E7765AXF datasheet(7/24 Pages) SEMTECH

7 / 24 page

TEST AND MEASUREMENT PRODUCTS

2006 Semtech Corp. , Rev. 11, 7/18/06

www.semtech.com

E7765

Circuit Description (continued)

Driver Slew Rate Adjustment

The driver rising and falling transition times are indepen-

dently adjustable. The RADJ and FADJ pins are analog

current inputs which establish the driver rise and fall times.

Ideally, an adjustable external current source would be

used for RADJ and FADJ. However, for applications where

the rise and fall times are fixed, precision external resis-

tors to a positive voltage can be used. The currents into

RADJ and FADJ follow the equation:

RADJ, FADJ = (VCC - 0.7) / (Rext + 550

Ω).

The diagrams opposite show how driver rise and fall are

adjusted by RADJ, FADJ and DBIAS.

Power Down of the Driver

Referring to Table 1, there are configurations in which a

driver can be put into a power down mode, and others in

which the driver is powered and ready for operation.

PON[0:3] are the TTL inputs controlling power to the indi-

vidual driver circuits. A logical 1 will power up the driver.

The PON inputs remain effective on a per-driver basis in

differential mode.

550

Ω

Rise/Fall

Adjust Current

RADJ, FADJ

VEE

Rext

VCC

Thermal Monitor

An on-chip thermal diode string of five diodes in series

exists (see figure below). This string allows accurate die

temperature measurements.

An external bias current of 100 µA is injected through the

string, and the measured voltage corresponds to a spe-

cific junction temperature with the following equation:

Tj[°C] = {(ANODE – CATHODE) / 5 – 0.768} / (–0.00169).

Power Supply Sequencing

In order to avoid the possibility of latch-up, the following

power-up requirements must be satisfied:

1. VEE <= GND <= VCC at all times

2. VEE <= Analog Inputs <= VCC

3. VEE <= Digital Inputs <= input max voltage or

VCC, whichever is less

The following sequencing can be used as a guideline when

powering up the E7765:

1. VEE

2. VCC

3. Digital Inputs

4. Analog Inputs

The recommended power-down sequence is the reverse

order of the power-up sequence.

ANODE

CATHODE

Temperature Coefficient =

-7.9 mV / °C

Bias Current

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