LTC1840

6

1840f

BLOCK DIAGRA

START

CONDITION

STOP

CONDITION

REPEATED START

CONDITION

START

CONDITION

1840 TD01

SDA

SCL

TI I G DIAGRA

8-BIT

IDACs

GPI/O

INTERFACE

8-BIT

COUNTER

8-BIT

COUNTER

FAULT

DETECT

REF

OSC

÷ 2, 4,

8, 16

15

1

2

3

4

14

5

13

10

11

12

9

7

6

FAULT

BLAST

GPIO1

GPIO2

GPIO3

GPIO4

TACHB

TACHA

SCL

SDA

A1

A0

SERIAL

INTERFACE

1840 BD

8

GND

II

PI FU CTIO S

BLAST (Pin 13): Blast/Timer Function Input. This is a

multifunction digital input pin that controls blast and timer

operation. If this pin is in a logic high state at power-up or

is transitioned from high to low, it will “blast” the current

DAC outputs to full scale (100

µA) no matter what their

previous state was and set a fault condition. In addition, if

BLAST is in a logic high state, the serial access timer is

active; this circuit measures time between serial commu-

nications to the LTC1840 and forces a blast and trips a fault

if the part hasn’t been accessed for about 1.5 minutes. This

pin has a 1V logic threshold.

impedance output with a sinking current output of 0

µA to

100

µA. This current can be programmed to one of 256

values through the serial interface or it can be “blasted”

immediately to full scale using the BLAST pin or by the

serial access timer if it is enabled and the LTC1840 is not

accessed for about 1.5 minutes. This pin will maintain the

programmed current to a very tight tolerance from as low

guaranteed to be monotonic over its full 8-bit range.

decoupled to ground (pin 8). A 10

µF tantalum and a 0.1µF

ceramic capacitor in parallel are recommended.