LTC3736EUF Linear Technology, LTC3736EUF Datasheet - Page 19

• Manufacturer Part Number: LTC3736EUF
• Description: IC CTRLR SW SYNC DUAL 2PH 24QFN
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3736EUF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 9.8 V
• Current - Output: 1A
• Frequency - Switching: 550kHz ~ 750kHz
• Voltage - Input: 2.75 ~ 9.8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
For coincident tracking (V
The ramp time for V
is:
For coincident tracking,
where V
V
V
is desired, then the TRACK pin may be tied to V
ever, in this situation there would be no (internal nor
external) soft-start on V
Phase-Locked Loop and Frequency Synchronization
The LTC3736 has a phase-locked loop (PLL) comprised
of an internal voltage-controlled oscillator (VCO) and a
phase detector. This allows the turn-on of the external P-
channel MOSFET of controller 1 to be locked to the rising
edge of an external clock signal applied to the SYNC/FCB
pin. The turn-on of controller 2’s external P-channel
MOSFET is thus 180 degrees out of phase with the
external clock. The phase detector is an edge sensitive
digital type that provides zero degrees phase shift
OUT1
OUT2
R2A = R
R2B = R
t
t
SS
SS
2
2
when using the TRACK pin. If no tracking function
and V
OUT1F
=
=
t
t
TRACKB
TRACKA
SS
SS
OUT2
1
1
and V
•
•
R
V
V
. V
OUT F
TRACKA
OUT F
R A
U
OUT2F
OUT2
OUT1
1
2
(7b) Coincident Tracking
1
OUT2
to rise from 0V to its final value
U
are the final, regulated values of
should always be greater than
OUT1
•
R
.
TRACKA
Figures 7b and 7c. Two Different Modes of Output Voltage Tracking
= V
TIME
R A R B
OUT2
1
W
+
+
R
during start-up),
1
TRACKB
U
V
V
OUT1
OUT2
IN
. How-
Figure 8. Relationship Between Oscillator Frequency and Voltage
at the PLLLPF Pin When Synchronizing to an External Clock
between the external and internal oscillators. This type of
phase detector does not exhibit false lock to harmonics of
the external clock.
The output of the phase detector is a pair of complemen-
tary current sources that charge or discharge the external
filter network connected to the PLLLPF pin. The relation-
ship between the voltage on the PLLLPF pin and operating
frequency, when there is a clock signal applied to SYNC/
FCB, is shown in Figure 8 and specified in the Electrical
Characteristics table. Note that the LTC3736 can only be
synchronized to an external clock whose frequency is
within range of the LTC3736’s internal VCO, which is
nominally 200kHz to 1MHz. This is guaranteed, over
temperature and variations, to be between 300kHz and
750kHz. A simplified block diagram is shown in Figure 9.
1400
1200
1000
800
600
400
200
(7c) Ratiometric Tracking
0
0
0.5
PLLLPF PIN VOLTAGE (V)
TIME
1
1.5
3736 F07b,c
V
V
2
OUT1
OUT2
3736 F08
LTC3736
2.4
19
3736fa