RT3607CE Datasheet, PDF (32/69 Pages) Richtek Technology Corporation – Multi-Phase PWM Controller for CPU Core Power Supply

RT3607CE
V_IN 5V
VCC
R1
4.34V
DVD
R2
2V
V_TT
1.05V
EN
0.7V
CP
+
-
CP
+
-
+ ^CP
-
Figure 9. POR Detection
POR
Chip
Enable
VCC
DVD
POR
EN
2ms
SVID ^Invalid
Valid
Invalid
Figure 10. Timing Chart for POR Process
Core VR
Phase Disable (Before POR)
The number of active phases is determined by the internal
circuitry that monitors the ISENxN voltages during startup.
Normally, the VR operates as a 4-phase PWM controller.
Pulling ISEN4N to VCC programs a 3-phase operation,
pulling ISEN3N and ISEN4N to VCC programs a 2-phase
operation, and pulling ISEN2N, ISEN3N and ISEN4N to
VCC programs a 1-phase operation. Before POR, VR
detects whether the voltages of ISEN2N, ISEN3N and
ISEN4N are higher than “VCC − 1V”, respectively to
decide how many phases should be active. Phase
selection is only active during POR. When POR = high,
the number of active phases is determined and latched.
The unused ISENxP pins are recommended to be
connected to VCC and unused PWM pins can be left
floating.
Switching Frequency Setting
The RT3607CE is one kind of constant on-time control.
The patented CCRCOT (Constant Current Ripple COT)
technology can generate an adaptive on-time, the on-time
will vary with the input voltage and VID code to obtain a
constant current ripple, so that the output voltage ripple
can be controlled nearly like a constant as different input
and output voltages change.
For Core VR, connect a resistor R_TON between input
terminal and the TONSET pin to set the on-time width.
T_ON

R_TON  4.73p 1.2
V_IN  V_DAC
(V_DAC  1.2)
T_ON

R_TON  4.73p  V_DAC
V_IN  V_DAC
(V_DAC  1.2)
For better efficiency of the given load range, the maximum
switching frequency is suggested to be :
F_SW(MAX) 
VID1
IccTDC
N



DCR


R_{ON_LS,max}
n_LS
 NR_LL



  ^

V_IN(MAX)


IccTDC
N



R_{ON_LS,max}
n_LS

R_{ON_HS,max}
n_HS

 ^

T_ON  T_D  T_ON,VAR

IccTDC
N



R_{ON_LS,max}
n_LS



T_D

where F_SW(MAX) is the maximum switching frequency, VID1
is the typical VID of application, V_IN(MAX) is the maximum
application input voltage, IccTDC is the thermal design
current of application, N is the phase number. The
R_{ON_HS,max} is the maximum equivalent high-side R_DS(ON) ,
and n_HS is the number of high-side MOSFETs ; R_{ON_LS,max}
is the maximum equivalent low-side R_DS(ON), and n_LS is
the number of low-side MOSFETs. T_D is the summation
of the high-side MOSFET delay time and the rising time,
T_{ON, VAR} is the T_ON variation value. DCR is the inductor
DCR, and R_LL is the loadline setting. In addition, Richtek
provides a Microsoft Excel-based spreadsheet to help
design the R_TON for RT3607CE.
When load increases, on-time keeps constant. The off-
time width will be reduced so that loading can load more
power from input terminal to regulate output voltage.
Hence, the loading current usually increases in case the
switching frequency also increases. Higher switching
frequency operation can reduce power components' size
and PCB space, trading off the whole efficiency since
switching related loss increases, vice versa.
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
www.richtek.com
32
is a registered trademark of Richtek Technology Corporation.
DS3607CE-01 June 2016