LTM8061 datasheet(13/20 Pages) LINER

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LTM8061

8061f

Figure 4. LTM8061 Input Current vs System

Load Current with 1.5A Input Current Limit

8061 F04

SYSTEM LOAD

CURRENT

LTM8061 INPUT

CURRENT (IVIN)

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:

RRNG/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:

IBAT = 2A • VRNG/SS

where IBAT is the maximum charge current and VRNG/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:

RRNG/SS = VRNG/SS/50μA

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