RT9986 datasheet(18/24 Pages) RICHTEK

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DS9986-00 May 2011

www.richtek.com

RT9986

Application Information

The RT9986 is a multiple output power supply system for

digital still cameras and other small handheld devices. It

includes six DC/DC converters as well as one WLED driver,

one RTC LDO, one voltage detector, and one system reset.

The WLED works in either current source mode or step-

up mode.

CH1 : Step-up synchronous current modeDC/DC converter

with internal power MOSFETs and compensation network.

The P-MOSFET body can be controlled to disconnect the

load.

CH2 : Step-up or step-down synchronous current mode

DC/DC converter with internal power MOSFETs and

com pensation network. Ex ternal circuit topology

automatically determines whether CH2 is in step-up or

step-down mode. During step-up mode, the P-MOSFET

body can be controlled to disconnect the load if input

voltage is not higher than the VBAT.

CH3 : Step-down synchronous current mode DC/DC

conv erter wit h int ernal power MOS FETs and

compensation network.

CH4 : Step-down synchronous current mode DC/DC

conv erter wit h int ernal power MOS FETs and

compensation network.

CH5 : Step-up synchronous current modeDC/DC converter

with internal power MOSFET and compensation network.

The P-MOSFET body can be controlled to disconnect the

load.

CH6 : Asynchronous inverting current mode DC/DC

converter with internal power MOSFET and compensation

network.

CH7 : A WLED driver operating in either current source

mode or synchronous step-up mode with internal power

MOSFET and compensation network. Operation mode is

determined by LX7 initial voltage The P-MOSFET body in

step-up mode can be controlled to disconnect the load

disconnected.

CH1 to CH4 operate in PWM mode with 2MHz, while

CH5 to CH7 operate in PWM mode with 1MHz switching

frequency.

RTC_LDO : A 3.1V output LDO with low quiescent current

and high output voltage accuracy.

System Reset : Accurate voltage detector for checking

CH2 output voltage status.

Voltage Detector : A general, low quiescent current voltage

detector for monitoring status of a node voltage such as

for RTC_LDO output or others.

CH1 : Synchronous Step-Up DC/DC Converter

CH1 is a synchronous step-up converter which can be

used for motor power. The converter operates at fixed

frequency and PWM current mode. The conv erter

integrates internal MOSFETs, compensation network and

synchronous rectifier for up to 95% efficiency.

The output voltage can be set by the following equation :

VOUT_CH1 = (1 + R1 / R2) x VFB1

where VFB1 is 0.8V typically.

CH2 : Synchronous Step-Up / Step-Down

Selectable DC/DC Converter

CH2 is a synchronous step-up / step-down auto-select

converter, typically for system I/O power. In either step-

up or step-down, the converter operates in fixed frequency

PWM mode, Continuous Current Mode (CCM), and

Discontinuous Current Mode (DCM) with internal

MOSFETs, compensation network and synchronous

rectifiers for up to 95% efficiency.

Step-Up :

In step-up mode, CH2 also disconnects the load from its

input power node and discharges output node of CH2 when

it is turned off.

Step-Down :

In step-down mode, the CH2 converter can be operated

at 100% maximum duty cycle to extend the input

operating voltage range. When the input voltage is close

to the output voltage, the converter enters low dropout

mode.

The output voltage can be set by the following equation :

VOUT_CH2 = (1 + R3 / R4) x VFB2

where VFB2 is 0.8V typically.

RT9986 Datasheet(PDF) 18 Page - Richtek Technology Corporation

RT9986 Datasheet(HTML) 18 Page - Richtek Technology Corporation

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