SN6507 datasheet(17/44 Pages) TI

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Table 8-2. Slew Rate Control Look-up Table (continued)

VCC (V)

RSR (kΩ)

Typical SLEW RATE (V/μs)

Floating (Default)

369

273

218

8.3.6 Protection Features

SN6507 is protected by multiple protection features to improve the system level robustness and reliability. The

protection features include programmable input undervoltage protection (UVLO), input over-voltage protection

(OVP), programmable over current protection (OCP), and over-temperature protection (TSD).

8.3.6.1 Over Voltage Protection (OVP)

As SN6507 is a open-loop transformer driver, the over voltage protection feature is implemented to prevent

the output voltage from rising too high. The overvoltage protection threshold is a fixed value and cannot be

programmed. If the VCC pin voltage exceeds the overvoltage rising threshold, device stops switching after a 550

ns (typical) response time. To recover from an over voltage event, the input voltage must drop below the OVP

falling threshold.

8.3.6.2 Over Current and Short Circuit Protection (OCP)

The SN6507 is protected from overcurrent conditions with cycle-by-cycle current limiting on both NMOS

switches. OCP is disabled during soft-start. After soft-start finishes, the OCP is enabled, and the threshold

is set at the programmed value. The switch current is sensed and compared to the current threshold that is

programmed by the external resistor on SS/ILIM pin, RILIM. Common current limit thresholds (ILIM) and their

corresponding resistor values for RILIM are listed in Table 8-3 below. Leaving the ILIM/SS pin floating is not

recommended for this device.

Table 8-3. Recommended 1% RILIM values

RILIM

ILIM (Typical)

18 kΩ

1.3 A

20 kΩ

1.2 A

22 kΩ

1.1 A

24 kΩ

1.0 A

27 kΩ

900 mA

30 kΩ

800 mA

35 kΩ

700 mA

40 kΩ

600 mA

50 kΩ

500 mA

62 kΩ

400 mA

85 kΩ

300 mA

127 kΩ

200 mA

261 kΩ

100 mA

In case of an extreme over-load condition on the isolated output due to a short circuit, the device behaves as

follows:

• In the event of a transient overload or short circuit, if the resulting voltage dip is lower than 2.5 V (typical)

on the SS/ILIM pin, the device considers it as a “soft-short” condition. In soft-shorts, the converter goes into

hiccup mode: on hitting the programmed OCP threshold, the driver will be shut-off for 100 ns (typical), and

then retry driving. If the OCP trips again, the cycle continues. This retry keeps occurring for entire TON time of

SW1 and SW2 until OCP does not trip or a "hard-short" is triggered. During the OCP retry events, both FETs

are turned OFF, and the transient peak current may go higher than OCP limit.

• If the voltage dip is more than 2.5 V (typical), the devices considers it as a “hard-short” condition. The

hard-short OCP threshold is fixed at 5 A (typical). If a hard-short condition lasts more than 200 μs, it indicates

that the system is in a serious short-circuit fault condition, the device will fully discharge the soft-start cap

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SN6507

SLLSFM0A – MARCH 2022 – REVISED JUNE 2022

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