A8504EECTR-T 查看數據表（PDF） - Allegro MicroSystems
零件编号
产品描述 (功能)
生产厂家
A8504EECTR-T Datasheet PDF : 18 Pages
| |||
A8504
WLED/RGB Backlight Driver for Medium Size LCDs
7. Select output capacitor COUT (connect between the A8504
and the LEDs), given:
COUT = IOUT × ton / ∆VOUT ,
(9)
where IOUT is the total output current, and ∆VOUT is the
output voltage ripple, 0.5% of VOUT (0.05 × 27.7 = 0.14 V).
Then:
COUT = (40 mA × 6) × 370 ns / 0.14 = 0.63 μF .
Select a ceramic capacitor with a 35 or 50 V rating, X5R or
X7R grade. Usually capacitance at 35 V drops significantly
compared to the 0 V specification. Typically, this requires the
selection of a 2.2 μF capacitor to compensate for DC voltage
bias derating.
The rms current through capacitor should be selected such
that internally-generated temperature rise is limited to 10°C
to 20°C. The rms current through COUT is given by:
ICOUTrms = IOUT × [(D+r2 / 12) / (1 – D)] 1/2 , (10)
where r = ∆IL / IBAT = 0.554 mA /0.923 mA = 0.6.
COUT should have an rms current rating greater than:
(40 mA × 6 )× {[0.74 + (0.36 / 12)]/(1–0.74)}1/2 = 0.48 A.
The rms current through capacitor should be selected such
that internally-generated temperature rise is limited to 10°C.
The rms current through CBAT is given by:
IBATrms = (IOUT × r) / [(1 – D) × 3.46 ],
(12)
= [(40 mA× 6 )× 0.6] /
[(1 – 0.74) × 3.46] = 160 mA .
9. Select the boost diode D1 (connect between the SW pins and
the output). D1 should be a Schottky diode with low forward
drop and junction capacitance.
The diode reverse voltage rating should be greater than VOUT.
A 50 V diode rating is recommended.
The diode DC current rating should be greater than IOUT
and the peak repetitive current rating should be greater than
IBAT + ∆IL / 2.
10. Select the compensation capacitor CC (connect between
the COMP pin and ground. Typically, use a 0.1 to 0.47 μF
capacitor for stability.
8. Select input capacitor CBAT (connect to battery input),
given:
CBAT = ∆IL / (VBAT(min) × fSW × ∆VINripple , (11)
where ∆VINripple is the input ripple voltage, which can be as-
sumed to be 1% of VBAT. Then:
CIN = 0.554 mA/(8 × 2 MHz × 0.08) = 0.4 μF .
Select a 1 μF or higher, 25 or 35 V, ceramic capacitor, X5R or
X7R grade.
High Output Current Operation
LED strings can be paralleled for higher current. The A8504
can sink up to 40 mA through each sink. These outputs can be
connected together with various possibilities for higher current
as shown in figure 7. As an example, for an application with up
to 50 mA using 3 parallel strings: LED1 connected with LED2,
LED3 with LED4, and LED5 with LED6; LED7 and LED8 open;
SEL1 and SEL3 set logic high, and SEL2 set low.
ILED(max)
25
25
25
25
25
25
25
25
50
50
50
50
100
100
200
Quantity
of Strings
8
7
6
5
4
3
2
1
4
3
2
1
2
1
1
SEL1
H
L
H
L
H
L
H
L
H
H
H
H
H
H
H
SEL2
H
H
L
L
H
H
L
L
H
L
H
L
H
H
H
SEL3
H
H
H
H
L
L
L
L
H
H
L
L
H
L
H
LED1 LED2 LED3 LED4 LED5 LED6 LED7 LED8
NC
NC NC
NC NC NC
NC NC NC NC
NC NC NC NC NC
NC NC NC NC NC NC
NC NC NC NC NC NC NC
Connect
Connect
Connect
Connect
Connect
Connect
Connect
NC NC
Connect
Connect
NC NC NC NC
Connect
NC NC NC NC NC NC
Connect
Connect
Connect
NC NC NC NC
Connect
Figure 7. LED strings can be combined to allow various maximum current levels to be applied.
The “Connect” notes indicate LED strings connected together.
Allegro MicroSystems, Inc.
12
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Share Link: 