LTC3118_15 Datasheet, PDF (23/38 Pages) Linear Technology – 18V, 2A Buck-Boost DC/DC Converter with Low-Loss Dual Input PowerPath

LTC3118
Applications Information
Inactive V_IN Leakage Currents
The inactive input (V_IN1 or V_IN2) consumes a small amount
of bias current and will exhibit some amount of leakage
current, through the disabled switches, depending on the
temperature of the die and the average DC voltage between
the inactive V_IN and SW1 (stand-off voltage). Please refer to
the Die Temperature Rise and N-Channel MOSFET leakage
curves in the Typical Performance Characteristics of the
data sheet. The stand-off voltage can be positive or negative
depending on the V_IN1 and V_IN2 voltages and varies with
SW1 duty cycle. Figure 6 shows typical currents into the
inactive input as a function of its voltage at various levels
of inductor current as the LTC3118 operates in PWM mode
from an active 12V input and 12V output. Higher inductor
currents generally translate to higher leakage currents due
to power dissipation, resulting in a die temperature rise.
Referring to the curves in Figure 6, leakage currents are
generally supplied from the inactive source into its re-
spective V_IN pin above a few volts. At lower voltages, it is
possible to get reverse current back-fed into the source,
causing a depleted battery or unplugged input to slowly
charge. In some cases, a dummy load resistor across the
inactive input may be needed to prevent that input from
rising above its UVLO causing a momentary turn-on. A
good thermal design will help to reduce unwanted leakage
currents into or out of the inactive input, especially at high
switch currents where die temperatures increase. A tight
board layout near the V_IN1/CM1 and V_IN2/CM2 pins to
ground is advised to reduce leakage that may occur due
to SW1 edge rates and parasitic inductances in the traces.
100
I_L = 0A
I_L = 0.5A
80
I_L = 1A
I_L = 2A
60
40
20
0
–20
0
3
6
9 12 15 18
INACTIVE INPUT VOLTAGE (V)
3118 F06
Figure 6. Inactive V_IN Current vs Voltage and Inductor Current (I_L)
Active V_IN = V_OUT = 12V in PWM Mode
For more information www.linear.com/LTC3118
3118f
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