r2j20751np Renesas Electronics Corporation., r2j20751np Datasheet - Page 21

• Manufacturer Part Number: r2j20751np
• Description: Peak Current Mode Synchronous Buck Controller With Power Mos Fets
• Manufacturer: Renesas Electronics Corporation.

R2J20751NP
Phase Control
The device incorporates a comparator for control of the phase number. Pulling the voltage on the FB pin up to that on
VCIN exchanges the phase control comparator for the error amplifier, and the device operates as a slave. In this case,
the output of the comparator (CO) is exchanged for the output of the error amplifier (EO), and the positive input
(REFIN) of the error amplifier is exchanged for the positive input (POS) for the comparator. Furthermore, the inverse
input for the comparator is internally connected to the Share pin. The level where the phase number is switched is set by
an external resistor.
Design example;
1. Deriving the voltage on the Share pins to return to single-phase operation with Iout = 6.52 A (3.48 A of hysteresis)
R07DS0240EJ0100 Rev.1.00
Jan 26, 2011
R3
R4
Specification: L = 470 nH, Fsw = 500 kHz, Vin = 5 V, Vout = 1.5 V, RCS = 820 ,
from two-phase operation with Iout = 10 A.
The peak of the output ripple current is:
When Iout = 6.52 A in two-phase mode, current from each device is 3.26 A. Thus,
The ratio between currents for the sense MOS FET and main MOS FET is 1:13700, so a bias current of 300 A
flows through the CS pin.
Thus, voltages on the CS pin are:
The non-inverted input terminal of the internal current sense comparator has an offset voltage of 0.2 V, and 40-k
and 10-k resistors are connected to the inverted input terminal.
Therefore, the Share voltages are:
VCIN
Ipp (10 A) = (VIN – Vout) / L  Vout / VIN / Fsw / 2 + Iout (10 A) = 12.23 A
Ipp (3.26 A) = (VIN – Vout) / L  Vout / VIN / Fsw / 2 + Iout (3.26 A) = 5.49 A
Vcs (10 A) = (Ipp (10 A) / 13700 + 300 A)  Rcs = 978 mV and
Vcs (3.26 A) = (Ipp (3.26 A) / 13700 + 300 A)  Rcs = 575 mV.
Vshare (10 A) = (Vcs (10 A) + 0.2 V)  5 / 4 = 1.473 V and ......(11)
Vshare (3.26 A) = (Vcs (3.26 A) + 0.2 V)  5 / 4 = 0.969 V. ......(12)
REFIN/POS
Phase switching level is Iout = 10 A, hysteresis = 3.48 A
R5
Slave chip
Phase control
comparator
Figure 6 Phase Switching Control
EO/CO
Share
EO/CO
Share
10k
40k
Master chip
Current Sense
comparator
0.2V
35k
Page 21 of 25
Preliminary
Sense
current
RCS