MAX780CENG datasheet(6/12 Pages) MAXIM

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Dual-Slot PCMCIA Analog Power Controller

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AVPP1

AVPP0

AVPP

000

VCCIN

VPPIN

High-Z

100

101

VCCIN

VPPIN

BVPP1

BVPP0

BVPP

000

VCCIN

VPPIN

High-Z

100

101

VCCIN

VPPIN

AVCC1

AVCC0

ADRV3

ADRV5

Hi-Z

BVCC1

BVCC0

BDRV3

BDRV5

000

Hi-Z

011

100

101

Hi-Z

Table 1. AVPP Control Logic

Table 2. BVPP Control Logic

Table 3. ADRV3 and ADRV5 Control Logic

Table 4. BDRV3 and BDRV5 Control Logic

________________

Detailed Description

VPP Switching

All four versions (A, B, C, and D) of the MAX780 allow

simple switching of PCMCIA card VPP to 0V, 5V, and

12V. On-chip power MOSFETs connect AVPP and

BVPP to either GND, VCCIN, or VPPIN. The AVPP0

and AVPP1 control logic inputs determine the state of

AVPP. Likewise, BVPP0 and BVPP1 control BVPP.

To prevent VPP overshoot due to parasitic inductance

in the +12V supply, the VPPIN bypass capacitor (CIN)

should be 10 times greater than the capacitance from

AVPP (CA) or BVPP (CB) to GND. Hence, when CA

and CB are 0.1µF, CIN should be 1.0µF.

The

AGPI and BGPI status outputs signal when the VPP

lines are valid.

AGPI goes low when AVPP exceeds

11.05V;

BGPI goes low when BVPP exceeds 11.05V.

The status outputs and the reference are only active

when

SHDN is high.

Pulling

SHDN low puts the MAX780 into a low supply-

current mode and disables the reference and the

AGPI

and

BGPI status outputs. The VCC level shifters

ADRV5, ADRV3, BDRV5, BDRV3 are all forced low

when

SHDN is low. VPP switching is not affected by the

state of

SHDN. Program AVPP and BVPP to 0V for low-

est power consumption when

SHDN is low. Wait at

least 200µs after bringing the MAX780 out of shutdown

before checking

AGPI or BGPI since the reference

needs time to stabilize.

VCC Switching

The MAX780 contains level shifters that simplify driving

external power MOSFETs to switch PCMCIA card VCC

to 3.3V and 5V. While a PCMCIA card is being insert-

ed into the socket, the VCC pins on the card edge con-

nector should be powered down to 0V so that “hot

insertion” does not damage the PCMCIA card. The

simplest way to accomplish this is to pull out a

mechanical switch before the PCMCIA card is inserted.

The mechanical switch can be pushed in only when

the card has been fitted snugly into its socket. The

MAX780

Detailed Operating Circuit shows this method.

In the

Detailed Operating Circuit, (with the mechanical

interlock switch closed) the PCMCIA card VCC cannot

be pulled more than a diode drop below 3.3V. The N-

channel power MOSFET that connects VCC to 3.3V has

its drain tied to VCC and its source tied to 3.3V, so that

its body diode prevents the card’s VCC from falling to

0V. If it were rotated so that the source connected to

VCC, then applying 5V to VCC would short the 5V sup-

ply to the 3.3V supply via the MOSFET’s body diode.

MAX780CENG Datasheet(PDF) 6 Page - Maxim Integrated Products

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