TPS2201DF datasheet(17/23 Pages) TI

17 / 23 page

TPS2201, TPS2201Y

DUAL-SLOT PC CARD POWER-INTERFACE SWITCHES

FOR PARALLEL PCMCIA CONTROLLERS

SLVS094B – AUGUST 1994 – REVISED AUGUST 1995

6–17

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

overcurrent and thermal protection

The TPS2201 uses sense FETs to check for overcurrent conditions in each of the VCC and Vpp outputs. Unlike

sense resistors or polyfuses, these FETs do not add to the series resistance of the switch; therefore, voltage

and power losses are reduced. Overcurrent sensing is applied to each output separately. When an overcurrent

condition is detected, only the power output affected is limited; all other power outputs continue to function

normally. The OC indicator, normally a logic high, is a logic low when any overcurrent condition is detected,

providing for initiation of system diagnostics and/or sending a warning message to the user.

During power up, the TPS2201 controls the rise time of the VCC and Vpp outputs and limits the current into a

faulty card or connector. If a short circuit is applied after power is established (e.g., hot insertion of a bad card),

current is initially limited only by the impedance between the short and the power supply. In extreme cases, as

much as 10 A to 15 A may flow into the short before the current limiting of the TPS2201 engages. If the VCC

or Vpp outputs are driven below ground, the TPS2201 may latch nondestructively in an off state. Cycling power

will reestablish normal operation.

Overcurrent limiting for the VCC outputs is designed to engage if powered up into a short in the range of

0.75 A to 1.9 A, typically at about 1.3 A; the Vpp outputs limit from 120 mA to 400 mA, typically around 200 mA.

The protection circuitry acts by linearly limiting the current passing through the switch, rather than initiating a

full shutdown of the supply. Shutdown occurs only during thermal limiting.

Thermal limiting prevents destruction of the IC from overheating when the package power-dissipation ratings

are exceeded. Thermal limiting, disables all power outputs (both A and B slots) until the device has cooled.

calculating junction temperature

The switch resistance, rDS(on), is dependent on the junction temperature, TJ, of the die. The junction temperature

is dependent on both rDS(on) and the current through the switch. To calculate TJ, first find rDS(on) from Figures

16, 17, and 18 using an initial temperature estimate about 50

°C above ambient. Then calculate the power

dissipation for each switch, using the formula:

D +

DS(on) @

Next, sum the power dissipation and calculate the junction temperature:

J + S

D @

RqJA ) TA,RqJA + 108 C W

Compare the calculated junction temperature with the initial temperature estimate. If they are not within a few

degrees of each other, reiterate using the calculated temperature as the initial estimate.

logic input and outputs

The TPS2201 was designed to be compatible with most popular PCMCIA controllers and current PCMCIA and

JEIDA standards. However, some controllers require slightly counterintuitive connections to achieve desired

output states. The TPS2201 control logic inputs A_VCC3, A_VCC5, B_VCC3 and B_VCC5 are defined active

low (see Figure 23 and control-logic table). As such, they are directly compatible with the Cirrus Logic

CL-PD6720 controller’s logic outputs (see Figure 24). The TPS2201 separate Vpp power good indicators can

be ORed together to provide a single input to the Cirrus controller.

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