DC1645A-D Linear Technology, DC1645A-D Datasheet - Page 13

• Manufacturer Part Number: DC1645A-D
• Description: BOARD EVAL LTM8061-8.4
• Manufacturer: Linear Technology
• Series: LTM®, uModule®r

Specifications of DC1645A-D

• Main Purpose: Power Management, Battery Charger
• Embedded: No
• Utilized Ic / Part: LTM8061
• Primary Attributes: 2 Cell- Li-Ion, 8.2V 2A Output
• Secondary Attributes: LED Status Indicators
• Lead Free Status / RoHS Status: Not applicable / Not applicable

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.
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:
where I
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:
I
R
BAT
RNG/SS
= 2A • V
BAT
1.5A
1.0A
0.5A
Figure 4. LTM8061 Input Current vs System
Load Current with 1.5A Input Current Limit
is the maximum charge current and V
= V
LTM8061 INPUT
CURRENT (I
RNG/SS
RNG/SS
VIN
/50μA
)
SYSTEM LOAD
CURRENT
8061 F04
RNG/SS
is
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:
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.
R
RNG/SS
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 Amplifi er
LTM8061
LTM8061
= 0.5V/50μA = 10kΩ
RNG/SS
RNG/SS
8061 F06
8061 F05
10k
LOGIC HIGH = HALF CURRENT
+
–
SERVO REFERENCE
LTM8061
13
8061f