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参数资料
| 型号： | A6268KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 12/19页 |
| 文件大小： | 0K |
| 描述： | IC LED CTLR AUTOMOBILE 16TSSOP |
| 标准包装： | 1 |
| 恒定电流： | 是 |
| 拓扑： | 低端，PWM，SEPIC，降压（降压），升压（升压） |
| 输出数： | 1 |
| 内部驱动器： | 无 |
| 类型 - 主要： | 车载，背光 |
| 频率： | 100kHz ~ 700kHz |
| 电源电压： | 5 V ~ 50 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 供应商设备封装： | 16-TSSOP-EP |
| 包装： | 标准包装 |
| 工作温度： | -40°C ~ 150°C |
| 其它名称： | 620-1473-6 |
A6268
Automotive High Current LED Controller
be deactivated when the temperature drops below the recovery
threshold provided by the specified hysteresis.
LED Diagnostics The voltage with respect to ground at the
three pins LP, LF, and LA, namely V LP , V LF , and V LA , determine
the status of the LEDs in the load. These voltages provide two
differential voltage measurements:
? the voltage across a single reference LED:
V LED = V LF – V LP (7)
? the ratio of the voltage across all LEDs in a single string:
V STR = V LA – V LP (8)
These measurements are used to determine if there is an open
circuit, if one or more LEDs are shorted, if the output is shorted,
or if there is a short across the LED string.
The voltage, V STR , is derived from the voltage across all LEDs in
the string, by an external resistor divider with a ratio equal to the
quantity of LEDs in the string. To minimize the effects of the bias
currents introducing an offset voltage, it is recommended that the
resistor between LP and LA should be approximately 560 Ω .
So for example, if eight LEDs were used, the ratio required
would be an eighth, therefore the resistor connected between LA
and the anode end of the LED string would be 3.9 k Ω ;
560 / [560 + 3900] = 1/8 .
Open LED –An open circuit is evaluated when:
V STR > V OP (9)
where V OP is the LED open circuit voltage defined in the Electri-
cal Characteristics table.
Because the output is current-controlled it is possible for an open
circuit on the output to cause extremely high voltages to be pres-
ent. Therefore, to prevent any hazardous voltages or damage to
the circuits, the gate drive output, SG, is immediately driven low
when an open circuit is detected. After an open circuit fault has
been detected, FF2 will become high impedance, and the open
circuit fault state will remain until the open fault time-out period,
t OTO , expires.
Note that the open fault time-out period is derived from the oscil-
lator period by a ratio of 32,768:1, so any variation in the oscilla-
tor frequency will change the open fault time-out period. For the
default switching frequency of 350 kHz, this means the open fault
time-out period would be:
t OTO = 32,768 × ( 1 / 350 × 10 3 ) = 94 ms (10)
When the gate drive output is re-enabled at the end of the open
fault time-out period, the output is again monitored for an open
circuit. If the open circuit is still present, then the fault will again
be flagged and the switch drive disabled. This cycle will con-
tinue, as long as the open circuit condition is present.
Shorted LED – A short circuit on one or more LEDs is detected
when:
? for the first (reference) LED:
V STR > V LED + V SCOR (11)
? for other than the first (reference) LED:
V LED > V STR + V SCO (12)
where V STR and V LED are as defined above, V SCO is the nonrefer-
ence LED short offset voltage, and V SCOR is the reference LED
short offset voltage. V SCO and V SCOR are defined in the Electrical
Characteristics table.
When a short is present, the fault flag FF2 is high impedance, but
the regulator continues to operate and drives the remaining LEDs
with the correct regulated current. FF2 will remain high imped-
ance while the short circuit condition is present.
A short circuit on one or more LEDs will not cause a hazard
because the output is current-controlled. If one LED fails and
becomes a short circuit, then the remaining LEDs will continue
to be lit with the same current through, and voltage across,
each LED.
Note—Accuracy: The output status monitor relies on all the
LEDs in the load having a similar forward voltage drop. Where
possible all the LEDs forming the load for a single controller
should be taken from the same voltage bin. The selection of
LEDs from the same bin is more critical when higher numbers of
LEDs are used in a single string. With only two or three LEDs a
wider variation in forward voltage is acceptable.
LED Undercurrent – Under some circuit conditions, particu-
larly during a low input voltage condition, it is possible that there
could be insufficient drive to maintain the current to the LEDs
at the required level. If the voltage across the LED current sense
resistor, R SS , falls below the target sense voltage, V IDL , by an
amount that is more than the LED undercurrent voltage differ-
ence, V UCL , the A6268 will indicate an LED undercurrent condi-
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
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