6

Other Considerations

Grounds

The HS-565BRH has two ground terminals, pin 5 (REF GND)

and pin 12 (PWR GND). These should not be tied together

near the package unless that point is also the system signal

ground to which all returns are connected. (If such a point

exists, then separate paths are required to pins 5 and 12).

The current through pin 5 is near zero DC (Note); but pin 12

carries up to 1.75mA of code - dependent current from bits

1, 2, and 3. The general rule is to connect pin 5 directly to

the system “quiet” point, usually called signal or analog

ground. Connect pin 12 to the local digital or power ground.

Then, of course, a single path must connect the

analog/signal and digital/power grounds.

NOTE: Current cancellation is a two step process within the

HS-565BRH in which code dependent variations are eliminated, the

resulting DC current is supplied internally. First an auxiliary 9-bit

R-2R ladder is driven by the complement of the DACs input code.

Together, the main and auxiliary ladders draw a continuous 2.25mA

from the internal ground node, regardless of input code. Part of the

DC current is supplied by the zener voltage reference, and the

remainder is sourced from the positive supply via a current mirror

which is laser trimmed for zero current through the external terminal

(pin 5).

Layout

Connections to pin 9 (IOUT) on the HS-565BRH are most

critical for high speed performance. Output capacitance of the

DAC is only 20pF, so a small change of additional

capacitance may alter the op amp’s stability and affect settling

time. Connections to pin 9 should be short and few.

Component leads should be short on the side connecting to

pin 9 (as for feedback capacitor C). See the Settling Time

section.

Bypass Capacitors

Power supply bypass capacitors on the op amp will serve

the HS-565BRH also. If no op amp is used, a 0.01

µF

ceramic capacitor from each supply terminal to pin 12 is

sufficient, since supply current variations are small.

FIGURE 3A. .

FIGURE 3B.

VLSB

SUPPLY

0.1

µF

DVM

COMPARATOR

OUT

B

C

10

90

200K

+

-

5

9

10

NC

11

8

2.5K

5K

5K

20V

± 20%

BIAS

TURN ON

TURN OFF

9.95K

2mA

12

HS-565BRH

D

PULSE

GENERATOR

NO. 2

OUT

14

13

23

24

.

.

.

.

.

.

.

.

.

.

.

.

.

5V

P

PULSE

GENERATOR

NO. 1

SYNC

IN

TRIG

OUT

OUT

A

~100

kHz

STROBE IN

LSB

50%

DIGITAL

INPUT

DAC

OUTPUT

COMP.

STROBE

COMP.

OUT

“EQUAL BRIGHTNESS”

+3V

0V

0V

-400mV

2V

0.8V

4V

0V

(TURN OFF)

A

B

C

D

50%

tX

tD = COMPARATOR DELAY

SETTLING TIME

-0.50LSB

HS-565BRH