ADN8835ACPZ-R7 datasheet(16/27 Pages) AD

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ADN8835

Data Sheet

Rev. B | Page 16 of 27

Figure 30. Soft Start Profile in Cooling Mode

TEC VOLTAGE/CURRENT MONITOR

The TEC real-time voltage and current are detectable at VTEC

and ITEC, respectively.

Voltage Monitor

VTEC is an analog voltage output pin with a voltage proportional

to the actual voltage across the TEC. A center VTEC voltage of

1.25 V corresponds to 0 V across the TEC. Convert the voltage

at VTEC and the voltage across the TEC using the following

equation:

VVTEC = 1.25 V + 0.25 × (VLDR − VSFB)

Current Monitor

ITEC is an analog voltage output pin with a voltage proportional

to the actual current through the TEC. A center ITEC voltage of

1.25 V corresponds to 0 A through the TEC. Convert the

voltage at ITEC and the current through the TEC using the

following equations:

VITEC_COOLING = 1.25 V + ILDR × RCS

where the current sense gain (RCS) is 0.285 V/A.

VITEC_HEATING = 1.25 V − ILDR × RCS

MAXIMUM TEC VOLTAGE LIMIT

The maximum TEC voltage is set by applying a voltage divider

at the VLIM/SD pin to protect the TEC. The voltage limiter

operates bidirectionally and allows the cooling limit to be

different from the heating limit.

Using a Resistor Divider to Set the TEC Voltage Limit

Separate voltage limits are set using a resistor divider. The

internal current sink circuitry connected to VLIM/SD draws a

current when the ADN8835 drives the TEC in a heating direction,

which lowers the voltage at VLIM/SD. The current sink is not

active when the TEC is driven in a cooling direction; therefore,

the TEC heating voltage limit is always lower than the cooling

voltage limit.

Figure 31. Using a Resistor Divider to Set the TEC Voltage Limit

Calculate the cooling and heating limits using the following

equations:

VVLIMC = VREF × RV2/(RV1 +RV2)

where VREF = 2.5 V.

VVLIMH = VVLIMC − ILIMH × RV1||RV2

where ILIMH = 10 µA.

VTEC_MAX_COOLING = VVLIMC × AVLIM

where AVLIM = 2 V/V.

VTEC_MAX_HEATING = VVLIMH × AVLIM

MAXIMUM TEC CURRENT LIMIT

To protect the TEC, separate maximum TEC current limits in

cooling and heating directions are set by applying a voltage

combination at the ILIM pin.

Using a Resistor Divider to Set the TEC Current Limit

The internal current sink circuitry connected to ILIM draws a

40 µA current when the ADN8835 drives the TEC in a cooling

direction, which allows a high cooling current. Use the following

equations to calculate the maximum TEC currents:

VILIMH = VREF × RC2/(RC1 +RC2)

where VREF = 2.5 V.

VILIMC = VILIMH + ILIMC × RC1||RC2

where ILIMC = 40 µA.

ILIMC

COOLING

MAX

TEC

−

where RCS = 0.285 V/A.

ILIMH

HEATING

MAX

TEC

−

VILIMH must not exceed 1.2 V and VILIMC must be more than

1.3 V to leave proper margins between the heating and the

cooling modes.

LDR

SFB

TIME

DISCHARGE

PREBIAS

SOFT START

BEGINS

TEC VOLTAGE

BUILDS UP

REACH

VOLTAGE LIMIT

VLIM/SD

TEC VOLTAGE

LIMIT AND

INTERNAL

SOFT START

10µA

HEATING

CLK

DISABLE

VREF

RV1

RV2

SW OPEN = VVLIMC

SW CLOSED = VVLIMH

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