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	Reset IC			with
DSP
	1.2 V	Step Down	Step Up		Connector
				5 V		Power
		ADJ 700 mA	ADJ 800mA
DRAM	3.3 V	Step Down	5 V
		3.3 V 700 mA
Flash			STODD01		ATA
	5 V
		Motor
Motors		Control IC			AM07854v1

The integrated low RDSon, for N-channel and P-channel MOSFET switches, contributes to 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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AN3302	Block diagram

1 Block diagram

Figure 2. Block diagram and reference circuit

C1	L1
VIN
STODD01		SW1	Out1
VIN_A				R1		VOUT1
C3	Step Up		FB1		C4
						6.5V-14V
				R2
EN			SW2	L2
S-Wire			FB2			VOUT2
					C5	3.3V
		Step Down
TX
VIN_P			SW3
				L3
C2				R3		VOUT3
R5			FB3
Reset
		Step Down			0.8V-0.94*Vin
Reset
					C6
Reset
	GND	GND	GND	R4
GND
					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 kΩ (VOUT1 = 8.8 V)	(2)	0603
R2		3.3 kΩ		0603
R3		27 kΩ (VOUT3 = 1.2 V)	(3)	0603
R4		47 kΩ		0603
R5		100 kΩ	(4)	0603

If the S-wire function Is not used, the TX pin must be connected to GND. List of external components (1)

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

2.R1 and R2 are calculated according to the following formula: R1 = R2 (VOUT1 / VFB1-1)

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

3.R3 and R4 are calculated according to the following formula: R3 = R4 (VOUT3 / VFB3-1) 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.

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Recommended PCB Iayout	AN3302

2 Recommended PCB Iayout

Figure 3. Recommended PCB layout

AM07857v1

2.1Layout 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.

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