CS1630-FSZ datasheet(20/56 Pages) APEX

20 / 56 page

CS1630/31

DS954F2

illustrates the functional block diagram when connecting an

optional external NTC temperature sensor to the eOTP circuit.

Figure 21. eOTP Functional Diagram

Current ICONNECT is generated from an 8-bit controlled current

source with a full-scale current of 80

A. See Equation 8:

When the loop is in equilibrium, the voltage on the eOTP pin

fluctuates around VCONNECT(th). The digital ‘CODE’ output by

the ADC is used to generate ICONNECT. In normal operating

mode, the ICONNECT current is updated once every seventh

half line-cycle by a single ± LSB step. See Equation 9.

Solving Equation 9 for CODE:

The tracking range of this ADC is approximately 15.5k

 to

. The series resistor RS is used to adjust the resistance

of the NTC to fall within this ADC tracking range so that the

entire 8-bit dynamic range of the ADC is well used. A 14k



(±1% tolerance) series resistor is required to allow

measurements of up to 130°C to be within the eOTP tracking

range when a 100k

 NTC with a Beta of 4334 is used. The

eOTP tracking circuit is designed to function accurately with

an external capacitance of a maximum of 470 pF. A higher 8-

bit code output reflects a lower resistance and hence a higher

external temperature.

The ADC output code is filtered to suppress noise. This filter

is the faster low-pass filter with a programmable time constant

configured using bits EOTP_FLP[2:0] in register Config55

(see "Configuration 55 (Config55) – Address 87" on page 47)

and compared against a programmable code value that

corresponds to the desired shutoff temperature set point.

Shutoff temperature TempShutdown is set using bits

SHUTDWN[3:0] in register Config58 (see "Configuration 58

(Config58) – Address 90" on page 48). If the temperature

exceeds this threshold, the chip enters an external

overtemperature state and shuts down. The external

overtemperature state is not a latched protection state, and

the ADC keeps tracking the temperature in this state in order

to clear the fault state once the temperature drops below a

temperature code corresponding to TempWakeup programmed

using

bits

WAKEUP[3:0]

Config46

(see

"Configuration 46 (Config46) – Address 78" on page 40). If an

external overtemperature protection thermistor is not used,

connect the eOTP pin to GND using a 50k

 to 500k resistor

to disable the eOTP feature so that the programmed

TempWakeup and TempShutdown codes are greater than the

measured 8-bit code corresponding to the total resistance on

the pin.

When exiting reset, the chip enters startup and the ADC

quickly (<5ms) tracks the external temperature to check if it is

below the TempWakeup reference code (CODEWakeup) before

the boost and second stages are powered up. If this check

fails, the chip will wait until this condition becomes true before

initializing the rest of the system.

For external overtemperature protection, a second low-pass

filter with a programmable time constant of 2 minutes is

configured using bits EOTP_SLP[2:0] in register Config55

(see "Configuration 55 (Config55) – Address 87" on page 47).

The filter is applied to the ADC output and uses it to scale

down the internal dim level of the system (and hence ILED) if

the temperature exceeds a programmable 8-bit threshold that

corresponds to TempeOTP (see Figure 22). The large time

constant for this filter ensures that the dim scaling does not

happen spontaneously and is not noticeable (suppress

spurious glitches). Temperature threshold must be set such

that

TempeOTP<TempWakeup<TempShutdown.

Config59 sets TempeOTP (see "Configuration 59 (Config59) –

Address 91" on page 48). Register Config46 sets TempWakeup

(see "Configuration 46 (Config46) – Address 78" on page 40).

(Config58) – Address 90" on page 48).

For example, the system can be set up such that ILED starts

reducing when RNTC ~6.3k (assuming a 14k 1%

tolerance, series resistor RS), which corresponds to a

temperature of 95°C (TempeOTP code is 196) for a 100k

NTC with a Beta of 4334 (100 kW at 25°C). The ILED current

is scaled based on the programmed slope using bits

RATE[1:0] in register Config44 (see "Configuration 44

(Config44) – Address 76" on page 39) until it reaches

TempShutdown. The CS1630/31 uses this calculated value to

CS1630/31

ICONNECT

VCONNECT(th)

Comp_Out

eOTP

Control

eOTP

CNTC

NTC

ICONNECT

VCONNECT th



-------------------------------------

[Eq.8]

CODE

ICONNECT

---------------------------



VCONNECT th



RNTC RS

-------------------------------------

[Eq.9]

CODE

N V

CONNECT th





ICONNECT RNTC RS





-----------------------------------------------------------------

[Eq.10]



RNTC RS



---------------------------------

256 1.25 V



A

 R

NTC





----------------------------------------------------------

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