FEATURES
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LTC3838-2
Dual, Fast, Accurate
Step-Down DC/DC Controller with
External Reference Voltage and
Dual Differential Output Sensing
DESCRIPTION
The LTC
®
3838-2 is a dual-channel, PolyPhase
®
synchro-
nous step-down DC/DC switching regulator controller. Two
independent channels drive all N-channel power MOSFETs.
The two channels can also be combined into a multiphase
single output configuration with external reference.
The controlled on-time, valley current mode control architec-
ture allows for not only fast response to transients without
a clock delay, but also constant frequency switching at a
steady-load condition. Its proprietary load-release transient
detection feature (DTR) significantly reduces overshoot at
low output voltages.
The switching frequency can be programmed from 200kHz
to 2MHz with an external resistor, and can be synchronized
to an external clock. Very low t
ON
and t
OFF
times allow for near
0% and near 100% duty cycles, respectively. Voltage track-
ing soft start-up and multiple safety features are provided.
See Table 1 for a comparison of LTC3838, LTC3838-1 and
LTC3838-2.
L,
LT, LTC, LTM, PolyPhase, OPTI-LOOP, Linear Technology and the Linear logo are registered
trademarks and Hot Swap is a trademark of Linear Technology Corporation. All other trademarks
are the property of their respective owners. Protected by U.S. Patents, including 5481178,
5847554, 6580258, 6304066, 6476589, 6774611.
n
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Wide V
IN
Range: 4.5V to 38V
V
OUT1
: 0.6V to 5.5V, ±0.67% Output Regulation
Accuracy, with Internal 0.6V V
REFERENCE
V
OUT2
: 0.4V to 5.5V, ±4mV Regulation Accuracy, with
Differential External V
REFERENCE
Sensing
Differential Remote Output Sensing; Up to ±500mV
(V
OUT1
) and ±200mV (V
OUT2
) Ground Deviations
Fast Load Transient Response Without Clock Delay
Detect Transient Release (DTR) Reduces V
OUT
Overshoot
Frequency Programmable from 200kHz to 2MHz,
Synchronizable to External Clock
t
ON(MIN)
= 30ns, t
OFF(MIN)
= 90ns
R
SENSE
or Inductor DCR Current Sensing
Overvoltage Protection and Current Limit Foldback
Power Good Output Voltage Monitor
Thermally Enhanced 38-Pin (5mm
×
7mm) QFN Package
Power for ASICs with Dynamic Voltage Scaling
Low Voltage, High Current, High Step-Down Ratio
Converters That Demand Tight Transient Regulation
APPLICATIONS
n
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TYPICAL APPLICATION
V
IN
4.5V TO 38V
1.2V/15A and 0.8V to 2.5V/15A, 350kHz Step-Down Converter (See Figure 16 for Complete Design)
SENSE1
–
SENSE1
+
V
IN
TG1
V
OUT1
1.2V
15A
330µF
×2
0.56µH
SW1
0.1µF
LTC3838-2
SENSE2
–
SENSE2
+
INTV
CC
TG2
EFFICIENCY (%)
SW2
0.1µF
10k
0.56µH
20k
V
OUT2
0.8V TO 2.5V
15A
330µF
×2
Efficiency/Power Loss
100
90
80
EFFICIENCY
70
60
50
40
POWER
LOSS
FORCED CONTINUOUS MODE
DISCONTINUOUS MODE
2.5
2.0
POWER LOSS (W)
BOOST1
BOOST2
DRV
CC2
BG2
EXTV
REF2
+
1.5
+
10k
10k
DRV
CC1
4.7µF
BG1
PGND
V
OUTSENSE1
V
OUTSENSE1–
ITH1
RT
SGND
EXTV
CC
RUN1
+
1.0
0.4V TO
1.25V
20k
0.5
V
IN
= 12V
V
OUT
= 1.2V
0.1
1
LOAD CURRENT (A)
10
38382 TA01b
V
DFB2
V
DFB2–
ITH2
+
TRACK/SS1 TRACK/SS2
115k
MODE/PLLIN
CLKOUT
PHASMD
RUN2
0
38382 TA01a
38382f
For more information
www.linear.com/3838-2
1
LTC3838-2
ABSOLUTE MAXIMUM RATINGS
V
IN
Voltage ................................................. –0.3V to 40V
BOOST1, BOOST2 Voltages ....................... –0.3V to 46V
SW1, SW2 Voltages ...................................... –5V to 40V
INTV
CC
, DRV
CC1
, DRV
CC2
, EXTV
CC
, PGOOD1,
PGOOD2, RUN1, RUN2, (BOOST1-SW1),
(BOOST2-SW2), MODE/PLLIN Voltages ...... –0.3V to 6V
SENSE1
+
, SENSE2
+
,SENSE1
–
, SENSE2
–
Voltages ....................................................... –0.6V to 6V
V
OUTSENSE1+
, Voltage .............. –0.6V to (INTV
CC
+ 0.3V)
V
OUTSENSE1–
, Voltage ....................–0.6V to V
OUTSENSE1+
TRACK/SS1, TRACK/SS2 Voltages .............. –0.3V to 5V
DTR1, DTR2, PHASMD, RT, EXTV
REF2
, V
DFB2+
, V
DFB2–
,
ITH1, ITH2 Voltages ................ –0.3V to (INTV
CC
+ 0.3V)
Operating Junction Temperature Range
(Notes 2, 3, 4) ........................................ –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
(Note 1)
PIN CONFIGURATION
TOP VIEW
SENSE2
+
SENSE2
–
PGOOD2
BOOST2
31 TG2
30 SW2
29 BG2
28 DRV
CC2
27 EXTV
CC
39
PGND
26 INTV
CC
25 PGND
24 V
IN
23 DRV
CC1
22 BG1
21 SW1
20 TG1
13 14 15 16 17 18 19
V
OUTSENSE1–
DTR1
RUN1
SENSE1
+
SENSE1
–
PGOOD1
BOOST1
V
DFB2–
RUN2
DTR2
38 37 36 35 34 33 32
V
DFB2
+
1
EXTV
REF2
2
ITH2 3
TRACK/SS2 4
MODE/PLLIN 5
CLKOUT 6
SGND 7
RT 8
PHASMD 9
ITH1 10
TRACK/SS1 11
V
OUTSENSE1+
12
UHF PACKAGE
38-LEAD (5mm
×
7mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS PGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3838EUHF-2#PBF
LTC3838IUHF-2#PBF
TAPE AND REEL
LTC3838EUHF-2#TRPBF
LTC3838IUHF-2#TRPBF
PART MARKING*
38382
38382
PACKAGE DESCRIPTION
38-Lead (5mm
×
7mm) Plastic QFN
38-Lead (5mm
×
7mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping
container.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/
Table 1. Comparison of LTC3838 Options
PART NUMBER
LTC3838
DESCRIPTION
±0.67% Differential Output Regulation on Channel 1
±1% Output Regulation on Channel 2
Separate-Per-Channel Continuous 30mV to 100mV Current Sense Range Controls
±0.67% on Channel 1 and ±0.75% on Channel 2, Differential Output Regulation on Both Channel 1 and 2
Single-Pin 30mV/60mV Current Sense Range Control
±0.67% Differential Output Regulation with Internal Reference on Channel 1
±4mV Differential Output Regulation with External Reference Voltage on Channel 2
Fixed 30mV Current Sense Range
LTC3838-1
LTC3838-2
38382f
2
For more information
www.linear.com/3838-2
LTC3838-2
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
OUT1,2
I
Q
PARAMETER
Input Voltage Operating Range
Regulated Output Voltage Operating Range
V
OUT1
Regulated Differentially with Respect to
V
OUTSENSE1–
, V
OUT2
Regulated Differentially with
Respect to V
DFB2–
MODE/PLLIN = 0V, No Load
RUN1 or RUN2 (But Not Both) = 0V
RUN1 = RUN2 = 0V
ITH1 = 1.2V, V
OUTSENSE1–
= 0V (Note 5)
T
A
= 25°C
T
A
= 0°C to 85°C
T
A
= –40°C to 125°C
V
IN
= 4.5V to 38V, ITH1 = 0.5V to 1.9V,
T
A
= –40°C to 125°C (Note 5)
–0.5V < V
OUTSENSE1–
< 0.5V
V
DFB2–
= 0V, ITH2 = 1.2V (Note 5)
EXTV
REF2
= 0.6V, T
A
= 25°C
ITH2 = 0.5V to 1.9V, –0.2V < V
DFB2–
< 0.2V,
T
A
= –40°C to 125°C (Note 5)
EXTV
REF2
= 0.6V, V
IN
= 4.5V to 38V
EXTV
REF2
= 1.5V, V
IN
= 4.5V to 38V
EXTV
REF2
= 2.5V, V
IN
= 5.5V to 38V
V
OUTSENSE1+
= 0.6V, V
OUTSENSE1–
= 0V
V
OUTSENSE1+
= 0.6V, V
OUTSENSE1–
= 0V
EXTV
REF2
= 0.6V
V
IN
≥ INTV
CC
≥ 5V, TRACK/SS2 > 2.5V
V
IN
≥ INTV
CC
≥ 4V, TRACK/SS2 > 1.5V
V
DFB2+
= 0.3V, V
DFB2–
= 0V
V
DFB2+
= 0.3V, V
DFB2–
= 0V
ITH = 1.2V (Note 5)
V
IN
= 38V, V
OUT
= 0.6V, R
T
= 20k (Note 6)
(Note 6)
V
OUTSENSE1+
= 0.57V, V
OUTSENSE1–
= 0V,
EXTV
REF2
= 0.6V, V
DFB2+
= 0.285V, V
DFB2–
= 0V,
V
SENSE1,2–
= 2.5V
V
OUTSENSE1+
= 0.63V, V
OUTSENSE1–
= 0V,
EXTV
REF2
= 0.6V, V
DFB2+
= 0.315V, V
DFB2–
= 0V,
V
SENSE1,2–
= 2.5V
V
SENSE+
= 0.6V
V
SENSE+
= 5V
V
SENSE–
= 0.6V
V
SENSE–
= 5V
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l
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The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V unless otherwise noted (Note 3).
CONDITIONS
MIN
4.5
0.6
TYP
MAX UNITS
38
5.5
V
V
Main Control Loops
Input DC Supply Current
Both Channels Enabled
Only One Channel Enabled
Shutdown Supply Current
Regulated Feedback Voltage on Channel 1
(V
OUTSENSE1+
– V
OUTSENSE1–
)
Regulated Feedback Voltage on Channel 1
Over Line, Load and Common Mode
3
2
15
0.5985
0.596
0.594
0.6
0.6
0.6
0.6015
0.604
0.606
mA
mA
µA
V
V
V
V
FB1
l
l
l
0.591
0.598
0.6
0.6
0.609
0.602
V
V
V
FB2
Regulated Feedback Voltage on Channel 2
(2 • V
DFB2+
– V
DFB2–
)
Regulated Feedback Voltage on Channel 2
Over Line, Load and Common Mode
l
l
l
0.596
1.494
2.493
0.6
1.5
2.5
0
–25
–5
0.604
1.506
2.507
±25
–50
±50
V
V
V
nA
µA
nA
V
V
I
VOUTSENSE1+
I
VOUTSENSE1–
I
EXTVREF2
V
EXTVREF2
V
OUTSENSE1+
Input Bias Current
V
OUTSENSE1–
Input Bias Current
EXTV
REF2
Input Bias Current
Maximum EXTV
REF2
Input Operating Voltage
Minimum EXTV
REF2
Input Operating Voltage
2.5
1.5
0.4
0
–6
1.7
30
90
24
30
36
±25
–12
V
nA
µA
mS
ns
ns
mV
I
VDFB2+
I
VDFB2–
g
m(EA)1,2
t
ON(MIN)1,2
t
OFF(MIN)1,2
V
DFB2+
Input Bias Current
V
DFB2–
Input Bias Current
Error Amplifier Transconductance
(∆I
TH1,2
/∆V
FB1,2
)
Minimum Top Gate On-Time
Minimum Top Gate Off-Time
Current Sensing
V
SENSE(MAX)1,2
Maximum Valley Current Sense Threshold
(V
SENSE1,2+
– V
SENSE1,2–
)
V
SENSE(MIN)1,2
Minimum Valley Current Sense Threshold
(V
SENSE1,2+
– V
SENSE1,2–
)
(Forced Continuous Mode)
I
SENSE1,2+
I
SENSE1,2–
SENSE1,2
+
Pins Input Bias Current
SENSE1,2
–
Pins Input Bias Current (Internal
500k Resistor to SGND)
–15
mV
±5
1
1.2
10
±50
±2
nA
µA
µA
µA
38382f
For more information
www.linear.com/3838-2
3
LTC3838-2
ELECTRICAL CHARACTERISTICS
SYMBOL
V
RUN1,2
I
RUN1,2
UVLO
I
TRACK/SS1,2
f
PARAMETER
RUN Pin On Threshold
RUN Pin On Hysteresis
RUN Pin Pull-Up Current when Off
RUN Pin Pull-Up Current Hysteresis
INTV
CC
Undervoltage Lockout
Soft-Start Pull-Up Current
Clock Output Frequency
(Steady-State Switching Frequency)
Channel 2 Phase (Relative to Channel 1)
Start-Up and Shutdown
V
RUN1,2
Rising
V
RUN1,2
Falling from On Threshold
RUN1,2 = SGND
I
RUN1,2(HYS)
= I
RUN1,2(ON)
– I
RUN1,2(OFF)
INTV
CC
Falling
INTV
CC
Rising
0V < TRACK/SS1,2 < 0.6V
R
T
= 205k
R
T
= 80.6k
R
T
= 18.2k
PHASMD = SGND
PHASMD = Floating
PHASMD = INTV
CC
PHASMD = SGND
PHASMD = Floating
PHASMD = INTV
CC
2
0.5
With Respect to SGND
TG High
TG Low
BG High
BG Low
(Note 6)
(Note 6)
6V < V
IN
< 38V
I
DRVCC1
= 0mA to –100mA
EXTV
CC
Rising
V
EXTVCC
= 5V, I
DRVCC2
= –100mA
V
FB1,2
Rising from Regulated Voltage
V
FB1,2
Falling from Regulated Voltage
V
FB1,2
Returning to Regulated Voltage
I
PGOOD
= 2mA
5
–5
4.4
5.0
600
2.5
1.2
2.5
0.8
20
15
5.3
–1.5
4.6
200
200
7.5
–7.5
15
0.1
50
20
0.3
10
–10
5.6
–3
4.8
l
l
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V unless otherwise noted (Note 3).
CONDITIONS
MIN
1.1
TYP
1.2
100
1.2
5
3.3
3.7
4.2
1
200
500
2000
180
180
240
60
90
120
4.5
MAX UNITS
1.3
V
mV
µA
µA
V
V
µA
kHz
kHz
kHz
Deg
Deg
Deg
Deg
Deg
Deg
V
V
kΩ
Ω
Ω
Ω
Ω
ns
ns
V
%
V
mV
mV
%
%
mV
V
µs
µs
Frequency and Clock Synchronization
450
550
CLKOUT Phase (Relative to Channel 1)
V
PLLIN(H)
V
PLLIN(L)
R
MODE/PLLIN
Gate Drivers
R
TG(UP)1,2
R
TG(DOWN)1,2
R
BG(UP)1,2
R
BG(DOWN)1,2
t
D(TG/BG)1,2
t
D(BG/TG)1,2
V
DRVCC1
V
EXTVCC
Clock Input High Level Into MODE/PLLIN
Clock Input Low Level Into MODE/PLLIN
MODE/PLLIN Input DC Resistance
TG Driver Pull-Up On Resistance
TG Driver Pull-Down On Resistance
BG Driver Pull-Up On Resistance
BG Driver Pull-Down On Resistance
Top Gate Off to Bottom Gate On Delay Time
Bottom Gate Off to Top Gate On Delay Time
Internally Regulated DRV
CC1
Voltage
DRV
CC1
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Switchover Hysteresis
EXTV
CC
to DRV
CC2
Voltage Drop
Internal V
CC
Regulator
PGood Output
OV
UV
V
PGOOD(L)1,2
t
D(PGOOD)1,2
PGOOD Overvoltage Threshold
PGOOD Undervoltage Threshold
PGOOD Threshold Hysteresis
PGOOD Low Voltage
Delay from V
FB
Fault (OV/UV) to PGOOD Falling
Delay from V
FB
Good (OV/UV Cleared) to
PGOOD Rising
38382f
4
For more information
www.linear.com/3838-2
LTC3838-2
ELECTRICAL CHARACTERISTICS
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:
The junction temperature (T
J
, in °C) is calculated from the ambient
temperature (T
A
, in °C) and power dissipation (P
D
, in Watts) according to
the formula:
T
J
= T
A
+ (P
D
•
θ
JA
)
where
θ
JA
(in °C/W) is the package thermal impedance.
Note 3:
The LTC3838-2 is tested under pulsed load conditions such that T
J
≈ T
A
. The LTC3838E-2 is guaranteed to meet specifications over the 0°C to
85°C operating junction temperature range. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3838I-2 is guaranteed to meet specifications over the –40°C to 125°C
operating junction temperature range . Note that the maximum ambient
temperature consistent with these specifications is determined by specific
operating conditions in conjunction with board layout, the rated package
thermal impedance and other environmental factors.
Note 4:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. The maximum
rated junction temperature will be exceeded when this protection is active.
Continuous operation above the specified absolute maximum operating
junction temperature may impair device reliability or permanently damage
the device.
Note 5:
The LTC3838-2 is tested in a feedback loop that adjusts voltages
on V
OUTSENSE1+
and V
DFB2+
pins to achieve specified error amplifier output
voltages (ITH1,2).
In order to simplify the total system error computation, the regulated
voltage is defined in one combined specification which includes the effects
of line, load and common mode variation. The combined regulated voltage
specification is tested by independently varying line, load, and common
mode, which by design do not significantly affect one another. For any
combination of line, load, and common mode variation, the regulated
voltage should be within the limits specified that are tested in production
to the following conditions:
Line: V
IN
= 4.5V to 38V, ITH = 1.2V, V
OUTSENSE1–
= 0V, V
DFB2–
= 0V
Load: V
IN
= 15V, ITH = 0.5V to 1.9V, V
OUTSENSE1–
= 0V, V
DFB2–
= 0V
Common mode: V
IN
= 15V, ITH = 1.2V, V
OUTSENSE1–
= ±0.5V, ±0.2V,
V
DFB2–
= ±0.2V
Note 6:
Delay times are measured with top gate (TG) and bottom gate
(BG) driving minimum load, and using 50% levels.
38382f
For more information
www.linear.com/3838-2
5
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