FEATURES
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LTC3828
Dual, 2-Phase Step-Down
Controller with Tracking
DESCRIPTION
The LTC
®
3828 is a dual high performance step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant frequency
current mode architecture allows for a phase-lockable
frequency of up to 550kHz. The TRCKSS pin provides both
soft-start and tracking functions. Multiple LTC3828s can
be daisy-chained in applications requiring more than two
voltages to be tracked.
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance
and ESR values. The precision 0.8V reference and power
good output indicator are compatible with a wide 4.5V to
28V (30V maximum) input supply range, encompassing
all battery chemistries.
The RUN pins control their respective channels indepen-
dently. The FCB/PLLIN pin selects among Burst Mode
®
operation, skip-cycle mode and continuous current mode.
Current foldback limits MOSFET dissipation during short-
circuit conditions. Reverse current and current foldback
functions are disabled during soft-start.
L,
LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5481178, 5705919, 5929620, 6144194, 6177787,
6304066, 6580258
Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
Tracking for Both Outputs
Constant Frequency Current Mode Control
Wide V
IN
Range: 4.5V to 28V Operation
Power Good Output Voltage Indicator
Adjustable Soft-Start Current Ramping
Foldback Output Current Limiting–
Disabled at Start-Up
No Reverse Current During Soft-Start Interval
Clock Output for 3-, 4-, 6-Phase Operation
Dual N-Channel MOSFET Synchronous Drive
±1% Output Voltage Accuracy
Phase-Lockable Fixed Frequency 260kHz to 550kHz
OPTI-LOOP
®
Compensation Minimizes C
OUT
Very Low Dropout Operation: 99% Duty Cycle
Output Overvoltage Protection
Small 28-Lead SSOP and 5mm
×
5mm QFN
Packages
APPLICATIONS
n
n
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Telecom Infrastructure
ASIC Power Supply
Industry Equipment
TYPICAL APPLICATION
High Efficiency Dual 2.5V/3.3V Step-Down Converter with Tracking
+
4.7μF
V
IN
PGOOD INTV
CC
TG1
0.1μF
3.2μH
BOOST1
SW1
BG1
500kHz
LTC3828
TG2
BOOST2
SW2
BG2
PGND
SENSE2
+
1000pF
SENSE1
–
V
OSENSE1
63.4k 1%
63.4k 1%
20k
1%
20k
1%
TRCKSS2
I
TH1
220pF
15k
RUN1
SGND
SENSE2
–
V
OSENSE2
TRCKSS1
I
TH2
RUN2
220pF
15k
0.1μF
TRCKSS1
42.5k
1%
20k
1%
0.01Ω
2.5V
5A
0.1μF
3.2μH
1μF
CERAMIC
4.5V TO 28V
22μF
50V
CERAMIC
FCB/PLLIN
SENSE1
+
0.01Ω
3.3V
5A
1000pF
+
47μF
4V
SP
+
56μF
4V
SP
3828 TA01
3828fc
1
LTC3828
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (V
IN
) ........................ 30V to –0.3V
Top Side Driver Voltages
BOOST1, BOOST2................................. 36V to –0.3V
Switch Voltage (SW1, SW2) ........................ 30V to –5V
INTV
CC
, DRV
CC
, RUN1, RUN2, (BOOST1-SW1),
(BOOST2-SW2)........................................... 7V to –0.3V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages ........................ (1.1)INTV
CC
to –0.3V
FCB/PLLIN, PLLFLTR, CLKOUT,
PHSMD Voltage .................................. INTV
CC
to –0.3V
TRCKSS1, TRCKSS2 ............................. INTV
CC
to –0.3V
PGOOD...................................................... 5.5V to –0.3V
I
TH1
, I
TH2
, V
OSENSE1
, V
OSENSE2
Voltages ... 2.7V to –0.3V
Peak Output Current <10μs (TG1, TG2, BG1, BG2) .... 3A
INTV
CC
Peak Output Current (Note 8) ................... 50mA
Operating Temperature Range (Note 7)
LTC3828E............................................ –40°C to 85°C
Junction Temperature (Note 2) ............................ 125°C
Storage Temperature Range.................. –65°C to 125°C
Reflow Peak Body Temperature (UH Package) ..... 260°C
Lead Temperature (Soldering, 10 sec)
G Package ......................................................... 300°C
PIN CONFIGURATION
TOP VIEW
TRCKSS1
SENSE1
–
SENSE1
+
CLKOUT
PGOOD
TOP VIEW
TRCKSS1
I
TH1
SENSE1+
SENSE1–
V
OSENSE1
PLLFLTR
RUN1
FCB/PLLIN
SGND
1
2
3
4
5
6
7
8
9
28 CLKOUT
27 PGOOD
26 BOOST1
25 TG1
24 SW1
23 V
IN
22 INTV
CC
21 PGND
20 BG1
19 BG2
18 SW2
17 TG2
16 BOOST2
15 RUN2
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W
V
OSENSE1
1
PLLFLTR 2
RUN1 3
PHSMD 4
FCB/PLLIN 5
SGND 6
TRCKSS2 7
NC 8
9 10 11 12 13 14 15 16
RUN2
BOOST2
SENSE2
–
SENSE2
+
I
TH2
V
OSENSE2
TG2
NC
33
BOOST1
I
TH1
TG1
24 SW1
23 V
IN
22 INTV
CC
21 DRV
CC
20 PGND
19 BG1
18 BG2
17 SW2
32 31 30 29 28 27 26 25
TRCKSS2 10
SENSE2
–
11
SENSE2
+
12
I
TH2
13
V
OSENSE2
14
UH PACKAGE
32-LEAD (5mm 5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 33) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3828EG#PBF
LTC3828EUH#PBF
TAPE AND REEL
LTC3828EG#TRPBF
LTC3828EUH#TRPBF
PART MARKING
LTC3828EG
3828
PACKAGE DESCRIPTION
28-Lead Plastic SSOP
32-Lead (5mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
3828fc
2
LTC3828
ELECTRICAL CHARACTERISTICS
SYMBOL
V
OSENSE1, 2
V
REFLNREG
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Reference Voltage Line Regulation
Output Voltage Load Regulation
Main Control Loops
(Note 3); I
TH1, 2
Voltage = 1.2V
(Note 3)
V
IN
= 4.6V to 28V (Note 3)
(Note 3)
Measured in Servo Loop;
ΔI
TH
Voltage = 1.2V to 0.7V
l
Measured in Servo Loop;
ΔI
TH
Voltage = 1.2V to 2.0V
l
I
TH1, 2
= 1.2V; Sink/Source 5μA; (Note 3)
I
TH1, 2
= 1.2V; (Note 3)
(Note 4)
V
OUT1
= 5V
V
RUN/SS1, 2
= 0V
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN1, 2
= 5V unless otherwise noted.
CONDITIONS
MIN
0.792
TYP
0.800
±5
0.002
0.1
–0.1
1.3
3
2
20
0.76
–0.50
0.800
–0.18
4.3
l
l
MAX
0.808
±50
0.02
0.5
–0.5
UNITS
V
nA
%/V
%
%
mmho
MHz
I
VOSENSE1, 2
Feedback Current
g
m1, 2
g
mGBW1, 2
I
Q
Transconductance Amplifier g
m
Transconductance Amplifier GBW
Input DC Supply Current
Normal Mode
Shutdown
Forced Continuous Threshold
Forced Continuous Pin Current
Burst Inhibit (Constant Frequency)
Threshold
Undervoltage Lockout
Feedback Overvoltage Lockout
Sense Pins Total Source Current
Maximum Duty Factor
Soft-Start Charge Current
3
100
0.84
–0.1
4.8
4
0.88
mA
μA
V
μA
V
V
V
μA
%
μA
V
FCB
I
FCB
V
BINHIBIT
UVLO
V
OVL
I
SENSE
DF
MAX
I
TRCKSS1,2
V
FCB
= 0.85V
Measured at FCB pin
V
IN
Ramping Down
Measured at V
OSENSE1, 2
(Each Channel); V
SENSE1–, 2–
= V
SENSE1+, 2+
= 0V
In Dropout
V
TRCKSS1, 2
= 0.2V
V
RUN1
, V
RUN2
Rising
V
OSENSE1, 2
= 0.7V,V
SENSE1–, 2–
= 5V
V
OSENSE1, 2
= 0.7V,V
SENSE1–, 2–
= 5V
(Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
Tested with a Square Wave (Note 6)
6V < V
IN
< 30V
I
CC
= 0mA to 20mA
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥ 2.4V
V
PLLFLTR
= 1.2V
f
PLLIN
< f
NOM
f
PLLIN
> f
NOM
l
3.5
0.84
–90
98
0.5
1.0
62
60
0.86
–65
99.4
1.2
1.5
75
75
55
55
65
55
60
80
120
4.8
5.0
0.2
360
230
480
400
260
550
–17
17
V
RUN1, 2
ON RUN Pin ON Threshold
V
SENSE(MAX)
Maximum Current Sense Threshold
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
Nominal Frequency
Lowest Frequency
Highest Frequency
Phase Detector Output Current
Sinking Capability
Sourcing Capability
2.0
85
88
100
100
120
100
V
mV
mV
ns
ns
ns
ns
ns
ns
ns
TG1, 2 tr
TG1, 2 tf
BG1, 2 tr
BG1, 2 tf
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCC
V
LDO
INT
f
NOM
f
LOW
f
HIGH
I
PLLFLTR
INTV
CC
Linear Regulator
5.2
2.0
440
290
590
V
%
kHz
kHz
kHz
μA
μA
Oscillator and Phase-Locked Loop
3828fc
3
LTC3828
ELECTRICAL CHARACTERISTICS
SYMBOL
V
PGL
I
PGOOD
V
PG
PARAMETER
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
PGOOD Output
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
OSENSE
with Respect to Set Output Voltage
V
OSENSE
Ramping Down
V
OSENSE
Ramping Up
–6
6
–7.5
7.5
0.1
0.3
±1
–9.5
9.5
V
μA
%
%
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN1, 2
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
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
according to the following formulas:
LTC3828UH: T
J
= T
A
+ (P
D
• 34°C/W)
LTC3828G: T
J
= T
A
+ (P
D
• 95°C/W)
Note 3:
The IC is tested in a feedback loop that servos V
ITH1, 2
to a
specified voltage and measures the resultant V
OSENSE1, 2
.
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 5:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 6:
The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥40% of I
MAX
(see minimum on-time
considerations in the Applications Information section).
Note 7:
The LTC3828E is guaranteed to meet performance specifications
over the –40°C to 85°C operating temperature range as assured by design,
characterization and correlation with statistical process controls.
Note 8:
This parameter is guaranteed by design.
TYPICAL PERFORMANCE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Efficiency vs Output Current
and Mode (Figure 14)
100
Burst Mode
90 OPERATION
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.001
FORCED
CONTINUOUS
MODE
V
IN
=15V
V
OUT
= 5V
f = 260kHz
10
3828 G01
Efficiency vs Output Current
(Figure 14)
100
V
IN
= 7V
90
V
IN
= 15V
EFFICIENCY (%)
90
100
Efficiency vs Input Voltage
(Figure 14)
CONSTANT
FREQUENCY
(BURST DISABLE)
80
80
70
V
IN
= 20V
60
V
OUT
= 5V
f = 260kHz
0.01
1
0.1
OUTPUT CURRENT (A)
10
3828 G02
70
60
0.01
1
0.1
OUTPUT CURRENT (A)
50
0.001
50
5
10
15
20
INPUT VOLTAGE (V
V
OUT
= 5V
I
OUT
= 3A
f = 260kHz
25
30
3828 G03
3828fc
4
LTC3828
TYPICAL PERFORMANCE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Supply Current vs Input Voltage
(Figure 14)
1200
1000
SUPPLY CURRENT (μA)
800
600
400
200
SHUTDOWN
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
3828 G04
Internal 5V LDO Line Regulation
5.2
I
LOAD
= 1mA
UNDERVOLTAGE LOCKOUT (V)
3.8
Undervoltage Lockout
vs Temperature
BOTH CONTROLLERS ON
INTV
CC
VOLTAGE (V)
5.0
4.8
4.6
4.4
4.2
4.0
3.6
3.4
3.2
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
3828 G05
3.0
–50
–25
0
25
50
75
100
125
TEMPERATURE (°C)
3828 G06
Oscillator Frequency vs
Temperature
700
600
FREQUENCY (kHz)
500
400
300
200
100
0
–50 –25
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 2.4V
TRCKSS CURRENT (μA)
1.5
TRCKSS Current vs Temperature
37
CURRENT SENSE INPUT CURRENT (μA)
Current Sense Pin Input Current vs
Temperature
1.3
35
1.1
33
V
PLLFLTR
= 0V
0.9
0.7
31
50
25
75
0
TEMPERATURE (°C)
100
125
0.5
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
29
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3828 G07
3828 G08
3828 G09
Maximum Current Sense
Threshold vs Temperature
80
V
OUT
= 5V
78
5.0
5.1
INTV
CC
Voltage vs Temperature
0
Load Regulation
FCB = 0V
V
IN
= 15V
FIGURE 14
NORMALIZED V
OUT
(%)
76
INTV
CC
VOLTAGE (V)
–0.1
V
SENSE
(mV)
4.9
–0.2
74
72
4.8
–0.3
70
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
4.7
–50 –25
–0.4
50
25
75
0
TEMPERATURE (°C)
100
125
0
1
3
2
LOAD CURRENT (A)
4
5
3828 G12
3828 G10
3828 G11
3828fc
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