DC/DC switching regulator controller. Two independent
channels drive all N-channel power MOSFETs. The controlled
on-time, valley current mode control architecture allows for
fast transient response and constant frequency switching
in steady-state operation, independent of V
IN
, V
OUT
and
load current. Its load-release transient detection feature
significantly reduces overshoot at low output voltages.
Differential output voltage sensing, along with a preci-
sion internal reference, offers an accurate ±0.67% output
regulation on Channel 1, even if the remote output ground
deviates from local ground by ±500mV. The second channel
can either provide an independent ±1% output, or together
with the first channel of this controller, serve as one of the
PolyPhase channels for a single-output voltage.
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.
L,
LT, LTC, LTM, PolyPhase, OPTI-LOOP Linear Technology and the Linear logo are registered
,
trademarks and Hot Swap, No R
SENSE
and UltraFast are trademarks 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
n
n
n
n
n
n
n
n
n
n
Wide V
IN
Range: 4.5V to 38V, V
OUT
: 0.6V to 5.5V
±0.67% Output Voltage Accuracy Over Temperature,
Differential Output Voltage Sensing, Allowing Up to
±500mV Line Loss at Remote Ground on Channel 1
±1% Output on the Independent 2nd Channel
Controlled On-Time, Valley Current Mode Control
Fast Load Transient Response
Detect Transient (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
Output Voltage Tracking and Adjustable Soft Start-Up
Thermally Enhanced 38-Pin (5mm
×
7mm) QFN and
TSSOP packages
APPLICATIONS
n
n
n
n
Distributed Power Systems
Point-of-Load Converters
Computing Systems
Data Communication Systems
TYPICAL APPLICATION
1.2V/1.5V, 15A, 350kHz, DCR Sense, Step-Down Converter (Refer to Figure 16 for Full Design)
V
IN
4.5V TO 38V
SENSE1
–
SENSE1
+
V
IN
TG1
V
OUT1
1.2V
15A
330μF
2
0.56μH
0.1μF
DRV
CC1
BG1
10k
4.7μF
PGND
V
OUTSENSE1+
V
OUTSENSE1–
ITH1
RT
SGND
V
FB2
40
0.1
DRV
CC2
BG2
10k
SW1
BOOST1
LTC3838
SENSE2
–
SENSE2
+
INTV
CC
EFFICIENCY (%)
TG2
SW2
BOOST2
0.1μF
15k
0.56μH
V
OUT2
1.5V
15A
80
EFFICIENCY
70
60
50
POWER
LOSS
1.0
1.5
90
Efficiency/Power Loss
100
FORCED CONTINUOUS MODE
DISCONTINUOUS MODE
2.5
2.0
POWER LOSS (W)
+
10k
+
330μF
2
0.5
V
IN
= 12V
V
OUT
= 1.2V
1
LOAD CURRENT (A)
10
3838 F16b
0
TRACK/SS1 TRACK/SS2
115k
ITH2
3838 TA01a
3838fa
1
LTC3838
ABSOLUTE MAXIMUM RATINGS
(Note 1)
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
V
OUTSENSE1+
, V
OUTSENSE1–
, SENSE1
+
, SENSE2
+
,
SENSE1
–
, SENSE2
–
Voltages ....................... –0.6V to 6V
TRACK/SS1, TRACK/SS2 Voltages .............. –0.3V to 5V
DTR1, DTR2, PHASMD, RT, V
RNG1
, V
RNG2
, V
FB2
,
ITH1, ITH2 Voltages ................ –0.3V to (INTV
CC
+ 0.3V)
Operating Junction Temperature Range
(Note 2, 3, 4) .......................................... –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Package ....................................................... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
SENSE2
+
SENSE2
–
PGOOD2
BOOST2
RUN2
DTR2
V
FB2
DTR2
SENSE2
–
SENSE2
+
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
+
1
2
3
4
5
6
7
8
9
39
PGND
38 RUN2
37 PGOOD2
36 BOOST2
35 TG2
34 SW2
33 BG2
32 DRV
CC2
31 EXTV
CC
30 INTV
CC
29 PGND
28 V
IN
27 DRV
CC1
26 BG1
25 SW1
24 TG1
23 BOOST1
22 PGOOD1
21 RUN1
20 DTR1
38 37 36 35 34 33 32
TRACK/SS2 1
ITH2 2
V
RNG2
3
PHASMD 4
MODE/PLLIN 5
CLKOUT 6
SGND 7
RT 8
V
RNG1
9
ITH1 10
TRACK/SS1 11
V
OUTSENSE1+
12
V
FB2
TRACK/SS2
ITH2
V
RNG2
PHASMD
MODE/PLLIN
CLKOUT 10
SGND 11
RT 12
V
RNG1
13
ITH1 14
TRACK/SS1 15
V
OUTSENSE1+
16
V
OUTSENSE1–
17
SENSE1
+
18
SENSE1
–
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
19
FE PACKAGE
38-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 28°C/W
EXPOSED PAD (PIN 39) IS PGND, MUST BE SOLDERED TO PCB
3838fa
2
LTC3838
ORDER INFORMATION
LEAD FREE FINISH
LTC3838EUHF#PBF
LTC3838IUHF#PBF
LTC3838EFE#PBF
LTC3838IFE#PBF
TAPE AND REEL
LTC3838EUHF#TRPBF
LTC3838IUHF#TRPBF
LTC3838EFE#TRPBF
LTC3838IFE#TRPBF
PART MARKING*
3838
3838
LTC3838FE
LTC3838FE
PACKAGE DESCRIPTION
38-Lead (5mm
×
7mm) Plastic QFN
38-Lead (5mm
×
7mm) Plastic QFN
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–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/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
OUT1,2(REG)
PARAMETER
Input Voltage Operating Range
Main Control Loops
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
38
5.5
UNITS
V
V
Regulated Output Voltage Operating Range V
OUT1
Regulated Differentially with Respect to
V
OUTSENSE1–
, V
OUT2
Regulated with Respect to
SGND
Input DC Supply Current
Both Channels Enabled
Only One Channel Enabled
Shutdown Supply Current
MODE/PLLIN = 0V, No Load
RUN1 or RUN2 (But Not Both) = 0V
RUN1 = RUN2 = 0V
I
Q
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
OUTSENSE1(REG)
Regulated Differential Feedback Voltage on ITH1 = 1.2V (Note 5)
Channel 1 (V
OUTSENSE1+
– V
OUTSENSE1–
)
T
A
= 25°C
T
A
= 0°C to 85°C
T
A
= –40°C to 125°C
Regulated Differential Feedback Voltage on V
IN
= 4.5V to 38V, ITH1 = 0.5V to 1.9V (Note 5),
Channel 1 Over Line, Load and Common
–0.5V < V
OUTSENSE1–
< 0.5V
Mode
T
A
= 0°C to 85°C
T
A
= –40°C to 125°C
V
FB2(REG)
Regulated Feedback Voltage on Channel 2
ITH2 = 1.2V (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, ITH2 = 0.5V to 1.9V (Note 5)
T
A
= 0°C to 85°C
T
A
= –40°C to 125°C
V
OUTSENSE1+
– V
OUTSENSE1–
= 0.6V
V
OUTSENSE1+
– V
OUTSENSE1–
= 0.6V
V
FB2
= 0.6V
ITH = 1.2V (Note 5)
V
IN
= 38V, V
OUT
= 0.6V, R
T
= 20k (Note 6)
(Note 6)
l
l
l
l
0.594
0.591
0.597
0.594
0.592
0.592
0.588
0.6
0.6
0.6
0.6
0.6
0.6
0.6
±5
–25
–5
1.7
30
90
0.606
0.609
0.603
0.606
0.608
0.608
0.612
±25
–50
±50
V
V
V
V
V
V
V
nA
μA
nA
mS
ns
ns
l
l
l
l
Regulated Feedback Voltage on Channel 2
Over Line, Load
I
VOUTSENSE1+
I
VOUTSENSE1–
I
VFB2
g
m(EA)1,2
t
ON(MIN)1,2
t
OFF(MIN)1,2
V
OUTSENSE1+
Input Bias Current
V
OUTSENSE1–
Input Bias Current
V
FB2
Input Bias Current
Error Amplifier Transconductance
Minimum Top Gate On-Time
Minimum Top Gate Off-Time
3838fa
3
LTC3838
ELECTRICAL CHARACTERISTICS
SYMBOL
Current Sensing
V
SENSE(MAX)1,2
Maximum Valley Current Sense Threshold
(V
SENSE1,2+
– V
SENSE1,2–
)
Minimum Valley Current Sense Threshold
(V
SENSE1,2+
– V
SENSE1,2–
)
(Forced Continuous Mode)
SENSE1,2
+
Pins Input Bias Current
SENSE1,2
–
Pins Input Bias Current
(Internal 500k Resistor to SGND)
RUN Pin On Threshold
RUN Pin On Hysteresis
I
RUN1,2
UVLO
I
TRACK/SS1,2
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)
V
RNG
= 2V, V
FB
= 0.57V, V
SENSE–
= 2.5V
V
RNG
= 0V, V
FB
= 0.57V, V
SENSE–
= 2.5V
V
RNG
= INTV
CC
, V
FB
= 0.57V, V
SENSE–
= 2.5V
V
RNG
= 2V, V
FB
= 0.63V, V
SENSE–
= 2.5V
V
RNG
= 0V, V
FB
= 0.63V, V
SENSE–
= 2.5V
V
RNG
= INTV
CC
, V
FB
= 0.63V, V
SENSE–
= 2.5V
V
SENSE+
= 0.6V
V
SENSE+
= 5V
V
SENSE–
= 0.6V
V
SENSE–
= 5V
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
600
2.5
1.2
2.5
0.8
20
15
l
l
l
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).
PARAMETER
CONDITIONS
MIN
80
21
39
TYP
100
30
50
–50
–15
–25
±5
1
1.2
10
1.1
1.2
100
1.2
5
3.3
3.7
4.2
1
200
500
2000
180
180
240
60
90
120
4.5
1.3
±50
±2
MAX
120
40
61
UNITS
mV
mV
mV
mV
mV
mV
nA
μA
μA
μA
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
SENSE(MIN)1,2
I
SENSE1,2+
I
SENSE1,2–
Start-Up and Shutdown
V
RUN1,2
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
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 (Note 6)
Bottom Gate Off to Top Gate On Delay Time (Note 6)
3838fa
4
LTC3838
ELECTRICAL CHARACTERISTICS
SYMBOL
V
DRVCC1
V
EXTVCC
PARAMETER
Internally Regulated DRV
CC1
Voltage
DRV
CC1
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Switchover Hysteresis
EXTV
CC
to DRV
CC2
Voltage Drop
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 to PGOOD Rising
V
FB1,2
Rising, with Respect to Regulated Voltage
V
FB1,2
Falling, with Respect to Regulated Voltage
V
FB1,2
Returning to Reference Voltage
I
PGOOD
= 2mA
5
–5
7.5
–7.5
2
0.1
50
20
0.3
10
–10
%
%
%
V
μs
μs
V
EXTVCC
= 5V, I
DRVCC2
= –100mA
Internal V
CC
Regulator
6V < V
IN
< 38V
I
DRVCC1
= 0mA to –100mA
EXTV
CC
Rising
4.4
5.0
5.3
–1.5
4.6
200
200
5.6
–3
4.8
V
%
V
mV
mV
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
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:
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 is tested under pulsed loading conditions such that
T
J
≈ T
A
. The LTC3838E 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 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 is tested in a feedback loop that adjusts
(V
OUTSENSE1+
– V
OUTSENSE1–
) or V
FB2
to achieve specified error amplifier
output voltages (ITH1,2).
Note 6:
Delay times are measured with top gate (TG) and bottom gate
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