LTC3836 LINER [Linear Technology], LTC3836 Datasheet - Page 17

• Manufacturer Part Number: LTC3836
• Description: Dual 2-Phase, No RSENSETM Low VIN Synchronous Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
A small (0.1μF to 1μF) bypass capacitor between the chip
V
suggested. A 10Ω resistor placed between C
the V
channels.
The selection of C
resistance (ESR). Typically, once the ESR requirement
is satisfi ed, the capacitance is adequate for fi ltering. The
output ripple (ΔV
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 LTC3836 output voltages are each set by an external
feedback resistor divider carefully placed across the out-
put, as shown in Figure 5. The regulated output voltage
is determined by:
IN
V
pin and ground, placed close to the LTC3836, is also
OUT
V
IN
OUT
RIPPLE
pin provides further isolation between the two
= 0.6V • 1+
Figure 5. Setting Output Voltage
I
RIPPLE
1/2 LTC3836
increases with input voltage.
OUT
RIPPLE
OUT
V
ESR +
FB
) is approximated by:
R
R
is driven by the effective series
B
A
is the ripple current in the induc-
V
8fC
OUT
R
R
3836 F05
1
B
A
OUT
C
FF
OUT
is the output
IN
(C1) and
To improve the frequency response, a feedforward ca-
pacitor, C
route the V
inductor or the SW line.
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 LTC3836.
Pulling the RUN/SS pin below 0.65V puts the LTC3836 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 LTC3836 comes out of shutdown
and is given by:
This pin can be driven directly from logic as shown in
Figure 6. Diode D
but allows C
function. This diode (and capacitor) can be deleted if the
external soft-start is not needed.
t
3.3V OR 5V
DELAY
FF
= 0.65V •
, may be used. Great care should be taken to
FB
SS
D
line away from noise sources, such as the
Figure 6. RUN/SS Pin Interfacing
SS
to ramp up slowly providing the soft-start
RUN/SS
SS
V
DD
0.65μA
in Figure 6 reduces the start delay
≤ V
C
C
3836 F06
SS
IN
SS
= 1s/μF • C
RUN/SS
(INTERNAL SOFT-START)
LTC3836
SS
Q
= 6.5μA). If
RUN/SS
17
C
SS
3836fa