LTC3870_15 Datasheet, PDF (6/22 Pages) Linear Technology – PolyPhase Step-Down Slave Controller for LTC3880/LTC3883 with Digital Power System Management

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 500
kΩ 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.
I_SENSE0+/I_SENSE1+ (Pin 2/Pin 7): Current Sense Comparator
positive inputs, normally connected to the positive node
of the DCR sensing networks or current sensing resistors.
I_SENSE0−/I_SENSE1− (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
LTC3880/LTC3883 RUN pins.
I_TH0/I_TH1 (Pin 28/Pin 9): Current Control Threshold. Each
associated channel’s current comparator tripping threshold
increases with its I_TH voltage. In multiphase operation,
these pins are connected to the master controller’s I_TH
pins for current sharing.
I_LIM (Pin 10): Program Current Comparators’ Sense
Voltage Range. This pin can be tied to SGND or INTV_CC
to select the maximum current sense threshold for each
current comparator. SGND sets both channels’ current low
range with maximum 50mV sensing voltage. INTV_CC sets
both channels’ current high range with maximum 75mV
sensing voltage. For equal current sharing, the setup on
the I_LIM pin has to be same as the setup on the bit 7 of
MFR_PWM_MODE_3880/3883 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 con-
nected to LTC3880/LTC3883 the SYNC pin for frequency
synchronization. Do not float the SYNC pin.
PHASMD (Pin 12): Phase Set Pin. This pin can be tied to
SGND, INTV_CC or a resistor divider from INTV_CC 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 INTV_CC 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 V_IN.
BOOST0/BOOST1 (Pin 22/Pin 15): Boosted Floating Driver
Supplies. The (+) terminal of the bootstrap capacitors con-
nect to these pins. These pins swing from a diode voltage
drop below INTV_CC up to V_IN + INTV_CC.
BG0/BG1 (Pin 21/Pin 16): Bottom Gate Driver Outputs.
These pins drive the gates of the bottom N-Channel MOS-
FETs between PGND and INTV_CC.
INTV_CC (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. INTV_CC is enabled as
soon as V_IN is powered.
EXTV_CC (Pin 18): External power input to an internal LDO
connected to INTV_CC. This LDO supplies INTV_CC power
bypassing the internal LDO powered from V_IN whenever
EXTV_CC is higher than 4.8V. See EXTV_CC 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 EXTV_CC pin
is not used, leave it open or tie it to ground. EXTV_CC can
be present before V_IN. However, EXTV_CC is enabled only
if V_IN 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 C_IN.
V_IN (Pin 20): Main Input Supply. Bypass this pin to PGND
with a capacitor (0.1μF to 1μF).
3870fa
6
For more information www.linear.com/LTC3870