LTC3831-1
High Power Synchronous
Switching Regulator Controller
for DDR Memory Termination
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
s
V
OUT
as Low as 0.4V
High Power Switching Regulator Controller
for DDR Memory Termination
V
OUT
Tracks 1/2 of V
IN
or External V
REF
No Current Sense Resistor Required
Low V
CC
Supply: 3V to 8V
Maximum Duty Cycle > 91% Over Temperature
Drives All N-Channel External MOSFETs
High Efficiency: Up to 95%
Programmable Fixed Frequency Operation:
100kHz to 500kHz
External Clock Synchronization Operation
Programmable Soft-Start
Low Shutdown Current: <10µA
Overtemperature Protection
Available in 16-Pin Narrow SSOP Package
The LTC
®
3831-1 is a high power, high efficiency switch-
ing regulator controller designed for DDR memory termi-
nation. The LTC3831-1 generates an output voltage equal
to 1/2 of an external supply or reference voltage. The
LTC3831-1 uses a synchronous switching architecture
with N-channel MOSFETs. Additionally, the chip senses
output current through the drain-source resistance of the
upper N-channel FET, providing an adjustable current
limit without a current sense resistor.
The LTC3831-1 operates with input supply voltage as low
as 3V and with a maximum duty cycle of > 91%. It includes
a fixed frequency PWM oscillator for low output ripple
operation. The 300kHz free-running clock frequency can
be externally adjusted or synchronized with an external
signal from 100kHz to above 500kHz. In shutdown mode,
the LTC3831-1 supply current drops to <10µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
DDR SDRAM Termination
SSTL_2, SSTL_3 Interface
HSTL Interface
TYPICAL APPLICATIO
0.75V DDR Memory Termination Application
V
DDQ
1.5V
100
12V
+
220µF
0.1µF
EFFICIENCY (%)
3.3V
4.7µF
PV
CC2
V
CC
SS
PV
CC1
TG
I
MAX
4.7k
2.2µF
0.01µF
1k
1.3µH
LTC3831-1 I
FB
FREQSET
BG
PGND
GND
R
+
R
–
FB
SHDN
68pF
SHDN
COMP
+
180µF
V
TT
(V
OUT
)
0.75V
±10A
1k
22nF
38311 TA01a
U
Efficiency vs Load Current
90
80
70
60
50
40
30
20
10
0
0
1
2
3 4 5 6 7
LOAD CURRENT (A)
8
9
10
T
A
= 25°C
V
DDQ
= 1.8V
V
DDQ
= 1.5V
3831 TAO1b
U
U
38311f
1
LTC3831-1
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
TG
PV
CC1
PGND
GND
R
–
FB
R
+
SHDN
1
2
3
4
5
6
7
8
16 BG
15 PV
CC2
14 V
CC
13 I
FB
12 I
MAX
11 FREQSET
10 COMP
9
SS
Supply Voltage
V
CC
....................................................................... 9V
PV
CC1,2
................................................................ 14V
Input Voltage
I
FB
, I
MAX
............................................... – 0.3V to 14V
R
+
, R
–
, FB, SHDN, FREQSET ..... – 0.3V to V
CC
+ 0.3V
Junction Temperature (Note 9) ............................. 125°C
Operating Temperature Range (Note 4) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC3831EGN-1
GN PART MARKING
38311
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
CC
, PV
CC1
, PV
CC2
= 5V, V
R
+ = 1.5V, V
R
– = GND, unless otherwise noted. (Note 2)
SYMBOL
V
CC
PV
CC
V
UVLO
V
FB
∆V
OUT
I
VCC
I
PVCC
∆f
OSC
V
SAWL
V
SAWH
V
COMPMAX
A
V
g
m
I
COMP
I
MAX
PARAMETER
Supply Voltage
PV
CC1
, PV
CC2
Voltage
Undervoltage Lockout Voltage
Feedback Voltage
Output Load Regulation
Output Line Regulation
Supply Current
PV
CC
Supply Current
Internal Oscillator Frequency
V
COMP
at Minimum Duty Cycle
V
COMP
at Maximum Duty Cycle
Maximum V
COMP
Error Amplifier Open-Loop DC Gain
Error Amplifier Transconductance
Error Amplifier Output Sink/Source Current
I
MAX
Sink Current
I
MAX
Sink Current Tempco
V
IMAX
= V
CC
(Note 10)
V
IMAX
= V
CC
(Notes 6, 10)
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
q
MIN
3
3
q
TYP
5
2.4
MAX
8
13.2
2.9
0.762
UNITS
V
V
V
V
mV
mV
(Note 7)
V
R
+ = 1.5V, V
R
– = 0V, V
COMP
= 1.25V
I
OUT
= 0A to 10A (Note 6)
V
CC
= 4.75V to 5.25V
Figure 1, V
SHDN
= V
CC
V
SHDN
= 0V
Figure 1, V
SHDN
= V
CC
(Note 3)
V
SHDN
= 0V
FREQSET Floating
q
0.738
0.75
2
0.1
q
q
q
q
q
0.7
1
20
0.1
230
300
1.2
2.2
1.6
10
30
10
360
V
FB
= 0V, PV
CC1
= 7V
q
q
2.85
10
50
1600
9
4
65
2000
100
12
12
3300
15
20
2400
∆f
OSC
/∆I
FREQSET
Frequency Adjustment
kHz/µA
dB
µmho
µA
µA
µA
ppm/°C
2
U
mA
µA
mA
µA
kHz
V
V
V
38311f
W
U
U
W W
W
LTC3831-1
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
CC
, PV
CC1
, PV
CC2
= 5V, V
R
+ = 1.5V, V
R
– = GND, unless otherwise noted. (Note 2)
SYMBOL
V
IH
V
IL
I
IN
I
SS
I
SSIL
R
+
t
r
, t
f
t
NOV
DC
MAX
PARAMETER
SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Input Current
Soft-Start Source Current
Maximum Soft-Start Sink Current
Undercurrent Limit
R
+
Input Resistance
Driver Rise/Fall Time
Driver Nonoverlap Time
Maximum TG Duty Cycle
Figure 1, PV
CC1
= PV
CC2
= 5V (Note 5)
Figure 1, PV
CC1
= PV
CC2
= 5V (Note 5)
Figure 1, V
FB
= 0V (Note 7), PV
CC1
= 7V
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
q
q
MIN
2.4
TYP
MAX
0.8
UNITS
V
V
µA
µA
mA
kΩ
V
SHDN
= V
CC
V
SS
= 0V, V
IMAX
= 0V, V
IFB
= V
CC
V
IMAX
= V
CC
, V
IFB
= 0V, V
SS
= V
CC
(Note 8),
PV
CC1
= 7V (Note 7)
q
q
0.1
–8
–12
1.6
53.3
80
25
91
120
95
1
–16
250
250
ns
ns
%
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.
Note 3:
Supply current in normal operation is dominated by the current
needed to charge and discharge the external FET gates. This will vary with
the LTC3831-1 operating frequency, operating voltage and the external
FETs used.
Note 4:
The LTC3831EGN-1 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 5:
Rise and fall times are measured using 10% and 90% levels. Duty
cycle and nonoverlap times are measured using 50% levels.
Note 6:
Guaranteed by design, not subject to test.
Note 7:
PV
CC1
must be higher than V
CC
by at least 2V for TG to operate at
95% maximum duty cycle and for the current limit protection circuit to be
active.
Note 8:
The current limiting amplifier can sink but cannot source current.
Under normal (not current limited) operation, the output current will be
zero.
Note 9:
This IC includes overtemperature protection that is intended to protect
the device during momentary overload conditions. Junction temperature will
exceed 125°C when overtemperature protection is active. Continuous opera-
tion above the specified maximum operating junction temperature may impair
device reliability.
Note 10:
The minimum and maximum limits for I
MAX
over temperature
includes the intentional temperature coefficient of 3300ppm/°C. This induced
temperature coefficient counteracts the typical temperature coefficient of the
external power MOSFET on-resistance. This results in a relatively flat current
limit over temperature for the application.
38311f
3
LTC3831-1
TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation
0.762
T = 25°C
0.760
A
REFER TO FRONT PAGE APPLICATION
0.758 NEGATIVE OUTPUT CURRENT
0.756 INDICATES CURRENT SINKING
0.754
0.760
0.758
0.756
0.754
V
OUT
(V)
0.752
0.750
0.748
0.746
0.744
0.742
0.740
8
10
T
A
= 25°C
10
8
6
4
∆V
OUT
(mV)
2
0
–2
–4
–6
–8
ERROR AMPLIFIER TRANSCONDUCTANCE (µmho)
V
OUT
(V)
0.752
0.750
0.748
0.746
0.744
0.742
0.740
0.738
–10 –8 –6 –4 –2 0 2 4 6
OUTPUT CURRENT (A)
Output Voltage Temperature Drift
0.762
REFER TO FRONT PAGE APPLICATION
0.760
OUTPUT = NO LOAD
0.758
0.756
0.754
V
OUT
(V)
12
10
8
6
4
∆V
OUT
(mV)
ERROR AMPLIFIER SINK/SOURCE CURRENT (µA)
180
160
140
120
100
80
60
40
–50 –25
0
75
50
25
TEMPERATURE (°C)
100
125
ERROR AMPLIFIER OPEN-LOOP GAIN (dB)
0.752
0.750
0.748
0.746
0.744
0.742
0.740
0.738
–50
–25
0
25
75
50
TEMPERATURE (°C)
100
Oscillator Frequency
vs Temperature
360
350
FREQSET FLOATING
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)
340
330
320
310
300
290
280
270
260
250
240
–50
–25
25
0
75
50
TEMPERATURE (°C)
100
125
V
SAWH
– V
SAWL
(V)
4
U W
3831 G08
Line Regulation
2400
2300
2200
2100
2000
1900
1800
1700
Error Amplifier Transconductance
vs Temperature
3
4
6
7
5
V
CC
SUPPLY VOLTAGE (V)
8
3831 G03
–10
1600
–50
–25
0
75
50
25
TEMPERATURE (°C)
100
125
3831 G02
3831 G04
Error Amplifier Sink/Source
Current vs Temperature
200
70
Error Amplifier Open-Loop Gain
vs Temperature
65
2
0
–2
–4
–6
–8
60
55
–10
–12
125
50
–50 –25
75
0
25
50
TEMPERATURE (°C)
100
125
3831 G05
3831 G06
3831 G07
Oscillator Frequency
vs FREQSET Input Current
700
600
1.3
Oscillator (V
SAWH
– V
SAWL
)
vs External Sync Frequency
T
A
= 25°C
1.5
1.4
T
A
= 25°C
500
400
300
200
100
0
1.2
1.1
1.0
0.9
0.8
0.7
0.6
30
20
10
0
10
20
FREQSET INPUT CURRENT (µA)
30
3831 G09
0.5
100
300
200
400
EXTERNAL SYNC FREQUENCY (kHz)
500
3831 G10
38311f
LTC3831-1
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum TG Duty Cycle
vs Temperature
100
99
MAXIMUM G1 DUTY CYCLE (%)
V
FB
= 0V
REFER TO FRONT PAGE APPLICATION
I
MAX
SINK CURRENT (µA)
97
96
95
94
93
92
91
–50
–25
25
0
75
50
TEMPERATURE (°C)
100
125
OUTPUT VOLTAGE (V)
98
Output Current Limit Threshold
vs Temperature
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1 REFER TO FRONT PAGE APPLICATION
0
50
25
0
75 100
–50 –25
TEMPERATURE (°C)
–8
SOFT-START SOURCE CURRENT (µA)
–10
–11
–12
–13
–14
–15
–16
– 50 – 25
0
75
50
25
TEMPERATURE (°C)
100
125
SOFT-START SINK CURRENT (mA)
OUTPUT CURRENT LIMIT (A)
UNDERVOLTAGE LOCKOUT THRESHOLD VOLTAGE (V)
Undervoltage Lockout Threshold
Voltage vs Temperature
3.0
1.6
V
CC
OPERATING SUPPLY CURRENT (mA)
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2.0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
PV
CC
SUPPLY CURRENT (mA)
U W
3831 G11
3831 G14
3831 G17
I
MAX
Sink Current
vs Temperature
20
18
16
14
12
10
8
6
4
– 50 – 25
0
75
50
25
TEMPERATURE (°C)
100
125
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Output Overcurrent Protection
T
A
= 25°C
REFER TO FRONT PAGE APPLICATION
0
2
8
6
10
4
OUTPUT CURRENT (A)
12
14
3831 G12
3831 G13
Soft-Start Source Current
vs Temperature
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
–9
Soft-Start Sink Current
vs (V
IFB
– V
IMAX
)
T
A
= 25°C
125
0
–150
–125
–100
–50
–75
V
IFB
– V
IMAX
(mV)
–25
0
3831 G16
3831 G15
V
CC
Operating Supply Current
vs Temperature
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
FREQSET FLOATING
90
80
70
60
50
40
30
20
10
0
PV
CC
Supply Current
vs Oscillator Frequency
T
A
= 25°C
TG AND BG LOADED
WITH 6800pF,
PV
CC1,2
= 12V
TG AND BG
LOADED
WITH 1000pF,
PV
CC1,2
= 5V
TG AND BG
LOADED
WITH 6800pF,
PV
CC1,2
= 5V
0
400
100
300
200
OSCILLATOR FREQUENCY (kHz)
500
3831 G19
3831 G18
38311f
5
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