< 500Hz range. The PLL frequency capture window is

The PLL is disabled in DPWM mode; consequently, the

BRT frequency is determined by the minimum BRT on-

time of 50µs and the minimum acceptable dimming

factor. If a 1% dimming factor is needed, the maximum

BRT frequency is 200Hz. If a 10% dimming factor is

acceptable, the maximum BRT frequency is 2kHz.

In analog dimming mode, load-current transients can

occur when the BRT duty cycle abruptly changes on

the fly. Large regulation transients induce a flash on the

LED load that is observable with the naked eye and

should therefore be avoided. Such annoying flashes

can be eliminated by dynamically changing the ENA

pin setting. When a capacitor is connected to the CPLL

pin and the ENA pin is grounded, the PLL continues to

run but does not affect the dimming. When fast PLL

lockup transitions are required, the ENA pin can be

momentarily pulled to ground; after the PLL is locked

up, ENA can be pulled high to reenable PLL in dim-

ming control.

Thermal Shutdown

The MAX8790 includes a thermal-protection circuit.

When the local IC temperature exceeds +170°C (typ),

the controller and current sources shut down and do

not restart until the die temperature drops by 15°C.

Design Procedure

All MAX8790 designs should be prototyped and tested

prior to production. Table 3 provides a list of power

Six-String White LED Driver with Active

Current Balancing for LCD Panel Applications

16

______________________________________________________________________________________

Table 3. Component List

CIRCUIT

FIGURE 1

FIGURE 1

FIGURE 1

FIGURE 3

Switching

Frequency

1MHz

750kHz

500kHz

750kHz

White LED

3.2V (typ), 3.5V (max) at

20mA

Nichia NSSW008C

3.2V (typ), 3.5V (max) at

20mA

Nichia NSSW008C

3.2V (typ), 3.5V (max) at

20mA

Nichia NSSW008C

3.2V (typ), 3.5V (max) at

20mA

Nichia NSSW008C

Number of

White LEDs

6 series x 6 parallel,

20mA (max)

8 series x 6 parallel,

20mA (max)

10 series x 6 parallel,

25mA (max)

6 series x 6 parallel,

20mA (max)

7V to 21V

7V to 21V

Inductor L1

2.2µH, 2.5A power inductor

Sumida CDRH5D16-2R2

4.7µH, 2.05A power inductor

Sumida CDRH5D16-4R7

4.7µH, 3.6A power inductor

Sumida CDRH8D28-4R7

0.9µH, 4.7A power inductor

Sumida CDRH5D16-0R9

Input

Capacitors

10µF ±10%, 10V X5R

ceramic capacitor (1206)

Murata GRM31MR61A106K

10µF ±10%, 25V X5R

ceramic capacitor (1206)

Murata GRM31CR61E106KA

10µF ±10%, 25V X5R

ceramic capacitor (1206)

Murata GRM31CR61E106KA

10µF ±10%, 10V X5R

ceramic capacitor (1206)

Murata GRM31MR61A106K

Capacitor

2.2µF ±10%, 50V X7R

ceramic capacitor (1x)

Murata GRM31CR71H225K

2.2µF ±10%, 50V X7R

ceramic capacitor (1206)

(1x)

Murata GRM31CR71H225K

4.7µF ±10%, 50V X7R

ceramic capacitor (1210)

(1x)

Murata GRM32ER71H475K

2.2µF ±10%, 50V X7R

ceramic capacitor (1x)

Murata GRM31CR71H225K

MOSFET N1

30V, 3A n-channel MOSFET

(6-pin SC70)

Vishay Si1402DH

60V, 2.8A n-channel

MOSFET (6-pin TSOP)

Fairchild Semiconductor

FDC5612

Sanyo Semiconductor

CPH6424

60V, 6A n-channel MOSFET

(PowerPAK 1212-8)

Vishay Si7308DN

30V, 4.9A n-channel

MOSFET (6-pin TSOP)

Vishay Si3456BDV

Diode

Rectifier D1

2A, 30V Schottky diode

Nihon EC21QS03L

2A, 40V Schottky diode

Toshiba CMS11

Nihon EC21QS04

3A, 60V Schottky diode

Nihon EC31QS06

3A, 30V Schottky diode

Nihon EC31QS03L

Sense

Resistor

50m

Ω ±1%, 1/2W

IRC LRC-LRF-1206LF-01-

R050-F

56m

Ω ±1%, 1/2W

IRC LRC-LRF-1206LF-01-

R056-F

40m

Ω ±1%, 1/2W

IRC LRC-LRF-1206LF-01-

R040-F

30m

Ω ±1%, 1/2W

IRC LRC-LRF-1206LF-01-

R030-F