RT5035A/B
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 :
V
LX1
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)
ILpk
I
L1
Toff ³ min off time
Next cycle activated
by EA
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.
(if VOUT1 < 3.6V)
Ton = constant on time
Ton let IL1 increase to ILpk
(where Vf is forward voltage of external Schottky diode.)
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.
OVP high threshold = 5.8V
OVP hysteresis low threshold = 5.5V
I_discharge
30mA
Longer BEMF
5.8V
5.5V
5V
BEMF
0V
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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20
DS5035A/B-03 February 2020
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
