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PDF LTC3870 Data sheet ( Hoja de datos )
| Número de pieza | LTC3870 | |
| Descripción | PolyPhase Step-Down Slave Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
LTC3870
PolyPhase Step-Down
Slave Controller for Digital
Power System Management
Description
n LTC3880 Family Phase Extender Supporting
LTC3880/3880-1, LTC3883/3883-1, LTC3886,
LTC3887 Master Controllers
n Cascade with Multiple Chips for Very Large Current
Applications
n Accurate PolyPhase Current Sharing
n EXTVCC Capable of 5V to 14V Input
n Wide VIN Range: 4.5V to 60V
n Wide Output Voltage Range : 0.5V to 14V
n Wide SYNC Frequency Range: 100kHz to 1MHz
n Pin Programmable of CCM/DCM Operation
n Pin Programmable of Phase-Shift Control
n Integrated Powerful N-Channel MOSFET Gate Drivers
n Available in a 28-Pin (4mm × 5mm) QFN Package
Applications
n High Power Distributed Power Systems
n Telecom Systems
n Industrial Applications
The LTC®3870 is a PolyPhase® step-down slave control-
ler 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 pro-
vides 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.
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
Typical Application
VIN
4.7µF
VOUT0
30A
1.0µH
+ 530µF
2.15k
0.2µF
0.1µF
LTC3880*
RUN0
3.3V
VSENSE0+
RUN1
GPIO0
GPIO1
1.8V VSENSE1
ITH0
ITH1
SYNC
* REFER TO LTC3880 DATA SHEET
FOR MASTER SETUP
VIN INTVCC
TG0 TG1
BOOST0 BOOST1
SW0 SW1
BG0 BG1
PGND
EXTVCC
LTC3870
IISSEENNSSEE00+– IISSEENNSSEE11+–
0.1µF
RUN0
RUN1
FAULT0
FAULT1
ITH0
ITH1
SYNC
FREQ
PHASMD
ILIM
MODE0
MODE1
SGND
100k
0.56µH
VOUT1
40A
1.74k
0.2µF
+ 530µF
Load Transient Response of a
2-Phase Master (3880)/Slave
(3870) Converter
ILOAD
10A/DIV
0A TO 10A TO 0A
IL_3880(CH1)
10A/DIV
IL_3870(CH1)
10A/DIV
VOUT1
100mV/DIV
AC-COUPLED
VIN = 12V
VOUT1 = 1.8V
50µs/DIV
3870 TA01b
3870 TA01a
3870fb
For more information www.linear.com/LTC3870
1
1 page  
LTC3870
Typical Performance Characteristics
Load Step (Discontinuous
Conduction Mode) 4-Phase
Operation LTC3880 and LTC3870
Load Step (Forced Continuous
Mode) 4-Phase Operation
LTC3880 and LTC3870
Inductor Current at Light Load
ILOAD
20A/DIV
0A TO 20A TO 0A
IL_3880(CH0)
10A/DIV
IL_3870(CH0)
10A/DIV
VOUT
100mV/DIV
AC-COUPLED
ILOAD
20A/DIV
0A TO 20A TO 0A
IL_3880(CH0)
10A/DIV
IL_3870(CH0)
10A/DIV
VOUT
100mV/DIV
AC-COUPLED
IL_3870(CH0)
FORCED CONTINUOUS
MODE
5A/DIV
IL_3870(CH0)
DISCONTINUOUS
CONDUCTION MODE
5A/DIV
VIN = 12V
VOUT = 1.8V
50µs/DIV
3870 G04
VIN = 12V
VOUT = 1.8V
50µs/DIV
3870 G05
VIN = 12V
VOUT = 1.8V
ILOAD = 1A
1µs/DIV
3870 G06
Start-Up Into a Pre-Biased
Output 4-Phase Operation
LTC3880 and LTC3870
RUN
ALL RUN PINS
TIED TOGETHER
2V/DIV
VOUT
LTC3870 IN DCM
500mV/DIV
VIN = 12V
VOUT = 1.8V
2ms/DIV
3870 G07
Current Sense Threshold
vs ITH Voltage
80 RANGE HIGH
RANGE LOW
60
40
20
0
–20
–40
0 0.5 1 1.5 2 2.5
VITH (V)
3870 G08
DC Output Current Matching
Between LTC3880 and LTC3870
25
Dynamic Current Sharing During
a Load Transient in a 4-Phase
Operation LTC3880 and LTC3870
20
15
10
5
LTC3880 CH0
LTC3880 CH1
LTC3870 CH0
0 LTC3870 CH1
0 10 20 30 40 50 60 70 80 90
TOTAL OUTPUT CURRENT (A)
3870 G10
IL_3880(CH0)
IL_3880(CH1)
IL_3870(CH0)
IL_3870(CH1)
5A/DIV
50µs/DIV
ILOAD 0A TO 32A TO 0A
3870 G11
For more information www.linear.com/LTC3870
INTVCC Line Regulation
6
5
4
3
2
1
0
0 10 20 30 40 50 60
INPUT VOLTAGE (V)
3870 G09
Quiescent Current vs Input
Voltage Without EXTVCC
3.5
3
2.5
2
1.5
1
0.5
0
0 10 20 30 40 50 60
INPUT VOLTAGE (V)
3870 G12
3870fb
5
5 Page 
Operation
2+2
CH0 CH1
0° 180°
LTC3880
CH0 CH1
180° 0°
LTC3870
PHASMD = GND
4 PHASE OPERATION
LTC3870
1+3
CH0
120°
CH1
240°
CH0
0°
CH1
180°
LTC3870
PHASMD = 2/3 INTVCC OR FLOAT
LTC3880
6 PHASE OPERATION
CH0
90°
CH1
270°
CH0
0°
CH1
180°
CH0
0°
CH1
180°
CH0
60°
CH1
300°
CH0
120°
CH1
240°
LTC3870
LTC3880
LTC3880
LTC3870
LTC3870
PHASMD = INTVCC
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)
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 main-
tain 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 us-
ing 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 control-
lers. The PLL loop filter network is integrated inside the
LTC3870. The phase-locked loop is capable of locking to
any frequency within the range of 100kHz to 1MHz.
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.
For more information www.linear.com/LTC3870
3870fb
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet LTC3870.PDF ] | |
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