in input supply voltage. An internal
phase-lock loop allows the IC to be synchronized to an
external clock.
Fault protection is provided by an overvoltage comparator
and input undervoltage lockout. The regulator current limit
is user programmable. A wide supply range allows volt-
ages as high as 32V to be stepped down to as low as a 0.6V
output. Power supply sequencing is accomplished using
an external soft-start timing capacitor.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
R
SENSE
is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5481178, 5487554, 6580258, 6304066, 6476589,
6774611.
APPLICATIO S
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Distributed Power Systems
Server Power Supply
TYPICAL APPLICATIO
0.01µF
PGOOD
MARGIN
10k
PLLFLTR
PLLIN
0.1µF
I
ON
V
IN
TG
SW
0.22µF
CMDSH-3
68k
High Efficiency Step-Down Converter
V
IN
5V TO 28V
Si4884
1.8µH
10µF
35V
V
OUT
x3
2.5V
10A
180µF
4V
x2
Efficiency and Power Loss vs Load Current
100
V
IN
= 5V
95 V
OUT
= 2.5V
90
EFFICIENCY
10
EFFICIENCY (%)
85
80
75
70
65
60
POWER LOSS
TRACK/SS
BOOST
I
TH
+
1000pF
10k
LTC3770
SGND
RUN
V
ON
V
RNG
V
REFOUT
INTV
CC
DRV
CC
BG
SENSE
+
V
OUT
Si4874
4.7µF
B340A
95.3k
55
50
0.01
0.1
1
LOAD CURRENT (A)
0.01
10
3770 TA01b
10k
V
REFIN
MPGM
82k
SENSE
–
PGND
V
FB
3770 TA01
30.1k
U
POWER LOSS (W)
1
0.1
U
U
3770fb
1
LTC3770
ABSOLUTE
(Note 1)
AXI U
RATI GS
INTV
CC
, ZV
IN
Voltages .................................7V to – 0.3V
TG, BG, INTV
CC
Peak Currents................................... 4A
TG, BG, INTV
CC
RMS Currents ............................. 50mA
Operating Ambient Temperature
Range (Note 4) ................................... – 40°C to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range ................. – 65°C to 125°C
QFN Reflow Peak Body Temperature .................... 245°C
Lead Temperature (Soldering, 10 sec).................. 300°C
Input Supply Voltage (V
IN
, V
INSNS
) ............32V to – 0.3V
Boosted Topside Driver Supply Voltage
(BOOST) ................................................38V to – 0.3V
SENSE
+
, SW Voltage ....................................32V to – 5V
DRV
CC
, (BOOST – SW) Voltages .................7V to – 0.3V
V
ON
, V
RNG
, PGOOD Voltages .... INTV
CC
+ 0.3V to – 0.3V
PLLFLTR, I
TH
, V
FB
, V
REFIN
Voltages ..........2.7V to – 0.3V
TRACK/SS, FCB, Z0, Z1, Z2, RUN, PLLIN, MARGIN0,
MARGIN1 Voltages ............... INTV
CC
+ 0.3V to – 0.3V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN
V
ON
PGOOD
V
RNG
V
FB
I
TH
SGND
MARGIN1
MARGIN0
1
2
3
4
5
6
7
8
9
28 FCB
27 Z0
26 BOOST
25 TG
24 SW
23 PGND
22 BG
21 INTV
CC
20 Z2
19 Z1
18 ZV
IN
17 V
IN
16 PLLIN
15 PLLFLTR
PGOOD
BOOST
RUN
V
ON
FCB
32 31 30 29 28 27 26 25
V
RNG
1
V
FB
2
I
TH
3
SGND 4
MARGIN1 5
MARGIN0 6
I
ON
7
V
REFIN
8
9 10 11 12 13 14 15 16
V
REFOUT
PLLFLTR
TRACK/SS
V
INSNS
MPGM
PLLIN
V
IN
ZV
IN
33
24 SENSE
+
23 SENSE
–
22 PGND
21 BG
20 DRV
CC
19 INTV
CC
18 Z2
17 Z1
I
ON
10
V
REFIN
11
V
REFOUT
12
MPGM 13
TRACK/SS 14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/ W
UH PACKAGE
32-LEAD (5mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/ W
EXPOSED PAD IS SGND (PIN 33)
MUST BE SOLDERED TO THE PCB
ORDER PART NUMBER
LTC3770EG
G PART MARKING
LTC3770EG
ORDER PART NUMBER
LTC3770EUH
UH PART MARKING
3770
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.
SW
TG
Z0
2
U
U
W
W W
U
W
TOP VIEW
3770fb
LTC3770
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
PARAMETER
Input DC Supply Current
Normal Operation
Shutdown Supply Current
Feedback Voltage Accuracy (Note 3)
Feedback Voltage Line Regulation
Feedback Voltage Load Regulation
Run Pin On Threshold
Soft-Start Charging Current
Feedback Pin 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
SENSE–
– V
SENSE+
Minimum Current Sense Threshold
V
SENSE–
– V
SENSE+
Output Overvoltage Fault Threshold Offset
Undervoltage Lockout
Undervoltage Lockout
MARGIN0, MARGIN1 Input Thresholds
MPGM Pin Voltage
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
TG High
TG Low
BG High
BG Low
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
V
IN
Falling
V
IN
Rising
●
●
The
●
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
Main Control Loop
1300
30
V
REFIN
= V
REFOUT
; I
TH
= 1.2V (0°C to 85°C)
V
REFIN
= V
REFOUT
; I
TH
= 1.2V
V
IN
= 4V to 30V, I
TH
= 1.2V (Note 3)
I
TH
= 0.5V to 1.9V (Note 3)
V
RUN
Rising
V
SS/TRACK
= 0V
I
TH
= 1.2V (Note 3)
V
FCB
= 0V
I
ON
= –60µA, V
ON
= 1.5V
I
ON
= –60µA, V
ON
= 0V
I
ON
= –180µA, V
ON
= 0V
Tested with a Square Wave (Note 5)
V
RNG
= 1V, V
FB
= V
REFIN
– 30mV
V
RNG
= 0V, V
FB
= V
REFIN
– 30mV
V
RNG
= INTV
CC
, V
FB
= V
REFIN
– 30mV
V
RNG
= 1V, V
FB
= V
REFIN
+ 30mV
V
RNG
= 0V, V
FB
= V
REFIN
+ 30mV
V
RNG
= INTV
CC
, V
FB
= V
REFIN
+ 30mV
7
●
●
●
●
●
●
2200
50
0.604
0.606
– 0.3
1.9
–1.7
100
1.6
0.63
–2
290
150
100
400
153
84
308
µA
µA
V
V
%/V
%
V
µA
nA
mS
V
µA
ns
ns
ns
ns
mV
mV
mV
mV
mV
mV
V
FB
V
FB(LINEREG)
V
FB(LOADREG)
V
RUN
I
SS/TRACK
I
FB
g
m(EA)
V
FCB
I
FCB
t
ON
t
ON(MIN)
t
OFF(MIN)
V
SENSE(MAX)
0.596
0.594
0.6
0.6
0.002
– 0.05
1
–1.1
–100
1
0.57
210
90
1.5
–1.4
–20
1.3
0.6
–1
250
115
50
250
113
50
228
133
67
268
– 60
– 30
– 120
10
3.2
3.3
1.4
1.18
1.9
1.2
1.9
0.7
20
20
20
20
V
SENSE(MIN)
∆V
FB(OV)
V
IN(UVLO+)
V
IN(UVLO–)
V
MGN(TH)
V
MPGM
TG R
UP
TG R
DOWN
BG R
UP
BG R
DOWN
TG t
r
TG t
f
BG t
r
BG t
f
13
3.9
4
%
V
V
V
V
2.5
2.5
3
1.5
Ω
Ω
Ω
Ω
ns
ns
ns
ns
3770fb
3
LTC3770
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V unless otherwise noted.
SYMBOL
V
INTVCC
∆V
LDO(LOADREG)
R
PLLIN
I
PLLFLTR
PARAMETER
Internal V
CC
Voltage
Internal V
CC
Load Regulation
PLLIN Input Resistance
Phase Detector Output Current
Sink Capability
Source Capability
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Low Voltage
f
PLLIN
< f
0
f
PLLIN
> f
0
V
FB
Rising
V
FB
Falling
V
FB
Returning
I
PGOOD
= 5mA
7
–7
CONDITIONS
6V < V
IN
< 30V
I
CC
= 0mA to 20mA
●
ELECTRICAL CHARACTERISTICS
Internal V
CC
Regulator
MIN
4.7
TYP
5
– 0.1
50
–15
15
10
– 10
1.5
0.15
MAX
5.3
±2
UNITS
V
%
kΩ
µA
µA
Phased-Locked Loop
PGOOD Output
∆V
FBH
∆V
FBL
∆V
FB(HYS)
V
PGL
13
– 13
3
0.4
%
%
%
V
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
as follows:
LTC3770EG: T
J
= T
A
+ (P
D
• 130°C/W)
LTC3770EUH: T
J
= T
A
+ (P
D
• 34°C/W)
Note 3:
The 3770 is tested in a feedback loop that adjusts V
FB
to achieve a
specified error amplifier output voltage (I
TH
). For these tests, V
REFOUT
=
V
REFIN
.
Note 4:
The LTC3770E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 5:
The minimum off-time condition is specified for large peak-to-
peak inductor ripple current (see Minimum Off-Time Considerations in
the Applications Information section).
TYPICAL PERFOR A CE CHARACTERISTICS
Current Sense Threshold
vs I
TH
Voltage
300
CURRENT SENSE THRESHOLD (mV)
V
RNG
=
2V
1.4V
1V
ON-TIME (ns)
100
0.7V
0.5V
1k
ON-TIME (ns)
10k
200
0
–100
–200
0
0.5
1.0
1.5
2.0
I
TH
VOLTAGE (V)
4
U W
2.5
3770 G01
On-Time vs I
ON
Current
V
VON
= 0V
1200
1000
800
600
400
200
10
1
10
I
ON
CURRENT (µA)
100
3770
G02
On-Time vs V
ON
Voltage
I
ION
= 60µA
100
3.0
0
0
1
3
V
ON
VOLTAGE (V)
2
4
5
3770
G03
3770fb
LTC3770
TYPICAL PERFOR A CE CHARACTERISTICS
On-Time vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
300
250
200
150
100
50
0
–50 –25
I
ION
= 30µA
V
VON
= 0V
300
250
200
150
100
50
0
MAXIMUM CURRENT SENSE THRESHOLD (mV)
ON-TIME (ns)
50
25
75
0
TEMPERATURE (°C)
Error Amplifier g
m
vs Temperature
1.6
2.5
SHUTDOWN CURRENT (µA)
1.4
INPUT CURRENT (mA)
g
m
(mS)
1.2
1.0
0.8
0.6
–50 –25
50
25
0
75
TEMPERATURE (°C)
INTV
CC
Load Regulation
0
0
–0.25
FCB PIN CURRENT (µA)
–0.1
∆INTV
CC
(%)
–0.50
–0.75
–1.00
–1.25
–0.4
UNDERVOLTAGE LOCKOUT THRESHOLD (V)
–0.2
–0.3
0
10
30
40
20
INTV
CC
LOAD CURRENT (mA)
U W
100
3770
G04
Maximum Current Sense
Threshold vs V
RNG
Voltage
150
Maximum Current Sense
Threshold vs Temperature
V
RNG
= 1V
140
130
120
110
125
0.5
0.75
1.0
1.25
1.5
V
RNG
VOLTAGE (V)
1.75
2.0
100
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3770 G05
3770 G06
Input Current vs Input Voltage
60
50
40
30
20
10
0
0
5
20
15
25
10
INPUT VOLTAGE (V)
30
35
Shutdown Current vs Input Voltage
2.0
1.5
1.0
0.5
0
100
125
0
5
20
15
25
10
INPUT VOLTAGE (V)
30
35
3770 G07
3770
G08
3770
G09
FCB Pin Current vs Temperature
4.0
Undervoltage Lockout Threshold
vs Temperature
3.5
3.0
2.5
50
3770 G10
–1.50
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
2.0
–50 –25
75
0
25
50
TEMPERATURE (°C)
100
125
3770
G11
3770 G12
3770fb
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