switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant frequency
current mode architecture allows a phase-lockable fre-
quency of up to 850kHz. Power loss and noise due to the
input capacitor ESR are minimized by operating the two
controller outputs out of phase.
The 170μA no-load quiescent current extends operating
life in battery-powered systems. OPTI-LOOP compensa-
tion allows the transient response to be optimized over
a wide range of output capacitance and ESR values. The
LTC3858 features a precision 0.8V reference and a power
good output indicator. A wide 4V to 38V input supply range
encompasses a wide range of intermediate bus voltages
and battery chemistries.
Independent soft-start pins for each controller ramp the
output voltages during start-up. The output latch-off feature
protects the circuit in short-circuit conditions.
For a leaded 28-lead SSOP package with a fixed current
limit and one PGOOD output, without phase modulation
or a clock output, see the LTC3858-1 data sheet.
L,
LT, LTC, LTM, Burst Mode, OPTI-LOOP μModule, PolyPhase, Linear Technology and the Linear
,
logo are registered trademarks and 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, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258.
Low Operating I
Q
: 170μA (One Channel On)
Wide Output Voltage Range: 0.8V ≤ V
OUT
≤ 24V
Wide V
IN
Range: 4V to 38V
R
SENSE
or DCR Current Sensing
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
OPTI-LOOP
®
Compensation Minimizes C
OUT
Phase-Lockable Frequency (75kHz-850kHz)
Programmable Fixed Frequency (50kHz-900kHz)
Selectable Continuous, Pulse-Skipping or
Burst Mode
®
Operation at Light Loads
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Output Voltage Soft-Start
Power Good Output Voltage Monitor
Output Overvoltage Protection
Output Latch-Off Protection During Short Circuit
Low Shutdown I
Q
: 8μA
Internal LDO Powers Gate Drive from V
IN
or EXTV
CC
No Current Foldback During Start-Up
Small 5mm
×
5mm QFN Package
APPLICATIONS
n
n
n
Automotive Systems
Battery Operated Digital Devices
Distributed DC Power Systems
TYPICAL APPLICATION
High Efficiency Dual 8.5V/3.3V Step-Down Converter
4.7μF
V
IN
TG1
0.1μF
3.3μH
BOOST1
SW1
BG1
LTC3858
SENSE1
0.007Ω
V
OUT1
3.3V
5A
SENSE1
–
62.5k
150μF
20k
V
FB1
I
TH1
680pF
15k
0.1μF
SS1
SGND
SENSE2
–
V
FB2
I
TH2
SS2
0.1μF
680pF
15k
20k
193k
+
22μF
50V
V
IN
9V TO 38V
100
Efficiency and Power Loss
vs Load Current
10000
90
INTV
CC
TG2
BOOST2
SW2
BG2
PGND
SENSE2
+
0.1μF
7.2μH
EFFICIENCY (%)
80
70
60
50
40
30
V
OUT2
8.5V
3.5A
150μF
20
10
0
0.0001
0.001
EFFICIENCY
1000
POWER LOSS (mW)
100
POWER LOSS
10
0.01Ω
V
IN
= 12V
V
OUT
= 3.3V
FIGURE 12 CIRCUIT
0.01
0.1
1
OUTPUT CURRENT (A)
10
3858 TA01b
1
0.1
3858 TA01
3858fc
1
LTC3858
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SENSE1
+
PGOOD1
SW1
24 BOOST1
23 BG1
22 V
IN
33
SGND
21 PGND
20 EXTV
CC
19 INTV
CC
18 BG2
17 BOOST2
9 10 11 12 13 14 15 16
SENSE2
–
SENSE2
+
V
FB2
PGOOD2
SW2
I
TH2
TG2
SS2
V
FB1
I
TH1
I
LIM
TG1
SS1
Input Supply Voltage (V
IN
) ......................... –0.3V to 40V
Topside Driver Voltages
BOOST1, BOOST2 ................................. –0.3V to 46V
Switch Voltage (SW1, SW2) ........................ –5V to 40V
PLLIN/MODE,(BOOST1-SW1),
(BOOST2-SW2) ........................................... –0.3V to 6V
RUN1, RUN2 ............................................... –0.3V to 8V
Maximum Current Sourced into Pin
from Source >8V...............................................100μA
SENSE1
+
, SENSE2
+
, SENSE1
–
SENSE2
–
Voltages...................................... –0.3V to 28V
FREQ Voltages ..................................... –0.3V to INTV
CC
I
LIM
, PHASMD Voltages ....................... –0.3V to INTV
CC
EXTV
CC
...................................................... –0.3V to 14V
I
TH1
, I
TH2
,V
FB1
, V
FB2
Voltages ...................... –0.3V to 6V
PGOOD1, PGOOD2 Voltages ....................... –0.3V to 6V
SS1, SS2, INTV
CC
Voltages ......................... –0.3V to 6V
Operating Junction Temperature Range
(Note 2).................................................. –40°C to 125°C
Maximum Junction Temperature (Note 3) ............ 125°C
Storage Temperature Range................... –65°C to 150°C
32 31 30 29 28 27 26 25
SENSE1
–
1
FREQ 2
PHASMD 3
CLKOUT 4
PLLIN/MODE 5
SGND 6
RUN1 7
RUN2 8
UH PACKAGE
32-LEAD (5mm 5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 33) IS SGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3858EUH#PBF
LTC3858IUH#PBF
TAPE AND REEL
LTC3858EUH#TRPBF
LTC3858IUH#TRPBF
PART MARKING*
3858
3858
PACKAGE DESCRIPTION
32-Lead (5mm
×
5mm) Plastic QFN
32-Lead (5mm
×
5mm) 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/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
FB1,2
PARAMETER
Input Supply Operating Voltage Range
Regulated Feedback Voltage
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 12V, V
RUN1,2
= 5V, EXTV
CC
= 0V unless
otherwise noted.
CONDITIONS
(Note 4) I
TH1,2
= 1.2V
–40°C to 125°C
–40°C to 85°C
(Note 4)
(Note 4) V
IN
= 4.5V to 38V
MIN
4
l
TYP
MAX
38
UNITS
V
V
V
nA
%/V
3858fc
0.788
0.792
0.800
0.800
±5
0.002
0.812
0.808
±50
0.02
I
FB1,2
V
REFLNREG
Feedback Current
Reference Voltage Line Regulation
2
LTC3858
ELECTRICAL CHARACTERISTICS
SYMBOL
V
LOADREG
PARAMETER
Output Voltage Load Regulation
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 12V, V
RUN1,2
= 5V, EXTV
CC
= 0V unless
otherwise noted.
CONDITIONS
(Note4)
Measured in Servo Loop,
∆I
TH
Voltage = 1.2V to 0.7V
(Note4)
Measured in Servo Loop,
∆I
TH
Voltage = 1.2V to 2V
l
MIN
TYP
0.01
MAX
0.1
UNITS
%
l
–0.01
2
1.3
2
170
300
8
–0.1
%
mmho
mA
mA
g
m1,2
I
Q
Transconductance Amplifier g
m
Input DC Supply Current
Pulse Skip or Forced Continuous Mode
(One Channel On)
Pulse Skip or Forced Continuous Mode
(Both Channels On)
Sleep Mode (One Channel On)
Sleep Mode (Both Channels On)
Shutdown
(Note 4) I
TH1,2
= 1.2V, Sink/Source = 5μA
(Note 5)
RUN1 = 5V and RUN2 = 0V V
FB1
= 0.83V (No Load) or
,
RUN1 = 0V and RUN2 = 5V V
FB2
= 0.83V (No Load)
,
RUN1,2 = 5V, V
FB1,2
= 0.83V (No Load)
RUN1 = 5V and RUN2 = 0V V
FB1
= 0.83V (No Load) or
,
RUN1 = 0V and RUN2 = 5V V
FB2
= 0.83V (No Load)
,
RUN1,2 = 5V, V
FB1,2
= 0.83V (No Load)
RUN1,2 = 0V
INTV
CC
Ramping Up
INTV
CC
Ramping Down
Measured at V
FB1,2
, Relative to Regulated V
FB1,2
Each Channel
Each Channel
V
OUT1,2
< INTV
CC
– 0.5V
V
OUT1,2
> INTV
CC
+ 0.5V
In Dropout, FREQ = 0V
V
SS1,2
= 0V
V
RUN1
, V
RUN2
Rising
l
l
l
250
450
20
4.2
4
13
±1
±1
950
1.4
1.33
2.1
1.7
13
36
57
86
μA
μA
μA
V
V
%
μA
μA
μA
%
μA
V
mV
V
V
μA
mV
mV
mV
Ω
Ω
Ω
Ω
ns
ns
ns
ns
ns
3858fc
UVLO
V
OVL
I
SENSE+
I
SENSE–
Undervoltage Lockout
Feedback Overvoltage Protection
SENSE
+
Pin Current
SENSE
–
Pin Current
3.6
7
4.0
3.8
10
550
98
0.7
1.23
1.9
1.3
7
l
l
l
DF
MAX
I
SS1,2
V
RUN1,2
On
V
SS1,2
LA
V
SS1,2
LT
I
DSC1,2
LT
V
SENSE(MAX)
Maximum Duty Factor
Soft-Start Charge Current
RUN Pin On Threshold Voltage
99.4
1.0
1.28
50
2
1.5
10
30
50
75
2.5
1.5
2.4
1.1
V
RUN1,2
Hyst RUN Pin Hysteresis Voltage
SS Pin Latch-Off Arming Threshold Voltage V
SS1
, V
SS2
Rising from 1V
SS Pin Latch-Off Threshold Voltage
SS Discharge Current
V
SS1
, V
SS2
Falling from 2V
Short-Circuit Condition V
FB1,2
= 0V,
V
SS1,2
= 5V
Maximum Current Sense Threshold Voltage V
FB1,2
= 0.7V, V
SENSE1
–,
2
– = 3.3V, I
LIM
= 0
V
FB1,2
= 0.7V, V
SENSE1
–,
2
– = 3.3V, I
LIM
= FLOAT
V
FB1,2
= 0.7V, V
SENSE1
–,
2
– = 3.3V, I
LIM
= INTV
CC
Pull-Up On-Resistance
Pull-Down On-Resistance
Pull-Up On-Resistance
Pull-Down On-Resistance
TG Transistion Time:
Rise Time
Fall Time
BG Transistion Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
22
43
64
Gate Driver
TG1,2
BG1,2
TG1,2 t
r
TG1,2 t
f
BG1,2 t
r
BG1,2 t
f
TG/BG t
1D
25
16
28
13
30
3
LTC3858
ELECTRICAL CHARACTERISTICS
SYMBOL
BG/TG t
1D
t
ON(MIN)
V
INTVCCVIN
V
LDOVIN
V
INTVCCEXT
V
LDOEXT
V
EXTVCC
V
LDOHYS
f
25kΩ
f
65kΩ
f
105kΩ
f
LOW
f
HIGH
f
SYNC
V
PGL
I
PGOOD
V
PG
PARAMETER
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Hysteresis Voltage
Programmable Frequency
Programmable Frequency
Programmable Frequency
Low Fixed Frequency
High Fixed Frequency
Synchronizable Frequency
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level
R
FREQ
= 25k, PLLIN/MODE = DC Voltage
R
FREQ
= 65k, PLLIN/MODE = DC Voltage
R
FREQ
= 105k, PLLIN/MODE = DC Voltage
V
FREQ
= 0V, PLLIN/MODE = DC Voltage
V
FREQ
= INTV
CC
, PLLIN/MODE = DC Voltage
PLLIN/MODE = External Clock
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
FB
with Respect to Set Regulated Voltage
V
FB
Ramping Negative
Hysteresis
V
FB
with Respect to Set Regulated Voltage
V
FB
Ramping Positive
Hysteresis
t
PG
Delay for Reporting a Fault (PGOOD Low)
–13
–10
2.5
10
2.5
25
l
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 12V, V
RUN1,2
= 5V, EXTV
CC
= 0V unless
otherwise noted.
CONDITIONS
C
LOAD
= 3300pF Each Driver
(Note 7)
6V < V
IN
< 38V, V
EXTVCC
= 0V
I
CC
= 0mA to 50mA, V
EXTVCC
= 0V
6V < V
EXTVCC
< 13V
I
CC
= 0mA to 50mA, V
EXTVCC
= 8.5V
EXTV
CC
Ramping Positive
4.5
4.85
4.85
MIN
TYP
30
95
5.1
0.7
5.1
0.6
4.7
250
105
375
320
485
75
0.2
440
835
350
535
380
585
850
0.4
±1
–7
505
5.35
1.1
5.35
1.1
4.9
MAX
UNITS
ns
ns
V
%
V
%
V
mV
kHz
kHz
kHz
kHz
kHz
kHz
V
μA
%
%
%
%
μs
INTV
CC
Linear Regulator
Oscillator and Phase-Locked Loop
PGOOD1 and PGOOD2 Outputs
7
13
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Ratings for extended periods may affect device reliability and
lifetime.
Note 2:
The LTC3858 is tested under pulsed conditions such that T
J
≈ T
A
.
The LTC3858E is guaranteed to meet performance specifications from
0°C to 85°C. Specifications over the –40°C to 125°C operating junction
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3858I is guaranteed over the
full –40°C to 125°C operating junction temperature range. Note that
the maximum ambient temperature is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
resistance and other environmental factors.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
• 34°C/W)
Note 4:
The LTC3858 is tested in a feedback loop that servos V
ITH1,2
to a
specified voltage and measures the resultant V
FB1,2
. The specification at
85°C is not tested in production. This specification is assured by design,
characterization and correlation to production testing at 125°C.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications information.
Note 6:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels
Note 7:
The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥ of 40% I
MAX
(See Minimum On-Time
Considerations in the Applications Information section).
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