R2J20701NP_08 RENESAS [Renesas Technology Corp], R2J20701NP_08 Datasheet - Page 10

• Manufacturer Part Number: R2J20701NP_08
• Description: Peak Current Mode Synchronous Buck Controller with Power MOS FETs
• Manufacturer: RENESAS [Renesas Technology Corp]

R2J20701NP
Oscillator and Pulse Generator
The frequency of oscillation is set by the value of the external capacitor connected to the CT pin. This frequency is
twice as high as the actual switching frequency. The frequencies are determined by the following equations:
When the chip is operating in standalone mode or as the master chip for parallel operation, it requires a capacitor on the
CT pin. In this case, the SYNC pin outputs a synchronization signal with a frequency of Fsw.
In operation as a slave chip, the CT pin must be connected to SGND or REG5, after which it acts as an input pin for the
synchronized operation by external clock. The internal circuit is synchronized its rising edge when CT<0.8 V, falling
edge when CT>4.4 V. In two-phase operation in parallel configuration, the CT pin should be at a voltage over 4.4 V.
CT pin
SYNC pin
Synchronizing trigger
The internal RES pulse and maximum duty-cycle-control pulses are produced from the signal at half the oscillator
frequency in standalone and master operating modes. In slave mode, internal pulses are produced from the externally
supplied input signal on the SYNC pin.
Current Sharing
It is easy to obtain balanced-current operation in a parallel configuration due to the application of peak current control.
To obtain current-sharing operation, simply tie the buffered error-amplifier outputs of all of the devices (Ishare pins)
together.
No more than five devices can operate in parallel.
Soft Start
Both simple soft starting and tracking start-up can be realized with the setup of the TRK-SS pin provided for soft-starts.
The error amplifier has three inputs, two of which are designed to give priority to low-level non-inverting inputs for the
amplifier. All that is required to realize soft-start operation is to simply attach an RC charging circuit to the TRK-SS
pin.
The soft-start period is determined by the following equation, with C and R as the values for the RC charging circuit
attached to the TRK-SS pin.
REJ03G1459-0400 Rev.4.00 Jun 30, 2008
Page 10 of 27
Oscillator frequency; Fct = 160 µA / {2 × (CT(F) + 18 pF) × 1 V}
Switching frequency; Fsw = 0.5 × Fct
Tss = –C · R · Ln (1 – 0.6 V / REG5)
Item
Output mode
Standalone
Has a cap.
—
(s)
(Hz)
Output mode
Has a cap.
Master
—
Mode
Input mode
Slave –0°
(in Hz)
< 0.8 V
Rising
Slave –180°
Input mode
> 4.4 V
Falling