VIV0104THJ

Rev. 1.3

9/2009

Page 12 of 16

V•I CHIP INC. (A VICOR COMPANY) 25 FRONTAGE RD. ANDOVER, MA 01810 800-735-6200

vicorpower.com

5.0 USING THE CONTROL SIGNALS VC, PC, TM, IM

The VTM Control VC pin is an input pin which powers the

internal VCC circuitry when within the specified voltage range

of 12 V to 17 V. This voltage is required in order for the VTM to

start, and must be applied as long as the input is below 26 V.

In order to ensure a proper start, the slew rate of the applied

voltage must be within the specified range. Depending on the

sequencing of the VC with respect to the input voltage, the

behavior during startup will vary as follows:

the controller is active prior to the input. When the input

voltage is applied, the VTM output voltage will track the

input allowing for a soft start (See Figure 11). If the VC

voltage is removed prior to the input reaching 26 V, the

VTM will shut down.

case the VTM output will begin to rise upon the application

of the VC voltage (See Figure 10). The output rate of rise will

vary depending on the amount of output capacitance in

order to limit the inrush current. In this mode of operation,

the maximum output capacitance is 4,000 µF due to

limitations of the inrush limiting circuitry.

Some additional notes on the using the VC pin:

• In most applications, the VTM will be powered by an

upstream PRM, in which case the PRM will provide a 10 ms

VC pulse during startup. In these applications the VC pins of

the PRM and VTM should be tied together.

• The fault response of the VTM is latching. A positive edge on

VC is required in order to restart the unit.

• The VTM is not designed for continuous operation with

VC applied. The VC voltage should be removed within 20 ms

of application.

• The VTM is capable of reverse operation. If a voltage is

present at the output of the VTM which satisfies the

condition

at the time the VC voltage is applied, then energy will be

transferred from secondary to primary. The input to output

ratio of the VTM will be maintained. The VTM will continue

to operate in reverse once the VC voltage is removed as long

as the input and output voltages are within the specified

range.

The VIV0104THJ has not been qualified for continuous

reverse operation.

The Primary Control (PC) pin can be used to accomplish the

following functions:

• Delayed start: Upon the application of VC, the PC pin will

source a constant 100 µA current to the internal RC

network. Adding an external capacitor will allow further

delay in reaching the 2.5 V threshold for module start

• Auxiliary voltage source: Once enabled in regular

operational conditions (no fault), each VTM PC provides a

regulated 5 V, 2 mA voltage source

• Output Disable: PC pin can be actively pulled down in order

to disable the module. Pull down impedance shall be lower

than 850

Ω.

• Fault detection flag: The PC 5 V voltage source is internally

turned off as soon as a fault is detected. For system

monitoring purposes (microcontroller interface) faults are

detected on falling edges of PC signal. It is important to

notice that PC doesn’t have current sink capability (only 150

k

Ω pull down is present), therefore in an array PC line will

not be capable of disabling all the modules if a fault is

detected on one of them.

The Temperature Monitor (TM) pin provides a voltage

proportional to the absolute temperature of the converter

control IC.

It can be used to accomplish the following functions:

• Monitor the control IC temperature: The temperature in

degrees Kelvin is equal to the voltage on the TM pin scaled

by x100. (i.e. 3.0 V = 300°K = 27ºC). It is important to

temperature distribution greatly vary for each part number as

well with input/output conditions, thermal management and

environmental conditions. Therefore, TM cannot be used to

thermally protect the system.

• Fault detection flag: the TM voltage source is internally

turned off as soon as a fault is detected.

The Current Monitor (IM) pin provides a voltage proportional

to the output current of the VTM. The voltage will vary

between 0.5 V and 2.4 V over the output current range of the

VTM (See Figure 7). The accuracy of the IM pin will be within

25% under all line and temperature conditions between 50%

and 100% load. The accuracy of the pin can be improved

using a predictive algorithm based on the input voltage and

internal temperature. Please contact Applications Engineering

for more information.