LINER LTC2977 Polyphase step-down slave controller for digital power system management Datasheet

LTC3870
PolyPhase Step-Down
Slave Controller for Digital
Power System Management
Description
Features
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LTC3880 Family Phase Extender Supporting
LTC3880/3880-1, LTC3883/3883-1, LTC3886,
LTC3887 Master Controllers
Cascade with Multiple Chips for Very Large Current
Applications
Accurate PolyPhase Current Sharing
EXTVCC Capable of 5V to 14V Input
Wide VIN Range: 4.5V to 60V
Wide Output Voltage Range : 0.5V to 14V
Wide SYNC Frequency Range: 100kHz to 1MHz
Pin Programmable of CCM/DCM Operation
Pin Programmable of Phase-Shift Control
Integrated Powerful N-Channel MOSFET Gate Drivers
Available in a 28-Pin (4mm × 5mm) QFN Package
The LTC®3870 is a PolyPhase® step-down slave controller specially designed for multiphase operation with the
LTC3880 family digital power system management DC/DC
controllers. It provides a small and cost effective solution
for supplying very large currents by cascading it with a
master controller. A peak current mode architecture provides the LTC3870 with excellent current sharing from
phase to phase and from chip to chip.
Coherently working with the LTC3880 family, the LTC3870
does not require additional I2C addresses, and it supports
all programmable features as well as fault protection.
The constant switching frequency can be synchronized
to an external clock from the master controller from
100kHz to 1MHz.
Applications
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L, LT, LTC, LTM, PolyPhase, Linear Technology and the Linear logo 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,
6580258, 5408150
High Power Distributed Power Systems
Telecom Systems
Industrial Applications
Typical Application
Load Transient Response of a
2-Phase Master (3880)/Slave
(3870) Converter
VIN
4.7µF
VOUT0
30A
+
VIN
INTVCC
TG0
1.0µH
530µF
0.1µF
TG1
BOOST0
BOOST1
SW0
BG0
2.15k
BG1
PGND
0.2µF
0.1µF
SW1
1.74k
EXTVCC
LTC3880*
RUN0
3.3V
RUN1
VSENSE0+ GPIO0
GPIO1
ITH0
1.8V
VSENSE1
ITH1
SYNC
* REFER TO LTC3880 DATA SHEET
FOR MASTER SETUP
RUN0
RUN1
FAULT0
FAULT1
ITH0
ITH1
SYNC
+
530µF
0.2µF
LTC3870
ISENSE0+
ISENSE0–
VOUT1
40A
0.56µH
IL_3880(CH1)
10A/DIV
IL_3870(CH1)
10A/DIV
ISENSE1+
ISENSE1–
FREQ
PHASMD
ILIM
MODE0
MODE1
SGND
ILOAD
10A/DIV
0A TO 10A TO 0A
VOUT1
100mV/DIV
AC-COUPLED
100k
VIN = 12V
VOUT1 = 1.8V
50µs/DIV
3870 TA01b
3870 TA01a
3870fb
For more information www.linear.com/LTC3870
1
LTC3870
Absolute Maximum Ratings
Pin Configuration
(Note 1)
VIN.............................................................. –0.3V to 65V
BOOST0, BOOST1........................................–0.3V to 71V
SW0, SW1..................................................... –5V to 65V
ISENSE0+, ISENSE0−, ISENSE1+, ISENSE1–..........–0.3V to 15V
(BOOST0-SW0), (BOOST1-SW1).................. –0.3V to 6V
INTVCC, RUN0/RUN1.................................... –0.3V to 6V
EXTVCC....................................................... –0.3V to 14V
MODE0/MODE1, FREQ, PHASMD, ILIM....–0.3V to INTVCC
FAULT0/FAULT1, ITH0/ITH1, SYNC............... –0.3V to 3.6V
INTVCC, EXTVCC Peak Current (Note 9)................100mA
Operating Junction Temperature Range
........................................................... –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
SW0
TG0
FAULT1
FAULT0
FREQ
ITH0
TOP VIEW
28 27 26 25 24 23
22 BOOST0
MODE0 1
ISENSE0+ 2
21 BG0
ISENSE0– 3
20 VIN
29
SGND
RUN0 4
RUN1 5
19 PGND
18 EXTVCC
ISENSE1– 6
17 INTVCC
ISENSE1+ 7
16 BG1
MODE1 8
15 BOOST1
SW1
TG1
PHASMD
SYNC
ILIM
ITH1
9 10 11 12 13 14
UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 43°C/W, θJC_BOT = 3.4°C/W
EXPOSED PAD (PIN 29) IS SGND, MUST BE SOLDERED TO PCB
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3870EUFD#PBF
LTC3870EUFD#TRPBF
3870
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LTC3870IUFD#PBF
LTC3870IUFD#TRPBF
3870
28-Lead (4mm × 5mm) Plastic QFN
–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 nonstandard 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
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 15V, VRUN0,VRUN1 = 3.3V, fSYNC = 350kHz
(externally driven) unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
VIN
Input Voltage Range
(Note 3)
4.5
60
V
VOUT
Output Voltage Range
(Note 4)
0.5
14
V
IQ
Input Voltage Supply Current
Normal Operation
VRUN0,VRUN1 = 0V (Note 5)
VRUN0,VRUN1 = 3.3V, No Caps on TG and BG
1.1
2.6
mA
mA
VUVLO
Undervoltage Lockout Threshold
When VIN > 4.2V
VINTVCC Falling
VINTVCC Rising
3.7
4.0
V
V
2
TYP
MAX
UNITS
3870fb
For more information www.linear.com/LTC3870
LTC3870
Electrical Characteristics
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 15V, VRUN0,VRUN1 = 3.3V, fSYNC = 350kHz
(externally driven) unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
IISENSE0+,
IISENSE1+
Current Sense + Pin Current
VISENSE0,1+ = 3.3V
IISENSE0–,
IISENSE1–
Current Sense − Pin Current
VIILIMIT
MIN
TYP
MAX
UNITS
l
±0.1
±1
µA
VISENSE0,1– = 3.3V
l
±0.1
±1
µA
Maximum Current Sense threshold
(High Range)
VITH = 2.22V, ILIM = INTVCC
l
70
75
80
mV
Maximum Current Sense threshold
(Low Range)
VITH = 2.22V, ILIM = GND
l
45
50
55
mV
Control Loop
Gate Drivers
TG RUP
Pull-Up On-Resistance
TG High
2.5
Ω
TG RDOWN
Pull-down On-Resistance
TG Low
1.5
Ω
BG RUP
Pull-Up On-Resistance
BG High
2.4
Ω
BG RDOWN
Pull-down On-Resistance
BG Low
1.1
Ω
TG0, TG1
tr
tf
TG Transition Time:
Rise Time
Fall Time
(Note 6)
CLOAD = 3300pF
CLOAD = 3300pF
30
30
ns
ns
BG0, BG1
tr
tf
BG Transition Time:
Rise Time
Fall Time
(Note 6)
CLOAD = 3300pF
CLOAD = 3300pF
30
30
ns
ns
TG/BG t1D
Top Gate Off to Bottom Gate On Delay Time
(Note 6)
CLOAD = 3300pF Each Driver
30
ns
BG/TG t2D
Bottom Gate Off to Top Gate On Delay Time
(Note 6)
CLOAD = 3300pF Each Driver
30
ns
tON(MIN)
Minimum On-Time
(Note 7)
90
ns
INTVCC Regulator
VINTVCC_VIN
Internal VCC Voltage No Load
6.0V <VIN <60V, VEXTVCC = 0 V
VLDO INT
INTVCC Load Regulation
ICC = 0mA to 50mA, VEXTVCC = 0V
VINTVCC_EXT
Internal VCC Voltage No Load
VEXTVCC = 8.5V (Note 8)
VLDO EXT
INTVCC Load Regulation with EXTVCC
ICC = 0 to 20mA, VEXTVCC = 8.5V
VEXTVCC
EXTVCC Switchover Voltage
VEXTVCC Ramping Positive (Note 8)
VHYS_EXTVCC
EXTVCC HYSTERESIS
4.85
4.85
4.7
5.1
5.35
V
0.8
±2
%
5.1
5.35
V
0.5
±2
%
4.8
4.9
V
200
mV
Oscillator and Phase-Locked Loop
fSNYC
Oscillator SYNC Range
VTH,SYNC
SYNC Input Threshold
VTH,sync Falling (Note 9)
VTH,sync Rising
fNOM
Nominal Frequency
VFREQ = 1.0V
IFREQ
FREQ setting current
θ SYNC-θ0
SYNC to Ch0 Phase Relationship Based on
the Falling Edge of Sync and Rising Edge of
TG0
PHASMD = 0
PHASMD = 1/3 INTVCC
PHASMD = 2/3 INTVCC
PHASMD = INTVCC
180
60
120
90
Deg
Deg
Deg
Deg
θ SYNC-θ1
SYNC to Ch1 Phase Relationship Based on
the Falling Edge of Sync and Rising Edge of
TG1
PHASMD = 0
PHASMD = 1/3 INTVCC
PHASMD = 2/3 INTVCC
PHASMD = INTVCC
0
300
240
270
Deg
Deg
Deg
Deg
l
100
1000
0.4
2.0
V
V
500
9
10
kHz
kHz
11
µA
3870fb
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3
LTC3870
Electrical Characteristics
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 15V, VRUN0,VRUN1 = 3.3V, fSYNC = 350kHz
(externally driven) unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Digital Inputs RUN0/RUN1, MODE0/MODE1, FAULT0/FAULT1
VIH
Input High Threshold Voltage
l
VIL
Input Low Threshold Voltage
l
Note 1: Stresses beyond those listed in 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 LTC3870 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3870E is guaranteed to meet specifications from
0°C to 85°C junction temperature. Specifications over the –40°C to
125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3870I is guaranteed over the full –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 related package thermal
impedance and other environmental factors. The junction temperature TJ
is calculated from the ambient temperature TA and power dissipation PD
according to the following formula:
TJ = TA + (PD • 43°C/W)
2.0
V
1.4
V
Note 3: When VIN >15V, EXTVCC is recommended to reduce IC
Temperature.
Note 4: Output voltage is set and controlled by the master controller in
multiphase operations.
Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Application 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 corresponds to an inductor
peak-to-peak ripple current ≥40% of IMAX (see Minimum On-Time
Considerations in the Applications Information section.
Note 8: EXTVCC is enabled only if VIN is higher than 6.5V.
Note 9: Guaranteed by design.
Typical Performance Characteristics
90
100
DCM
CCM
90
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
VIN = 12V
VOUT = 1.8V
fSW = 400kHz
L = 0.56µH
DCR = 1.8mΩ
1
10
LOAD CURRENT (A)
100
3870 G01
4
93
80
70
60
50
40
20
10
0
0.1
VIN = 12V
VOUT = 3.3V
fSW = 400kHz
L = 0.56µH
DCR = 1.8mΩ
1
10
LOAD CURRENT (A)
100
3870 G02
3
2.5
92
70
30
POWER LOSS
EFFICIENCY
2
91
1.5
90
1
89
88
87
0.5
VIN = 12V
VOUT = 1.8V
5
7
9
POWER LOSS (W)
EFFICIENCY (%)
80
94
DCM
CCM
EFFICIENCY (%)
100
Full Load Efficiency and Power
Loss vs Input Voltage
Efficiency vs Load Current
Efficiency vs Load Current
11
13
15
INPUT VOLTAGE (V)
17
19
0
3870 G03
3870fb
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LTC3870
Typical Performance Characteristics
Load Step (Forced Continuous
Mode) 4-Phase Operation
LTC3880 and LTC3870
Load Step (Discontinuous
Conduction Mode) 4-Phase
Operation LTC3880 and LTC3870
ILOAD
20A/DIV
0A TO 20A TO 0A
ILOAD
20A/DIV
0A TO 20A TO 0A
IL_3880(CH0)
10A/DIV
IL_3880(CH0)
10A/DIV
IL_3870(CH0)
10A/DIV
IL_3870(CH0)
10A/DIV
VOUT
100mV/DIV
AC-COUPLED
VOUT
100mV/DIV
AC-COUPLED
IL_3870(CH0)
FORCED CONTINUOUS
MODE
5A/DIV
IL_3870(CH0)
DISCONTINUOUS
CONDUCTION MODE
5A/DIV
3870 G04
50µs/DIV
3870 G05
50µs/DIV
VIN = 12V
VOUT = 1.8V
Start-Up Into a Pre-Biased
Output 4-Phase Operation
LTC3880 and LTC3870
Current Sense Threshold
vs ITH Voltage
80
INTVCC Line Regulation
6
RANGE HIGH
RANGE LOW
5
2ms/DIV
3870 G07
VIN = 12V
VOUT = 1.8V
INTVCC VOLTAGE (V)
VISENSE (mV)
60
VOUT
LTC3870 IN DCM
500mV/DIV
40
20
0
4
3
2
1
–20
–40
3870 G06
1µs/DIV
VIN = 12V
VOUT = 1.8V
ILOAD = 1A
VIN = 12V
VOUT = 1.8V
RUN
ALL RUN PINS
TIED TOGETHER
2V/DIV
Inductor Current at Light Load
0
0.5
1
1.5
VITH (V)
2
0
2.5
0
10
20
30
40
INPUT VOLTAGE (V)
50
3870 G09
3870 G08
Dynamic Current Sharing During
a Load Transient in a 4-Phase
Operation LTC3880 and LTC3870
DC Output Current Matching
Between LTC3880 and LTC3870
Quiescent Current vs Input
Voltage Without EXTVCC
3.5
25
3
SUPPLY CURRENT (mA)
CHANNEL CURRENT (A)
20
IL_3880(CH0)
IL_3880(CH1)
IL_3870(CH0)
IL_3870(CH1)
5A/DIV
15
10
LTC3880 CH0
LTC3880 CH1
LTC3870 CH0
LTC3870 CH1
5
0
60
0
10
20 30 40 50 60 70 80
TOTAL OUTPUT CURRENT (A)
50µs/DIV
ILOAD 0A TO 32A TO 0A
3870 G11
90
2.5
2
1.5
1
0.5
0
0
10
20
30
40
INPUT VOLTAGE (V)
50
60
3870 G12
3870 G10
3870fb
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5
LTC3870
Pin Functions
MODE0/MODE1 (Pin 1/Pin 8): DCM/CCM Mode Control
Pins. Channel0/Channel1 operates in forced continuous
mode if MODE0/MODE1 pin is logic high. There is a 500kΩ
pull down resistor on MODE0/MODE1 internally. The
default operation mode in each channel is discontinuous
mode operation unless these pins are actively driven high.
ISENSE0+/ISENSE1+ (Pin 2/Pin 7): Current Sense Comparator
positive inputs, normally connected to the positive node
of the DCR sensing networks or current sensing resistors.
ISENSE0−/ISENSE1− (Pin 3/Pin 6): Current Sense Comparator
negative inputs, normally connected to the negative node
of the DCR sensing network or current sensing resistors.
RUN0/RUN1 (Pin 4/Pin 5): Enable RUN Input Pins. Logic
high on these pins enables the corresponding channel. In
multiphase operation, these pins are connected to master
RUN pins.
ITH0/ITH1 (Pin 28/Pin 9): Current Control Threshold. Each
associated channel’s current comparator tripping threshold
increases with its ITH voltage. In multiphase operation,
these pins are connected to the master controller’s ITH
pins for current sharing.
ILIM (Pin 10): Program Current Comparators’ Sense
Voltage Range. This pin can be tied to SGND or INTVCC
to select the maximum current sense threshold for each
current comparator. SGND sets both channels’ current low
range with maximum 50mV sensing voltage. INTVCC sets
both channels’ current high range with maximum 75mV
sensing voltage. For equal current sharing, the setup on
the ILIM pin has to be same as the setup on the bit 7 of
MFR_PWM_MODE_3880/3883/3886/3887 register in the
master controller. See Table 2 in the Operation Section
for details.
SYNC (Pin 11): External Clock Synchronization Input. If an
external clock is present at this pin, the switching frequency
will be synchronized to the falling edge of the external
clock. In multiphase operation, this pin is connected to
the master's SYNC pin for frequency synchronization. Do
not float the SYNC pin.
6
PHASMD (Pin 12): Phase Set Pin. This pin can be tied to
SGND, INTVCC or a resistor divider from INTVCC to SGND.
This pin determines the relative phases between the ext­
ernal clock on the SYNC pin and the internal controllers.
See Table 1 in the Operation Section for details.
TG0/TG1 (Pin 24/Pin 13): Top Gate Driver Outputs. These
are the outputs of floating drivers with a voltage swing
equal to INTVCC superimposed on the switch node voltages.
SW0/SW1 (Pin 23/Pin 14): Switch Node Connections to
Inductors. Voltage swings at the pins are from a Schottky
diode (external) voltage drop below ground to VIN.
BOOST0/BOOST1 (Pin 22/Pin 15): Boosted Floating Driver
Supplies. The (+) terminal of the bootstrap capacitors connect to these pins. These pins swing from a diode voltage
drop below INTVCC up to VIN + INTVCC.
BG0/BG1 (Pin 21/Pin 16): Bottom Gate Driver Outputs.
These pins drive the gates of the bottom N-Channel MOSFETs between PGND and INTVCC.
INTVCC (Pin 17): Internal Regulator 5V Output. The
internal control circuits are powered from this voltage.
Bypass this pin to PGND with a minimum of 4.7µF low
ESR tantalum or ceramic capacitor. INTVCC is enabled as
soon as VIN is powered.
EXTVCC (Pin 18): External power input to an internal LDO
connected to INTVCC. This LDO supplies INTVCC power
bypassing the internal LDO powered from VIN whenever
EXTVCC is higher than 4.8V. See EXTVCC connection in the
Applications Information Section. Do not exceed 14V on
this pin. Bypass this pin to PGND with a minimum of 4.7µF
low ESR tantalum or ceramic capacitor. If the EXTVCC pin
is not used, leave it open or tie it to ground. EXTVCC can
be present before VIN. However, EXTVCC is enabled only
if VIN is higher than 6.5V.
PGND (Pin 19): Power Ground Pin. Connect this pin closely
to the sources of the bottom N-Channel MOSFETs and the
(–) terminals of CIN.
VIN (Pin 20): Main Input Supply. Bypass this pin to PGND
with a capacitor (0.1µF to 1µF).
3870fb
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LTC3870
Pin Functions
FAULT0/FAULT1 (Pin 26/Pin 25): Fault Input Pins. Connect these pins to the master chip GPIO pins to respond
to fault signals from the master controller. If this pin is
low, both TG and BG pins are pulled down at the corresponding channel. There is a 500k pull down resistor on
FAULT0/FAULT1 internally. These pins have to be driven
high externally for normal operation.
FREQ (Pin 27): Frequency Set Pin. There is a precision
10µA current flowing out of this pin. A resistor to ground
sets a voltage which in turn programs the frequency. This
pin sets the default switching frequency when there is no
external clock on the SYNC pin. Set the frequency close
to the external clock to help the internal PLL sync to the
SYNC pin clock quickly and smoothly. See the application
section for the detailed information.
SGND (Exposed Pad Pin 29): Signal Ground. All smallsignal and compensation components should connect to
this ground, which in turn connects to PGND at one point.
The exposed pad must be soldered to the PCB, providing
a local ground for the control components of the IC, and
be tied to PGND under the IC.
3870fb
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7
LTC3870
Block Diagram
(CH0 Shown)
SYNC
PHASMD
11
12
10µA SYNC
DET
EXTVCC
18
4.8V
PFD
27
VIN
+
–
PHASE
PROGRAM
20
FREQ
OSC
VCO
S
R
–
+
ICMP
3K
5.0V
LDO
EN
Q
5.0V
LDO
EN
–
+
BOOST0
22
REV
UVLO
10
ILIM RANGE SELECT
HI: 1:1
LO: 1:1.5
FAULTB
INTVCC
VIN
CIN
INTVCC
17
IREV
TG0
24
SW0
23
ON
ILIM
+
FCNT
UVLO
RUN
SWITCH
LOGIC
AND
ANTISHOOTTHROUGH
CB
M1
L
DB
BG0
21
PGND
19
SLOPE
COMPENSATION
CVCC
RC
CC
+
VOUT0
COUT0
M2
ISENSE0+
2
ISENSE0–
3
1
71.1k
+
–
+
–
+
–
INTVCC
1.7V
ITH0 28
1
4
26
MODE0
RUN0
FAULT0
REF
29
SGND
3870 BD
8
3870fb
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LTC3870
Operation
Main Control Loop
The LTC3870 is a constant frequency, current mode
step-down slave controller for parallel operation with the
LTC3880 family master controllers. During normal operation, each top MOSFET is turned on when the clock for
that channel sets the RS latch, and turned off when the
main current comparator, ICMP, resets the RS latch. The
peak inductor current at which ICMP resets the RS latch
is controlled by the voltage on the ITH pin, which is tied
directly to the corresponding ITH pin of the master controllers. When the load current increases, master controllers
drive and increase the ITH voltage, which in turn cause
the peak current in the corresponding slave channels to
increase, until the average inductor current matches the
new load current. After the top MOSFET has been turned
off, the bottom MOSFET is turned on until the beginning
of the next cycle in Continuous Conduction Mode (CCM)
or until the inductor current starts to reverse, as indicated
by the reverse current comparator IREV, in Discontinuous
Conduction Mode (DCM). The LTC3870 slave controllers
DO NOT regulate the output voltage but regulate the current
in each channel for current sharing with master controllers.
Output voltage regulation is achieved through the voltage
feedback loops in master controllers.
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTVCC pin.
Normally an internal 5.0V linear regulator supplies INTVCC
power from VIN. In high VIN applications, if a high efficiency external voltage source is available for the EXTVCC
pin, another internal 5.0V linear regulator is enabled and
supplies INTVCC power from EXTVCC. To enable the linear
regulator driven by the EXTVCC pin, VIN has to be higher
than 6.5V and EXTVCC pin voltage has to be higher than
4.8V. Do not exceed 14V on the EXTVCC pin.
Each top MOSFET driver is biased from the floating
bootstrap capacitor CB, which normally recharges during
each off cycle through an external diode when the top
MOSFET turns off. If the input voltage VIN decreases to
a voltage close to VOUT, the loop may enter dropout and
attempt to turn on the top MOSFET continuously. The
dropout detector detects this and forces the top MOSFET
off for about one-twelfth of the clock period plus 100ns
every three cycles to allow CB to recharge. However, it is
recommended that a load be present or the IC operates
at low frequency during the drop-out transition to ensure
CB is recharged.
Start-Up and Shutdown (RUN0, RUN1)
The two channels of the LTC3870 can independently
start up and shut down using the RUN0 and RUN1 pins.
Pulling either of these pins below 1.4V shuts down the
control circuits for that channel. During shutdown, both
TG and BG are pulled down to turn off the external power
MOSFETs. Pulling either of these pins above 2V enables
the corresponding channel and internal circuits. During
startup, the RUN0/RUN1 pins are actively pulled down
until the INTVCC voltage passes the under-voltage lockout
threshold of 4V. For multiphase parallel operation, the
RUN0/RUN1 pins have to be connected and driven by
the RUN pins of the master controller. Do not exceed the
Absolute Maximum Rating of 6V on these pins.
The start-up of each channel’s output voltage VOUT is
controlled and programmed by the master controller. After
the RUN pins are released, the master controller drives the
output based on the programmed delay time and rise time,
and the slave controller LTC3870 just follows the master
to supply equivalent current to the output during startup.
Light Load Current Operation (Discontinuous
Conduction Mode, Continuous Conduction Mode)
The LTC3870 can be set to operate either in Discontinuous
Conduction Mode (DCM) or forced Continuous Conduction Mode (CCM). To select forced Continuous Mode of
operation, tie the MODE pin to a DC voltage above 2V
(e.g., INTVCC). To select discontinuous conduction mode
of operation, tie the MODE pin to a DC voltage below 1.4V
(e.g., SGND). In forced continuous operation, the inductor current is allowed to reverse at light loads or under
large transient conditions. The peak inductor current is
determined by the voltage on the ITH pin. In this mode,
the efficiency at light loads is lower than in discontinuous Mode operation. However, continuous mode has the
advantages of lower output ripple and less interference
with audio circuitry. When the MODE pin is connected to
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9
LTC3870
Operation
SGND, the LTC3870 operates in discontinuous mode at
light loads. At very light loads, the current comparator
ICMP may remain tripped for several cycles and force the
external top MOSFET to stay off for the same number of
cycles (i.e., skipping pulses). This mode provides higher
light load efficiency than forced continuous mode and the
inductor current is not allowed to reverse. There are 500k
pull down resistors internally connected to the MODE0/
MODE1 pins. If MODE0/MODE1 pins are floating, both
channels default to discontinuous conduction mode.
Multichip Operation (PHASMD and SYNC Pins)
The PHASMD pin determines the relative phases between
the internal channels as well as the external clock signal on
the SYNC pin, as shown in Table 1. The phases tabulated
are relative to zero degree phase being defined as the
falling edge of the clock on SYNC.
Table 1.
PHASMD
Channel 0 Phase
Channel 1 Phase
GND
180°
0°
1/3 INTVCC
60°
300°
2/3 INTVCC or Float
120°
240°
INTVCC
90°
270°
The SYNC pin is used to synchronize switching frequency
between master and slave controllers. Input capacitance
ESR requirements and efficiency losses are substantially
reduced because the peak current drawn from the input
capacitor is effectively divided by the number of phases
used and power loss is proportional to the RMS current
squared. A two-phase, single output voltage implementation can reduce input path power loss by 75% and radically reduce the required RMS current rating of the input
capacitor(s).
10
Single Output Multiphase Operation
The LTC3870 is designed for multiphase converters with
the master controller by making these connections:
Tie all the ITH pins of paralleled channels together for
current sharing between masters and slaves. Note that
ILIM setup on slaves has to match MFR_PWM_MODE
current range setup in masters.
Tie all SYNC pins together between master and slaves for
same switching frequency synchronization; one and only
one of the master controllers has to be programmed
as master to generate clock signal on the SYNC pin.
Tie all the RUN pins of paralleled channels together between
master and slaves for startup and shutdown sequences.
Tie the GPIO pin of the master controller to the FAULT pin
of slave controllers and program the master GPIO as
fault sharing for fault protections.
Examples of single output multiphase converters are
shown in Figure 1.
Inductor Current Sensing
Like the LTC3880/LTC3883, LTC3870 can use either inductor DCR or RSENSE to sense the inductor current. Inductor
DCR current sensing provides a lossless method of sensing the instantaneous current. Therefore, it can provide
higher efficiency for applications with high output currents.
However, the DCR of a copper inductor typically has 10%
tolerance. For precise current sensing, a precision sensing
resistor RSENSE can be used to sense the inductor current.
It is important to match the current sensing circuit between
master controllers and slave controllers to guarantee balanced load sharing and overcurrent protection.
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LTC3870
Operation
2+2
CH0 CH1
1+3
CH0
0°
CH1
120°
180°
CH0
240°
LTC3870
LTC3880
CH1
0°
180°
LTC3880
PHASMD = 2/3 INTVCC OR FLOAT
CH0
CH1
180°
0°
LTC3870
PHASMD = GND
4 PHASE OPERATION
CH0
CH1
90°
270°
LTC3870
6 PHASE OPERATION
CH0
CH1
0°
CH0
180°
LTC3880
CH1
0°
180°
CH0
LTC3880
PHASMD = INTVCC
CH1
60°
300°
CH0
CH1
120°
240°
LTC3870
LTC3870
PHASMD = 1/3 INTVCC
PHASMD = 2/3 INTVCC
3870 F01
Figure 1. Examples of Single/Dual Output Multiphase Converters
Frequency Selection and Phase-Locked Loop (FREQ
and SYNC Pins)
LTC3870. The phase-locked loop is capable of locking to
any frequency within the range of 100kHz to 1MHz.
The selection of switching frequency is a trade-off between
efficiency and component size. Low frequency operation
increases efficiency by reducing MOSFET switching losses,
but requires larger inductance and/or capacitance to maintain low output ripple voltage. The switching frequency of
the LTC3870 controllers can be synchronized to the falling
edge of the external clock on the SYNC pin or selected using the FREQ pin. A phase-locked loop (PLL) is integrated
in the LTC3870 to synchronize the internal oscillator to an
external clock source that is connected to the SYNC pin;
this source is normally provided by the master controllers. The PLL loop filter network is integrated inside the
If the SYNC pin is not being driven by an external clock
source, the FREQ pin can be used to program the LTC3870’s
operating frequency from 100kHz to 1MHz. There is a
precision 10µA current flowing out of the FREQ pin, so
the user can program the controller’s switching frequency
with a single resistor to SGND. A curve is provided later in
the application section showing the relationship between
the voltage on the FREQ pin and switching frequency. The
frequency setting resistor should always be present to set
the controller’s initial switching frequency before locking
to the external clock.
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11
LTC3870
Applications Information
The Typical Application on the first page of this data sheet is
a basic LTC3870 application circuit featuring the LTC3880
as a slave controller. In paralleled operation, the current
sensing scheme as well as the power stage parameters
in LTC3870 must be the same as the master controller to
achieve balanced current sharing between masters and
slaves. Finally, input and output capacitors are selected
based on RMS current rating, ripple, and transient specs.
Current Limit Programming
To match the master controller current limit, each channel of LTC3870 can be programmed separately with two
current ranges. The ILIM pin of LTC3870 is a 4-level logic
input which sets the current limit of LTC3870. When ILIM
is grounded, both channel0 and channel1 are set to be low
current range. When ILIM is tied to INTVCC, both channel0
and channel1 are set to be high current range. Here, low
current range means the current sense threshold linearly
increases from 0mV to 50mV as ITH voltage is increased
from 0.5V to 2.22V without slope compensation. High current range means the current sense threshold increases to
75mV as ITH voltage is increased to 2.22V without slope
compensation. Set ILIM to one-third INTVCC for channel0
high current range and channel1 low current range. Set
ILIM to two-thirds INTVCC or float for channel0 low current
range and channel1 high current range. The summary of
ILIM pin setups is shown in Table 2. For balanced load
current sharing, use the same current range setting as
in the master controller. Note that the LTC3870 does not
have active clamping circuit on ITH pin for peak current
limit and over current protection. Over current protection
relies on the master controller to drive and clamp the ITH
pin voltage not to exceed the programmed voltage through
the PMBus command.
Table 2.
ILIM
Channel 0
Current limit
Channel 1
Current limit
GND
Range Low
Range Low
1/3 INTVCC
Range High
Range Low
2/3 INTVCC or Float
Range Low
Range High
INTVCC
Range High
Range High
12
INTVCC Regulators and EXTVCC
The LTC3870 features a PMOS LDO that supplies power
to INTVCC from the VIN supply. INTVCC powers the gate
drivers and most of the LTC3870’s internal circuitry. The
linear regulator regulates the voltage at the INTVCC pin
to 5.0V when VIN is greater than 6V. EXTVCC connects to
INTVCC through another PMOS LDO and can supply the
needed power when its voltage is higher than 4.8V and
VIN is higher than 6.5V. Each of these LDOs can supply a
peak current of 100mA and must be bypassed to ground
with a minimum of 4.7µF ceramic capacitor or low ESR
electrolytic capacitor. No matter what type of bulk capacitor is used, an additional 0.1µF ceramic capacitor placed
directly adjacent to the INTVCC and PGND pins is highly
recommended. Good bypassing is needed to supply the
high transient currents required by the MOSFET gate
drivers and to prevent interaction between the channels.
High input voltage applications in which large MOSFETs are
being driven at high frequencies may cause the maximum
junction temperature rating for the LTC3870 to be exceeded.
The INTVCC current, which is dominated by the gate charge
current, may be supplied by either the 5.0V linear regulator from VIN or the linear regulator from EXTVCC. When
the voltage on the EXTVCC pin is less than 4.8V, the linear
regulator from VIN is enabled. Power dissipation for the
IC in this case is highest and is equal to VIN • IINTVCC. The
gate charge current is dependent on operating frequency.
The junction temperature can be estimated by using the
equations given in Note 2 of the Electrical Characteristics.
For example, the LTC3870 INTVCC current is limited to less
than 34mA from a 38V supply in the UFD package and not
using the EXTVCC supply:
TJ = 70°C + (34mA)(38V)(43°C/W) = 125°C
where ambient temperature is 70°C and thermal resistance
from junction to ambient is 43°C/W.
To prevent the maximum junction temperature from being exceeded, the input supply current must be checked
while operating in continuous conduction mode (MODE
= INTVCC) at maximum VIN. When the voltage applied to
EXTVCC rises above 4.8V and VIN above 6.5V, the INTVCC
linear regulator is turned off and the EXTVCC linear regulator
is turned on. Using the EXTVCC allows the MOSFET driver
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LTC3870
Applications Information
and control power to be derived from other high efficiency
sources such as +5V or +12V rails in the system. Using
EXTVCC can significantly reduce the IC temperature in
high VIN applications. Tying the EXTVCC pin to a 5V supply
reduces the junction temperature in the previous example
from 125°C to: TJ = 70°C + (34mA) (5V) (43°C/W) = 77°C.
Do not apply more than 14V to the EXTVCC pin.
For applications where the main input power is 5V, tie
the VIN and INTVCC pins together and tie the combined
pins to the 5V input with a 1Ω or 2.2Ω resistor as shown
in Figure 2 to minimize the voltage drop caused by the
gate charge current. This will override the INTVCC linear
regulator and will prevent INTVCC from dropping too low
due to the dropout voltage. Make sure the INTVCC voltage
is at or exceeds the RDS(ON) test voltage for the MOSFET
which is typically 4.5V for logic-level devices.
LTC3870
VIN
INTVCC
RVIN
1Ω
5V
CINTVCC
4.7µF
+
CIN
3870 F04
Figure 2. Setup for a 5V Input
Topside MOSFET Driver Supply (CB, DB)
External bootstrap capacitor CB, connected to the BOOST
pin, supplies the gate drive voltages for the topside MOSFET. Capacitor CB in the Functional Diagram is charged
though external diode DB from INTVCC when the SW pin
is low. When the topside MOSFET is to be turned on, the
driver places the CB voltage across the gate source of the
MOSFET. This enhances the MOSFET and turns on the
topside switch. The switch node voltage, SW, rises to VIN
and the BOOST pin follows. With the topside MOSFET on,
the boost voltage is above the input supply:
VBOOST = VIN + VINTVCC – VDB
The value of the boost capacitor, CB, needs to be 100 times
that of the total input capacitance of the topside MOSFET(s).
The reverse breakdown of the external Schottky diode must
be greater than VIN(MAX). When adjusting the gate drive level,
the final arbiter is the total input current for the regulator.
If a change is made and the input current decreases, then
the efficiency has improved. If there is no change in input
current, then there is no change in efficiency.
Undervoltage Lockout
The LTC3870 has a precision UVLO comparator constantly
monitoring the INTVCC voltage to ensure that an adequate
gate-drive voltage is present. It locks out the switching
action and pulls down RUN pins when INTVCC is below
3.7V. To prevent oscillation when there is a disturbance on
the INTVCC, the UVLO comparator has 300mV of precision
hysteresis. In multiphase operation, when LTC3870 is in
undervoltage lockout, the RUN0 and RUN1 pins are pulled
down to disable the master’s switching action.
Phase-Locked Loop and Frequency Synchronization
The LTC3870 has a phase-locked loop (PLL) comprised
of an internal voltage-controlled oscillator (VCO) and a
phase detector. This allows the internal clock to be locked
to the falling edge of an external clock signal applied to
the SYNC pin. The turn-on of channel 0/channel 1’s top
MOSFET is synchronized or out-of-phase with the falling
edge of the external clock. The phase detector is an edge
sensitive digital type that provides zero degree phase shift
between the external and internal oscillators. This type of
phase detector does not exhibit false lock to harmonics
of the external clock.
The output of the phase detector is a pair of complementary
current sources that charge or discharge the internal filter
network. There is a precision 10µA of current flowing out of
the FREQ pin. This allows the user to use a single resistor
to SGND to set the switching frequency when no external
clock is applied to the SYNC pin. The voltage on the FREQ
pin is equal to the resistance multiplied by 10µA current
(e.g. the voltage is 1V with a 100k resistor from the FREQ
pin to SGND). The internal switch between FREQ pin and
the integrated PLL filter network is ON, allowing the filter
network to be pre-charged to the same voltage potential
as the FREQ pin. The relationship between the voltage
on the FREQ pin and the operating frequency is shown
in Figure 3 and specified in the Electrical Characteristic
table. If an external clock is detected on the SYNC pin, the
internal switch mentioned above will turn off and isolate
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13
LTC3870
Applications Information
the influence of FREQ pin. Note that the LTC3870 can only
be synchronized to an external clock whose frequency is
within the range of the LTC3870’s internal VCO. This is
guaranteed to be between 100kHz and 1MHz. A simplified
block diagram is shown in Figure 4.
1400
SWITCHING FREQUENCY (kHz)
1200
1000
If the external clock frequency is greater than the internal oscillator’s frequency, fOSC, then current is sourced
continuously from the phase detector output, pulling up
the filter network. When the external clock frequency is
less than fOSC, current is sunk continuously, pulling down
the filter network. If the external and internal frequencies
are the same but exhibit a phase difference, the current
sources turn on for an amount of time corresponding to
the phase difference. The voltage on the filter network is
adjusted until the phase and frequency of the internal and
external oscillators are identical. At the stable operating
point, the phase detector output is high impedance and
the filter capacitor holds the voltage.
Typically, the external clock (on SYNC pin) input high
threshold is 2V, while the input low threshold is 0.4V.
Fault Protection and Responses
LTC3880 family master controllers monitor system voltage,
current, and temperature and provide many protection
features during fault conditions. LTC3870 slave controllers do not provide as many fault monitors as master
controllers and have to respond to fault signals from the
master controller. FAULT0 and FAULT1 pins are designed
to share fault signals between masters and slaves. In a
typical parallel application, connect the FAULT pins on
LTC3870 to the master GPIO pins of the corresponding
paralleled channels and program the master GPIO as
fault sharing, so that the slave controller can respond to
all fault protections from the master. When the FAULT pin
is pulled below 1.4V, both TG and BG in the corresponding channel are pulled down and external MOSFETs are
turned off. When the FAULT pin voltage is above 2V, the
corresponding channel is back to the normal operation.
During fault conditions, all internal circuits in LTC3870 are
still running so the slave controllers can immediately go
back to normal operation when the FAULT pin is released.
LTC3870 has internal thermal shutdown protection which
pulls all TG and BG pins low when the junction temperature
14
800
600
400
200
0
0
0.5
1
1.5
FREQ PIN VOLTAGE (V)
2
2.5
3870 F02
Figure 3. Relationship Between Oscillator
Frequency and Voltage at the FREQ Pin
2.4V 5V
RSET
10µA
FREQ
EXTERNAL
OSCILLATOR
SYNC
DIGITAL
SYNC
PHASE/
FREQUENCY
DETECTOR
VCO
3870 F03
Figure 4. Phase-Locked Loop Block Diagram
is higher than 160°C. In thermal shutdown, FAULT0 and
FAULT1 pins are also pulled low. There is a 500k pull down
resistor on each FAULT pin which sets the default voltage
on Fault pins low if FAULT pins are floating.
Transient Response and Loop Stability
In a typical parallel operation, LTC3870 cooperates with
master controllers to supply more current. To achieve
balanced current sharing between master and slave, it is
recommended that each slave channel copy the design
from the master channel. Select same inductors, same
power MOSFETs, same current sensing circuit and same
output capacitors between the master channel and slave
channels. Control loop and compensation design on the
ITH pin should start with the single phase operation of the
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LTC3870
Applications Information
master controller. If the master and slave channels are
exactly the same, then the transient response and loop
stability of the multiphase design is almost the same as
the single phase operation of the master by tying the ITH
pins together between the master and slaves. For example,
design the compensation for a single phase 1.8V/20A output
using LTC3880 with a 0.56µH inductor and 530µF output
capacitors. To extend the output to 1.8V/40A, simply parallel
one channel of LTC3870 with the same inductor and output
capacitors (total output capacitors are 1060µF) and tie the
ITH pin of LTC3870 to the master ITH. The loop stability
and transient responses of the two phase converter are
very similar to the single phase design without any extra
compensator on the ITH pin of LTC3870 slave controller.
Furthermore, LTpowerCAD is provided on the LTC website
as a free download for transient and stability analysis.
To minimize the high frequency noise on the ITH trace
between master and slave ITH pins, a small filter capacitor
in the range of tens of pF can be placed closely at each ITH
pin of the slave controller. This small capacitor normally
does not significantly affect the closed loop bandwidth but
increases the gain margin at high frequency.
Mode Selection and Pre-Biased Startup
There may be situations that require the power supply to
start up with a pre-bias on the output capacitors. In this
case, it is desirable to start up without discharging the
output capacitors. The LTC3870 can be configured to DCM
mode for pre-biased start-up. If PGOOD signal is available
on the master controller (e.g. LTC3883), the PGOOD pin
can be connected to MODE pins of LTC3870 to ensure DCM
operation at startup and CCM operation at steady state.
Minimum On-Time Considerations
Minimum on-time tON(MIN) is the smallest time duration
that the LTC3870 is capable of turning on the top MOSFET.
It is determined by internal timing delays and the gate
charge required to turn on the top MOSFET. Low duty
cycle applications may approach this minimum on-time
limit and care should be taken to ensure that:
tON(MIN) <TSW VOUT/VIN
where TSW is the switching period.
If the duty cycle falls below what can be accommodated
by the minimum on-time, the controller will begin to skip
cycles. The output voltage will continue to be regulated, but
the ripple voltage and current will increase. The minimum
on-time for the LTC3870 is approximately 90ns, with reasonably good PCB layout, minimum 30% inductor current
ripple and at least 10mV ripple on the current sense signal.
The minimum on-time can be affected by PCB switching noise in the current loop. As the peak sense voltage
decreases, the minimum on-time gradually increases to
130ns. This is of particular concern in forced continuous
applications with low ripple current at light loads. If the
duty cycle drops below the minimum on-time limit in this
situation, a significant amount of cycle skipping can occur
with correspondingly larger current and voltage ripple.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the IC. These items are also illustrated graphically in the
layout diagram of Figure 5. Figure 6 illustrates the current
waveforms present in the various branches of the 2-phase
synchronous regulators operating in the continuous mode.
Check the following in the PC layout:
1. Are the top N-channel MOSFETs M1 and M3 located
within 1cm of each other with a common drain connection
at CIN? Do not attempt to split the input bypassing for
the two channels as it can cause a large resonant loop.
2. Are the signal and power grounds kept separate? The
combined IC signal ground pin and the ground return of
CINTVCC must return to the combined COUT (–) terminals.
The ITH traces should be as short as possible. The path
formed by the top N-channel MOSFET, Schottky diode
and the CIN capacitor should have short leads and PC
trace lengths. The output capacitor (–) terminals should
be connected as close as possible to the (–) terminals of
the input capacitor by placing the capacitors next to each
other and away from the Schottky loop described above.
3. Are the ISENSE+ and ISENSE– leads routed together with
minimum PC trace spacing? The filter capacitor between
ISENSE+ and ISENSE– should be as close as possible to
the IC. Ensure accurate current sensing with Kelvin
connections at the sense resistor or inductor, whichever
is used for current sensing.
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15
LTC3870
Applications Information
4. Is the INTVCC bypassing capacitor connected close to
the IC, between the INTVCC and the power ground pins?
This capacitor carries the MOSFET drivers current peaks.
An additional 1µF ceramic capacitor placed immediately
next to the INTVCC and PGND pins can help improve
noise performance substantially.
5. Keep the switching nodes (SW1, SW0), top gate nodes
(TG1, TG0), and boost nodes (BOOST1, BOOST0) away
from sensitive small-signal nodes, especially from the
opposite channel’s current sensing feedback pins. All
of these nodes have very large and fast moving signals
and therefore should be kept on the “output side” of
the LTC3870 and occupy minimum PC trace area. If
DCR sensing is used, place the right resistor (Block
Diagram, “RC”) close to the switching node.
6. Use a modified “star ground” technique: a low impedance, large copper area central grounding point on
the same side of the PC board as the input and output
capacitors with tie-ins for the bottom of the INTVCC
bypassing capacitor, the bottom of the voltage feedback
resistive divider and the SGND pin of the IC.
PC Board Layout Debugging
Start with one controller at a time. It is helpful to use a DC50MHz current probe to monitor the current in the inductor
while testing the circuit. Monitor the output switching node
(SW pin) to synchronize the oscilloscope to the internal
oscillator and probe the actual output voltage as well. Check
for proper performance over the operating voltage and
current range expected in the application. The frequency
of operation should be maintained over the input voltage
range down to dropout and until the output load drops below
the low current operation threshold—typically 10% of the
maximum designed current level in Burst Mode operation.
The duty cycle percentage should be maintained from cycle
to cycle in a well-designed, low noise PCB implementation.
Variation in the duty cycle at a sub-harmonic rate can suggest noise pickup at the current or voltage sensing inputs
or inadequate loop compensation. Overcompensation of
the loop can be used to tame a poor PC layout if regulator
bandwidth optimization is not required. Only after each
controller is checked for its individual performance should
both controllers be turned on at the same time. A particularly
16
difficult region of operation is when one controller channel
is nearing its current comparator trip point when the other
channel is turning on its top MOSFET. This occurs around
50% duty cycle on either channel due to the phasing of
the internal clocks and may cause minor duty cycle jitter.
Reduce VIN from its nominal level to verify operation of
the regulator in dropout. Check the operation of the undervoltage lockout circuit by further lowering VIN while
monitoring the outputs to verify operation.
Investigate whether any problems exist only at higher output
currents or only at higher input voltages. If problems coincide
with high input voltages and low output currents, look for
capacitive coupling between the BOOST, SW, TG, and possibly BG connections and the sensitive voltage and current
pins. The capacitor placed across the current sensing pins
needs to be placed immediately adjacent to the pins of the
IC. This capacitor helps to minimize the effects of differential
noise injection due to high frequency capacitive coupling. If
problems are encountered with high current output loading
at lower input voltages, look for inductive coupling between
CIN, Schottky and the top MOSFET components to the
sensitive current and voltage sensing traces. In addition,
investigate common ground path voltage pickup between
these components and the SGND pin of the IC.
Design Example
As a design example using master chip LTC3880 and slave
chip LTC3870 for a 4-phase high current regulator, assume
VIN = 12V (nominal), VIN = 15V (maximum), VOUT = 1.0V,
IMAX = 100A, and f = 425kHz (see Typical Applications).
The master chip LTC3880 design can be found in the
LTC3880 data sheet Design Example section.
LTC3880's SYNC pin is connected to LTC3870's SYNC
pin and LTC3870's PHASMD is connected to LTC3870’s
INTVCC.
Slave chip LTC3870 should use the same inductor, power
MOSFET, CIN, and COUT as the master chip. DCR sensing
is also used for the slave chip.
LTC3870's ILIM pin is forced to 0V to match the master
chip's 50mV current limit. Both chips' VIN, VOUT, RUN,
ITH pins are connected together. LTC3880's GPIO pins are
connected to LTC3870's FAULT pins so the slave controller
will be disabled during fault conditions.
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LTC3870
Applications Information
L1
ITH1
ISENSE1+
TG1
ISENSE1–
SW1
VOUT1
CB1
BOOST1
LTC3870
SYNC
VIN
COUT1
RIN
+
CVIN
PGND
VIN
CINTVCC
INTVCC
ISENSE0+
BG0
+
ISENSE0–
COUT0
1µF
CERAMIC
M3
BOOST0
GND
CIN
+
SGND
M4
D0
CB0
SW0
ITH0
D1
1µF
CERAMIC
BG1
RUN0
RUN1
M2
+
fIN
M1
VOUT0
TG0
L0
3870 F06
Figure 5. Recommended Printed Circuit Layout Diagram
SW1
L1
VOUT1
COUT1
D1
RL1
VIN
RIN
CIN
SW0
BOLD LINES INDICATE
HIGH SWITCHING
CURRENT. KEEP LINES
TO A MINIMUM LENGTH.
L0
D0
VOUT0
COUT0
RL0
3870 F07
Figure 6. Branch Current Waveforms
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17
18
530µF
+
1µF
0.9k
1µF
0.9k
L0
0.19µH
VIN
6V TO 15V
LTC3880
RUN0
RUN1
SYNC
ITH0
10k
10k
VOUT1_CFG
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SGND
ITH1
FREQ_CFG
ASEL
VTRIM1_CFG
VTRIM0_CFG
VOUT0_CFG
SHARE_CLK
VDD33
VDD25
VSENSE1
TSNS1
ISENSE1–
ALERT
SCL
SDA
WP
TSNS0
VSENSE0
VSENSE0–
+
ISENSE0–
ISENSE0+
ISENSE1+
BG1
PGND
SW1
BG0
BOOST1
TG1
INTVCC
SW0
BOOST0
10k
10k
10k
10k
10k
VIN
TG0
GPIO0
GPIO1
10nF
0.22µF
M3
0.1µF
M1
10µF
4700pF
4.32k
24.9k
10nF
2.55k
15k
20k
0.22µF
M4
0.1µF
1µF
M2
15k
20k
0.9k
1µF
1µF
L1
0.19µH
22µF
0.9k
+
530µF
VOUT
1.0V
100A
+
530µF 1µF
0.9k
3870 TA02
0.9k
L2
0.19µH
22µF
M7
0.1µF
220pF
VIN
TG1
INTVCC
ISENSE1
+
ITH1
ITH0
SYNC
RUN1
RUN0
FAULT1
FAULT0
SGND
MODE1
MODE0
FREQ
ILIM
PHASMD
ISENSE0– ISENSE1–
ISENSE0
+
BG1
SW1
EXTVCC
LTC3870
PGND
BG0
SW0
BOOST0 BOOST1
TG0
100k
0.22µF
M8
0.1µF
M6
L0 TO L3 VISHAY IHLP-4040DZ-01 0.19µH
M1, M2, M5, M6: INFINEON BSC050N03LS
M3, M4, M7, M8: INFINEON BSC010NE2LSI
0.22µF
M5
4.7µF
High Efficiency 425kHz 4-phase 1.0V Step-Down Converter
0.9k
1µF
L3
0.19µH
0.9k
+
530µF
LTC3870
Typical Applications
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LTC3870
Typical Applications
High Efficiency 425kHz 3-phase 1.8V Step-Down Converter with Input Current Sensing
VIN
6V TO 14V
5mΩ
D1
10µF
100Ω
100Ω
1µF
BOOST
VIN_SNS
10nF
LTC3883
VIN
M2
BG
10k
10k
SCL
VSENSE+
VSENSE–
SDA
VDD25
ALERT
10k
24.9k
SHARE_CLK
VDD33
10k
GPIO
RUN
SYNC
PGOOD
ITH
10k
10k
10k
20k
16.2k
1µF
VOUT_CFG
VTRIM_CFG
530µF
0.22µF
ISENSE–
10k
1.43k
1.43k
ISENSE+
10nF
+
1µF
PGND
TSNS
MMBT3906
VOUT
1.8V
50A
L0
0.56µH
0.1µF
SW
10nF
3Ω
1µF
M1
TG
IIN_SNS
10µF
1µF
INTVCC
11.3k
17.4k
ASEL
17.8k
FREQ_CFG
WP
GND
4.99k
2200pF
22µF
D2
M3
L1
0.56µH
D3
VIN
TG0
SW0
530µF
M5
+
BG0
1µF
0.22µF
LTC3870
BG1
PGND
EXTVCC
ISENSE0+
ISENSE1+
ISENSE0–
ISENSE1–
FAULT0
FAULT1
0.1µF
L2
0.56µH
SW1
1.43k
1.43k
M4
BOOST1
BOOST0
0.1µF
4.7µF
INTVCC
TG1
M6
+
1µF
1.43k
0.22µF
530µF
1.43k
PHASMD
RUN0
RUN1
SYNC
MODE0
MODE1
ITH0
100pF
FREQ
100k
ILIM
SGND
ITH1
3870 TA03
D1 TO D3: CENTRAL CMDSH-3TR
L0 TO L2: VISHAY IHLP-4040DZ-11 0.56µH
M1, M3, M4: INFINEON BSC050NE2LS
M2, M5, M6: INFINEON BSC010NE2LSI
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For more information www.linear.com/LTC3870
19
LTC3870
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
UFD Package
28-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1712 Rev B)
0.70 ±0.05
4.50 ±0.05
3.10 ±0.05
2.50 REF
2.65 ±0.05
3.65 ±0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
3.50 REF
4.10 ±0.05
5.50 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10
(2 SIDES)
0.75 ±0.05
R = 0.05
TYP
PIN 1 NOTCH
R = 0.20 OR 0.35
× 45° CHAMFER
2.50 REF
R = 0.115
TYP
27
28
0.40 ±0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
5.00 ±0.10
(2 SIDES)
3.50 REF
3.65 ±0.10
2.65 ±0.10
(UFD28) QFN 0506 REV B
0.200 REF
0.00 – 0.05
0.25 ±0.05
0.50 BSC
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X).
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
20
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For more information www.linear.com/LTC3870
LTC3870
Revision History
REV
DATE
DESCRIPTION
PAGE NUMBER
A
8/14
Added Note 9
2
B
7/15
Miscellaneous typographical changes
Changed title and added master parts supported
1, 3, 8, 13, 16
1
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representaFor more
information
www.linear.com/LTC3870
tion that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
21
LTC3870
Typical Application
4-Phase 1.5V Step-Down Converter with Sensing Resistors and External VCC
VIN
6V TO 24V
4.7µF
INTVCC
VIN
TG0
PHASMD BOOST0
EXTVCC
SW0
5VCC
FREQ
84.5k
0.1µF
+
100Ω
+
ISENSE0
ISENSE0–
SYNC
* REFER TO LTC3880 DATA SHEET
FIGURE TA04 FOR MASTER SETUP
530µF
1000pF
100Ω
LTC3870
RUN0
RUN1
FAULT0
FAULT1
ITH0
ITH1
SYNC
VOUT
1.5V
80A
0.0015Ω
BG0
MODE0
MODE1
ILIM
SGND
LTC3880-1*
RUN0
5VCC
EXTVCC
RUN1
GPIO0
1.5V
VSENSE0+ GPIO1
ITH0
VSENSE1
ITH1
0.42µH
TG1
BOOST1
SW1
0.42µH
0.1µF
+
BG1
PGND
ISENSE1+
ISENSE1–
0.0015Ω
530µF
100Ω
1000pF 100Ω
3870 TA04
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
LTC3886
60V Dual Output Step-Down Controller
with Digital Power System Management
4.5V ≤ VIN ≤ 60V, 0.5V ≤ VOUT ≤ 13.8V, Programmable Loop Compensation,
Input Current Sense
LTM4676/
LTM4676A
Dual 13A or Single 26A Step-Down DC/DC µModule
Regulator with Digital Power System Management
4.5V ≤ VIN ≤ 17V/26.5V, 0.5V ≤ VOUT ≤ 4V/5.5V, ±1% VOUT Accuracy,
Fault Logging, I2C/PMBus Interface, 16mm × 16mm × 5mm, BGA Package
LTC3887/
LTC3887-1
Dual Output Multiphase Step-Down DC/DC Controller
with Digital Power System Management, 70ms Start-Up
4.5V ≤ VIN ≤ 24V, 0.5V ≤ VOUT ≤ 5.5V, 70mS Start-Up, Analog Control Loop,
I2C/PMBus Interface, -1 Version Drives DrMOS and Power Blocks
LTC3880/
LTC3880-1
Dual Output Multiphase Step-Down DC/DC Controller
with Digital Power System Management
4.5V ≤ VIN ≤ 24V, 0.5V ≤ VOUT0 ≤ 5.4V, Analog Control Loop,
I2C/PMBus Interface with EEPROM and 16-Bit ADC
LTC3883/
LTC3883-1
Single Phase Step-Down DC/DC Controller
with Digital Power System Management
VIN Up to 24V, 0.5V ≤ VOUT ≤ 5.5V, Input Current Sense Amplifier,
I2C/PMBus Interface with EEPROM and 16-Bit ADC
LTC3882
Dual Output Multiphase Step-Down DC/DC Voltage Mode VIN Up to 38V, 0.5V ≤ VOUT1,2 ≤ 5.25V, ±0.5% VOUT Accuracy
I2C/PMBus Interface, Drives DrMOS and Power Blocks
Controller with Digital Power System Management
LTC3892-1
60V Low IQ Dual, 2-Phase Synchronous Step-Down
DC/DC Controller
VIN Up to 60V, 0.8V ≤ VOUT ≤ 99%•VIN, 29µA Quiescent Current Adjustable
Gate Drive Voltage
LTC2977
8-Channel PMBus Power System Manager Featuring
Accurate Output Voltage Measurement
Sequence and Supervise Eight Power Supplies Margin or Trim Supplies to
0.25% Accuracy
22 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC3870
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC3870
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LT 0715 REV B • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2014