LT6700-1/LT6700-2/LT6700-3

11

6700123fb

APPLICATIO S I FOR ATIO

LT6700-1

10k

GND

1

5

+INA

–INB OUTB

OUTA

2

6

3

4

100k*

100k*

0.22

+

–

412k*

10k**

470

Ω

Lithium

COIN CELL

10k

10k

750

Ω

10k

750**

†

3V/5V

3V/5V

∆Σ

SAMPLE

IN

MOC-207

MOC-207**

PWM OUT

(OR

∆Σ SENSE)

2

1

5

6

5

6

2

1

0.1

µF

0.1

µF

6700123 F03

22

µF

1% METAL FILM

DELETE FOR PWM MODE

CONNECT FOR PWM MODE

OPTIMIZED FOR 2kHz

*

**

†

††

309k*

NC7S14

309k*

0V TO 2V

+

Figure 3. Isolated PWM or

∆Σ Converter

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

APPLICATIO S I FOR ATIO

ence, rather like an isolated instrumentation amplifier. The

section B comparator is used to generate a 2V reference

supply level for the CMOS NOT gate (inverter), which

serves as the precision switch element for the charge

balancer. The heart of the charge balancer is the section A

comparator, which is detecting slight charge or discharge

states on the 0.22

µF “integration” capacitor as it remains

balanced at

≈400mV by feedback through the NOT gate.

current that the NOT gate duty cycle is continually correct-

ing for, thus the digital waveform at the section A com-

to the 2V “full scale.” In this particular circuit, the PWM

information drives the LED of an optocoupler, allowing the

As an additional option to the circuit, the feedback loop can

be broken and a second optocoupler employed to provide

the charge balance management. This configuration al-

lows for clocking the comparator output (externally to this

circuit) and providing synchronous feedback such that a

simple

∆Σvoltage-to-frequencyconversioncanbeformed

if desired. Approximately 11-bit accuracy and noise per-

formance was observed in a one second integration period

for duty factors from 1% to 99%.