ltc1702a Linear Technology Corporation, ltc1702a Datasheet - Page 5

• Manufacturer Part Number: ltc1702a
• Description: Dual 550khz Synchronous 2-phase Switching Regulator Controller
• Manufacturer: Linear Technology Corporation

PIN
PV
power to the two BG n output drivers. PV
connected to a voltage high enough to fully turn on the
external MOSFETs QB1 and QB2. PV
be connected directly to V
bypass capacitor directly to PGND.
BOOST1 (Pin 2): Controller 1 Top Gate Driver Supply. The
BOOST1 pin supplies power to the floating TG1 driver.
BOOST1 should be bypassed to SW1 with a 1µF capacitor.
An additional Schottky diode from V
create a complete floating charge-pumped supply at
BOOST1. No other external supplies are required. A 5Ω to
10Ω resistor in series with this pin can help control ringing
at the switch node. See the EXTERNAL COMPONENTS
SELECTION/MOSFET Series Resistors section for more
information.
BG1 (Pin 3): Controller 1 Bottom Gate Drive. The BG1 pin
drives the gate of the bottom N-channel synchronous
switch MOSFET, QB1. BG1 is designed to drive up to
10,000pF of gate capacitance directly. If RUN/SS1 goes
low, BG1 will go low, turning off QB1. If FAULT mode is
tripped, BG1 will go high and stay high, keeping QB1 on
until the V
to the MOSFET gate. Do not use a series resistor. See the
EXTERNAL COMPONENTS SELECTION/MOSFET Series
Resistors section for more information.
TG1 (Pin 4): Controller 1 Top Gate Drive. The TG1 pin drives
the gate of the top N-channel MOSFET, QT1. The TG1 driver
draws power from the BOOST1 pin and returns to the SW1
pin, providing true floating drive to QT1. TG1 is designed to
drive up to 10,000pF of gate capacitance directly. In
shutdown or fault modes, TG1 will go low. TG1 should be
directly connected to the MOSFET gate. Do not use a series
resistor. See the EXTERNAL COMPONENTS SELECTION/
MOSFET Series Resistors section for more information.
SW1 (Pin 5): Controller 1 Switching Node. SW1 should be
connected to the switching node of converter 1. The TG1
driver ground returns to SW1, providing floating gate
drive to the top N-channel MOSFET switch, QT1. The
voltage at SW1 is compared to I
comparator while the bottom MOSFET, QB1, is on.
I
pin sets the current limit comparator threshold for
MAX1
CC
U
(Pin 1): Driver Power Supply Input. PV
(Pin 6): Controller 1 Current Limit Set. The I
FUNCTIONS
CC
U
is cycled. BG1 should be directly connected
U
IN
. PV
CC
MAX1
requires at least a 1µF
IN
CC
by the current limit
to BOOST1 pin will
should generally
CC
CC
provides
must be
MAX1
controller 1. If the voltage drop across the bottom MOSFET,
QB1, exceeds the magnitude of the voltage at I
controller 1 will go into current limit. The I
internal 10µA current source pull-up, allowing the current
threshold to be set with a single external resistor to PGND.
See the Current Limit Programming section for more
information on choosing R
PGOOD1 (Pin 7): Controller 1 Power Good. PGOOD1 is an
open-drain logic output. PGOOD1 will pull low whenever
FB1 falls 5% below its programmed value. When RUN/SS1
is low (side 1 shut down), PGOOD1 will go high.
FCB (Pin 8): Force Continuous Bar. The FCB pin forces
both converters to maintain continuous synchronous
operation regardless of load when the voltage at FCB
drops below 0.8V. FCB is normally tied to V
continuous operation, tie FCB to SGND. FCB can also be
connected to a feedback resistor divider from a secondary
winding on one converter’s inductor to generate a third
regulated output voltage. Do not leave FCB floating.
RUN/SS1 (Pin 9): Controller 1 Run/Soft-start. Pulling
RUN/SS1 to SGND will disable controller 1 and turn off
both of its external MOSFET switches. Pulling both
RUN/SS pins down will shut down the entire LTC1702A,
dropping the quiescent supply current below 100µA. A
capacitor from RUN/SS1 to SGND will control the turn-on
time and rate of rise of the controller 1 output voltage at
power-up. An internal 3.5µA current source pull-up at
RUN/SS1 pin sets the turn-on time at approximately
500ms/µF.
COMP1 (Pin 10): Controller 1 Loop Compensation. The
COMP1 pin is connected directly to the output of the first
controller’s error amplifier and the input to the PWM
comparator. An RC network is used at the COMP1 pin to
compensate the feedback loop for optimum transient
response.
SGND (Pin 11): Signal Ground. All internal low power
circuitry returns to the SGND pin. Connect to a low
impedance ground, separated from the PGND node. All
feedback, compensation and soft-start connections should
return to SGND. SGND and PGND should connect only at
a single point, near the PGND pin and the negative plate of
the C
IN
bypass capacitor.
IMAX
.
LTC1702A
MAX1
CC
pin has an
. To force
MAX1
1702afa
5
,