ISL25700FRUZ-TK【PDF 10/18 页】IC TEMP SWITCH MFET DRVR 10TQFN

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ISL25700

FN6885.0

September 3, 2010

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

target temperature set point (T

SET

), set by the user

through the I

C serial interface. Temperature is 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癈 within a +15癈 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

MAP on page 11. A +15癈 temperature coarse range

window can be centered on T

SET

point based on the

thermistors 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

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 registers 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

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.

FIGURE 12. GP DAC GAIN ERROR

Typical Performance Curves (Continued)

-0.5

-0.3

-0.1

0.1

0.3

0.5

105

155

205

255

CODE (DECIMAL)

= 5V

= 15V

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