RT5035B datasheet(20/44 Pages) RICHTEK

20 / 44 page

RT5035A/B

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS5035A/B-02

February

2017

Application Information

CH1 : Step-Up DC-DC Converter

CH1 is a step-up converter for motor driver power in DSC system. The converter operates at Async PFM or fixed

frequency PWM current mode which can be set by I2C. The converter integrates internal MOSFETs, FB resistors,

compensation network and synchronous rectifier for up to 95% efficiency. The output voltage of CH1 is adjustable

by the I2C interface in the range of 3.6V to 5.3V. When CH1 operates at Async. PFM mode, LX1 switches as below

waveform :

VLX1

IL1

ILpk

Ton = constant on time

Ton let IL1 increase to ILpk

Toff

³ min off time

Next cycle activated

by EA

(if VOUT1 < 3.6V)

EA monitor VOUT1

³ 3.6V to activate the switching.

If VIN (BAT)-Vf > 3.6V à async boost not switch.

If VIN-Vf < 3.6V, LX1 switch as the above waveform.

Max Iout would be limited by peak current limit and

switching frequency.

(where Vf is forward voltage of external Schottky diode.)

Output charge per cycle :

Qo = Ilpk x Ilpk x L/(Vo-Vi) /2 = L x Ilpk^2 /2/(Vo-Vi)

Qo/Cout determines the output voltage ripple.

Iout = Qo x (switching frequency)

CH1 OVP Operation

Usually, CH1 suffers BEMF of motor, and OVP would occur abnormally. To eliminate this, the operation of CH1 is as

follows. When OVP (5.8V) occurs, CH1 stops switching and CH1 discharges VOUT1 through internal MOS (only for

discharge, I~30mA) until OVP hysteresis (5.5V) low threshold. If there is longer BEMF, the charging and discharging

period will repeat. PMU itself doesn

’t shut down immediately, but shuts down when continuous 100mS OVP occurs.

BEMF

Longer BEMF

30mA

5.5V

5.8V

I_discharge

OVP high threshold = 5.8V

OVP hysteresis low threshold = 5.5V

CH2 : Synchronous Step-Up / Down DC-DC Converter

CH2 is a synchronous step-up / down converter for system I/O power. The converter operates at fixed frequency

PWM Current Mode. The converter integrates internal MOSFETs, FB resistors, compensation network and

synchronous rectifier for up to 95% efficiency. The output voltage of CH2 can be adjusted by the I2C interface in the

range of 2.9V to 3.65V.

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