Rohm BD9302FP User manual

Dec. 2008
2-output High-efficiency Step-down
Switching Regulators
with Built-in Power MOSFET
Single-chip Type with Built-in FET Switching Regulator Series
Description
TECHNICAL NOTE
BD9302FP
The BD9302FP is a 2-channel step-down switching regulator controller with a 2.5-MHz, 2-Apower switch and available for
2.5-MHz high speed switching operation, which facilitates settings of switching frequency with external resistance, supporting
for a wide input voltage range of 6 to 18 V. Furthermore, due to a low reference voltage of 0.6 V, this BD9302FP is an L/C best
suited to high-voltage input/low-voltage output applications, for example, to step down a voltage from 12 V to 1.2 V.
Features
1) A wide input voltage range of 6 V to 18 V
2) Easy switching frequency setting in the range of 200 k to 2.5 MHz.
3) Two built-in power switches of 0.4 Ω, 2 A.
4) 180˚phase shift
5) Built-in Under Voltage Lock Out circuit
6) Built-in overcurrent protection circuit
7) Built-in Thermal Shutdown circuit
Use
Power supply for DPS requiring two power sources
ADSL modem/plasma display
Audio devices
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Absolute maximum ratings (Ta=25˚C)
Electrical characteristics
* Should be derated by 11.6 mW/˚C at Ta=25˚C or more. When mounted on a glass epoxy PCB of 70¥70¥1.6 mm)
** Should not exceed Pd-value.
[Triangular wave oscillator block]
Oscillation frequency
Frequency variation
[Overcurrent protection circuit block]
Overcurrent limit
[Under-voltage malfunction prevention circuit block]
Upper limit threshold voltage
Lower limit threshold voltage
[Soft start circuit block]
Source current
Sink current
Clamp voltage
Shutdown voltage
FOSC
FDVO
Isw
VtH
VtL
Isso
ISSI
Vcl
VSDWN
1800
–
2
3.0
2.7
6
0.6
1.75
–
2000
1
4
3.3
3.0
10
1.7
1.95
–
2200
–
6
3.6
3.3
14
5
2.15
0.3
kHz
%
A
V
V
uA
mA
V
V
RT=10kΩ
~ 18V
Vss=1V
Vss=1V, Vcc=3V
Vcc=3V
Not designed for radiation resistance.
Electrical characteristics (Unless otherwise specified, Ta=25˚C, Vcc=12 V, RT=10 kΩ)
Typ Max
Item Symbol Limits
Min Unit Conditions
Power supply voltage
Power dissipation
Operating temperature
Storage temperature
Output current
Maximum junction temperature
Vcc
Pd
Topr
Tstg
Io
Tjmax
20
1450*
- 40 ~ +85
- 55 ~ +150
2**
150
Item Symbol Rating Unit
Recommended operating range (Ta=25˚C)
Power supply voltage
Output current
Timing resistance
Oscillation frequency
6
–
10
100
12
–
–
–
V
A
kΩ
kHz
Item Min
Vcc
Io
RT
Fosc
Symbol Typ
Limits Unit
18
1.8
100
2500
Max
* Design guarantee (No 100% pre-shipment inspections are conducted.)
*
V
mW
˚C
˚C
˚C
A
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Electrical characteristics
Measurement circuit diagram
[Error amplifier block]
Input bias current
Voltage gain
COMP maximum output voltage
COMP minimum output voltage
Output sink current
Output source current
Feedback voltage
[Output block]
Upper-side ON resistance
Low-side ON resistance
OFF current
[Total device]
Average supply current
IIB
AV
VOH
VOL
IOI
IOO
VFB
Ronh
Ronl
IOFF
ICC
–
–
1.75
–
1
– 8
0.588
–
–
0.1
–
0.4
200
1.95
0.8
2
–4
0.600
0.4
2
0.2
5
1
–
–
1.0
4
–1
0.612
0.6
3
0.4
–
uA
V/V
V
V
mA
mA
V
Ω
Ω
mA
mA
ICOMP=
- 0.1mA
ICOMP=0.1mA
VFB=0.8V
VFB=0.4V
Buffer
Io=1A*
Io=20mA*
SW=0V
RT=1.0V
Electrical characteristics (Unless otherwise specified, Ta=25˚C, Vcc=12 V, RT=10 kΩ)
Typ Max
Item Symbol Limits
Min Unit Conditions
Fig. 1 Typical measurement circuit
–
+
A
V
A
V
V
A
A
V
A
A
V
A
V
–
+
A
Ω
A
NULL AMP
10kΩ
1000pF
1000pF
100kΩ
1kΩ
0.6V
10pF 30kΩ
30kΩ
10K
1V
1V
12V
10pF 30kΩ
30kΩ
100kΩ
1kΩ
0.6V
NULL AMP
10kΩ
1000pF
1000pF
1uF 5V
1uF 5V
1V
PGND1
COMP1
FB1
RT
NC
SS1
Vcc
SS2
NC
FB2
COMP2
GND
PGND2
SW1L
SW1
SW1
BOOT1
PVcc
PVcc
PVcc
PVcc
BOOT2
SW2
SW2
SW2L
Ω
V
V
Not designed for radiation resistance.
* Design guarantee (No 100% pre-shipment inspections are conducted.)
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Reference characteristics data
(*) The data shown above represent real values sampled but not guarantee values.
Fig.2
Feedback voltage –
Ambient temperature
0.50
0.51
0.52
0.53
0.54
0.55
0.56
0.57
0.58
0.59
0.60
0.61
0.62
0.63
0.64
0.65
0.66
FEED BACK VOLTAGE : VFB [V]
- 40 - 30 - 20 - 100102030405060708085
Fig.3
Switching frequency –
Ambient temperature
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
-
40 - 30 - 20 - 10 0 10 20 30 40 50 60 70 80 85
SWITCHING FREQUENCY : FSW [kHz]
AMBIENT TEMPERATURE : Ta [˚C]
AMBIENT TEMPERATURE : Ta [˚C]
AMBIENT TEMPERATURE : Ta [˚C]
Fig.4
Power supply voltage –
Circuit current
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
CIRCUIT CURRENT : ICC [mA]
0123456789 10 1112 13 1415 161718
INPUT VOLTAGE : VCC [V]
- 40˚C25˚C
85˚C
Fig.5
SW ON resistance –
Ambient temperature
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
-
40 - 30 - 20 - 100 102030405060708085
AMBIENT TEMPERATURE : Ta [˚C]
-
40 - 30 - 20 - 100 102030405060708085
SW ON RESISTANCE : RONH [Ω]
Fig.6
SWL ON resistance –
Ambient temperature
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
SWL ON RESISTANCE : RONL [Ω]
Fig.7
Setting resistance –
Switching frequency
10
100
1000
10000
100000
SWITCHING FREQUENCY : FSW [kHz]
10 100
TIMING RESISTANCE : RT [kΩ]
Fig.8
Switching frequency – MAX Duty
0
10
20
30
40
50
60
70
80
90
100
MAX DUTY [%]
1000200 2000
SWITCHING FREQUENCY : FSW [kHz]
Fig.9
Switching frequency – Power supply voltage
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
6 7 8 9 10 11 12 13 14 15 16 17 18
INPUT VOLTAGE : VCC [V]
SWITCHING FREQUENCY : FSW [kHz]
EFFICIENCY : h[%]
Fig.10
Output current – Efficiency
0
10
20
30
40
50
60
70
80
90
100
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
OUTPUT CURRENT : IO [A]
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Reference characteristics data
Application measurement circuit diagram
(*) The data shown above represent real values sampled but not guarantee values.
0
10
20
30
40
50
60
70
80
90
100
6 7 8 9 10 11 12 13 14 15 16 17 18
EFFICIENCY : h[%] EFFICIENCY : h[%]
INPUT VOLTAGE : VCC [V]
Fig.13
Set capacitance – Delay time
SS CAPACITOR : CSS [μF]
DELAY TIME : TV01 [ms]
Fig.11
Power supply voltage – Efficiency
0
10
20
30
40
50
60
70
80
90
100
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
SWITCHING FREQUENCY : FSW [kHz]
Fig.12
Switching frequency – Efficiency
0
1
10
100
INPUT
VOLTAGE
OUTPUT
VOLTAGE
OUTPUT
CURRENT
OUTPUT
VOLTAGE
(AC)
OUTPUT
CURRENT
OUTPUT
VOLTAGE
(AC)
Fig.16
Load transient response No. 2
Fig.14
Startup waveform Fig.15
Load transient response No. 1
Fig.17 Application measurement circuit diagram
0.01 0.10 1.00
1.47ms
12V
2.5V
Vcc
12V
BD9302FP
Vo1=3.3V
10μF
10μF
10μF
0.1μF
0.1μF
0.1μF
20kΩ
30kΩ
51kΩ
20kΩ
33
pF
33pF
3300
pF
3300pF
30
kΩ
22
kΩ
100
kΩ
0.1μF
10μH
10μHVo2=1.2V
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Pin assignment Block diagram
Pin assignment / functions
Ground
Error amplifier output
Error amplifier inverting input
Frequency setting resistor connection
N.C.
Soft start capacitor connection
(Shutdown at Low)
Power supply input
Soft start capacitor connection
(Shutdown at Low)
N.C.
Error amplifier inverting input
Error amplifier output
Ground
PGND1
COMP1
FB1
RT
–
SS1/SDWN
VCC
SS2/SDWN
–
FB2
COMP2
GND
1
2
3
4
5
6
7
8
9
10
11
12
Pin namePin No. Function
Ground
Switching output 2 (Low side)
Switching output 2
Switching output 2
Boot capacitor connection
Power supply input
Power supply input
Power supply input
Power supply input
Boot capacitor connection
Switching output 1
Switching output 1
Switching output 1 (Low side)
PGND2
SW2L
SW2
SW2
BOOT2
Pvcc
Pvcc
Pvcc
Pvcc
BOOT1
SW1
SW1
SW1L
13
14
15
16
17
18
19
20
21
22
23
24
25
Pin namePin No. Function
Fig.18 Pin assignment / Block diagram
COMP1
FB1
RT
SS1/SDWN
VCC
N.C.
FB2
COMP2
GND
SS2/SDWN
PGND1
N.C.
PGND2
17
16
8
9
10
11
12
3
4
6
7
2OCP 24
23
22
20
19
18
21
SW1
SW1
BOOT1
PVCC
PVCC
PVCC
PVCC
BOOT2
SW2
SW2
+
+
-
VREF
- +
-
Current
Sense
Current
Sense
SDWN
SDWN
DRV1
Set
Reset
UVLO
TSD
- +
15
ERR
PWM
OSC 5V
PWM
ERR
0.6V
0.6V
Internal
Bias
slope
slope
1 25
5
13 14 SW2L
TOP VIEW
SDWN
SDWN
DRV1
Set
Reset
DRV2
DRV2
SW1L
OCP
SW1L
SW1
SW1
BOOT1
PVCC
PVCC
Fin
PVCC
PVCC
BOOT2
SW2
SW2
SW2L
25
24
23
22
21
20
19
18
17
16
15
14
1
2
3
4
5
6
7
8
9
10
11
12
13
PGND1
COMP1
FB1
RT
N.C.
SS1/SDWN
Fin
VCC
SS2/SDWN
N.C.
FB2
COMP2
GND
PGND2
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üError amplifier (ERR) block
The ERR block is a circuit used to compare between the 0.6-V reference voltage and the feedback voltage of output
voltage. The COMP voltage, a result of this comparison, determines the switching Duty. Furthermore, soft start function is
activated with the SS voltage while in startup operation. Consequently, the COMP voltage is limited to the SS voltage.
üOscillator (OSC) block
The OSC block is a block to determine the switching frequency through the RT pin, which is settable in the range of 100
kHz to 2500 kHz.
üSLOPE block
The SLOPE block is a block to generate a triangular wave from the clock generated with the OSC and then to transmit the
triangular wave to the PWM comparator.
üPWM block
The PWM block is used to make comparison between the output COMP voltage of the error amplifier block and the
triangular wave of the SLOPE block, thus determining the switching Duty. The switching duty is limited with the maximum
duty ratio, which is internally determined, and will not reach 100%.
üReference voltage (UREF) block
The UREF block is a block to generate a 2.9-V internal reference voltage.
üProtection circuit (UVLO/TSD) block
The UVLO (Under Voltage Lock Out) circuit is used to shut down the circuit when the voltage falls below approximately 3.3
V, while the TSD (Thermal Shutdown) circuit is used to shut down the circuit at a temperature of 175˚C and reset it at a
temperature of 160˚C.
üOvercurrent protection circuit (OCP)
This function is used to detect a current passing through the power transistor FET with the CURRENT SENSE and activate
the overcurrent protection when the current reaches approximately 4 A. If the overcurrent protection is activated, switching
will be turned OFF to discharge the SS pin capacitance.
Fig.19 Typical application circuit
17
16
8
9
10
11
12
3
4
6
7
2OCP 24
23
22
20
19
18
21
COMP1
FB1
RT
SS1/SDWN
VCC
VCC
N.C.
30
kΩ
20
kΩ
3300
pF
33
pF
30
kΩ
22kΩ
20kΩ
51kΩ
3300
pF
0.1μF
0.1μF
33pF 100kΩ
FB2
COMP2
GND
SW1
SW1
BOOT1
PVCC
PVCC
PVCC
PVCC
BOOT2
SW2
SW2
+
+
-
VREF
- +
-
Current
Sense
Current
Sense
SDWN
SDWN
DRV1
Set
Reset
UVLO
TSD
- +
15
ERR
PWM
OSC 5V
PWM
ERR
0.6V
0.6V
Internal
Bias
slope
slope
SS2/SDWN
1
PGND1 25
5
N.C.
13
PGND2
14 SW2L
SDWN
SDWN
DRV1
Set
Reset
DRV2
DRV2
SW1L
OCP
VCC
VO : 1.2V
10
μF
10
μF
0.1
μF10
μH
VO : 3.3V
10μF
0.1μF
10
μH
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Timing chart
Startup sequence
Vcc
SS
SW
VOUT
SW
Vo
Io
VdC
Normal operation
Fig.20 Startup sequence
Fig.21 While in normal operation
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External component setting procedure
(1) Setting of output L constant
The coil L used for output is determined according to the rated current ILR and the maximum load current value IOMAX
of the coil.
Adjust so that (IOMAX + DIL) will not conflict with the rating. At this time, DILcan be obtained according to the formula
shown below.
Furthermore, since the coil L value may also vary by approximately ±30%, set this value with an adequate margin. If the
coil current ILexceeds the rated coil current ILR, the internal IC element may be damaged. It is recommended to make
setting of coil value in the range of 4.7 μF to 100 μF.
(2) Setting of output Co constant
For output capacitor, select the allowable ripple voltage VPP or the allowable drop voltage at a sharp change of load,
whichever larger for the capacitor. The output ripple voltage can be obtained according to the formula shown below.
Design the component so that this constant will fall within the allowable ripple voltage.
Furthermore, estimate the drop voltage VDR at a sharp change of load according to the formula shown below.
However, 10 μsec will be the estimated value of the DC/DC converter response speed.
Make setting of capacitance with thorough consideration given to the margin so that these two values will fall into the
specified values. It is recommended to make setting of the capacitance in the range of 10 μF to 100 μF. if a short circuit
occurs, an inverse current passes through the parasitic diode to cause damage to the internal circuits. To prevent that,
insert a backflow prevention diode.
Step-down DIL =[A] . . . (1.1)¥(VCC – VO) ¥¥
VO
VCC 1
f
1
L,where f: Switching frequency
,where f: Switching frequency
Step-down DVPP = DIL[V]¥RESR +¥
VO
VCC
¥
DIL
2CO1
f
VDR =[V]¥10μsec
DI
CO
ILR
Average IOMAX current
Adjust so that (IOMAX + DIL) will
not conflict with the rating.
t
IL
Fig.22 Fig.23
LCO
ILVO
VCC
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(3) Setting of feedback resistance constant
In order to make settings of feedback resistance, refer to the formula shown. It is recommended to make setting of
resistance in the range of 10 kΩto 330 kΩ. Setting the resistance to 10 kΩor less will result in degraded power
efficiency, while setting it to 330 kΩor more will increase the offset voltage due to the input bias current of 0.4 μA (TYP)
of the internal error amplifier.
(4) Setting of oscillation frequency
Connecting a resistor to the RT pin (pin 4) will allow for the setting of triangular wave oscillation frequency. The RT
determines the charge/discharge current to the internal capacitor, with which the frequency varies. Referring to Figure
shown below, make settings of the RT resistor. Recommended setting range is 10 to 100 kΩ. Be noted that any setting
outside of this range may turn OFF switching, thus impairing the operation guarantee.
(5) Setting of soft start time
The soft start function will be required to prevent an excessive increase in the coil current and overshoot of the output
voltage, while in startup operation. Figure below shows the relationship between the capacitor and the soft start time.
Referring to this Figure, make the capacitor setting.
It is recommended to make setting of capacitance value in the range of 0.01 to 10 μF. Setting the capacitance value to
0.01 μF or less may cause overshoot to the output voltage. If any startup-related function (sequence) of other power
supply is provided, use a high-accuracy product (e.g. ¥5R) or the like.
Furthermore, since the soft start time varies with the input voltage, output voltage, load, coil, output capacitor, or else,
be sure to check to be sure this soft start time on the actual system.
10
100
1000
10000
100000
SWITCHING FREQUENCY : FSW [kHz]
10 100
TIMING RESISTANCE : RT [kΩ]
SS CAPACITOR : CSS [μF]
DELAY TIME : TV01 [ms]
0
1
10
100
0.01 0.10 1.00
VO= ¥0.6 [V]
R8+R9
R9
VO
R8
R9 FB
Internal reference voltage: 0.6 V
Fig.24
Fig.25 RT vs. Switching frequency
Fig.26 SS capacitance vs. Delay time
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