Data Sheet

ADN8835

Rev. B | Page 13 of 27

THEORY OF OPERATION

The ADN8835 is a single-chip TEC controller that sets and

stabilizes a TEC temperature. A voltage applied to the input of

the ADN8835 corresponds to the temperature setpoint of the

target object attached to the TEC. The ADN8835 controls an

internal FET H bridge whereby the direction of the current fed

through the TEC can be either positive (for cooling mode) to

pump heat away from the object attached to the TEC, or

negative (for heating mode) to pump heat into the object attached

to the TEC.

Temperature is measured with a thermal sensor attached to the

target object, and the sensed temperature (voltage) is fed back

to the ADN8835 to complete a closed thermal control loop of

the TEC. For the best overall stability, couple the thermal sensor

close to the TEC. In most laser diode modules, a TEC and a

NTC thermistor are already mounted in the same package to

regulate the laser diode temperature.

The TEC is differentially driven in an H bridge configuration.

The ADN8835 drives its internal MOSFET transistors to provide

the TEC current. To provide good power efficiency and zero-

crossing quality, only one side of the H bridge uses a PWM

driver. Only one inductor and one capacitor are required to filter

out the switching frequency. The other side of the H bridge uses a

linear output without requiring any additional circuitry. This pro-

prietary configuration allows the ADN8835 to provide efficiency of

>90%. For most applications, a 1 µH inductor, a 10 μF capacitor,

and a switching frequency of 2.0 MHz maintain less than 1% of the

worst-case output voltage ripple across a TEC.

The maximum voltage across the TEC and the current flowing

through the TEC are set by using the VLIM/SD and ILIM pins.

The maximum cooling and heating currents can be set indepen-

dently to allow asymmetric heating and cooling limits. For

additional details, see the Maximum TEC Voltage Limit section

and the Maximum TEC Current Limit section.

Figure 26. Typical Application Circuit with Analog PID Compensation in a Temperature Control Loop

ADN8835

L = 1µH

2.7V TO 5.5V

TEC

SW

SFB

LDR

PGNDS

PVINL

PVINS

VDD

ILIM

VLIM/SD

ITEC

TEC

VOLTAGE

LIMIT

SHUTDOWN

VTEC

+

–

EN/SY

TMPGD

10µF

0.1µF

10µF

0.1µF

PGNDL

NTC

TEC

VOLTAGE

TEC

CURRENT

ENABLE/

SYNC

TEMP

SET

IN1N

IN1P

IN2P

VREF

AGND

OUT1

IN2N

OUT2

TEC

CURRENT

LIMITS

0.1µF

R

THERMISTOR