NCP5021

http://onsemi.com

2

Table 1. PIN DESCRIPTIONS

PIN

Name

Type

Description

1

SCL

INPUT,

DIGITAL

This pin carries the I2C clock to control the DC/DC converter and to set up the output current and

the photo sensor. The SCL clock is associated with the SDA signal.

2

SDA

INPUT,

DIGITAL

This pin carries the data provided by the I2C protocol. The content of the SDA byte is used to pro-

gram the mode of operation and to set up the output current.

3

I2CADR

INPUT,

DIGITAL

This pin is used to select the I2C address of the NCP5021:

− I2CADR = Low ³ address = %0111 0010 = $72

− I2CADR = High ³ address = %0111 0100 = $74

In order to avoid any risk during the operation, the digital levels are intended to be hardwired prior to

power up the system.

4

VSB

POWER,

OUTPUT

This pin provides a switched voltage, derived from the Vbat supply, to bias the external photo sense.

The current capability of this voltage is 1 mA.

The VSB pin is disconnected when the Shutdown mode has been engaged.

5

AMBS

INPUT,

ANALOG

This pin senses the voltage developed across the external Photo Bias resistor. Since this is a very

high impedance input, cares must be observed to minimize the leakage current and the noise that

may influence the photo sense analog function. The bias parameters associated with the AMBS pin

are reloaded when the chip resumes from Shutdown to Normal operation.

6

INPUT,

ANALOG

This pin provides the inductor peak current during normal operation. In no case shall the voltage at

7

INPUT,

ANALOG

This pin provides the reference current, based on the internal band−gap voltage reference, to con-

trol the output current flowing in the LED. A 1% tolerance, or better, resistor shall be used to get the

highest accuracy of the LED biases. An external current source can be used to bias this pin to dim

the light coming out of the LED.

by the internal reference.

8

AGND

POWER

This pin is the GROUND signal for the analog and digital blocks and must be connected to the sys-

tem ground. A ground plane is strongly recommended.

9

FB

INPUT,

ANALOG

This pin is the current sense of the series arranged LED. The built−in current mirror will automatic-

ally adapt the voltage drop across this pin (typically 400 mV).

10

NC

This pin shall be left open for normal operation.

11

NC

This pin shall be left open for normal operation.

12

NC

This pin shall be left open for normal operation.

13

Lx

POWER

The external inductor shall be connected between this pin (drain of the internal Power switch) and

Vbat. The voltage is internally clamped at 40 V under worst case conditions. The external Schottky

diode shall be connected as close as possible to this pin. See Note 1 for ESR recommendations.

14

PGND

POWER

This pin is the GROUND reference for the DC/DC converter and the output current control. The pin

must be connected to the system ground, a ground plane being strongly recommended.

15

VBAT

INPUT,

POWER

Input Battery voltage to supply the analog , the digital blocks and the main Power switch driver. The

pin must be decoupled to ground by a 10 mF ceramic capacitor.

16

Vos

OUTPUT,

POWER

This pin senses the output voltage supplied by the DC/DC converter. The Vos pin must be by-

passed by 1.0 mF/50 V ceramic capacitor located as close as possible to the pin to properly bypass

the output voltage to ground. The circuit shall not operate without such bypass capacitor connected

to the Vos pin.

The output voltage is internally clamped to 40 V maximum in the event of no load situation.

NOTE: Due to the very fast dV/dt transient developed during the operation, using a low pass filter is

strongly recommended as depicted in the schematic diagram Figure 1.

NC

−

Not

Connected

Back side exposed pad is not internally connected and can be either left floating or connected to the

system Ground.

1. Using low ESR ceramic capacitor (X5R or better) and low ESR inductor with minimum Eddie losses is mandatory to optimize the DC/DC

efficiency.