PI2211 datasheet(11/26 Pages) VICOR

11 / 26 page

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Picor Corporation · picorpower.com

PI2211

Rev 1.1, Page 11 of 26

PI2211

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SOA Thermal Cycling:

The PI2211 continuously monitors the power dissipation in

the MOSFET by measuring the voltage drop across the

MOSFET (VDS) and the calculated current through the sense

resistor (IDRAIN).

As previously described the power

information is processed through two equivalent internal

networks whose individual responses emulate the MOSFET

RJ-C and RC-A thermal characteristics. These two responses

are summed together to create an accurate RJ-A thermal

response.

When the computed junction temperature rise in the

MOSFET is 60°C, the MOSFET is turned off and, while still

being continuously monitored, allowed to cool to a calculated

junction temperature rise of 21°C (an estimated drop of

39°C). The MOSFET is once again turned on and monitored.

The PI2211 will continue the thermal cycling of the MOSFET

16 times with this temperature hysteresis range before

dropping the cool down temperature to 3°C rise. Once at

3°C, the PI2211 will continue the thermal cycling indefinitely

with a 57°C temperature hysteresis range resulting in a long

cool down period. An example of this SOA thermal cycling is

shown below in Figure 5 and in Figure 11.

Figure 5 - SOA Thermal Cycling

Figure 5 shows the initial string of 16 SOA pulses. The VGS is

displayed on Ch1 (blue), the start-up current is shown on Ch3

(purple) and the BUS voltage is shown on Ch4 (green). Power

-good is shown on Ch2 (light blue), which is low during SOA.

VAUX Supply/Gate Drive:

The PI2211 is designed to be used in systems where the BUS

voltage range is from 0.9Vdc to 14Vdc. When using a BUS

voltage of 4.5Vdc or greater, the PI2211 internal LDO

regulator creates a VCC voltage of 4Vdc to bias the IC.

When using a BUS of less than 4.5Vdc, an external supply

(VAUX) is required to drive VCC; typically 5Vdc or greater with

a series current limiting resistor (RAUX), as is shown in Figure

6, to protect the internal clamp of the VCC pin. The RAUX

limiting resistor is calculated as: RAUX = (VAUX - 3.8V)/10mA.

Though the BUS pin is not used to generate VCC, it still must

be connected to the BUS supply for proper operation.

Figure 6 - External VAUX connection for lower BUS voltages.

The PI2211 has an internal charge pump that requires no

external components and is designed to be used with

MOSFET that can operate with a gate drive of 4.5Vdc.

Figure 7 - Enable, UV and OV thresholds.

PI2211 Datasheet(PDF) 11 Page - Vicor Corporation

PI2211 Datasheet(HTML) 11 Page - Vicor Corporation

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