CS1615/16

DS961F1

11

5.6.7 Overcurrent Protection

Overcurrent protection (OCP) is implemented by monitoring the

voltage across the sense resistor. If this voltage exceeds a

output is disabled and the controller attempts to restart after

approximately one second.

5.6.8 Open Loop Protection

Open loop protection (OLP) and sense resistor short protection

are implemented by monitoring the voltage across the resistor. If

the voltage on pin FBSENSE does not reach the protection

controller attempts to restart after approximately one second.

5.7 Overtemperature Protection

The

CS1615/16

incorporates

internal

overtemperature

protection (iOTP) and the ability to connect an external

overtemperature sense circuit for IC protection. Typically, an

NTC thermistor is used.

5.7.1 Internal Overtemperature Protection

Internal overtemperature protection (iOTP) is activated, and

switching is disabled when the die temperature of the devices

exceeds 135°C. There is a hysteresis of about 14°C before

resuming normal operation.

5.7.2 External Overtemperature Protection

The external overtemperature protection (eOTP) pin is used to

implement overtemperature protection. A negative temperature

coefficient (NTC) thermistor resistive network is connected to pin

samples the resistance connected to pin eOTP.

The total resistance on the eOTP pin gives an indication of the

temperature and is used in a digital feedback loop to adjust

full-scale current of 80

A. When the loop is in equilibrium, the

voltage on the eOTP pin fluctuates around reference

and compared against a reference that corresponds to 125°C. A

second low-pass filter with a time constant of two seconds filters

the ADC output and is used to scale down the internal dim level

exceeds 95°C. The large time constant for this filter ensures that

the dim scaling does not happen spontaneously and is not

noticeable (suppress spurious glitches). The eOTP tracking

circuit is designed to function accurately with external

capacitance up to 470pF.

The tracking range of this resistance ADC is approximately

15.5k

resistance of the NTC to fall within the ADC tracking range,

allowing the entire dynamic range of the ADC to be well used.

20.3k

 which corresponds to a temperature of 95°C, as the

beginning of an overtemperature dimming event and starts

reducing the power dissipation. The output current is scaled until

Beyond this temperature, the IC shuts down until the resistance

state, and the ADC keeps tracking the temperature in this state

in order to clear the fault state once the temperature drops below

110°C.

When exiting reset, the chip enters startup and the ADC quickly

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

110°C reference code before the controller is powered up. If this

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

before initializing the rest of the system.

For example, 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 4275. If the

6.3k

resistance of 20.3k

. The eOTP pin initiates protective dimming

action by reducing the power dissipation. At 125°C the thermistor

a resistance of 16.6k

 at the eOTP pin reaching the point where

a thermal shutdown fault intervenes. The CS1615/16 will

resume power conversion (see Figure 16).

If the external overtemperature protection feature is not required,

connect the eOTP pin to GND using a 50k

-to-500k resistor to

disable the eOTP feature.

CS1615/16

+

-

I

CONNE CT

V

CONNE CT

(th)

Comp_Out

eOTP

Control

eOTP

NTC

V

DD

10

(Optional )

Figure 15. eOTP Functional Diagram

Temperature (°C)

125

95

50%

100%

0

25

Figure 16. eOTP Temperature vs. Impedance