LTC3870_15 Datasheet, PDF (11/22 Pages) Linear Technology – PolyPhase Step-Down Slave Controller for LTC3880/LTC3883 with Digital Power System Management

LTC3870
Operation
2+2
CH0 CH1
0° 180°
LTC3880
CH0 CH1
180° 0°
LTC3870
PHASMD = GND
4 PHASE OPERATION
1+3
CH0
120°
CH1
240°
CH0
0°
CH1
180°
LTC3870
PHASMD = 2/3 INTV_CC 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 = INTV_CC
PHASMD = 1/3 INTV_CC PHASMD = 2/3 INTV_CC
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
3870fa
11