LTC1439 Linear Technology, LTC1439 Datasheet - Page 11

• Manufacturer Part Number: LTC1439
• Description: Dual High Efficiency/ Low Noise/ Synchronous Step-Down Switching Regulators
• Manufacturer: Linear Technology

OPERATION
Frequency Synchronization
A Phase-Locked Loop (PLL) is available on the LTC1439
to allow the oscillator to be synchronized to an external
source connected to the PLLIN pin. The output of the
phase detector at the PLL LPF pin is also the control input
of the oscillator, which operates over a 0V to 2.4V range
corresponding to – 30% to 30% in frequency. When
locked, the PLL aligns the turn-on of the top MOSFET to
the rising edge of the synchronizing signal. When PLLIN
is left open, PLL LPF goes low, forcing the oscillator to
minimum frequency.
Power-On Reset
The POR2 pin is an open drain output which pulls low
when the main regulator output voltage of the second
controller is out of regulation. When the output voltage
rises to within 7.5% of regulation, a timer is started which
releases POR2 after 2
function is not available on the LTC1438X.
Auxiliary Linear Regulator
The auxiliary linear regulator in the LTC1439 controls an
external PNP transistor for operation up to 500mA. A
precise internal AUXFB resistive divider is invoked when
U
(Refer to Functional Diagram)
16
(65536) oscillator cycles. This
the AUXDR pin is above 9.5V to allow regulated 12V
VPP supplies to be easily implemented. When AUXDR is
below 8.5V an external feedback divider may be used to set
other output voltages. Taking the AUXON pin low shuts
down the auxiliary regulator providing a convenient logic-
controlled power supply.
The AUX block can be used as a comparator having its
inverting input tied to the internal 1.19V reference. The
AUXDR pin is used as the output and requires an external
pull-up to a supply of less than 8.5V in order to inhibit the
invoking of the internal resistive divider.
INTV
Power for the top and bottom MOSFET drivers and most
of the other LTC1438/LTC1439 circuitry is derived from
the INTV
connected to INTV
internal 5V low dropout regulator supplies INTV
If EXTV
off and an internal switch is turned on to connect EXTV
to INTV
from a high efficiency external source such as the output
of the regulator itself or a secondary winding, as described
in the Applications Information section.
CC
CC
/ EXTV
CC
CC
. This allows the INTV
is taken above 4.8V, the 5V regulator is turned
pin. The bottom MOSFET driver supply is also
CC
Power
CC
. When the EXTV
LTC1438/LTC1439
CC
power to be derived
CC
pin is left open, an
CC
11
power.
CC