LTC3736EUF-1#TRPBF Linear Technology, LTC3736EUF-1#TRPBF Datasheet - Page 18

• Manufacturer Part Number: LTC3736EUF-1#TRPBF
• Description: IC CTRLR SW SYNC DUAL 2PH 24QFN
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3736EUF-1#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 9.8 V
• Current - Output: 1A
• Frequency - Switching: 450kHz ~ 580kHz
• 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: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
where f is the operating frequency, C
capacitance and I
tor. The output ripple is highest at maximum input voltage
since I
Setting Output Voltage
The LTC3736-1 output voltages are each set by an external
feedback resistor divider carefully placed across the out-
put, as shown in Figure 6. The regulated output voltage is
determined by:
To improve the frequency response, a feed-forward ca-
pacitor, C
route the V
inductor or the SW line. When spread spectrum operation
is enabled, it is recommended that R
valued, preferably on the order of hundreds of kilohms.
Run/Soft Start Function
The RUN/SS pin is a dual purpose pin that provides the
optional external soft-start function and a means to shut
down the LTC3736-1.
Pulling the RUN/SS pin below 0.65V puts the LTC3736-1
into a low quiescent current shutdown mode (I
RUN/SS has been pulled all the way to ground, there will
be a delay before the LTC3736-1 comes out of shutdown
and is given by:
This pin can be driven directly from logic as shown in
Figure 6. Diode D1 in Figure 7 reduces the start delay but
LTC3736-1
18
V
t
DELAY
OUT
RIPPLE
=
FF
=
0 6
FB
, may be used. Great care should be taken to
.
0 65
increases with input voltage.
line away from noise sources, such as the
.
V
Figure 6. Setting Output Voltage
1/2 LTC3736-1
•
RIPPLE
V
⎛
⎜
⎝
1
U
•
+
0 7
C
.
R
V
R
FB
SS
is the ripple current in the induc-
µ
B
A
U
A
⎞
⎟
⎠
=
V
0 93
OUT
.
R
R
37361 F06
B
A
W
s F C
/
µ
A
OUT
C
and R
FF
•
SS
is the output
B
Q
U
= 9µA). If
be large-
allows C
function. This diode (and capacitor) can be deleted if the
external soft-start is not needed.
During soft-start, the start-up of V
slowly ramping the positive reference to the error amplifier
from 0V to 0.6V, allowing V
to its final value. The default internal soft-start time is 1ms.
This can be increased by placing a capacitor between the
RUN/SS pin and SGND. In this case, the soft-start time will
be approximately:
It is recommended that C
that of the frequency filtering capacitor connected to the
FREQ pin when spread sprectrum operation is enabled
(see Operation Frequency section).
Tracking
The start-up of V
TRACK pin. Normally this pin is used to allow the start-up
of V
Figures 8a and 8b. When the voltage on the TRACK pin is
less than the internal 0.6V reference, the LTC3736-1
regulates the V
instead of 0.6V. The start-up of V
track that of V
divider (Figure 8c):
For coincident tracking (V
R2A/R2B = R
t
3.3V OR 5V
V
V
SS
OUT2
OUT
OUT
1
=
1
2
SS
to track that of V
C
=
SS
to ramp up slowly providing the soft-start
R
D1
Figure 7. RUN/SS Pin Interfacing
OUT1
•
TRACKA
R A
600
TRACKA
FB2
2
0 7
RUN/SS
OUT2
.
, according to a ratio set by a resistor
mV
µ
voltage to the TRACK pin voltage
A
C
is controlled by the voltage on the
•
/R
SS
R
TRACKB
SS
TRACKA
OUT1
OUT1
OUT1
have a value of at least twice
R B R A
2
= V
as shown qualitatively in
to rise smoothly from 0V
OUT2
+
+
OUT2
OUT1
R
2
TRACKB
may ratiometrically
during start-up),
is controlled by
RUN/SS
37361 F07
C
SS
37361f