PT4115BSOH-B 查看數據表（PDF） - Unspecified

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PT4115BSOH-B

30V, 1.2A Step-down High Brightness LED Driver with 5000:1 Dimming

Unspecified 

PT4115

30V, 1.2A Step-down High Brightness

LED Driver with 5000:1 Dimming

Shutdown mode

Taking the DIM pin to a voltage below 0.3V will turn

off the output and the supply current will fall to a low

standby level of 95μA nominal.

Soft-start

An external capacitor from the DIM pin to ground will

provide additional soft-start delay, by increasing the

time taken for the voltage on this pin to rise to the

turn-on threshold and by slowing down the rate of rise

of the control voltage at the input of the comparator.

Adding capacitance increases this delay by

approximately 0.8ms/nF.

Inherent open-circuit LED protection

If the connection to the LED(s) is open-circuited, the

coil is isolated from the SW pin of the chip, so the

device and LED will not be damaged.

Capacitor selection

A low ESR capacitor should be used for input

decoupling, as the ESR of this capacitor appears in

series with the supply source impedance and lowers

overall efficiency. This capacitor has to supply the

relatively high peak current to the coil and smooth the

current ripple on the input supply. A minimum value of

4.7uF is acceptable if the DC input source is close to

the device, but higher values will improve performance

at lower input voltages, especially when the source

impedance is high. For the rectified AC input, the

capacitor should be higher than 100uF and the tantalum

capacitor is recommended. The input capacitor should

be placed as close as possible to the IC.

For maximum stability over temperature and voltage,

capacitors with X7R, X5R, or better dielectric are

recommended. Capacitors with Y5V dielectric are not

suitable for decoupling in this application and should

NOT be used.

A suitable Murata capacitor would be

GRM42-2X7R475K-50.

The following web sites are useful when finding

alternatives:

www.murata.com

www.t-yuden.com

www.avxcorp.com

Inductor selection

Recommended inductor values for the PT4115 are in

the range 27uH to 100uH.

Higher values of inductance are recommended at lower

output current in order to minimize errors due to

switching delays, which result in increased ripple and

lower efficiency. Higher values of inductance also

result in a smaller change in output current over the

supply voltage range. (See graphs). The inductor should

be mounted as close to the device as possible with low

resistance connections to the SW and VIN pins.

The chosen coil should have a saturation current higher

than the peak output current and a continuous current

rating above the required mean output current.

Following table gives the guideline on inductor

selection:

Load current Inductor Saturation current

Iout>1A

27-47uH

0.8A<Iout≤1A 33-82uH 1.3-1.5 times of load

0.4A<Iout≤0.8A 47-100uH current

Iout≤0.4A

68-220uH

Suitable coils for use with the PT4115 are listed in the

table below:

Part

No.

MSS1038-333

MSS1038-333

MSS1038-473

MSS1038-683

MSS1038-104

L

(uH)

27

33

47

68

100

DCR

(Ω)

0.089

0.093

0.128

0.213

0.304

ISAT Manufacturer

(A)

2.48

2.3

CoilCraft

2

www.coilcraft.com

1.6

1.3

The inductor value should be chosen to maintain

operating duty cycle and switch 'on'/'off' times within

the specified limits over the supply voltage and load

current range.

The following equations can be used as a guide.

SW Switch 'On' time

L  I

TON



VIN

 VLED

 I avg  (Rs  rL  Rsw )

SW Switch 'Off' time

TOFF



VLED

 VD

L  I

 I avg  (Rs  rL)

Where:

L is the coil inductance (H)

rL is the coil resistance (Ω )

RS is the current sense resistance (Ω )

Iavg is the required LED current (A)

China Resources Powtech (Shanghai) Limited

PT4115_DS Rev EN_2.9

WWW.CRPOWTECH.COM

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