ISL25700 Datasheet, PDF (10/18 Pages) Intersil Corporation – Programmable Temperature Controlled MOSFET Driver

ISL25700
Typical Performance Curves (Continued)
0.5
0.3
0.1
-0.1
V_DD = 5V
V_DD = 15V
-0.3
-0.5
5
55
105
155
205
CODE (DECIMAL)
FIGURE 12. GP DAC GAIN ERROR
255
Principles of Operation
The ISL25700 allows for precisely controlling the
temperature of an external object and/or power
dissipation of the external P-MOSFET. The temperature
control is done by continuously sensing resistance of
the NTC thermistor, and adjusting the current flow
through the P-MOSFET (temperature controlling
element).
ISL25700 drives the P-MOSFET proportionally inverted
to the difference between the object temperature and
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sensed
by the external NTC thermistor and converted to a
driving voltage by the Wheatstone bridge and its
amplifier. One leg of the current-mode Wheatstone
bridge contains an external NTC thermistor with the
programmable 8-bit FTC DAC and another leg contains
the selectable current source K1 that feeds an internal
resistor R_INT.
The 8-bit FTC DAC allows fine-tuning the T_SET with
resolution better than +0.1°C within a +15°C coarse
temperature range window. The T_SET temperature is set
through the Temperature Coarse Range Control Register,
Reg.01h[2:0], and the Fine Temperature Control
Register, Reg.02h[7:0]; refer to “ISL25700 MEMORY
MAP” on page 11. A +15°C temperature coarse range
window can be centered on T_SET point based on the
thermistor’s parameters, such as resistance, R/T curve
type, tolerance and NTC slope and by adjusting a current
ratio flowing through the legs of the Wheatstone bridge.
Note that the T_SET target temperature should be higher
than the anticipated maximum ambient temperature for
the application.
There are total of 32 system gain settings available in
the Gain Control Register, Reg.03h[4:0], with 0.35dB
resolution per step. The gain control allows to prevent
the thermal system from oscillation by adjusting the
total system gain remotely, without use of external
components.
The internal current sensing circuitry provides the
ability to control and adjust the power dissipated in the
P-MOSFET through the Current Sense Register,
Reg.01h[7:3]. This function allows for adjusting the
initial turn on heating curve and protects from
over-heating of the P-MOSFET. An external current
sensing resistor R_SENSE, serial with the P-MOSFET, is
required. A current limit can be selected for the chosen
R_SENSE. It should have an effective voltage drop from
200mV to 1750mV and be inside the safe operating
area of the MOSFET.
A General Purpose 8-bit DAC, GP DAC provides a
programmable voltage output V_DAC through the General
Purpose DAC Register, Reg.04h[7:0]. The output swing of
General Purpose DAC can be set through the Gain
Control bit in Reg.03h[6] or totally disabled by resetting
the DAC Enable Bit in Reg.03h[7].
Memory Map
The are two types of memory banks in the chip;
volatile (RAM) and non-volatile (EEPROM). Volatile
registers from address 00h to 07h are identical to
non-volatile registers in terms of the register’s name
and bit definitions. All the data is recalled from
non-volatile registers and maintained in the volatile
registers at power-up. It is possible to do independent
write/read to the volatile and non-volatile banks after
power-up by setting NV bit in the Control/Status
Register, Reg.08h[7]. Note that the data written to the
non-volatile registers will be automatically written to
corresponding volatile registers, however no direct
reading from non-volatile registers is possible. All the
readings are from corresponding volatile registers.
The Memory Map of the chip is in Table 1.
10
FN6885.0
September 3, 2010