RT9911 Datasheet, PDF (20/32 Pages) Richtek Technology Corporation – 6 Channel DC/DC Converters

RT9911
Applications Information
The RT9911 includes the following six DC/DC converter
channels to build a multiple-output power-supply system.
CH1 : Selectable step-up or step-down synchronous
current mode DC/DC converter with internal power
MOSFETs.
CH2 : Step-down synchronous current mode DC/DC
converter with internal power MOSFETs.
CH3 : Step-up asynchronous current mode DC/DC
controller to drive external power MOSFETs.
CH4 : Step-up asynchronous voltage mode DC/DC
controller.
CH5 : Inverting DC/DC voltage mode controller.
CH6 : DC/DC voltage mode controller for WLED as well as
conventional boost application; provides open LED OVP
protection.
CH1 : Selectable Step-up or Step-down Converter
CH1 is selectable as step-up (SELECT pin = logic high)
or step-down (SELECT pin = logic low).
Step-up : With internal MOSFETs and synchronous
rectifier, the efficiency is up to 95%. The converter always
operates at fixed frequency PWM mode and CCM
(continuous current mode).
Step-down : With internal MOSFETs and synchronous
rectifier, the efficiency is up to 95%. The converter always
operates at fixed frequency PWM mode and CCM. While
the input voltage is close to output voltage, the converter
enters low dropout mode. Duty could be as long as 100%
to extend battery life. See Figure 3(a) for detailed functional
block.
CH2 : Step-down DC/DC Converter
With internal MOSFETs and synchronous rectifier, the
efficiency is up to 95%. The converter always operates at
fixed frequency PWM mode and CCM. While the input
voltage is close to output voltage, the converter enters
low dropout mode. Duty could be as long as 100% to
extend battery life. See Figure 3(b) for detailed functional
block.
CH3 : Step-up DC/DC Controller
With external MOSFETs and a synchronous rectifier, the
efficiency is up to 97%. The converter always operates at
fixed frequency PWM mode and CCM. The threshold of
current limit is estimated by R_DS(ON) of external NMOS.
See Protections for detailed information and detailed
functional block in Figure 3(c).
CH4, CH6 : Step-up DC/DC Controller
CH4 and CH6 are fixed frequency voltage mode PWM
controllers. EXT4 and EXT6 pins are designed to drive
external NMOS switch. CH6 is optimized for WLED
application. CFB6 is current-sensing feedback, and VFB6
provides over voltage protection (WLED open circuit). See
Protections for detailed information and detailed functional
block in Figure 3(d for CH4 and e for CH6).
CH5 : Inverting Controller
CH5 is a voltage mode, fixed frequency PWM controller
to generate negative output voltage. EXT5 is designed to
drive external PMOS switch. To turn off PMOS completely,
please note that PVDD5 should not be lower than the
source voltage of PMOS. See Figure 3(f) for detailed
functional block.
Reference Voltage
RT9911 provides a precise 1V reference voltage with
souring capability 100uA. Connect a 1uF ceramic capacitor
from VREF pin to GND. Reference voltage is enabled by
connecting EN5 to logic high.
www.richtek.com
20
DS9911-04 August 2007