LTM4622 datasheet(8/24 Pages) AD

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LTM4663

Rev. A

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THEORY OF OPERATION

The LTM4663 has two half-bridge type power stages, a

PWM switching mode regulator and a linear power stage,

to allow current flow in or out of the TEC device connected

in between (see Figure 2).

The object temperature is measured from an external

thermal sensor. The sensed temperature (voltage) is fed

back to the LTM4663 at TFB pin to complete a closed

thermal control loop. The thermistor input amplifier gains

the thermistor sensed voltage, then outputs to the PID

compensation amplifier. The PID compensation amplifier

then compensates a feedback loop response to drive both

the PWM switching mode regulator and the linear power

stage to drive the TEC to heat up or cool down the object.

OPERATION

The LTM4663 is a complete Thermoelectric Cooler (TEC)

µModule regulator that sets, stabilizes and monitors

TEC temperature. It can deliver up to 1.5A of sinking or

sourcing current with external input and output capac-

itors. Operating over 2.7V to 5.5V input voltage range,

the LTM4663 controls an internal FET H-bridge whereby

the direction of the current fed through the TEC can be

either positive (for cooling mode), or negative (for heating

mode).

The LTM4663 has two self-correcting, auto-zeroing

amplifiers(Chopper 1 and Chopper 2) to linearize the

thermal sensor input and to form an analog temperature

feedback control loop. With the zero drift chopper ampli-

fiers, extremely good long-term temperature stability is

maintained via an autonomous temperature control loop.

See Figure 18 for an overview of how to configure the

analog PID control, while see Figure 19 for configuring

the digital PID control.

The LTM4663 can also be configured for use in a soft-

ware controlled PID loop. In this scenario, the Chopper 1

amplifier can configure as a thermistor input amplifier

connected to an external temperature measurement ana-

log-to-digital converter (ADC). The Chopper 2 amplifier

is used as a buffer for the external digital-to-analog con-

verter (DAC), which controls the temperature setpoint.

Connect the DAC to TSET and short the PAMPN and

PAMPOUT pins together. See Figure 19 for an overview

of how to configure the LTM4463 external circuitry for

digital PID control.

To provide good efficiency and small solution size, the

LTM4663 utilizes a PWM switching mode power supply

on one side of the H-bridge while a linear power stage on

the other side. A default 2MHz switching frequency and a

10µF capacitor maintains less than 1% of the worst-case

output voltage ripple across the 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 independently to allow asymmetric cooling and

heating limits. The real time TEC voltage and current can

be monitored using VTEC and ITEC pins.

APPLICATIONS INFORMATION

INPUT AND OUTPUT DECOUPLING CAPACITORS

Benefiting from the unique topology and the 2MHz

default switching frequency, only one ceramic capacitor

is required at the input and output of the PWM switch-

ing regulator to maintain less than 1% of the worst-case

output voltage ripple across the TEC. Additional output

filtering may be required by the system designer if further

reduction of output ripples or dynamic transient spikes

is required.

ENABLE AND SHUTDOWN

To enable the LTM4663, apply a logic high voltage to the

EN/SY pin while the voltage at the VLIM/SD pin is above the

maximum shutdown threshold of 0.07V. If either the EN/

SY pin voltage is set to logic low or the VLIM/SD voltage is

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