R2J20701NP_08 RENESAS [Renesas Technology Corp], R2J20701NP_08 Datasheet - Page 13

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

R2J20701NP
Case 4)
Choice of The Resistance of CS Pin
The CS pin is a current-output pin. A current 1/18500 of that of the high-side MOS FET flows through this pin, which
also has a dc current offset of 490 µA. The converter’s maximum current is determined by the voltage on the CS pin,
i.e. 1.5 V, and by the value of the external resistor attached to this pin. The resistance is determined as shown below.
Current through the choke coil is
Peak choke current is the current when Io is at its maximum, i.e.
Maximum CS pin output current is;
The ideal resistance for attachment to the CS pin is
Therefore choose 750 Ω as the value of the resistor for attachment to the CS pin.
REJ03G1459-0400 Rev.4.00 Jun 30, 2008
Page 13 of 27
R
C
R
C
Specification: L = 360 nH, Vin = 12 V, Vout = 1.8 V, Fsw = 500 kHz, Iout(max) = 25 A
ILpp = (Vin – Vout) × Vout / (L × Vin × Fsw) = 8.5 A (p-p)
Ilmax = Io(max) + 0.5 × ILpp = 25A + 4.25A = 29.25 A
Icsmax = Ilmax / 18500 + Ics-dc = 29.25 A / 18500 + 490 µA = 2.071 mA
RCS = Vcl / Icsmax =1.5 V / 2.071 mA = 724 Ω
Current sharing or two-phase operation
In the case of master–slave operation, the TRK-SS pin on the master device should be attached to an RC
network for soft starts. TRK-SS pins of slave devices should be tied to the master’s TRK-SS pin. The error
amplifiers on the slave devices can be disabled by pulling up the corresponding FB pins to REG5, and the
slave devices do not require loop-compensation networks.
TRK-SS
Ishare
TRK-SS
Ishare
REG5
REG5
CT
CT
To SGND (for current sharing and synchronized operation)
To REG5 (for current sharing and two-phase operation)
Channel 1
Channel 2
(Master)
(Slave)
FB
FB
SW
SW
Vout1
R1
R2
Vout (nominal) = 0.6 V
(R1 + R2) / R2