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LTM8055

8055fb

For more information www.linear.com/LTM8055

APPLICATIONS INFORMATION

will source the same current to the load, assuming each

LTM8055 output current sense resistor is the same value.

ParalleledLTM8055sshouldnormallybeallowedtoswitch

in discontinuous mode to prevent current from flowing

from the output of one unit into another; that is, the

MODE pin should be tied to LL. In some cases, operating

the master in forced continuous (MODE open) and the

slaves in discontinuous mode (MODE = LL) is desirable.

If so, current from the output can flow into the master’s

input. Please refer to Input Precaution in this section for

a discussion of this behavior.

Minimum Input Voltage and RUN

The LTM8055 needs a minimum of 5V for proper opera-

tion, but system parameters may dictate that the device

operate only above some higher input voltage. For ex-

ample, a LTM8055 may be used to produce 12VOUT, but

the input power source may not be budgeted to provide

enough current if the input supply voltage is below 8V.

The RUN pin has a typical falling voltage threshold of

1.2V and a typical hysteresis of 25mV. In addition, the

pin sinks 3µA below the RUN threshold. Based upon the

above information and the circuit shown in Figure 2, the

VIN rising (turn-on) threshold is:

VIN = 3µA •R1

(

)+1.225V

R1+R2

and the VIN falling turn-off threshold is:

VIN =1.2

R1+R2

RUN

LTM8055

VIN

8055 F02

Figure 2. This Simple Resistor Network Sets the Minimum

Operating Input Voltage Threshold with Hysteresis

Figure 1. Two or More LTM8055s May Be Connected in a

Master/Slave Configuration for Increased Output Current

The design of a master-slave configuration is straight

forward:

1. Apply the FB resistor network to the master, choosing

the proper values for the desired output voltage. Sug-

gested values for popular output voltages are provided

in Table 1.

2. Apply a FB resistor network to the individual slaves

so that the resulting output is higher than the desired

output voltage.

3. Apply the appropriate output current sense resistors

between VOUT and IOUT. If the same value is used for the

master and slave units, they will share current equally.

4. Connect the master IOUTMON to the slaves’ CTL pin

through a unity gain buffer. The unity gain buffer is

requiredtoisolatetheoutputimpedanceoftheLTM8055

from the integrated pull-up on the CTL pins.

5. Tie the outputs together.

Note that this configuration does not require the inputs to

be tied together, making it simple to power a single heavy

load from multiple input sources. Ensure that each input

power source has sufficient voltage and current sourcing

capability to provide the necessary power. Please refer

to the Maximum Output Current vs VIN and Input Current

vs Output Current curves in the Typical Performance

Characteristics section for guidance.

Minimum Input Voltage and SVIN

The minimum input voltage of the LTM8055 is 5V, but this

is only if VIN and SVIN are tied to the same voltage source.

If SVIN is powered from a power source at or above 5VDC,

VIN can be allowed to fall below 5V and the LTM8055 can

MASTER

VOUT

IOUT

OUTPUT CURRENT

SENSE RESISTOR

OUTPUT CURRENT

SENSE RESISTOR

UNITY GAIN

BUFFER

IOUTMON

CTL

VOUT

IOUT

SLAVE

TO LOAD

8055 F01

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