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參數(shù)資料
| 型號： | TK61220AQ4 |
| 廠商： | TOKO INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, QCC24 |
| 封裝： | 4 X 4 MM, HQFN-24 |
| 文件頁數(shù)： | 8/23頁 |
| 文件大?。?/td> | 342K |
| 代理商： | TK61220AQ4 |
TK61220AQ4
GC3-N008B
Page 16
11-3. LED Overcurrent Protection
The
TK61220AQ4
controls
the
LED
current
by
controlling a step-up DC-DC converter. VIN<VOUT
consists as a relation between the supply voltage and the
output voltage. When VIN>VOUT, the IC loses control, and
changes the over-current-state.
The TK61220AQ4 has built in LED over-voltage
protection. When the FB pin voltage exceeds 0.7V, a
timer latch starts counting. If it recovers while the timer is
counting, the count of a timer is reset. If it doesn't recover
while the timer is counting, the timer latch functions, and
the driver output turns Off.
Even if the timer latch functions during a short between
VOUT-FB, and the driver output turns Off, the over-
current flows to the coil and the Schottky diode. Current
becomes VIN/RLED. It may exceed the allowable current
of the coil and the Schottky diode. It exceeds power
dissipation loss of RLED and may damage the coil and the
Schottky diode. If this is a concern, add the circuit shown
in figure 3.
The PGOOD pin changes to an "L" level when the timer
latch turns off the IC. The Pch FET at the input turns Off.
The route of the coil and Schottky diode is cut. The over-
current at the short state between VOUT-FB can be limited.
Figure 3: Additional protection circuitry example 2
SW2
FB2
EAOUT2
15
14
13
18
PWM COMP 2
DRIVER 2
Vref
LED CURRENT
SENSE 2
DTC
Vref
EAOUT
ERROR AMP 2
DIM T-LATCH 2
OSC
OVP AMP2
OUT
R1
C1
R2
R
IS
TR
R
LED
C
OUT
C
IN
V
FB
D
L
V
OUT
V
IN
On/Off
PGOOD2
FET
T-LATCH 2
TIMER
LATCH 2
11-4. Overvoltage Protection
In an LED open-state, the control of the feedback loop is
cut. Therefore Even if the output voltage (VOUT) rises, the
VFB does not rise, and the output voltage will continue to
rise. This condition could easily damage the external FET
and the Schottky diode by exceeding their dielectric
strength.
The TK61220AQ4 has built in over-voltage protection
and monitors the output voltage separately from an LED
control loop. When the output voltage is connected to the
OVP pin, it is possible to control that the OVP pin does
not exceed the voltage, which is set externally.
When the OVP pin voltage exceeds 1.5V, the IC limits
the output voltage, and the timer latch starts counting. If it
recovers in the count time, the count of a timer is reset. If
it doesn't recover in the count time, the timer latch
functions, and the driver output turns Off.
The OVP voltage can be set by two different methods.
The method used will depend on the application.
If a zener diode is used
: V
Z+1.5V
→There is no leak current when the IC is Off.
If resistor are used
: (1+R
OVP2/ROVP1)×1.5V
→It reduces of ambient temperature, low-cost.
Please set the dielectric strength value to each constant in
consideration of the output voltage when Vf of LED is
the maximum.
Figure 4: Additional protection circuitry example 3
SW2
OVP2
FB2
EAOUT2
16
15
14
18
PWM COMP 2
DRIVER 2
Vref
OVP AMP2
DTC
T-LATCH 2
1.5V
EAOUT
ERROR AMP 2
DIM T-LATCH 2
OSC
R1
C1
R2
R
IS
TR
R
LED
C
OUT
C
IN
V
FB
D
L
V
OUT
V
IN
FET
R
OVP1
V
Z or ROVP2
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