
RC5040
PRODUCT SPECIFICATION
8
Table 2. RC5040 Bill of Materials
Notes:
1. The inductor L2 is recommended to isolate the 5V input supply from current surges caused by MOSFET switching. L2 is not
required for normal operation and may be omitted if desired.
2. A total of 3 MOSFETs are recommended only for the synchronous DC-DC converter application. For the non-synchronous
application, the low side MOSFET M3 is not used.
Reference
C4, C5, C7–C10 Panasonic ECU-V1H104ZFX
C6
Panasonic ECSH1CY475R
C
EXT
Panasonic ECU-V1H121JCG
C12
Panasonic ECSH1CY105R
C1, C2, C3
Sanyo 6MV1000GX
C11
Panasonic ECU-V1H224ZFX
C13–C15
Sanyo 6MV1500GX
DS1
General Instrument SS32
DS2
General Instrument IN5817
8
Skynet 320-8107
L2
1
Skynet 320-6110
M1, M2
2
Fuji 2SK1388
Part Number
Description
0.1
m
F 50V capacitor
4.7
m
F 16V capacitor
39pF capacitor
1
m
F 16V capacitor
1000
m
F 6.3V electrolytic capacitor
0.22
m
F 50V capacitor
1500
m
F 6.3 electrolytic capacitor
Schottky Diode
7
1.3
m
H inductor
2.5
m
H inductor
N-Channel Logic Level
Enhancement Mode MOSFET
6 m
W
CuNi Alloy Wire Resistor
10K 5% Resistors
Relevant Spec.
ESR < 0.047
W
3A, 20V
8
R
DS(ON)
< 37m
W
V
GS
< 4V, I
D
> 20A
R
SENSE
R1–R4, R6, R7
Copel A.W.G #18
Panasonic ERJ-6ENF10.0KV
Application Information
Simple Step-Down Converter
Figure 3. Simple Buck DC-DC Converter
Figure 3 illustrates a step-down DC-DC converter with no
feedback control. The derivation of the basic step-down
converter will serve as a basis for the design equations for
the RC5040. Referring to Figure 3, the basic operation
begins by closing the switch S1. When S1 is closed, the input
voltage V
IN
is impressed across inductor L1. The current
flowing in this inductor is given by the following equation:
where T
ON
is the duty cycle (the time when S1 is closed).
When S1 opens, the diode D1 will conduct the inductor
current and the output current will be delivered to the load
according to the equation:
where: T
S
is the overall switching period.
(T
S
– T
ON
) is the time during which S1 is open.
By solving these two equations, we can arrive at the basic
relationship for the output voltage of a step-down converter:
In order to obtain a more accurate approximation for V
OUT
,
we must also include the forward voltage V
D
across diode
D1 and the switching loss, Vsw. After taking into account
these factors, the new relationship becomes:
Overview
The RC5040 is a programmable synchronous DC-DC con-
troller IC. When designed around the appropriate external
components, the RC5040 can be configured to deliver more
than 14.5A of output current. During heavy loading condi-
tions, the RC5040 functions as a current-mode PWM step-
down regulator. Under light loads, the regulator functions in
the PFM (pulse frequency modulation), or pulse skipping
mode. The controller will sense the load level and switch
between the two operating modes automatically, thus opti-
mizing its efficiency under all loading conditions.
C1
R
L
Vout
+
–
D1
V
IN
65-5040-11
L1
S1
I
L
V
--------------–
V
L1
(
)
T
ON
=
L
V
T
-----------------L1
T
–
)
=
V
OUT
V
IN
T
T
S
----------
è
=
V
OUT
V
IN
V
D
V
SW
–
+
(
)
T
S
-T
V
D
–
=