FEATURES
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LTC3828
Dual, 2-Phase Step-Down
Controller with Tracking
DESCRIPTIO
The LTC
®
3828 is a dual high performance step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant fre-
quency 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 bat-
tery 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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
APPLICATIO S
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Telecom Infrastructure
ASIC Power Supply
Industry Equipment
TYPICAL APPLICATIO
High Efficiency Dual 2.5V/3.3V Step-Down Converter with Tracking
+
4.7µF
V
IN
PGOOD INTV
CC
TG1
3.2µH
BOOST1
0.1µF
SW1
BG1
500kHz
LTC3828
TG2
BOOST2
SW2
BG2
PGND
SENSE2
+
1000pF
SENSE1
V
OSENSE1
63.4k 1%
63.4k 1%
20k
20k
1%
1%
0.1µF
TRCKSS2
I
TH1
220pF
15k
RUN1
SGND
–
1µF
CERAMIC
0.1µF
FCB/PLLIN
SENSE1
+
0.01Ω
1000pF
SENSE2
V
OSENSE2
–
3.3V
5A
TRCKSS1
I
TH2
RUN2
220pF
15k
TRCKSS1
20k
1%
0.1µF
+
47µF
4V
SP
U
U
U
4.5V TO 28V
22µF
50V
CERAMIC
3.2µH
0.01Ω
42.5k
1%
2.5V
5A
56µF
4V
SP
+
3828 TA01
3828f
1
LTC3828
ABSOLUTE
AXI U
RATI GS
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
PACKAGE/ORDER I FOR ATIO
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
TRCKSS1
SENSE1
–
SENSE1
+
CLKOUT
BOOST1
PGOOD
I
TH1
LTC3828EG
32 31 30 29 28 27 26 25
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
33
24 SW1
23 V
IN
22 INTV
CC
21 DRV
CC
20 PGND
19 BG1
18 BG2
17 SW2
TG1
ORDER PART
NUMBER
TRCKSS2 10
SENSE2
–
11
SENSE2
+
12
I
TH2
13
V
OSENSE2
14
SENSE2
–
SENSE2
+
RUN2
I
TH2
V
OSENSE2
BOOST2
TG2
NC
T
JMAX
= 125°C,
θ
JA
= 95°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
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.
SYMBOL
V
OSENSE1, 2
I
VOSENSE1, 2
V
REFLNREG
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Feedback Current
CONDITIONS
(Note 3); I
TH1, 2
Voltage = 1.2V
(Note 3)
●
ELECTRICAL CHARACTERISTICS
Main Control Loops
0.792
0.800
±5
0.002
●
●
Reference Voltage Line Regulation V
IN
= 4.6V to 28V (Note 3)
Output Voltage Load Regulation
(Note 3)
Measured in Servo Loop;
∆I
TH
Voltage = 1.2V to 0.7V
Measured in Servo Loop;
∆I
TH
Voltage = 1.2V to 2.0V
Transconductance Amplifier g
m
I
TH1, 2
= 1.2V; Sink/Source 5uA; (Note 3)
g
m1, 2
2
U
U
W
W W
U
W
(Note 1)
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 ................................ 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)
(GN Package) ................................................... 300°C
TOP VIEW
ORDER PART
NUMBER
LTC3828EUH
UH PART
MARKING
3828
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 PCB
MIN
TYP
MAX
0.808
±50
0.02
0.5
– 0.5
UNITS
V
nA
%/V
%
%
mmho
3828f
0.1
– 0.1
1.3
LTC3828
The
●
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.
SYMBOL
g
mGBW1, 2
I
Q
PARAMETER
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
RUN Pin ON Threshold
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
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
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
= 0 to 20mA
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥
2.4V
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
OSENSE
with Respect to Set Output Voltage
V
OSENSE
Ramping Negative
V
OSENSE
Ramping Positive
–6
6
–7.5
7.5
360
230
480
4.8
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
I
TH1, 2
= 1.2V; (Note 3)
(Note 4)
V
IN
= 15V; V
OUT1
= 5V
V
RUN/SS1, 2
= 0V
●
MIN
TYP
3
2
20
MAX
UNITS
MHz
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
RUN1, 2
ON
V
SENSE(MAX)
0.76
– 0.50
0.800
– 0.18
4.3
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
●
●
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
5.0
0.2
400
260
550
–17
17
0.1
2.0
85
88
100
100
120
100
V
mV
mV
ns
ns
ns
ns
ns
ns
ns
TG1, 2 t
r
TG1, 2 t
f
BG1, 2 t
r
BG1, 2 t
f
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
0.3
±1
– 9.5
9.5
V
µA
%
%
Oscillator and Phase-Locked Loop
PGOOD Output
V
PGL
I
PGOOD
V
PG
3828f
3
LTC3828
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Output Current
and Mode (Figure 14)
100
100
V
IN
= 7V
90
V
IN
= 15V
Burst Mode
90 OPERATION
80
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
V
IN
= 20V
70
60
50
40
30
20
10
0
0.001
CONSTANT
FREQUENCY
(BURST DISABLE)
FORCED
CONTINUOUS
MODE
0.01
1
0.1
OUTPUT CURRENT (A)
Supply Current vs Input Voltage
(Figure 14)
1200
1000
BOTH CONTROLLERS ON
5.2
5.0
UNDERVOLTAGE LOCKOUT (V)
SUPPLY CURRENT (µA)
800
600
400
200
SHUTDOWN
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
3828 G04
INTV
CC
VOLTAGE (V)
4
U W
V
IN
=15V
V
OUT
= 5V
F = 260kHz
3828 G01
T
A
= 25°C unless otherwise noted.
Efficiency vs Input Voltage
(Figure 14)
100
Efficiency vs Output Current
(Figure 14)
90
80
80
70
70
60
V
OUT
= 5V
F = 260kHz
0.01
1
0.1
OUTPUT CURRENT (A)
10
3828 G02
60
10
50
0.001
50
5
10
15
20
INPUT VOLTAGE (V
V
OUT
= 5V
I
OUT
= 3A
F = 260kHz
25
30
3828 G03
Internal 5V LDO Line Regulation
I
LOAD
= 1mA
3.8
Undervoltage Lockout vs
Temperature
3.6
4.8
4.6
4.4
4.2
4.0
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
3828f
LTC3828
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency vs
Temperature
700
600
V
PLLFLTR
= 2.4V
1.5
1.3
CURRENT SENSE INPUT CURRENT (µA)
50
25
75
0
TEMPERATURE (°C)
100
125
FREQUENCY (kHz)
500
400
300
200
100
0
–50 –25
V
PLLFLTR
= 1.2V
TRCKSS CURRENT (µA)
V
PLLFLTR
= 0V
50
25
75
0
TEMPERATURE (°C)
Maximum Current Sense
Threshold vs Temperature
80
V
OUT
= 5V
78
5.0
5.1
76
NORMALIZED V
OUT
(%)
INTV
CC
VOLTAGE (V)
V
SENSE
(mV)
74
72
70
–50 –25
50
25
75
0
TEMPERATURE (°C)
Maximum Current Sense
Threshold vs Duty Factor
75
80
70
60
V
SENSE
(mV)
V
SENSE
(mV)
50
V
SENSE
(mV)
25
0
0
20
40
60
DUTY FACTOR (%)
3828 G13
U W
100
3828 G07
T
A
= 25°C unless otherwise noted.
Current Sense Pin Input Current vs
Temperature
37
TRCKSS Current vs Temperature
35
1.1
33
0.9
0.7
31
125
0.5
–50 –25
29
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3828 G08
3828 G09
INTV
CC
Voltage vs Temperature
0
Load Regulation
FCB = 0V
V
IN
= 15V
FIGURE 14
– 0.1
4.9
– 0.2
4.8
– 0.3
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
Maximum Current Sense
Threshold vs Percent of Nominal
Output Voltage (Foldback)
80
Maximum Current Sense
Threshold vs Sense Common
Mode Voltage
75
50
40
30
20
10
0
70
65
80
100
60
0
0.25
0.5
0.75
1.0
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
3828 G14
0
1
3
4
2
COMM0N MODE VOLTAGE (V)
5
3828 G15
3828f
5
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