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LTC4415

4415fa

applicaTions inForMaTion

operaTion

Stability Considerations

Any capacitance on the CLIM pins adds a pole to the cur-

rent control loop. Therefore, stray capacitance on these

pins must be kept to a minimum. Although the maximum

allowed value of the current limit adjust resistor is 1000Ω,

any additional capacitance on these pins reduces the

maximum allowed resistance, consequently increasing

the minimum allowed current limit. For stable operation,

the pole frequency at the CLIM pins should be kept above

800kHz. Therefore, if the CLIM pin parasitic capacitance

is C

, the following equation should be used to calculate

the maximum allowed resistor R

CLIM

≤

2π • 800kHz • C

When the voltage at the CLIM pins are monitored using a

long cable, such as an oscilloscope probe, decouple the

parasitic capacitance of the probe and the monitor system

using a series resistor as shown in Figure 3, where a 20k

resistor has been added between the CLIM pin and the

probe to ensure stable operation.

Input and Output Capacitors

High current transients through parasitic inductance on the

input and output sides of the ideal diodes can cause volt-

age spikes on the IN1/IN2/OUT1/OUT2 pins. These current

transients can occur on power plug-in, load disconnect

or switching, disable, or even thermal shutdown. Limit

inductance and/or increase bypass capacitors to prevent

pin voltages from exceeding the absolute maximum rat-

ing of 6V. Some ESR in these capacitors may be helpful

in dampening the resonances and minimizing the ringing

caused by hot plugging or load switching. Refer to Ap-

plication Note 88, entitled, “Ceramic Input Capacitors Can

Cause Overvoltage Transients” for a detailed discussion

and mitigation of this phenomenon.

The values of the input and output decoupling capacitors

also depends on the maximum allowable droop during

switchover in power supply ORing applications. Typical du-

ration for LTC4415 ideal diodes to switchover from reverse

turn-off to forward conduction, t

SWITCH

, is 9µs. Therefore,

the minimum decoupling capacitance, C, required for a

specified maximum output voltage droop, ∆V, when one

of the input voltages drops, can be calculated as follows:

C =

LOAD

• t

SWITCH

∆V

where I

LOAD

is the load current at the time of switchover.

For example, the required value of output capacitance for

a 100mV maximum droop in the output voltage during

quick switchover at 1A load would be 100µF. Note that both

supplies share the load during switchover, and therefore

reduce the droop, when the voltage on the falling supply

pin changes slowly.

Figure 3. Current Monitor with High Capacitance Probe/Instrument

Undervoltage Lockout

Each ideal diode contains an independent UVLO control

circuit so that one input experiencing undervoltage lockout

does not hinder normal operation of the other channel.

The diode conduction path is turned off and the status

signal, STAT1/STAT2, is deasserted during an undervolt-

age condition.

CLIM

4415 F03

MONITOR

CLIM

20k

MONITOR

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