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| 型号： | IR2521DSTRPBF |
| 厂商： | International Rectifier |
| 文件页数： | 10/17页 |
| 文件大小： | 0K |
| 描述： | IC BALLAST CTLR ADAPTIVE 8-SOIC |
| 标准包装： | 1 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOIC |
| 包装： | 标准包装 |
| 其它名称： | IR2521DSTRPBFDKR |
IR2520D(S)& (PbF)
over-current fault. By using the RDSon of the external low-
side MOSFET for current sensing and the VS-sensing
circuitry, the IR2520D eliminates the need for an additional
current sensing resistor, filter and current-sensing pin. To
cancel changes in the RDSon value due to temperature and
MOSFET variations, the IR2520D performs a crest factor
measurement that detects when the peak current exceeds
the average current by a factor of 5 (CSCF). Measuring the
crest factor is ideal for detecting when the inductor saturates
due to excessive current that occurs in the resonant tank
when the frequency sweeps through resonance and the
lamp does not ignite. When the VCO voltage ramps up for
the first time from zero, the resonant tank current and
voltages increase as the frequency decreases towards
resonance (Figure 8). If the lamp does not ignite, the inductor
current will eventually saturate but the crest factor fault
protection is not active until the VCO voltage exceeds 4.8V
(V VCO_RUN ) for the first time. The frequency will continue
decreasing to the capacitive side of resonance towards
the minimum frequency setting and the resonant tank current
and voltages will decrease again. When the VCO voltage
exceeds 4.8V (V VCO_RUN ), the IC enters Run Mode and
the non-ZVS protection and crest factor protection are both
faults. This can occur when a half-bridge MOSFET is
selected that has an RDSon that is too large for the application
causing the internal average to exceed the maximum limit.
FAULT MODE
During Run Mode, should the VCO voltage decrease below
0.82V (V VCOSD ) or a crest factor fault occur, the IR2520D
will enter Fault Mode (see State Diagram). The LO and HO
gate driver outputs are both latched ‘low’ so that the half-
bridge is disabled. The VCO pin is pulled low to COM and
the FMIN pin decreases from 5V to COM. VCC draws
micro-power current (I CCFLT ) so that VCC stays at the
clamp voltage and the IC remains in Fault Mode without the
need for the charge-pump auxiliary supply. To exit Fault
Mode and return to Frequency Sweep Mode, VCC must be
cycled below the UVLO- threshold and back above the
UVLO+ threshold.
LO
enabled. The non-ZVS protection will increase the
frequency again cycle-by-cycle towards resonance from
the capacitive side. The resonant tank current will increase
again as the frequency nears resonance until the inductor
saturates again.
INDUCTIVE SIDE
AVG*5
IMLS
CAPACITIVE SIDE
Inductor
saturation
The crest factor protection is now enabled and measures
the instantaneous voltage at the VS pin only during the time
when LO is ‘high’ and after an initial 1us blank time from the
rising edge of LO. The blank time is necessary to prevent
the crest factor protection circuit from reacting to a non-
ZVS condition. An internal averaging circuit averages the
instantaneous voltage at the VS pin over 10 to 20 switching
cycles of LO. During Run Mode, the first time the inductor
saturates when LO is ‘high’ (after the 1us blank time) and
the peak current exceeds the average by 5 (CSCF), the
IR2520D will enter Fault Mode and both LO and HO outputs
will be latched ‘low’. The half-bridge will be safely disabled
IL
4.6V
VVCO
OF RESONANCE
OF RESONANCE
before any damage can occur to the ballast components.
FREQUENCY SWEEP MODE
RUN MODE
FAULT MODE
The crest factor peak-to-average fault factor varies as a
function of the internal average (Figure 20). The maximum
internal average should be below 3.0 volts. Should the
average exceed this amount, the multiplied average voltage
can exceed the maximum limit of the VS sensing circuit and
the VS sensing circuit will no longer detect crest factor
10
Fig. 8 Crest factor protection timing diagram
www.irf.com
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