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BD7692FJ

Power Factor Correction Controller IC

ROHM Semiconductor 

BD7692FJ

Description of Blocks - continued

5 IS Pin

5.1 Zero Current Detection and Overcurrent Detection Function

The zero current detection circuit is a function to detect a zero cross of the inductor current (IL) (cf. Figure 8).

When the voltage of the IS pin becomes higher than the zero current detection voltage, the OUT output becomes High

after progress at zero current detection delay time (tZCDD 1.35 µs Typ). Please set the RIS value about the overcurrent

detection of the inductor current (IL) so that the IS pin voltage becomes VIS_OCP (-0.60 V Typ) or less. In addition, it

recommends that to add CR filter for switching noise reduction. Figure 9 shows the operation.

IS

Delay

Driver

Logic

-10mV

Over Current Protection

OUT

-0.60V

Figure 8. IS Current Detection Circuit

IS

-10mV

OUT

tZCDD

Figure 9. IS Zero Current Detection Delay Time

5.2 IS-GND Short Function

When the IS pin short-circuits with the GND pin, zero current detection is not possible. It is the IS voltage > -10 mV in off

timing of the OUT pin in the case of -10 mV, IC operates the restart timer. It can prevent CCM operation by discharging

the current which collected to the coil in a restart time.

6 RT Pin

This pin sets frequency of the slope voltage formed in the IC inside by external resistance. Figure 10 shows RT resistor

value and relations of the maximum frequency. The maximum ON width on the application is calculated in the following

formula. Figure 11 shows relations of RT resistor value and maximum ON width.

�� = ����_������

2������_������

������������ 2 ��_������

[s]

Where:

������������ is the minimum input voltage.

�� is the inductance.

����_������ is the maximum output power.

��_������ is the efficiency.

Necessary tON_MAX on application can be check as upper formula. Please set ON width in the RT pin tON_MAX or more.

In addition, it shows relations of RT resistor value and PFC zero current detection Delay in Figure 12.

The high-speed frequency in the light load is limited by RT pin to improve efficiency in the light load.

External resistance of the RT pin can set only 39 kΩ, 68 kΩ, 120 kΩ, 220 kΩ, 470 kΩ.

Do not set the fixed number except the designated value for RT external resistance.

The IC reads RT resistor value at the time of VCCUVLO cancellation and establishes setting. The setting is not changed

even if it changes RT resistor value after VCCUVLO cancellation.

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TSZ22111 • 15 • 001

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TSZ02201-0F2F0A200320-1-2

04.Oct.2018 Rev.001

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