LTC3736-2 Datasheet, PDF (6/28 Pages) Linear Technology – Dual 2-Phase, No RSENSE Synchronous Controller with Output Tracking

LTC3736-2
TYPICAL PERFOR A CE CHARACTERISTICS T_A = 25°C unless otherwise noted.
Shutdown Quiescent Current
vs Input Voltage
20
RUN/SS = 0V
18
16
14
12
10
8
6
4
2
0
2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
37362 G17
RUN/SS Start-Up Current
vs Input Voltage
0.9
RUN/SS = 0V
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2345678
INPUT VOLTAGE (V)
9 10
37362 G18
PI FU CTIO S _{(QFN/SSOP Package)}
I_TH1/I_TH2 (Pins 1, 8/Pins 4, 11): Current Threshold and
Error Amplifier Compensation Point. Nominal operating
range on these pins is from 0.7V to 2V. The voltage on
these pins determines the threshold of the main current
comparator.
PLLLPF (Pin 3/Pin 6): Frequency Set/PLL Lowpass Filter.
When synchronizing to an external clock, this pin serves
as the lowpass filter point for the phase-locked loop. Nor-
mally a series RC is connected between this pin and ground.
When not synchronizing to an external clock, this pin serves
as the frequency select input. Tying this pin to GND selects
300kHz operation; tying this pin to V_IN selects 750kHz op-
eration. Floating this pin selects 550kHz operation.
SGND (Pin 4/Pin 7): Small-Signal Ground. This pin serves
as the ground connection for most internal circuits.
V_IN (Pin 5/Pin 8): Chip Signal Power Supply. This pin pow-
ers the entire chip except for the gate drivers. Externally fil-
tering this pin with a lowpass RC network (e.g.,
R = 10Ω, C = 1µF) is suggested to minimize noise pickup,
especially in high load current applications.
TRACK (Pin 6/Pin 9): Tracking Input for Second Control-
ler. Allows the start-up of V_OUT2 to “track” that of V_OUT1 ac-
cording to a ratio established by a resistor divider on V_OUT1
connected to the TRACK pin. For one-to-one tracking of
V_OUT1 and V_OUT2 during start-up, a resistor divider with
6
values equal to those connected to V_FB2 from V_OUT2 should
be used to connect to TRACK from V_OUT1.
PGOOD (Pin 9/Pin 12): Power-Good Output Voltage Moni-
tor Open-Drain Logic Output. This pin is pulled to ground
when the voltage on either feedback pin (V_FB1, V_FB2) is not
within ±13.3% of its nominal set point.
PGND (Pins 12, 16, 20, 25/Pins 15, 19, 23): Power Ground.
These pins serve as the ground connection for the gate
drivers and the negative input to the reverse current com-
parators. The Exposed Pad must be soldered to PCB ground.
RUN/SS (Pin 14/Pin 17): Run Control Input and Optional
External Soft-Start Input. Forcing this pin below 0.65V shuts
down the chip (both channels). Driving this pin to V_IN or
releasing this pin enables the chip, using the chip’s inter-
nal soft-start. An external soft-start can be programmed by
connecting a capacitor between this pin and ground.
TG1/TG2 (Pins 17, 15/Pins 18, 20): Top(PMOS)GateDrive
Output. These pins drive the gates of the external P-channel
MOSFETs. These pins have an output swing from PGND to
SENSE⁺.
SYNC/FCB (Pin 18/Pin 21): This pin performs three
functions: 1) auxiliary winding feedback input, 2) external
clock synchronization input for phase-locked loop, and
3) pulse-skipping operation or forced continuous mode
select. For auxiliary winding applications, connect to a
37362fa