t1 =

CRES x 2.5V

22 PA

= 114 k: x CRES

OVP

LM5035B

STANDBY

NTC

THERMISTOR

T

R2

R1

1.25V

5V

23 PA

VREF

OVP

LM5035B

STANDBY

R2

100k

Q1

R1

2k

VREF

VOUT

5V

1.25V

23 PA

LM5035B

www.ti.com

SNVS613C – JULY 2009 – REVISED APRIL 2013

Figure 26. Latched Load Over-Voltage Protection

Figure 27 shows an application of the OVP comparator for Remote Thermal Protection using a thermistor (or

multiple thermistors) which may be located near the main heat sources of the power supply. The negative

temperature coefficient (NTC) thermistor is nearly logarithmic, and in this example a 100k

Ω thermistor with the β

material constant of 4500 kelvins changes to approximately 2 k

Ω at 130°C. Setting R1 to one-third of this

resistance (665

Ω) establishes 130°C as the desired trip point (for VREF = 5V). In a temperature band from 20°C

below to 20°C above the OVP threshold, the voltage divider is nearly linear with 25 mV per°C sensitivity.

R2 provides temperature hysteresis by raising the OVP comparator input by R2 x 23 µA. For example, if a 22k

Ω

resistor is selected for R2, then the OVP pin voltage will increase by 22 k

Ω x 23 µA = 506 mV. The NTC

temperature must therefore fall by 506mV / 25mV per°C = 20°C before the LM5035B switches from the standby

mode to the normal mode.

Figure 27. Remote Thermal Protection

HICCUP MODE CURRENT LIMIT RESTART (RES)

The basic operation of the hiccup mode current limit restart is described in the functional description. The delay

time to restart is programmed with the selection of the RES pin capacitor CRES as illustrated in Figure 27.

In the case of continuous cycle-by-cycle current limit detection at the CS pin, the time required for CRES to reach

the 2.5V hiccup mode threshold is:

(15)

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