NCP5008(2003) 데이터 시트보기 (PDF) - ON Semiconductor

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NCP5008
(Rev.:2003)

Backlight LED Boost Driver

ON Semiconductor 

NCP5008, NCP5009

PIN FUNCTION DESCRIPTION

Pin

Symbol

Type

1

Iref

INPUT

2

PHOTO

SIGNAL

3

CS

INPUT

4

VBIAS

POWER

5

CLOCK

INPUT

6

LOCAL

INPUT

7

GND

POWER

8

L2

POWER

9

L1

POWER

10

Vbat

POWER

Description

This pin provides the output current range adjustment by means of a resistor connected to

ground. The current output tolerance depends upon the accuracy of this resistor. Using a "1%

metal film resistor, or better, yields the best output current accuracy.

This pin provides an access to the output current control loop for the NCP5009 version. The

current sunk to ground from this pin is subtracted from the output current mirror. Primary use is

the ambient light automatic adjustment by means of an external photo transistor connected

across this pin and ground. The output current decreases as the ambient light increases. The

internal circuit provides a 1/1 current ratio with the Iref defined by the resistor connected from pin

1 to ground. This current shall be limited to 65 mA.

This functionality is NOT implemented on the NCP5008 type.

Negative going Chip Select logic input. This pin is used to select the NCP5008/ NCP5009 and

validate the clock/data when CS = Low. The internal shift register is automatically clear to zero

upon the falling edge, thanks to a 20 ns built−in one shoot. The built−in pull−up resistor disables

the device when the CS pin is left open.

This pin should be connected to Vbat.

The clock signal connected to this pin is used to serially shift right the internal preset high logic

level. The clock is valid between the falling edge and until the rising edge of the CS. There is

neither a feedback nor an overflow control. If the clock count exceeds 8 bits, the internal register

is clear, the output current is forced to zero and the device comes back to the shutdown mode.

This pin is used to select the mode of operation.

• When LOCAL = High or Open, the chip is controlled by two digital lines:

CS and CLOCK. The output current is programmed by the logic control

of these pins, allowing a current adjustment within the range defined by the

Iref resistor.

• When LOCAL = Low, the chip is turned ON /OFF by means of the CS line,

the CLOCK pins being deactivated. The output current is constant, as defined

by the Iref resistor value.

In order to minimize the standby current a dynamic pull−up resistor is activated when POR is

High, this pull−up resistor being disconnected when LOCAL = Low.

This pin is the system ground for the NCP5008/NCP5009 and carries both the Power and the

Digital signals. High quality ground must be provided to avoid spikes and/or uncontrolled

operation. Care must be observed to avoid high−density current flow in a limited PCB copper

track.

This pin is the power side of the external inductor and must be connected either to the external

Schottky diode (see Figure 22) or directly to one external LED (see Figure 23). It provides the

output current to the load. Since the boost converter operates in a current loop mode, the output

voltage can range up to +15 V but shall not extend this limit. The user must make sure this

voltage will not be exceeded during the normal operation of this part.

An external low cost ceramic capacitor (2.2 mF/16 V, ESR < 100 mW) is recommended to

smooth the current flowing into the diode(s), thus limiting the noise created by the fast transients

present in this circuitry.

Care must be observed to avoid EMI though the PCB copper tracks connected to this pin.

The return side of the external inductor shall be connected to this pin. Typical application will

use a 22 mH, size 1210, to handle the 2.8 to 364 mA max range. On the other hand, when the

desired output current is above 20 mA, the inductor shall have an ESR < 1.0 W. The output

current tolerance can be improved by using a larger inductor value.

The external voltage supply is connected to this pin. A high quality reservoir capacitor must be

connected across pin 10 and Ground to achieve the specified output voltage parameters. A

10 mF/6.3 V, low ESR capacitor must be connected as close as possible across pin 10 and

ground pin 7. The X5R ceramic types are recommended.

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