Datasheet

MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
12 ______________________________________________________________________________________
Setting Voltage and Current Limits
Certain TEC parameters must be considered to guaran-
tee a robust design. These include maximum positive
current, maximum negative current, and the maximum
voltage allowed across the TEC. These limits should be
used to set the MAXIP, MAXIN, and MAXV voltages.
Setting Max Positive and
Negative TEC Current
MAXIP and MAXIN set the maximum positive and nega-
tive TEC currents, respectively. The default current limit
is ±150mV / R
SENSE
when MAXIP and MAXIN are con-
nected to REF. To set maximum limits other than the
defaults, connect a resistor-divider from REF to GND to
set V
MAXI_
. Use resistors in the 10kΩ to 100kΩ range.
V
MAXI_
is related to I
TEC
by the following equations:
V
MAXIP
= 10(I
TECP(MAX
) x R
SENSE
)
V
MAXIN
= 10(I
TECN(MAX
) x R
SENSE
)
where I
TECP(MAX)
is the maximum positive TEC current
and I
TECN(MAX)
is the negative maximum TEC current.
Positive TEC current occurs when CS is less than OS1:
I
TEC
x R
SENSE
= V
OS1
-V
CS
when I
TEC
> 0.
I
TEC
x R
SENSE
= V
CS
-V
OS1
when I
TEC
< 0.
The MAX1969 controls the TEC current in one direction
(unipolar current flow from OS1 to CS). Set the maxi-
mum unipolar TEC current by applying a voltage to
MAXIN. Connect MAXIP to MAXIN. The equation for
setting MAXIN is the same for the MAX1968 and
MAX1969.
Take care not to exceed the positive or negative cur-
rent limit on the TEC. Refer to the manufacturer’s data
sheet for these limits.
Setting MAX TEC Voltage
Apply a voltage to the MAXV pin to control the maxi-
mum differential TEC voltage. MAXV can vary from 0 to
REF. The voltage across the TEC is four times V
MAXV
and can be positive or negative:
|V
OS1
- V
OS2
| = 4 x V
MAXV
Set V
MAXV
with a resistor-divider between REF and
GND using resistors from 10kΩ to 100kΩ. V
MAXV
can
vary from 0 to REF.
Control Inputs/Outputs
Output Current Control
The voltage at CTLI directly sets the TEC current. CTLI
is typically driven from the output of a temperature con-
trol loop. For the purposes of the following equations, it
is assumed that positive TEC current is cooling (see
Figure 1). The transfer function relating current through
the TEC (I
TEC
) and V
CTLI
is given by:
I
TEC
= (V
CTLI
- V
REF
)/(10 x R
SENSE
)
where V
REF
is 1.50V and:
I
TEC
= (V
OS1
- V
CS
)/R
SENSE
CTLI is centered around REF (1.50V). I
TEC
is zero when
CTLI = 1.50V. When VCTLI > 1.50V the MAX1968 is
cooling. Current flow is from OS2 to OS1. The voltages
on the pins relate as follows:
V
OS2
> V
OS1
> V
CS
The opposite applies when heating. When V
CTLI
<
1.50V current flows from OS1 to OS2:
V
OS2
< V
OS1
< V
CS
Shutdown Control
The MAX1968/MAX1969 can be placed in a power-sav-
ing shutdown mode by driving SHDN low. When the
MAX1968/MAX1969 are shut down, the TEC is off (OS1
and OS2 decay to GND) and supply current is reduced
to 2mA (typ).
ITEC Output
ITEC is a status output that provides a voltage proportion-
al to the actual TEC current. ITEC = REF when TEC cur-
rent is zero. The transfer function for the ITEC output is:
V
ITEC
= 1.50 + 8 x (V
OS1
- V
CS
)
Use ITEC to monitor the cooling or heating current
through the TEC. The maximum capacitance that ITEC
can drive is 100pF.