Datasheet

LTM8061
13
8061fa
For more information www.linear.com/LTM8601
Figure 4. LTM8061 Input Current vs System
Load Current with 1.5A Input Current Limit
8061 F04
SYSTEM LOAD
CURRENT
LTM8061 INPUT
CURRENT (I
VIN
)
!
1.5A
1.0A
0.5A
applicaTions inForMaTion
A 1.5A system limit, for example, would use a 33mΩ sense
resistor. Figure 4 gives an example of the system current
for the situation where the input current happens to be
1A, and then gets reduced as the additional system load
increases beyond 0.5A. The LTM8061 integrates the CLP
signal internally, so average current limiting is performed
in most cases without the need for external filter elements.
For example, to reduce the maximum charge current to
50% of the original value, set RNG/SS to 0.5V. The neces
-
sary resistor value is:
R
RNG/SS
= 0.5V/50µA = 10kΩ
This feature could be used, for example, to switch in a
reduced charge current level. Applying an active voltage
can also be used to control the maximum charge current
but only if the voltage source can sink current. Figures 5
and 6 give two examples of circuits that control the charg
-
ing current by sinking current. Active circuits that source
current cannot be used to drive the RNG/SS pin. Care
must be taken not to exceed the 2.5V absolute maximum
voltage on the pin.
RNG/SS
8061 F05
LTM8061
LOGIC HIGH = HALF CURRENT
10k
RNG/SS
8061 F06
LTM8061
SERVO REFERENCE
+
–
Figure 5. Using the RNG/SS Pin for Digital Control of
Maximum Charge Current
Figure 6. Driving the RNG/SS Pin with a
Current-Sink Active Servo Amplifier
RNG/SS: Dynamic Charge Current Adjust
The LTM8061 gives the user the capability to reduce the
maximum charge current dynamically through the RNG/
SS pin. The maximum charge current of the LTM8061 is
2A and the control voltage range on the RNG/SS pin is
1V, so the maximum charge current can be expressed as:
I
BAT
= 2A • V
RNG/SS
where I
BAT
is the maximum charge current and V
RNG/SS
is
between 0V to 1V. Voltages higher than 1V have no effect
on the maximum charge current.
The LTM8061 sources 50µA from the RNG/SS pin, such
that a current control voltage can be set by simply connect
-
ing an appropriately valued resistor to ground, following
the equation:
R
RNG/SS
= V
RNG/SS
/50µA