FEATURES
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LTC3831
High Power Synchronous
Switching Regulator Controller
for DDR Memory Termination
DESCRIPTION
The LTC
®
3831 is a high power, high efficiency switching
regulator controller designed for DDR memory termina-
tion. The LTC3831 generates an output voltage equal
to 1/2 of an external supply or reference voltage. The
LTC3831 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 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 200kHz free-running clock frequency can
be externally adjusted or synchronized with an external
signal from 100kHz to above 500kHz. In shutdown mode,
the LTC3831 supply current drops to <10μA.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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 Input Supply Voltage Range: 3V to 8V
Maximum Duty Cycle > 91% Over Temperature
Drives All N-Channel External MOSFETs
High Efficiency: Over 95% Possible
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
APPLICATIONS
n
n
n
DDR SDRAM Termination
SSTL_2 Interface
SSTL_3 Interface
TYPICAL APPLICATION
5V
V
DDQ
2.5V
Efficiency vs Load Current
+
C
IN
330μF
×2
EFFICIENCY (%)
100
90
80
70
60
50
40
30
C
OUT
470μF
×3
20
10
0
3831 F01
MBR0530T1
1μF
0.1μF
PV
CC2
V
CC
SS
0.01μF
130k
SHDN
C1
33pF
R
C
15k
C
C
1500pF
PV
CC1
TG
I
MAX
LTC3831 I
FB
FREQSET
SHDN
COMP
BG
PGND
GND
R
+
R
–
FB
C
IN
: SANYO POSCAP 6TPB330M
C
OUT
: SANYO POSCAP 4TPB470M
Q1, Q2: SILICONIX Si4410DY
Q2
MBRS340T3
1k
0.1μF
L
O
1.2μH
10k
Q1
MBRS340T3
0.1μF
+
4.7μF
V
TT
1.25V
±6A
+
T
A
= 25°C
V
IN
= 2.5V
V
OUT
= 1.25V
0
1
3
4
2
LOAD CURRENT (A)
5
6
2831 G01
Figure 1. Typical DDR Memory Termination Application
3831fb
1
LTC3831
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
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
to 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
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3831EGN#PBF
LTC3831IGN#PBF
LEAD BASED FINISH
LTC3831EGN
LTC3831IGN
TAPE AND REEL
LTC3831EGN#TRPBF
LTC3831IGN#TRPBF
TAPE AND REEL
LTC3831EGN#TR
LTC3831IGN#TR
PART MARKING
3831
3831
PART MARKING
3831
3831
PACKAGE DESCRIPTION
16-Lead Plastic SSOP
16-Lead Plastic SSOP
PACKAGE DESCRIPTION
16-Lead Plastic SSOP
16-Lead Plastic SSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
●
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
+ = 2.5V, V
R
– = GND, unless otherwise noted. (Note 2)
SYMBOL
V
CC
PV
CC
V
UVLO
V
FB
ΔV
OUT
I
VCC
I
PVCC
Δf
OSC
V
SAWL
V
SAWH
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
V
R
+ = 2.5V, V
R
– = 0V, V
COMP
= 1.25V
I
OUT
= 0A to 10A (Note 6)
V
CC
= 4.75V to 5.25V
Figure 2, V
SHDN
= V
CC
V
SHDN
= 0V
Figure 2, V
SHDN
= V
CC
(Note 3)
V
SHDN
= 0V
FREQSET Floating
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
l
MIN
3
3
l
TYP
5
2.4
MAX
8
13.2
2.9
1.269
UNITS
V
V
V
V
mV
mV
(Note 7)
1.231
1.25
2
0.1
0.7
1
14
0.1
1.6
10
20
10
240
mA
μA
mA
μA
kHz
V
V
3831fb
160
200
1.2
2.2
2
LTC3831
ELECTRICAL CHARACTERISTICS
SYMBOL
V
COMPMAX
Δf
OSC
/ΔI
FREQSET
A
V
g
m
I
COMP
I
MAX
PARAMETER
Maximum V
COMP
Frequency Adjustment
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
IH
V
IL
I
IN
I
SS
I
SSIL
R
+
t
r,
t
f
t
NOV
DC
MAX
SHDN
Input High Voltage
SHDN
Input Low Voltage
SHDN
Input Current
Soft-Start Current
Maximum Soft-Start Sink Current
Undercurrent Limit
R
+
Input Resistance
Driver Rise/Fall Time
Driver Nonoverlap Time
Maximum TG Duty Cycle
Figure 2, PV
CC1
= PV
CC2
= 5V (Note 5)
Figure 2, PV
CC1
= PV
CC2
= 5V (Note 5)
Figure 2, V
FB
= 0V (Note 5), PV
CC1
= 8V
●
●
●
●
●
The
●
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
+ = 2.5V, V
R
– = GND, unless otherwise noted. (Note 2)
CONDITIONS
V
FB
= 0V, PV
CC1
= 8V
46
520
MIN
TYP
2.85
10
55
650
100
V
IMAX
= V
CC
V
IMAX
= V
CC
(Note 6)
●
●
MAX
UNITS
V
kHz/μA
dB
780
μmho
μA
●
9
4
2.4
12
12
3300
15
20
μA
μA
ppm/°C
V
0.8
0.1
–8
–12
1.6
49.5
80
25
91
120
95
250
250
1
–16
V
μA
μA
mA
kΩ
ns
ns
%
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
= 8V
●
●
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:
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 operating frequency, operating voltage and the external FETs
used.
Note 4:
The LTC3831EGN 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. The LTC 3831IGN is
guaranteed to meet performance specifications over the full –40°C to 85°C
temperature range.
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 2.5V 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
operation above the specified maximum operating junction temperature may
impair device reliability.
3831fb
3
LTC3831
TYPICAL PERFORMANCE CHARACTERISTICS
Load Regulation
1.270
1.265
1.260
V
OUT
(V)
1.255
1.250
1.245
1.240
1.235
1.230
–6
–4
2
0
OUTPUT CURRENT (A)
–2
4
6
3831 G02
Line Regulation
ERROR AMPLIFIER TRANSCONDUCTANCE (μmho)
1.260
1.258
1.256
1.254
V
FB
(V)
1.252
1.250
1.248
1.246
1.244
1.242
1.240
3
4
6
7
5
SUPPLY VOLTAGE (V)
8
3831 G03
Error Amplifier Transconductance
vs Temperature
10
8
6
4
ΔV
FB
(mV)
2
0
–2
–4
–6
–8
–10
800
750
700
650
600
550
500
–50 –25
T
A
= 25°C
REFER TO FIGURE 1
NEGATIVE OUTPUT CURRENT
INDICATES CURRENT SINKING
T
A
= 25°C
50
25
75
0
TEMPERATURE (°C)
100
125
3831 G05
Output Temperature Drift
1.270
1.265
1.260
V
OUT
(V)
1.255
1.250
1.245
1.240
1.235
1.230
–50
–25
50
25
TEMPERATURE (°C)
0
75
REFER TO FIGURE 1
OUTPUT = NO LOAD
20
15
10
5
0
–5
ΔV
OUT
(mV)
ERROR AMPLIFIER SINK/SOURCE CURRENT (μA)
200
180
160
140
120
100
80
60
Error Amplifier Sink/Source
Current vs Temperature
60
ERROR AMPLIFIER OPEN-LOOP GAIN (dB)
0
50
75
25
TEMPERATURE (°C)
100
125
Error Amplifier Open-Loop Gain
vs Temperature
55
50
–10
–15
–20
100
3831 G04
45
40
–50 –25
40
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3831 G06
3831 G07
Oscillator Frequency
vs Temperature
250
240
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)
500
400
300
200
100
230
220
210
200
190
180
170
160
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
FREQSET FLOATING
600
Oscillator Frequency
vs FREQSET Input Current
T
A
= 25°C
1.5
1.4
1.3
V
SAWH
– V
SAWL
(V)
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0
–40
10
–20
–10
0
–30
FREQSET INPUT CURRENT (μA)
20
3831 G09
Oscillator (V
SAWH
– V
SAWL
)
vs External Sync Frequency
T
A
= 25°C
0.5
100
300
200
400
EXTERNAL SYNC FREQUENCY (kHz)
500
3831 G08
3831 G10
3831fb
4
LTC3831
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum TG Duty Cycle
vs Temperature
100
99
MAXIMUM G1 DUTY CYCLE (%)
98
97
96
95
94
93
92
91
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
V
FB
= 0V
REFER TO FIGURE 3
I
MAX
SINK CURRENT (μA)
20
18
OUTPUT VOLTAGE (V)
16
14
12
10
8
6
4
–50 –25
0
75
50
25
TEMPERATURE (°C)
100
125
I
MAX
Sink Current
vs Temperature
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Output Overcurrent Protection
T
A
= 25°C
REFER TO FIGURE 1
0
2
8
6
4
OUTPUT CURRENT (A)
10
3831 G13
3831 G11
3831 G12
Output Current Limit Threshold
vs Temperature
10
9
OUTPUT CURRENT LIMIT (A)
8
7
6
5
4
3
2
1
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
REFER TO FIGURE 1
SOFT-START SOURCE CURRENT (μA)
–8
–9
–10
–11
–12
–13
–14
–15
Soft-Start Source Current
vs Temperature
2.00
SOFT-START SINK CURRENT (mA)
1.75
1.50
1.25
1.00
0.75
0.50
0.25
Soft-Start Sink Current
vs (V
IFB
– V
IMAX
)
T
A
= 25°C
–16
–50 –25
0
75
50
25
TEMPERATURE (°C)
100
125
0
–150
–125
–100
–50
–75
V
IFB
– V
IMAX
(mV)
–25
0
3831 G16
3831 G14
3831 G15
UNDERVOLTAGE LOCKOUT THRESHOLD VOLTAGE (V)
Undervoltage Lockout Threshold
Voltage vs Temperature
3.0
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
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
V
CC
Operating Supply Current
vs Temperature
FREQSET FLOATING
PV
CC
SUPPLY CURRENT (mA)
90
80
70
60
50
40
30
20
10
–25
50
25
0
75
TEMPERATURE (°C)
100
125
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
0.4
–50
0
400
100
300
200
OSCILLATOR FREQUENCY (kHz)
500
3831 G19
3831 G17
3831 G18
3831fb
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