Step-down DC/DC Converter
with VR and Reset
R5212D SERIES
1
R5212x_E/2004/10/04
OUTLINE
The R5212x is CMOS-based PWM step-down DC/DC converter combined with a voltage regulator
(VR) and a voltage detector (VD), with low supply current.
Each of these ICs consists of an oscillator, a PWM control circuit, a reference voltage unit, an error
amplifier, a soft-start circuit, a current limit circuit, a phase compensation circuit, a resistor net for
voltage detect circuit, an output driver transistor, and so on. A low ripple, high efficiency step-down
DC/DC converter can be easily composed of this IC with some external components, or an inductor, a
diode, and capacitors.
The oscillator frequency is 1.2MHz, therefore small inductor and capacitor can be used with this IC.
Further, this IC equips the under voltage lockout function (UVLO). If the input voltage becomes 2.35V
(Typ.) or less, the output of DC/DC converter is turned off. However, embedded voltage regulator and
detector continue to operate.
The voltage regulator consists of a reference voltage unit, a resistor net for voltage detect circuit, an
error amplifier, an output driver transistor, and so on.
The input source voltage of the built-in voltage regulator is V
IN
pin (A/B version) or V
OUT1
pin, the
output of DC/DC converter (C/D version).
The built-in voltage detector supervises the input voltage and the output is N-channel open drain.
Power-on reset delay time is also included and internally set typically at 12ms(A-Under Mass Produc-
tion/C version-Under Development) or 40ms(B/D version-Under Development).
FEATURES
Wide Range of Input Voltage......... 3.0V~5.5V
Built-in Soft-start Function (Typ. 1ms) and built-in power-on reset delay (Typ. 12ms or 40ms)
Maximum Output Current ........... 500mA (DC/DC), 200mA (VR)
High Accuracy Output Voltage...... 2.0% (DC/DC and Voltage Regulator Output)
Accuracy of voltage detector ......... 2.5%
Output Voltage (VR) ..................... Stepwise Setting with a step of 0.1V in the range of 2.0V to 3.6V
Output Voltage (DC/DC) .............. Stepwise Setting with a step of 0.1V in the range of 1.2V to 3.6V
Output Voltage (VD) ..................... Stepwise Setting with a step of 0.1V in the range of 3.0V to 4.5V
Packages ..................................... HSON-6 (thickness: Max. 0.9mm)
APPLICATIONS
Power source for hand-held communication equipment, CD or DVD drives.
Power source for battery-powered equipment.
R5212D
2
BLOCK DIAGRAM
R5212DXXXA/B
OSC
V
IN
Lx
GND
V
OUT1
Vref
VD
OUT
Soft Start
Current Limit & Feedback
OUTPUT CONTROL Logic
Vref
Delay Circuit
V
OUT2
Vref
Current Limit
U.V.L.O.
R5212D
3
R5212DXXXC/D
OSC
V
IN
Lx
GND
V
OUT1
Vref
VD
OUT
Soft Start
Current Limit & Feedback
OUTPUT CONTROL Logic
Vref
Delay Circuit
V
OUT2
Vref
Current Limit
U.V.L.O.
VOUT1
SELECTION GUIDE
In the R5212x Series, the output voltage combination for the ICs can be selected at the user's re-quest.
The selection can be made with designating the part number as shown below;
R5212Dxxxx-TR Part Number
a b c
Code
Contents
a
Output Voltage Combination Code Number
b
Designation of Optional Function
A: VR input pin =
VIN
pin, VD delay =12ms (Mass Production)
B: VR input pin =
VIN
pin, VD delay =40ms (Under Development)
C: VR input pin = DC/DC Output (
VOUT
pin), VD delay =12ms (Under Development)
D: VR input pin = DC/DC Output (
VOUT
pin), VD delay =40ms (Under Development)
c
Designation of Taping Type: Refer to Taping specification.
R5212D
4
PIN CONFIGURATIONS
HSON-6
6
5
4
1
2
3
(Mark side)
PIN DESCRIPTION
Pin No.
Symbol
Description
1 Lx
Switching Pin (P-channel open-drain output type)
2
GND
Ground Pin
3
V
DOUT
Output Pin of Voltage Detector (N-channel open-drain out-put type)
4
V
OUT1
DC/DC converter Step-down Output monitoring Pin
5
V
OUT2
Output Pin of Voltage Regulator
6
V
IN
Voltage Supply Pin
ABSOLUTE MAXIMUM RATINGS
GND=0V
Symbol
Item
Rating
Unit
V
IN
V
IN
Pin Voltage
6.5
V
V
LX
Lx Pin Voltage
-0.3~V
IN
+0.3
V
V
OUT1
V
OUT1
Pin Voltage
-0.3~V
IN
+0.3
V
V
OUT2
V
OUT2
Pin Voltage
-0.3~V
IN
+0.3
V
V
DOUT
V
DOUT
Pin Voltage
-0.3~V
IN
+0.3
V
I
LX
Lx Pin Output Current
800
mA
I
OUT2
V
OUT2
Pin Output Current
400
mA
P
D
Power Dissipation (HSON-6)
400
mW
Topt
Operating Temperature Range
-40~+85
C
Tstg
Storage Temperature Range
-55~+125
C
R5212D
5
ELECTRICAL CHARACTERISTICS
R5212DXXXA
Topt=25C
Symbol
Item
Conditions
Min.
Typ.
Max.
Unit
V
IN
Operating Input Voltage
3.0
5.5
V
I
DD
Supply Current
V
IN
=5.5V, V
OUT1
=0V
400
800
A
V
UVLOHYS
UVLO Detector Threshold
Voltage Hysteresis
0.05
0.15
0.25
V
V
UVLO2
UVLO Release Voltage
2.35
2.50
2.65
V
DC/DC Part
Symbol
Item
Conditions
Min.
Typ.
Max.
Unit
V
OUT1
DC/DC Output Voltage
V
IN
=5.0V, at no load,
Open Loop
Vset
0.98
Vset
1.02
V
V
OUT1
/
T
DC/DC Output Voltage
Temperature Coefficient
-40C
Topt
85C
100
ppm
/C
f
OSC
Oscillator Frequency
V
IN
=5.0V
960
1200
1440
kHz
R
LX
Lx on Resistance
V
IN
=5.0V, I
LX
=100mA
0.4
0.8
I
LXleak
Lx Leakage Current
V
IN
=V
OUT1
=5.0V, V
LX
=0V
0.01
5.00
A
I
LXlim
Lx Current Limit
V
IN
=5.0V
600
850
mA
Maxdty
Maximum duty cycle
100
%
Tstart
Soft-start Time
V
IN
=5.0V
0.35
1.00
2.50
ms
VR part
Symbol
Item
Conditions
Min.
Typ.
Max.
Unit
V
OUT2
VR Output Voltage
V
IN
=5.0V
I
OUT2
=-10mA
Vset
0.98
Vset
1.02
V
I
OUT2
Maximum Output Current of VR
V
IN
=5.0V
200
mA
V
REG2
VR Load Regulation
V
IN
-V
OUT2
=1.0V
1mA
I
OUT2
80mA
20
60
mV
V
DIF2
Dropout Voltage
I
OUT2
=-100mA
0.2
0.3
V
I
LIM2
Short Current Limit
V
OUT2
=0V
50
mA
V
OUT2
/
T
VR Output Voltage Temperature
Coefficient
-40C
Topt
85C
100
ppm
/C
R5212D
6
VD part
Symbol
Item
Conditions
Min.
Typ.
Max.
Unit
-V
DET
VD Detector Threshold
Vset
0.975
Vset
1.025
V
-V
DET
/
T
VD Detector Threshold
Temperature Coefficient
-40C
Topt
85C
100
ppm
/C
V
HYS
Hysteresis Range
-V
DET
0.05
V
tPLH
VD Output Delay Time for
Release
3
12
22
ms
I
DOUTL
V
DOUT
"L" Output Current
V
IN
=2.0V, V
DOUT
=0.1V
2
7
20
mA
TYPICAL APPLICATION AND APPLICATION HINTS
R5212Dxxxx
V
OUT1
V
OUT2
V
OUT2
V
IN
V
DOUT
GND
V
OUT1
Lx
D1
C1
C3
R1
L1
C2
V
DOUT
Examples of Components
Inductor L1: LQH43C (Murata, 4.7H) or VLP56104R7 (TDK)
Shottky Diode D1: RB491D (Rohm) or EP05Q03L (Nihon Inter)
Pull-up Resistor R1: 50
Capacitors: C1=10F (Ceramic Capacitor) C2: 10F (Ceramic Capacitor) C3: 2.2F (Ceramic Capacitor)
When you use these ICs, consider the following issues;
R5212D
7
Set external components as close as possible to the IC and minimize the connection between the
components and the IC. In particular, a capacitor should be connected to between
VIN
and GND with the
minimum connection. Make sufficient grounding, and reinforce supplying. A large switching current
may flow through the connection of power supply, an inductor and the connection of V
OUT1
. If the
impedance of the connection of power supply or ground is high, the voltage level of power supply of the
IC fluctuates with the switching current. This may cause unstable operation of the IC.
Use a capacitor with a capacity of 10F or more for
VIN
and GND, and with low ESR ceramic type. In
terms of
VOUT1
, use a ceramic capacitor with a capacity of 10F or more. For V
OUT2
pin, use a ceramic
capacitor with a capacitance of 2.2F or around.
Choose an inductor that has a small D.C. resistance and large allowable current and which is hard to
reach magnetic saturation. If the value of inductance of an inductor is extremely small, the I
LX
, which
flows through Lx transistor and an inductor, may exceed the absolute maximum rating at the maxi-
mum loading.
Use an inductor with appropriate inductance.
Use a diode of a Schottky type with high switching speed, and also pay attention to its current ca-
pacity.
If the spike noise of Lx pin is too large, make snub circuit (such as serial connection of CR) between Lx
and GND, then the noise will be reduced. The time constant of the CR depends on the actual PCB, so
evaluate it on the actual PCB.
If the load current of the voltage regulator is small, because of the switching noise of DC/DC converter,
the output voltage of
VOUT2
may be large. To avoid this, use the voltage regulator with a load current at
least 0.5mA.
The performance of power source circuits using these ICs extremely depends upon the peripheral cir-
cuits.
Pay attention in the selection of the peripheral circuits. In particular, design the peripheral circuits in
a way that the values such as voltage, current, and power of each component, PCB patterns and the IC
do not exceed their respected rated values.
Operation of Step-down DC/DC converter and Output Current
The step-down DC/DC converter charges energy in the inductor when Lx transistor is ON, and
discharges the energy from the inductor when Lx transistor is OFF and controls with less energy loss,
so that a lower output voltage than the input voltage is obtained. The operation will be explained with
reference to the following diagrams:
R5212D
8
<Basic Circuits> <Current through L>
Step 1: Lx Tr. turns on and current IL (=i1) flows, and energy is charged into CL. At this moment, IL increases from
ILmin. (=0) to reach ILmax. in proportion to the on-time period(ton) of LX Tr.
Step 2: When Lx Tr. turns off, Schottky diode (SD) turns on in order that L maintains IL at ILmax, and current IL
(=i2) flows.
Step 3: IL decreases gradually and reaches ILmin. after a time period of topen, and SD turns off, provided that in
the continuous mode, next cycle starts before IL becomes to 0 because toff time is not enough. In this case, IL
value is from this ILmin (>0).
In the case of PWM control system, the output voltage is maintained by controlling the on-time period (ton), with
the oscillator frequency (fosc) being maintained constant.
q
Discontinuous Conduction Mode and Continuous Conduction Mode
The maximum value (ILmax) and the minimum value (ILmin) current which flow through the inductor is the same
as those when Lx Tr. is ON and when it is OFF.
The difference between ILmax and ILmin, which is represented by
I;
I = ILmax ILmin = V
OUT
topen / L = (V
IN
-V
OUT
)
ton/L
Equation 1
wherein, T=1/fosc=ton+toff
duty (%)=ton/T
100=ton
fosc
100
topen
toff
In Equation A, V
OUT
topen/L and (V
IN
-V
OUT
)
ton/L are respectively shown the change of the current at ON, and
the change of the current at OFF.
When the output current (I
OUT
) is relatively small, topen < toff as illustrated in the above diagram. In this case, the
energy is charged in the inductor during the time period of ton and is discharged in its entirely during the time
period of toff, therefore ILmin becomes to zero (ILmin=0). When Iout is gradually increased, eventually, topen
SD
L
CL
V
OU
I
OU
V
I
Lx
i1
i2
T=1/fos
c
tof
f
to n
ILma
x
ILmi n
topen
R5212D
9
becomes to toff (topen=toff), and when I
OUT
is further increased, ILmin becomes larger than zero (ILmin>0). The
former mode is referred to as the discontinuous mode and the latter mode is referred to as continuous mode.
In the continuous mode, when Equation 1 is solved for ton and assumed that the solution is tonc,
tonc=T
V
OUT
/V
IN
Equation 2
When ton<tonc, the mode is the discontinuous mode, and when ton=tonc, the mode is the continuous mode.
Output Current and Selection of External Components
When Lx Tr. is ON:
(Wherein, Ripple Current P-P value is described as I
RP
, ON resistance of LX Tr. is described as Rp the direct
current of the inductor is described as R
L
. The threshold level of Shottky diode is described as V
F
. )
V
IN
=V
OUT
+(Rp+R
L
)
I
OUT
+L
I
RP
/ton
Equation 3
When Lx Tr. is OFF:
L
I
RP
/toff = V
F
+V
OUT
+R
L
I
OUT
Equation 4
Put Equation 4 to Equation 3 and solve for ON duty, ton/(toff+ton)=D
ON
,
D
ON
=(V
OUT+
V
F
+R
L
I
OUT
)/(V
IN
+V
F
-Rp
I
OUT
)
Equation 5
Ripple Current is as follows;
I
RP
=(V
IN
-V
OUT
-Rp
I
OUT
-R
L
I
OUT
)
D
ON
/f/L
...
Equation 6
Wherein, peak current that flows through L, Lx Tr., and SD is as follows;
ILmax=I
OUT
+I
RP
/2
...
Equation 7
Consider ILmax, condition of input and output and select external components.
5
The above explanation is directed to the calculation in an ideal case in continuous mode.
R5212D
10
Timing Chart
(-V
DET
+V
HYS
)
-V
DET
V
UVLO2
V
UVLO1
V
IN
Voltage
V
OUT1
Voltage
V
DOUT
Voltage
V
OUT2
Voltage
L
X
Voltage
Soft-start
Time
VD Delay
for Release
VD Delay
for Release
The timing chart which is shown above describes the relation of supply voltage changes with time and
each output of DC/DC converter, voltage detector, and voltage regulator.
(1) DC/DC converter
When the power turns on and in the case of rising the V
IN
voltage, while the V
IN
voltage is at UVLO re-
leased level (V
UVLO2
) or less, the operation of the DC/DC converter stops and does not make switching,
therefore
VOUT1
voltage does not rise.
When the V
IN
voltage becomes UVLO release level or more, the DC/DC converter starts soft-start op-
eration, and start switching, then
VOUT1
will rise. After the soft-start time, if
VIN
voltage becomes set
V
OUT1
level or more,
VOUT1
will be settled at
VOUT1
set output voltage. If
VIN
voltage becomes UVLO detector
threshold level (V
UVLO2 -
V
UVLOHYS
) or less, the DC/DC converter stops switching then Lx transistor in the
IC turns off.
(2) Voltage Detector
If the V
IN
voltage is at VD detector threshold level or less, the N-channel transistor of V
DOUT
pin turns on
R5212D
11
and outputs "L" to V
DOUT
pin. Then, when the V
IN
voltage becomes VD detector threshold level + its
hysteresis range (-V
DET
+V
HYS
) or more, after VD delay for release (tpLH) passing, the N-channel tran-
sistor inside the IC turns off, V
DOUT
pin voltage reaches to the pull-up voltage. Besides, the release
circuit for VD starts from when V
IN
voltage reaches (-V
DET
+V
HYS
).
(3) Voltage Regulator
The voltage regulator always operates even if UVLO function would work. Therefore, V
OUT2
voltage is
nearly equal to V
IN
voltage. Actual value depends on the load current. When the V
IN
voltage becomes set
V
OUT2
voltage or more, V
OUT2
voltage will be the set output voltage. The short current limit can operate
after soft-start time.
TEST CIRCUITS
A) Supply Current
B) UVLO Detector Threshold/ Released Voltage
V
IN
V
OUT1
GND
A
V
IN
L
X
V
OUT1
GND
OSCILLOSCOPE
C) Lx Leakage Current
D) Lx On Resistance
V
IN
L
X
V
OUT1
GND
A
V
IN
L
X
V
OUT1
GND
V
E) Lx
Current
Limit
F) V
OUT1
Output Voltage
V
IN
L
X
V
OUT1
GND
OSCILLOSCOPE
V
IN
L
X
V
OUT1
GND
OSCILLOSCOPE
V
OUT2
R5212D
12
G) Oscillator
Frequency,
Soft-start
Time
V
IN
L
X
V
OUT1
V
OUT1
GND
OSCILLOSCOPE
OSCILLOSCOPE
H) V
OUT2
Output Voltage, Load Regulation, Dropout
I) V
DOUT
Detector Threshold, Hysteresis Range,
Voltage, Current Limit, Short Current Limit
VD Output Delay Time for Release
V
IN
L
X
V
OUT1
I
OUT2
GND
V
OUT2
V
J) V
DOUT
"L" Output Current
V
V
V
V
IN
IN
IN
IN
V
V
V
V
OUT1
OUT1
OUT1
OUT1
GND
GND
GND
GND
V
V
V
VDOUT
DOUT
DOUT
DOUT
A
R5212D
13
TYPICAL CHARACTERISTICS
1) DC/DC Output Voltage vs. Output Current
2) Efficiency vs. Output Current (Topt=25
C)
R5212D001A
(Topt=25
C) R5212D001A
3) VR Output Voltage vs. Output Current
4) VR Output Voltage vs. Output Current
R5212DN011A
(Topt=25
C) R5212D011A
(Topt=25
C)
5) VD Detector Threshold vs. Temperature
6) VD Released Delay Time vs. Temperature
R5212D011A
R5212D011A
1.58
1.59
1.60
1.61
1.62
1.63
0
100
200
300
400
500
Output Current I
OUT1
[mA]
O
u
t
put
V
o
l
t
a
ge
V
OUT
1
[
V]
VIN=4.0V
VIN=5.0V
VIN=5.5V
VOUT1=1.6V
0
10
20
30
40
50
60
70
80
90
0.1
1
10
100
1000
Output Current I
OUT1[
mA]
Ef
f
i
ciency [
]
VIN=4.0V
VIN=5.0V
VIN=5.5V
VIN=5V)
2.55
2.57
2.59
2.61
2.63
2.65
0
50
100
150
200
Output Current I
OUT2
[mA]
O
u
t
put
V
o
l
t
a
ge
V
OUT
2
[V]
VIN=5V
0.00
0.50
1.00
1.50
2.00
2.50
3.00
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
Output Current I
OUT2
[
A]
O
u
tput V
o
ltage V
OUT
2
[V
]
VIN=5V)
4.00
4.05
4.10
4.15
4.20
4.25
4.30
4.35
4.40
-50
0
50
100
Temperature Topt
Det
ect
or
T
h
r
e
s
hol
d
-Vd
e
t[V]
(
C)
VIN=5V)
0
2
4
6
8
10
12
14
16
18
20
-50
0
50
100
Temperature Topt
Out
put
De
l
a
y Ti
me
TPLH[
m
s
]
(
C)
R5212D
14
7) Soft-start time vs. Temperature
8) Frequency vs. Temperature
R5212D011A
R5212D011A
9) DC/DC Output Voltage vs. Temperature
10) VR Output Voltage vs. Temperature
R5212D011A
R5212D011A
11) Load Transient Response 1 (Topt=25
C)
12) Load Transient Response 2 (Topt=25
C)
V
IN
=5V)
0.0
0.5
1.0
1.5
2.0
-50
0
50
100
Temperature Topt
So
ft-start Time T
SS
[ms]
(
C)
(VIN=5V)
1050
1100
1150
1200
1250
1300
1350
-50
0
50
100
Temperature Topt
Fre
que
nc
y F
OSC
[kHz
]
(
C)
V
IN
=5V)
1.50
1.55
1.60
1.65
1.70
-50
0
50
100
Temperature Topt
Output Volta
ge
V
OUT
1
[V
]
(
C)
(VIN=5V)
2.50
2.55
2.60
2.65
2.70
-50
0
50
100
Temperature Topt
O
u
tput V
o
lta
ge
V
OUT
2
[V]
(
C)
R5212D011A
(L=4.7uH C=10uF Vin=5V )
1.10
1.20
1.30
1.40
1.50
1.60
1.70
-20
0
20
40
60
80
100
Time(us)
Ou
t
p
u
t
Vo
l
t
a
g
e
V
OUT
1
V
-200
0
200
400
600
800
1000
O
u
tput Cur
r
ent I
OUT
1
mA
R5212D011A
(L=4.7uH C=10uF Vin=5V)
1.20
1.30
1.40
1.50
1.60
1.70
1.80
-100
0
100
200
300
400
Time(us)
O
u
tput V
o
ltage V
OUT
1
V
-200
0
200
400
600
800
1000
O
u
tput Cur
r
e
nt I
OUT
1
mA
I
OUT1
: 200mA10mA
Iout: 10mA->200mA
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