ST AN3302 Application note

AN3302

Application note

Monolithic power management for high definition ODD with

true shutdown, reset, and programmable step-up voltage

Introduction

Blu-ray disc players have grown rapidly in popularity due to the increasing availability of digital services and high definition digital media content.

This application note describes how to use STODDO1, a complete power management for BIu-ray disc players, based on high density optical storage devices. It integrates two stepdown converters and one step-up.

The step-down converters are optimized for powering Iow-voltage digital core, up to 0.8 A, in ODD applications and, generally, to replace a high current linear solution when the power dissipation may cause an overheating of the application environment.

The step-up provides the needed voltage for supplying the blue laser in mobile applications where only 5 V is available. The output voltage is programmable, by using S-wire protocol, in the range of 6.5 V to 14 V, with a current capability of 0.7 A.

Figure 1. Blu-ray disc player power management architecture based on STODD01

BLUE Laser Driver

6 to 12 V

Reset

DSP

DRAM

Flash

Motors

The integrated low R

Reset

1.2 V

3.3 V

5 V

, for N-channel and P-channel MOSFET switches, contributes to

DSon

Reset IC

Step Down

ADJ 700 mA

Step Down

3.3 V 700 mA

Motor

Control IC

5 V

Step Up

ADJ 800mA

STODD01

5 V

ATA Connector with

AM07854v1

Power

obtaining high efficiency.

The enable function for the step-up section, and reset function for monitoring the input voltage, make the device particularly suitable for optical storage applications.

The high switching frequency (1.2 MHz typ.) allows the use of tiny surface-mounted components. Furthermore, a low output ripple is guaranteed by the current mode PWM topology and by the use of X7R or X5R and low ESR SMD ceramic capacitors.

The device includes soft-start control, thermal shutdown, and peak current limit, to prevent damage due to accidental overload.

January 2011 Doc ID 18163 Rev 1 1/13

www.st.com

Contents AN3302

Contents

1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Recommended PCB Iayout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Programming the output voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3 Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.1 S-wire protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.2 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.3 Input and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2/13 Doc ID 18163 Rev 1

AN3302 Block diagram

1 Block diagram

Figure 2. Block diagram and reference circuit

L1

C1

EN

TX

C1

R5

STODD01

V

IN_A

S-Wire

V

IN_P

Reset

GND

V

IN

C3

C2

Reset

L1

SW1

Step Up

Step Down

GNDGND

GND

Out1

FB1

SW2

FB2

SW3

FB3

L2

L3

R1

R2

R3

R4

V

OUT1

C4

6.5V-14V

V

OUT2

3.3V

C5

V

OUT3

0.8V-0.94*Vin

C6

AM07856v1

Table 1. List of external components

(1)

Component Manufacturer Part number Value Size

C1, C2, C3 Murata GRM21BR61A1O6KE19L 10 µF 0805

C4, C5, C6 Murata GRM32ER61C226KE2OL 22 µF 1210

L1 Coilcraft LPS6225-472MLB 4.7 µH 6 x 6 x 2.5

L2, L3 Coilcraft LPS4O18-332MLB 3.3 µH 4.1 x 4.1 x 1.8

R1 33 k

R2 3.3 k

R3 27 k

R4 47 k

R5 100 k

Ω (V

= 8.8 V)

OUT1

(2)

Ω 0603

= 1.2 V)

OUT3

(3)

Ω 0603

Ω

(4)

0603

If the S-wire function Is not used, the TX pin must be connected to GND. List of external components

1. Components listed above refer to a typical application. Operation of the STODD01 is not limited to the choice of these external components.

2. R

and R2 are calculated according to the following formula: R1 = R2 (V

1

It is recommended to use resistors with values in the range of 1 kΩ to 50 kΩ.

and R4 are calculated according to the following formula: R3 = R4 (V

3. R

3

It is recommended to use resistors with values in the range of 1 kΩ to 50 kΩ.

4. It is recommended to use resistors with values in the range of 100 kΩ to 1 MΩ.

OUT1

OUT3

/ V

FB1

FB3

-1)

(1)

Doc ID 18163 Rev 1 3/13

Recommended PCB Iayout AN3302

2 Recommended PCB Iayout

Figure 3. Recommended PCB layout

2.1 Layout considerations

The layout is an important design step for all switching power supplies due to the high switching frequency and peak current. If the layout is not performed carefully, important parameters such as efficiency and output voltage ripple may be out of specification.

Short, wide traces must be implemented for the main current and for power ground paths. The input capacitor must be placed as close as possible to the IO pins as well as the inductor and output capacitor.

The feedback pin (FB) connection to the external resistor divider is a high impedance node, so interference can be minimized by placing the routing of the feedback node as far as possible from the high current paths. To reduce pick-up noise, the resistor divider must be placed very close to the device.

A common ground node minimizes ground noise. The exposed pad of the package must be connected to the common ground node.

AM07857v1AM07857v1

4/13 Doc ID 18163 Rev 1