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PDF IZ9921 Data sheet ( Hoja de datos )
| Número de pieza | IZ9921 | |
| Descripción | HIGH-VOLTAGE LED DRIVER | |
| Fabricantes | Integral | |
| Logotipo |  |
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IZ9921, IZ9922, IZ9923
HIGH-VOLTAGE LED DRIVER WITH BUILT-IN MOSFET SWITCH
IZ9921, IZ9922, IZ9923 are high-voltage LED driver control ICs with built-in MOSFET switch and
intended for LED lighting control. They allow efficient operation of LED strings from voltage
sources ranging up to 400VDC. The IZ9921/22 includes an internal high-voltage switching
MOSFET controlled with fixed off-time TOFF of approximately 10µs. The LED string is driven at
constant current, thus providing constant light output and enhanced reliability. The output current is
internally fixed at 20mA for IZ9921, 50mA for IZ9922 and 30mA for IZ9923. The peak current con-
trol scheme provides good regulation of the output current throughout the universal AC line voltage
range of 85 to 264VAC or DC input voltage of 20 to 400V.
Main features:
• Operating temperature range -40 … +85 ºС;
• ON-resistance of the MOSFET switch 210 Ohm;
• OFF-state breakdown voltage of the MOSFET switch not less 500 V;
• ESD level 500V
Table 1 – Contact pad description
Contact pad
number
Symbol
01 TST Test pad
02 PR3 Test pad
03 PR2 Test pad
04 TR Test pad
05 PR1 Test pad
06 PR4 Test pad
07 UDD Supply voltage pad
08 TU Test pad
09
GND
Ground
10 PU1 Test pad
11 PU2 Test pad
12 PU3 Test pad
13
DRAIN
MOSFET switch drain pad
14
GND
Ground
Description
Note –
1 Contact pad 01 - 06, 08, 10, 11, 12, 14 (test pads) are used for testing process on manufactur-
ing fab only (have not to be bonded by customer).
2 Contact pad 09, 14 (Ground) are electrically connected
Ver.00/19.01.2009
1 IZ9921-TSe+
431104
1 page  
IZ9921, IZ9922, IZ9923
current will remain unaffected by the varying input voltage. Adding a filter capacitor across the LED
string can reduce the output current ripple even further, thus permitting a reduced value of L. How-
ever, one must keep in mind that the peak-to-average current error is affected by the variation of
TOFF. Therefore, the initial output current accuracy might be sacrificed at large ripple current in L.
Another important aspect of designing an LED driver with the IZ9921/22/23 is related to cer-
tain parasitic elements of the circuit, including distributed coil capacitance of L, junction capaci-
tance and reverse recovery of the rectifier diode D, capacitance of the printed circuit board traces
CPCB and output capacitance CDRAIN of the controller itself. These parasitic elements affect the effi-
ciency of the switching converter and could potentially cause false triggering of the current sense
comparator if not properly managed. Minimizing these parasitics is essential for efficient and reli-
able operation of the IZ9921/22/23. Coil capacitance of inductors is typically provided in the manu-
facturer’s data books either directly or in terms of the self-resonant frequency (SRF).
SRF = 1/(2π LCL )
(3)
where L is the inductance value, and CL is the coil capacitance.
Charging and discharging this capacitance every switching cycle causes high-current spikes
in the LED string. Therefore, connecting a small capacitor CO (~10nF) is recommended to bypass
these spikes. Using an ultra-fast rectifier diode for D is recommended to achieve high efficiency
and reduce the risk of false triggering of the current sense comparator. Using diodes with shorter
reverse recovery time tRR and lower junction capacitance CJ achieves better performance. The re-
verse voltage rating VR of the diode must be greater than the maximum input voltage of the LED
lamp. The total parasitic capacitance present at the DRAIN pin of the IZ9921/22/23 can be calcu-
lated as:
CP = CDRAIN + CPCB + CL + C J
(4)
where and CDRAIN is the DRAIN capacitance (CDRAIN < 5pF), and CPSB is the printed-circuit board
capacitance.
When the switching MOSFET turns on, the capacitance CP is discharged into the DRAIN pin
of the IC. The discharge current is limited to about 150mA typically. However, it may become lower
at increased junction temperature. The duration of the leading edge current spike can be estimated
as:
TSPIKE
= tRR
+ VIN * CP
I SAT
(5)
In order to avoid false triggering of the current sense comparator, CP must be minimized in accor-
dance with the following expression:
CP
<
I SAT
* (TBLANK_MIN
VIN _ MAX
− tRR )
(6)
where TBLANK_MIN is the minimum blanking time of 200ns, and VIN _MAX is the maximum instanta-
neous input voltage.
Estimating Power Loss
Discharging the parasitic capacitance CP into the DRAIN pin of the IZ9921/22/23 is responsi-
ble for the bulk of the switching power loss. It can be estimated using the following equation:
( )PSWITCH =
VIN 2 * CP
2
+ VIN
* I SAT
* t RR
* FS
(7)
where Fs is the switching frequency, ISAT is the saturated DRAIN current of the IZ921/22/23. The
switching loss is the greatest at the maximum input voltage. The switching frequency is given by
the following:
Ver.00/19.01.2009
5 IZ9921-TSe+
431104
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet IZ9921.PDF ] | |
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