LTC3831
High Power Synchronous
Switching Regulator Controller
for DDR Memory Termination
FEATURES
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DESCRIPTIO
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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
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-chan-
nel MOSFETs. Additionally, the chip senses output cur-
rent 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
DDR SDRAM Termination
SSTL_2 Interface
SSTL_3 Interface
TYPICAL APPLICATIO
5V
V
DDQ
2.5V
MBR0530T1
1µF
0.1µF
PV
CC2
V
CC
0.1µF
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
+
C
IN
330µF
×2
EFFICIENCY (%)
+
4.7µF
V
TT
1.25V
±6A
C
OUT
470µF
×3
+
3831 F01
Figure 1. Typical DDR Memory Termination Application
3831f
U
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
0
1
3
4
2
LOAD CURRENT (A)
5
6
2831 G01
U
U
T
A
= 25°C
V
IN
= 2.5V
V
OUT
= 1.25V
1
LTC3831
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
GN PART MARKING
3831
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
+ = 2.5V, 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
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
q
MIN
3
3
q
TYP
5
2.4
MAX
8
13.2
2.9
1.269
UNITS
V
V
V
V
mV
mV
(Note 7)
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
q
1.231
1.25
2
0.1
q
q
q
q
q
0.7
1
14
0.1
160
200
1.2
2.2
1.6
10
20
10
240
V
FB
= 0V, PV
CC1
= 8V
q
q
2.85
10
46
520
9
4
55
650
100
12
12
3300
15
20
780
∆f
OSC
/∆I
FREQSET
Frequency Adjustment
kHz/µA
dB
µmho
µA
µA
µA
ppm/°C
V
IMAX
= V
CC
(Note 6)
2
U
mA
µA
mA
µA
kHz
V
V
V
3831f
W
U
U
W W
W
LTC3831
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
+ = 2.5V, 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 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
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
= 8V
q
q
0.1
–8
–12
1.6
49.5
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 operating frequency, operating voltage and the external FETs
used.
Note 4:
The LTC3831EGN 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 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 opera-
tion above the specified maximum operating junction temperature may impair
device reliability.
3831f
3
LTC3831
TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation
1.270
1.265
1.260
T
A
= 25°C
REFER TO FIGURE 1
NEGATIVE OUTPUT CURRENT
INDICATES CURRENT SINKING
1.260
1.258
1.256
1.254
ERROR AMPLIFIER TRANSCONDUCTANCE (µmho)
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
V
FB
(V)
Output Temperature Drift
ERROR AMPLIFIER SINK/SOURCE CURRENT (µA)
1.270
1.265
1.260
15
10
5
0
–5
–10
–15
180
160
140
120
100
80
60
40
–50 –25
0
75
50
25
TEMPERATURE (°C)
100
125
ERROR AMPLIFIER OPEN-LOOP GAIN (dB)
REFER TO FIGURE 1
OUTPUT = NO LOAD
V
OUT
(V)
1.255
1.250
1.245
1.240
1.235
1.230
–50
–25
50
25
TEMPERATURE (°C)
0
75
Oscillator Frequency
vs Temperature
250
240
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)
FREQSET FLOATING
230
220
210
200
190
180
170
160
–50
–25
0
25
75
50
TEMPERATURE (°C)
100
125
400
300
200
100
0
–40
V
SAWH
– V
SAWL
(V)
4
U W
3831 G04
Line Regulation
T
A
= 25°C
10
8
6
4
800
750
700
650
600
550
Error Amplifier Transconductance
vs Temperature
∆V
FB
(mV)
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
2
0
–2
–4
–6
–8
–10
500
–50 –25
50
25
75
0
TEMPERATURE (˚C)
100
125
3831 G05
Error Amplifier Sink/Source
Current vs Temperature
20
200
Error Amplifier Open-Loop Gain
vs Temperature
60
55
∆V
OUT
(mV)
50
45
–20
100
40
–50 –25
75
0
25
50
TEMPERATURE (°C)
100
125
3831 G06
3831 G07
Oscillator Frequency
vs FREQSET Input Current
600
500
1.5
Oscillator (V
SAWH
– V
SAWL
)
vs External Sync Frequency
T
A
= 25°C
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
T
A
= 25°C
10
–20
–10
0
–30
FREQSET INPUT CURRENT (µA)
20
3831 G09
0.5
100
300
200
400
EXTERNAL SYNC FREQUENCY (kHz)
500
3831 G08
3831 G10
3831f
LTC3831
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum TG Duty Cycle
vs Temperature
100
99
MAXIMUM G1 DUTY CYCLE (%)
V
FB
= 0V
REFER TO FIGURE 3
I
MAX
SINK CURRENT (µA)
98
97
96
95
94
93
92
91
–50
–25
0
25
75
50
TEMPERATURE (°C)
100
125
OUTPUT VOLTAGE (V)
Output Current Limit Threshold
vs Temperature
10
9
OUTPUT CURRENT LIMIT (A)
REFER TO FIGURE 1
SOFT-START SOURCE CURRENT (µA)
8
7
6
5
4
3
2
1
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
–10
–11
–12
–13
–14
–15
–16
– 50 – 25
0
75
50
25
TEMPERATURE (°C)
100
125
SOFT-START SINK CURRENT (mA)
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
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 G12
Soft-Start Source Current
vs Temperature
–8
–9
2.00
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
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
3831f
5
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