CS1600_1007 Datasheet, PDF (10/18 Pages) Cirrus Logic – LOW-cost PFC Controller for Electronic Ballasts

CS1600
4.3.3 Overpower Protection
The nominal output power is estimated internally by the
CS1600 from the following equation
P_o
=
α
×
η
×
(V_in(min))²
×
-^V----^l-ⁱ--ⁿ--^k----–-----⁽--^V----ⁱ--ⁿ---⁽--^m----ⁱ-ⁿ---⁾---^×---------²----⁾-
2 × f_max × L_B× V_link
[Eq.3]
where
P_o = rated output power of the system
η = efficiency of the boost converter = estimated as 100% by
the internal PFC algorithm
V_in(min) = minimum RMS line voltage for operation
V_link = PFC output voltage
f_max = maximum switching frequency
L_B = boost inductor used in the application
α
=


-^V-----^l-ⁱ--ⁿ--^k--
400V
×
V^-----_i^9-_n^---0₍^--_m^-V---_i^--_n^---₎
2
×
-^V----^l-ⁱ--ⁿ--^k----–-----^---^4---V----⁰----^l--ⁱ⁰---^n-----V-^k-------×----⁹----⁰---^V------^×---------²---^-
V_link – V_in(min) × 2
Operation estimated to be at power levels higher than that
calculated by Eq. 3 above is tracked by the IC as an
overpower condition. During this phase, the PFC output
voltage, V_link, is reduced and will continue to decrease as the
power draw increases. When V_link reaches its undervoltage
threshold, it goes into the start-up mode as explained in
section 4.1.1.
At this point, the overpower protection timer is activated. If this
condition continues to exist for 112 ms, the gate drive is
disabled for a period of about 3 seconds. This “hiccup” mode
of operation continues until the fault is removed.
If a value of the boost inductor other than that obtained from
Eq. 3 above is used, the total output power capability as well
as the thresholds for the different operating conditions will
scale accordingly.
4.3.4 Open/short circuit protection
The CS1600 protects the system in case the feedforward
resistor tied to the IAC pin or the feedback resistor tied to the
FB pin is open or shorted to ground.
A fault seen on the resistor going into the FB pin would imply
no current being fed into the pin, which would trigger the V_link
undervoltage algorithm as described in Section 4.3.1.
A fault detected on the IAC pin would trigger the brownout
condition discussed in Section 4.3.5 below.
4.3.5 Brownout Protection
Brownout occurs when the current representing the rectified
input voltage, nominally 100% of the reference current used
for the output voltage, drops to 49% of its nominal value.
Detection of brownout for a period of 56 ms disables the gate
drive. The device continues to monitor the input voltage while
in this condition. The CS1600 exits the brownout mode when
the input current scales up to, and stays above 56.4% of its
nominal value for a period of 56 ms.
To minimize false detects, the brownout detection circuit
increases the brownout detection time by a factor of 1.6 mS/V
for every volt differential between the minimum operating
voltage and the brownout threshold, following half of a line
cycle of exceeding the brownout threshold. The following
diagram illustrates the brownout sequence whereby the
CS1600 enters standby, and upon recovery from brownout,
enters normal operation..
Brownout
Thresholds
Upper
Lower
TBrownout
56 ms
56 ms
Start
Timer
Enter Standby
Start Timer
Exit Standby
Figure 15. Brownout
4.3.6 Over-temperature Protection
Over-temperature protection is activated and PFC switching is
disabled when the die temperature of the device exceeds
125°C. There is a hysteresis of about 30°C before resumption
of normal operation.
4.4 Standby (STBY) Function
The standby (STBY) pin may be used as a means to force the
CS1600 into a non-operating, low-power state. The STBY
input should be driven by an open-collector/open-drain
device. Internal to the pin, there is a pull-up resistor connected
to the VDD pin as shown in Figure 16. A filter capacitance of
about 1000 pF is recommended while this pin is being used.
CAP
STBY
<1 nF
See Text
600 kΩ
C S1 6 0 0
GND
Figure 16. STBY Pin Connection
10
DS904A7