G570 datasheet(9/14 Pages) GMT

9 / 14 page

Ver 1.0

Nov 09, 2000

TEL: 886-3-5788833

http://www.gmt.com.tw

G570

Global Mixed-mode Technology Inc.

Output Ground Switches

Several PCMCIA power distribution switches on the

market do not have an active grounding FET switch.

These devices do not meet the PC Card specification

requiring a discharge of VCC within 100ms. PC Card

resistance can not be relied on to provide a discharge

path for voltages stored on PC Card capacitance be-

cause of possible high impedance isolation by power

management schemes. A method commonly shown to

alleviate this problem is to add to the switch output an

external 100kΩ resistor in parallel with the PC Card.

Considering that this is the only discharge path to

ground, a timing analysis show that the RC time con-

stant delays the required discharge time to more than

2 seconds. The only way to ensure timing compatibility

with PC Card standards is to use a power-distribution

switch that has an internal ground switch, like that of

the G570, or add an external ground FET to each of

the output lines with the control logic necessary to se-

lect it.

In summary, the G570 is a complete single-chip

dual-slot PC Card power interface. It meets all cur-

rently defined PCMCIA specifications for power deliv-

ery in 5V, 3.3V, and mixed systems, and offers a serial

control interface. The G570 offers functionality, power

savings, overcurrent and thermal protection, and fault

reporting in one 30 pin SSOP surface-mount package

for maximum value added to new portable designs.

Power Supply Considerations

The G570 has multiple pins for each of its 3.3V, 5V,

and 12V power inputs and for switched VCC outputs.

Any individual pin can conduct the rated input or out-

put current. Unless all pins are connected in parallel,

the series resistance is significantly higher than that

specified, resulting in increased voltage drops and lost

power. Both 12V inputs must be connected for proper

VPP switching; it is recommended that all input and

output power pins be paralleled for optimum operation.

Although the G570 is fairly immune to power input

fluctuations and noise, it is generally considered good

design practice to bypass power supplies typically with

a 1µF electrolytic or tantalum capacitor paralleled by a

0.047µF to 0.1µF ceramic capacitor. It is strongly re-

commended that the switched VCC and VPP outputs be

bypassed with a 0.1µF or larger capacitor; doing so

improves the immunity of the G570 to electrostatic

discharge (ESD). Care should be taken to minimize

the inductance of PCB traces between the G570 and

the load. High switching currents can produce large

negative-voltage transients, which forward biases

substrate diodes, resulting in unpredictable perform-

ance. Similarly, no pin should be taken below –0.3V.

RESET or RESET Inputs

To ensure that cards are in a known state after power

brownouts or system initialization, the PC Cards

should be reset at the same time as the host by ap-

plying a low impedance to the VCC and VPP terminals.

A low impedance output state allows discharging of

residual voltage remaining on PC Card filter capaci-

tance, permitting the system (host and PC Cards) to

be powered up concurrently. The RESET or RESET

input closes internal switches S1, S4, S7, and S10

with all other switches left open (see G570 control

logic table). The G570 remains in the low impedance

output state until the signal is deasserted and further

data is clocked in and latched. RESET or RESET is

provided for direct compatibility with systems that use

either an active-low or active-high reset voltage super-

visor. The unused pin is internally pulled up or down

and should be left unconnected.

Overcurrent and Thermal Protection

The G570 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 overcur-

rent condition is detected, only the power output af-

fected 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 G570 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 10A to 15A may flow into the short

before the current limiting of the G570 engages. If the

VCC or VPP outputs are driven below ground, the G570

may latch nondestructively in an off state. Cycling

power will reestablish normal operation.

Overcurrent limiting for the VCC outputs is designed to

activate, if powered up, into a short in the range of

0.8A to 2.2A. The VPP outputs limit from 120mA to

400mA. The protection circuitry acts by linearly limiting

the current passing through the switch rather than ini-

tiating a full shutdown of the supply. Shutdown occurs

only during thermal limiting.

Thermal limiting prevents destruction of the IC from

overheating if the package power-dissipation ratings are

exceeded. Thermal limiting disables all power outputs

(both A and B slots) until the device has cooled.

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