LTC3118_15 Datasheet, PDF (19/38 Pages) Linear Technology – 18V, 2A Buck-Boost DC/DC Converter with Low-Loss Dual Input PowerPath

LTC3118
Operation
RUN1 and RUN2 Pin Comparators
Forcing both RUN1 and RUN2 to a logic low places the
LTC3118 in a low current shutdown state. When the volt-
age on either pin is brought above a 0.65V logic threshold,
certain IC functions are enabled as shown in Figure 4a.
The RUN1 and RUN2 pins also include accurate internal
comparators that allow them to be used to set custom
rising and falling ON/OFF thresholds for V_IN1 and V_IN2,
respectively, with the addition of external resistor dividers.
If either RUN pin voltage is increased to exceed its accurate
comparator threshold (1.22V nominal), all functions of the
buck-boost converter will be enabled and switching will
commence, assuming the respective V_IN and V_CC UVLO
circuits are cleared (see Figure 2).
If both RUN1 and RUN2 are brought below the accurate
comparator threshold, the buck-boost converter will inhibit
switching, but the V_CC regulator and control circuitry will
remain powered unless both RUN pins are brought below
the logic threshold. Therefore, in order to completely
shut down the IC and reduce the V_IN currents to < 2µA
(typical), it is necessary to ensure that both RUN pins are
brought below the worst-case low logic threshold of 0.2V.
RUN1 and RUN2 are high voltage capable inputs but must
be connected to their respective V_IN1 and V_IN2 supplies
through a high value resistor greater than 200k to prevent
a potential latch condition at the pin. The RUN pins can
be driven above V_IN or V_OUT within their specified voltage
ratings. If either RUN pin is forced above 5V, it will sink a
small current, as given by the following equation:
I_RUN
≈
V_RUN − 5V
3MΩ
With the addition of optional resistor divider(s), as shown
in Figure 4a, the RUN pin(s) can be used to establish a
user-programmable turn-on and turn-off threshold.
The buck-boost converter is enabled when the voltage
on either RUN pin reaches 1.22V. Therefore, the turn-on
voltage threshold on V_IN is given by:
V_TURNON
=
⎛
1.22V _⎜1+
⎝
R_T
R_B
⎞
⎟
⎠
V_IN
R_T
R_B
RUN1 OR
RUN2
LTC3118
ACCURATE
THRESHOLD
1.22V –
+
ENABLE
SWITCHING
0.65V –
+
LOGIC
THRESHOLD
(a)
ENABLE LDO AND
CONTROL CIRCUITS
3118 F04a
V_IN2 V_IN1
LOGIC
SIGNAL
V_IN2 V_IN1
LOGIC
SIGNAL
RUN1
1M
100pF
RUN2
1M
100pF
3118 F04b
(b)
CN1
V_IN1 ACTIVE
1M
100pF
CN2
V_IN2 ACTIVE
1M
100pF
3118 F04c
(c)
Figure 4. (a) Accurate RUN1 or RUN2 Pin Comparators, (b) Manual V_IN Select with Overlap Timing, (c) Active V_IN Indicators
For more information www.linear.com/LTC3118
3118f
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