Fujitsu Power Supply MB39A105 User Manual

FUJITSU SEMICONDUCTOR  
DATA SHEET  
DS04-27233-2E  
ASSP For Power Supply Applications  
(General Purpose DC/DC Converter)  
1-ch DC/DC Converter IC  
for low voltage  
MB39A105  
DESCRIPTION  
The MB39A105 is 1-channel DC/DC converter IC using pulse width modulation (PWM). This IC is ideal for up  
conversion.  
The minimum operating voltage is low (1.8 V) , and the MB39A105 is best for built-in power supply such as LCD  
monitors. Also the short-circuit protection detection output function prevents input/output short on a chopper type  
up-converter.  
This product is covered by US Patent Number 6,147,477.  
FEATURES  
• Power supply voltage range : 1.8 V to 6 V  
• Reference voltage accuracy : ± 1 %  
• High-frequency operation capability : 1 MHz (Max)  
• Built-in standby function: 0 µA (Typ)  
• Built-in timer-latch short-circuit protection circuit  
• Built-in short-circuit protection detection output function  
• Built-in soft-start circuit independent of loads  
• Built-in totem-pole type output for Nch MOS FET  
• Package : TSSOP-8P (Thickness 1.1 mm Max)  
PACKAGE  
8-pin plastic TSSOP  
(FPT-8P-M05)  
 
MB39A105  
PIN DESCRIPTION  
Pin No.  
Symbol  
INE  
I/O  
Descriptions  
1
2
3
I
Error amplifiers (Error Amp) inverted input terminal  
CSCP  
VCC  
Timer-latch short-circuit protection capacitor connection terminal  
Power supply terminal  
Open drain output terminal for short-circuit protection detection  
During timer-latch short-circuit protection operation : Output “High-Z”  
During normal operation : Output “L”  
4
SCPOD  
O
O
5
6
7
8
OUT  
GND  
RT  
External Nch FET gate drive terminal  
Ground terminal  
Triangular wave oscillation frequency setting resistor connection terminal  
Error Amplifier (Error Amp) output terminal  
FB  
O
3
 
MB39A105  
BLOCK DIAGRAM  
VCC SCPOD  
3
4
1
8
INE  
VREF  
Error Amp  
PWM  
Comp.  
Drive  
+
+
+
Nch  
5
6
OUT  
GND  
(0.5 V ± 1%)  
FB  
IO = 400 mA  
at VCC = 3.3 V  
VREF  
(0.7 V)  
(0.3 V)  
SCP  
Comp.  
+
(0.9 V)  
+
2
CSCP  
S
R
Q
(1.0 V)  
RT Current  
Power  
VREF ON/OFF  
CTL  
OSC  
bias  
UVLO  
VREF  
(1.27 V)  
L : UVLO release  
±10%  
7
RT  
4
 
MB39A105  
ABSOLUTE MAXIMUM RATINGS  
Rating  
Parameter  
Symbol  
Condition  
VCC terminal  
Unit  
Max  
Min  
Power supply voltage  
Output current  
VCC  
IO  
7
V
OUT terminal  
35  
mA  
mA  
mW  
°C  
Output peak current  
Power dissipation  
Storage temperature  
IOP  
Duty 5% (t = 1/fOSC×Duty)  
Ta +25 °C  
700  
490*  
+125  
PD  
TSTG  
55  
* : The packages are mounted on the epoxy board (10 cm × 10 cm).  
WARNING: Semiconductor devices can be permanently damaged by application of stress (voltage, current,  
temperature, etc.) in excess of absolute maximum ratings. Do not exceed these ratings.  
RECOMMENDED OPERATING CONDITIONS  
Value  
Parameter  
Symbol  
Condition  
Unit  
Min  
1.8  
0
Typ  
Max  
6
Power supply voltage  
Input voltage  
VCC  
VINE  
VCC terminal  
INE terminal  
V
V
VCC 0.9  
6
SCPOD terminal output voltage  
SCPOD terminal output current  
Output current  
VSCPOD SCPOD terminal  
0
V
ISCPOT  
IO  
SCPOD terminal  
OUT terminal  
0
2
mA  
mA  
kHz  
kΩ  
µF  
°C  
30  
100  
3.3  
+30  
1000  
33  
Oscillation frequency  
fosc  
RT  
500  
7.5  
Timing resistor  
RT terminal  
Short-circuit detection capacitor  
Operating ambient temperature  
CSCP  
Ta  
CSCP terminal  
0.22  
+25  
1.0  
30  
+85  
WARNING: The recommended operating conditions are required in order to ensure the normal operation of the  
semiconductor device. All of the device’s electrical characteristics are warranted when the device is  
operated within these ranges.  
Always use semiconductor devices within their recommended operating condition ranges. Operation  
outside these ranges may adversely affect reliability and could result in device failure.  
No warranty is made with respect to uses, operating conditions, or combinations not represented on  
the data sheet. Users considering application outside the listed conditions are advised to contact their  
FUJITSU representatives beforehand.  
5
 
MB39A105  
ELECTRICAL CHARACTERISTICS  
(VCC = 3.3 V, Ta = +25 °C)  
Value  
Unit  
Pin  
No  
Symbol  
Parameter  
Conditions  
Min  
Typ  
Max  
1. Under voltage  
lockout  
Threshold voltage  
protection circuit  
VTLH  
3
VCC =  
1.15 1.35 1.55  
V
block [UVLO]  
Threshold voltage  
VTH  
2
2
0.95 1.00 1.05  
0.15 0.20 0.25  
V
V
Short-circuit detection time  
setting difference voltage  
VCSCP  
Input source current  
Reset voltage  
ICSCP  
2
3
CSCP = 0.85 V  
VCC =  
1.76 0.88 0.44 µA  
2. Short-circuit  
protection block  
[SCP]  
VRST  
1.1  
1.3  
1.5  
V
SCPOD terminal output  
leak current  
ILEAK  
4
SCPOD = 3.3 V  
0
1.0  
µA  
SCPOD terminal output on  
resistor  
RON  
4
5
5
SCPOD = 1 mA  
RT = 7.5 kΩ  
50  
500  
1*  
100  
Oscillation frequency  
fosc  
450  
550 kHz  
3. Triangular  
wave oscillator  
block [OSC]  
Frequency temperature  
variation  
fOSC/  
fOSC  
Ta = 0 °C to +85 °C  
%
4. Soft-start block  
[CS]  
Charge current  
ICS  
2
CSCP = 0 V  
16  
11  
6  
µA  
Threshold voltage  
Input bias current  
Voltage gain  
VTH  
IB  
1
1
8
8
8
8
8
8
FB = 0.5 V  
INE = 0 V  
DC  
0.495 0.5 0.505  
120 30  
70*  
V
nA  
dB  
MHz  
V
AV  
Frequency band width  
BW  
VOH  
VOL  
AV = 0 dB  
1.1*  
5. Error amplifier  
block [Error Amp]  
1.17 1.27 1.37  
Output voltage  
40  
200  
mV  
µA  
µA  
Output source current  
Output sink current  
ISOURCE  
ISINK  
FB = 0.5 V  
FB = 0.5 V  
80  
300  
50  
100  
85  
6. PWM compar-  
ator block  
[PWM Comp.]  
Maximum duty cycle  
Output source current  
Dtr  
ISOURCE  
ISINK  
5
5
5
RT = 7.5 kΩ  
90  
95  
%
OUT = 0 V,  
Duty 5%  
400*  
400*  
mA  
mA  
(t = 1/fosc×Duty)  
OUT = 3.3 V,  
Duty 5%  
(t = 1/fosc×Duty)  
7.Output block  
[Drive]  
Output sink current  
Output ON resistor  
ROH  
ROL  
ICCS  
ICC  
5
5
3
3
OUT = 15 mA  
OUT = 15 mA  
RT = OPEN  
4.0*  
3.0  
0
6.0  
10  
Standby current  
µA  
mA  
8. General block  
Power supply current  
RT = 7.5 kΩ  
1.2  
1.8  
*: Standard design value.  
6
 
MB39A105  
TYPICAL CHARACTERISTICS  
Power Supply Current vs. Power Supply Voltage  
Power Supply Current vs. RT Terminal Current  
5.0  
5
Ta = +25 °C  
RT = 7.5 kΩ  
Ta = +25 °C  
VCC = 3.3 V  
4.5  
4
4.0  
3.5  
3.0  
2.5  
3
2
1
0
2.0  
ICC  
1.5  
1.0  
0.5  
0.0  
0
2
4
6
8
10  
0
10  
20  
30  
40  
50  
Power supply voltage VCC (V)  
RT terminal current IRT (µA)  
Error Amplifier Threshold Voltage vs.  
Power Supply Voltage  
1.0  
Ta = +25 °C  
0.9  
0.8  
0.7  
0.6  
0.5  
0.4  
0.3  
0.2  
0.1  
0.0  
VCC = 3.3 V  
0
2
4
6
8
10  
Power supply voltage VCC (V)  
Triangular Wave Oscillation Frequency vs.  
Power supply voltage  
Error Amplifier Threshold Voltage vs.  
Ambient Temperature  
0.52  
0.51  
0.50  
0.49  
0.48  
600  
Ta = +25 °C  
RT = 7.5 kΩ  
VCC = 3.3 V  
RT = 7.5 kΩ  
550  
500  
450  
400  
1
2
3
4
5
6
7
40 20  
0
20  
40  
60  
80  
100  
Ambient temperature Ta (°C)  
Power supply voltage VCC (V)  
(Continued)  
7
 
MB39A105  
Triangular Wave Oscillation Frequency  
vs. Ambient Temperature  
Triangular Wave Oscillation Frequency  
vs. Timing Resistor  
600  
10000  
1000  
100  
Ta = +25 °C  
VCC = 3.3 V  
VCC = 3.3 V  
RT = 7.5 kΩ  
550  
500  
450  
400  
10  
40 20  
0
20  
40  
60  
80  
100  
1
10  
100  
Timing resistor RT (k)  
Ambient temperature Ta (°C)  
Max On Duty vs.  
Triangular Wave Oscillation Frequency  
100  
Ta = +25 °C  
VCC = 3.3 V  
95  
90  
85  
80  
75  
70  
10  
100  
1000  
10000  
Triangular wave oscillation frequency fOSC (kHz)  
Error Amplifier Gain and Phase  
vs. Frequency  
Ta = +25 °C  
40  
30  
180  
90  
VCC = 3.3 V  
240 kΩ  
AV  
ϕ
20  
10 kΩ  
1 µF  
10  
+
10  
11  
0
0
2.4 kΩ  
IN  
9
+
+
10  
20  
30  
40  
10 kΩ  
OUT  
Error Amp  
90  
180  
1.24 V  
100  
1 k  
10 k 100 k  
1 M  
10 M  
Frequency f (Hz)  
(Continued)  
8
 
MB39A105  
(Continued)  
Power Dissipation vs. Ambient Temperature  
600  
500  
490  
400  
300  
200  
100  
0
40 20  
0
20  
40  
60  
80  
100  
Ambient temperature Ta ( °C)  
9
 
MB39A105  
FUNCTIONS  
1. DC/DC Converter Functions  
(1) Triangular-wave oscillator block (OSC)  
The triangular wave oscillator incorporates a timing resistor connected to RT terminal (pin 7) to generate  
triangular oscillation waveform amplitude of 0.3 V to 0.7 V.  
The triangular waveforms are input to the PWM comparator in the IC.  
(2) Error amplifier block (Error Amp1, Error Amp2)  
The error amplifier detects the DC/DC converter output voltage and outputs PWM control signals. In addition,  
an arbitrary loop gain can be set by connecting a feedback resistor and capacitor from the output terminal to  
inverted input terminal of the error amplifier, enabling stable phase compensation to the system.  
Also, it is possible to prevent rush current at power supply start-up by connecting a soft-start capacitor with the  
CSCP terminal (pin 2) which is the non-inverted input terminal for Error Amp. The use of Error Amp for soft-start  
detection makes it possible for a system to operate on a fixed soft-start time that is independent of the output  
load on the DC/DC converter.  
(3) PWM comparator block (PWM Comp.)  
The PWM comparator is a voltage-to-pulse width modulator that controls the output duty depending on the input/  
output voltage.  
The comparator keeps output transistor on while the error amplifier output voltage and the DTC voltage remain  
higher than the triangular wave voltage.  
(4) Output block (Drive)  
The output block is in the totem pole configuration, capable of driving an external N-channel MOS FET.  
10  
 
MB39A105  
2. Power Control Function  
A switch in series with a resistor connected with the RT terminal (pin 7) allows you to turn on or turn off the power.  
On/off setting conditions of power supply  
RT  
CTL  
L
Power  
OFF (standby)  
ON (operating)  
ON/OFF CTL  
(L : OFF, H : ON)  
H
3. Protective Functions  
(1) Timer-latch short-circuit protection circuit (SCP)  
Short-circuit detection comparator detects the error amplifier output voltage level. If the load conditions for the  
DC/DC converter are stable, the short-circuit protection comparator is kept in equilibrium condition because the  
error amplifier is free from output variation. At this time the CSCP terminal (pin 2) is held at the soft-start end  
voltage (about 0.8 V) . If the DC/DC converter output voltage falls and error amplifier output is over 0.9 V, the  
timer circuits are actuated to start charging the external capacitor CSCP.  
When the capacitor voltage reaches about 1.0 V, the latch is set and the circuit is turned off the external FET  
and sets the dead time to 100 %. At this time, latch input is closed and the CSCP terminal is held at the “L” level.  
To reset the actuated protection circuit, turn off and on the power supply again and set VCC terminal voltage  
(pin 3) to 1.1 V (Min) or less. (See SETTING TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PRO-  
TECTION CIRCUIT.)  
(2) Under voltage lockout protection circuit (UVLO)  
The transient state or a momentary decrease in supply voltage, which occurs when the power supply is turned  
on, may cause the IC to malfunction, resulting in breakdown or degradation of the system. To prevent such  
malfunctions, undervoltagelockoutprotectioncircuitdetectsadecreaseininternalreferencevoltagewithrespect  
to the power supply voltage, turns off the output FET, and sets the dead time to 100% while holding the CSCP  
terminal (pin 2) at the “L” level.  
The circuit restores the output transistor to normal when the supply voltage reaches the threshold voltage of the  
undervoltage lockout protection circuit.  
(3) Short-circuit protection detection output function  
Connecting the Pch MOS FET to SCPOD terminal (pin 4) turns off the Pch MOS FET when the short-circuit  
protection is detected or under voltage lockout protection circuit operate. This allows you to prevent the short-  
circuit between the input and output when the short-circuit protection is detected, thus preventing the input  
voltage from occurring in the output region in the standby state.  
(4) Protection circuit operating function table  
This table refers to output condition when protection circuit is operating.  
Operating circuit  
Short-circuit protection circuit  
Under voltage lockout protection circuit  
SCPOD  
High-Z  
High-Z  
OUT  
L
L
11  
 
MB39A105  
SETTING THE OUTPUT VOLTAGE  
• Output Voltage Setting Circuit  
VO  
R1  
Error  
Amp  
1
0.5  
R2  
VO (V) =  
(R1 + R2)  
+
+
INE  
R2  
(0.5 V)  
CSCP  
2
SETTING THE TRIANGULAR OSCILLATION FREQUENCY  
The triangular oscillation frequency is determined by the timing resistor (RT) connected to the RT terminal (pin 7) .  
Triangular oscillation frequency : fosc  
3750  
fosc (kHz) =:  
RT (k)  
12  
 
MB39A105  
SETTING THE SOFT-START TIMES  
To prevent rush currents when the IC is turned on, you can set a soft-start by connecting soft-start capacitors  
(CSCP) to the CSCP terminal (pin 2). When IC starts (VCC UVLO threshold voltage), the external soft-start  
capacitors (CSCP) connected to CSCP terminal are charged at 11 µA. The error amplifier output (FB (pin 8) ) is  
determined by comparison between the lower one of the potentials at two non-inverted input terminals (0.5 V  
in an internal reference voltage, CSCP terminal voltages) and the inverted input terminal voltage (INE (pin 1)  
voltage).  
The FB terminal voltage is decided for the soft-start period by the comparison between 0.5 V in an internal  
reference voltage and the voltages of the CSCP terminal. The DC/DC converter output voltage rises in proportion  
to the CSCP terminal voltage as the soft-start capacitor connected to the CSCP terminal is charged.  
The soft-start time is obtained from the following formula:  
Soft-start time: ts (time to output 100%)  
ts (s)=: 0.045 × CSCP (µF)  
CSCP terminal voltage  
=: 0.8 V  
Error Amp block INE voltage  
=: 0.5 V  
=: 0 V  
t
Soft-start time (ts)  
• Soft-Start Circuit  
VO  
VREF  
11 µA  
R1  
R2  
INE  
1
L priority  
Error Amp  
+
+
2
CSCP  
(0.5 V)  
CSCP  
8
FB  
UVLO  
13  
 
MB39A105  
SETTINGTIMECONSTANTFORTIMER-LATCHSHORT-CIRCUITPROTECTIONCIRCUIT  
The error amplifier’s output level alaways does the comparison operation with the short-circuit protection com-  
parator (SCP Comp.) to the reference voltage.  
While DC/DC converter load conditions are stable, the short-circuit detection comparator output remains stable,  
and the CSCP terminal (pin 2) is held at soft-start end voltage (about 0.8 V) .  
If the load condition changes rapidly due to a short-circuit of the load and the DC/DC converter output voltage  
drops, the output of the error amplifier usually goes over 0.9 V. In that case, the capacitor CSCP is charged further.  
When the capacitor CSCP is charged to about 1.0 V, the latch is set and the external FET is turned off (dead time  
is set to 100%). At this time, the latch input is closed and the CSCP terminal (pin 2) is held at “L” level. When  
CSCP terminal becomes “L” level, SCPOD terminal Nch MOS FET becomes OFF. SCPOD terminal (pin 4) is  
held at “L” level and can be used as a short-circuit operating detection signal during normal operation.  
To reset the actuated protection circuit, the power supply turn off and on again to lower the VCC terminal (pin  
3) voltage to 1.1 V (Min) or less.  
Short-circuit detection time (tCSCP)  
tCSCP (s) =: 0.23 × CSCP (µF)  
Timer-latch short-circuit protection circuit  
VO  
8
1
FB  
R1  
R2  
Error  
Amp  
INE  
+
(0.5 V)  
VREF  
(0.88 µA)(10.1 µA)  
SCP  
Comp.  
+
(0.9 V)  
to Drive  
CSCP  
2
+
(1.0 V)  
VREF  
UVLO  
S
Latch  
R
14  
 
MB39A105  
Soft-start and short-circuit protection circuit timing chart  
FB voltage  
1.0 V  
CSCP voltage  
0.9 V  
0.8 V  
0.7 V  
OSC  
amplifier  
0.3 V  
Output  
short  
Output short  
Soft-start time  
tS  
Short-circuit detection time  
tCSCP  
t
15  
 
MB39A105  
I/O EQUIVALENT CIRCUIT  
⟨⟨Soft-start block (CS) ⟩⟩  
⟨⟨Short-circuit protection circuit block (SCP) ⟩⟩  
3
VCC  
VCC  
ESD  
protection  
element  
+
CSCP  
GND  
SCPOD  
4
ESD  
protection  
element  
1.0 V  
CSCP  
2
ESD  
protection  
element  
6
GND  
⟨⟨Error amplifier block⟩⟩  
⟨⟨Triangular wave oscillator block (RT) ⟩⟩  
VCC  
VCC  
(1.27 V)  
+
0.33 V  
CS  
1
INE  
0.5 V  
RT  
7
FB  
8
GND  
GND  
⟨⟨Output block⟩⟩  
VCC  
OUT  
5
GND  
16  
 
MB39A105  
APPLICATION EXAMPLE  
17  
 
MB39A105  
PARTS LIST  
COMPONENT  
ITEM  
SPECIFICATION  
VENDOR  
SANYO  
SANYO  
SANYO  
SUMIDA  
TDK  
PARTS No.  
MCH3306  
Q1  
Pch FET  
VDS = 20 V, ID = 2 A (Max)  
VDS = 20 V, Qg = 4.5 nC (Typ)  
VF = 0.40 V (Max) , at IF = 1 A  
Q2, Q3  
D1  
Nch FET  
Diode  
MCH3405  
SBS004  
L1  
Inductor  
6.8 µH  
1.4 A, 144 mΩ  
CMD5D13-6R8  
C1608JB1H104K  
C1, C7, C9 Ceramics Condenser  
C2 to C6  
C8  
0.1 µF  
4.7 µF  
0.22 µF  
50 V  
10 V  
10 V  
NeoCapacitor  
Ceramics Condenser  
NEC/TOKIN TEPSLA21A475M8R  
TDK  
C1608JB1A224K  
R1  
R4  
R5  
R6  
R7  
Resistor  
Resistor  
Resistor  
Resistor  
Resistor  
Resistor  
7.5 kΩ  
51 kΩ  
43 kΩ  
330 kΩ  
22 kΩ  
100 kΩ  
0.5 %  
0.5 %  
0.5 %  
0.5 %  
0.5 %  
0.5 %  
ssm  
ssm  
ssm  
ssm  
ssm  
ssm  
RR0816P-752-D  
RR0816P-513-D  
RR0816P-433-D  
RR0816P-334-D  
RR0816P-223-D  
RR0816P-104-D  
R8, R11  
Note : SANYO : SANYO Electric Co., Ltd.  
SUMIDA : SUMIDA Electric Co., Ltd.  
TDK : TDK Corporation  
NEC/TOKIN : NEC TOKIN Corporation  
ssm : SUSUMU Co., Ltd.  
18  
 
MB39A105  
SELECTION OF COMPONENTS  
• Nch MOS FET  
The N-ch MOSFET for switching use should be rated for at least 20% more than the maximum output voltage.  
To minimize continuity loss, use a FET with low RDS(ON) between the drain and source. For high output voltage  
and high frequency operation, on/off-cycle switching loss will be higher so that power dissipation must be  
considered. In this application, the SANYO MCH3405 is used. Continuity loss, on/off switching loss, and total  
loss are determined by the following formulas. The selection must ensure that peak drain current does not exceed  
rated values.  
Continuity loss : PC  
2
PC = ID × RDS(ON) × Duty  
On-cycle switching loss : PS (ON)  
VD (Max) × ID × tr × fOSC  
PS (ON) =  
6
Off-cycle switching loss : PS (OFF)  
VD (Max) × ID (Max) × tf × fOSC  
PS (OFF) =  
6
Total loss : PT  
PT = PC + PS (ON) + PS (OFF)  
Example: Using the SANYO MCH3405  
Input voltage VIN (Max) = 2.4 V, output voltage VO = 9 V, drain current ID = 0.94 A, Oscillation frequency  
fOSC = 500 kHz, L = 6.8 µH, drain-source on resistance RDS (ON) =: 160 m, tr = 18 ns, tf = 8 ns.  
Drain current (Max) : ID (Max)  
VO × IO  
VIN(Min)  
VIN(Min)  
2L  
VO VIN(Min)  
ID (Max) =  
+
ton  
ton =  
t
VO  
9 × 0.25  
2.4× (92.4)  
1
=
+
×
2.4  
2 × 6.8 × 106 × 9  
500 × 103  
=: 1.20 (A)  
Drain current (Min) : ID (Min)  
VO × IO  
VIN(Min)  
2L  
ID (Min) =  
ton  
VIN(Min)  
9 × 0.25  
2.4× (92.4)  
1
=
×
2.4  
2 × 6.8 × 106 × 9  
500 × 103  
=: 0.68 (A)  
19  
 
MB39A105  
2
PC = ID × RDS (ON) × Duty  
92.4  
9
= 0.94 2 × 0.16 ×  
=: 0.104 W  
VD (Max) × ID × tr × fOSC  
PS (ON)  
=
=
6
9 × 0.94 × 18 × 109 × 500 × 103  
6
=: 0.013 W  
VD (Max) × ID (Max) × tf × fOSC  
PS (OFF)  
=
6
9 × 1.20 × 8 × 109 × 500 × 103  
=
6
=:  
0.007 W  
PT  
= PC + PS (ON) + PS (OFF)  
=: 0.104 + 0.013 + 0.007  
=: 0.124 W  
The above power dissipation figures for the MCH3405 is satisfied with ample margin at 0.8 W.  
• Inductors  
In selecting inductors, it is of course essential not to apply more current than the rated capacity of the inductor,  
but also to note that the lower limit for ripple current is a critical point that if reached will cause discontinuous  
operation and a considerable drop in efficiency. This can be prevented by choosing a higher inductance value,  
which will enable continuous operation under light loads. Note that if the inductance value is too high, however,  
direct current resistance (DCR) is increased and this will also reduce efficiency. The inductance must be set at  
the point where efficiency is greatest.  
Note also that the DC superimposition characteristics become worse as the load current value approaches the  
rated current value of the inductor, so that the inductance value is reduced and ripple current increases, causing  
loss of efficiency. The selection of rated current value and inductance value will vary depending on where the  
point of peak efficiency lies with respect to load current.  
Inductance values are determined by the following formulas.  
Inductance value : L  
2
VIN  
L ≥  
ton  
2IOVO  
20  
 
MB39A105  
Example:  
2
VIN (Max)  
L ≥  
ton  
2IOVO  
42  
94  
9
1
×
×
2 × 0.25 × 9  
500 × 103  
3.95 µH  
Inductance values derived from the above formulas are values that provide sufficient margin for continuous  
operation at maximum load current, but at which continuous operation is not possible at light loads. It is therefore  
necessary to determine the load level at which continuous operation becomes possible. In this application, the  
Sumida CMD5D13-6R8 is used. At 6.8 µH, the load current value under continuous operating conditions is  
determined by the following formula.  
Load current value under continuous operating conditions : IO  
2
VIN (Max)  
IO  
ton  
2LVO  
42  
94  
9
1
×
×
2 × 6.8 × 106 × 9  
500 × 103  
145.2 mA  
To determine whether the current through the inductor is within rated values, it is necessary to determine the  
peak value of the ripple current as well as the peak-to-peak values of the ripple current that affect the output  
ripple voltage. The peak value and peak-to-peak value of the ripple current can be determined by the following  
formulas.  
Peak value : IL  
VO × IO  
VIN  
VIN  
2L  
VO VIN  
IL  
+
ton  
ton =  
t
VO  
Peak-to-peak value : IL  
VIN  
L
IL =  
ton  
Example: Using the CMD5D13-6R8  
6.8 µH (allowable tolerance ±20%) , rated current = 1.4 A  
Peak value:  
VO × IO  
VIN  
VIN  
2L  
VO VIN  
IL  
+
ton  
ton =  
t
VO  
9 × 0.25  
2.4 × (9 2.4)  
1
+
×
2.4  
2 × 6.8 × 106 × 9  
500 × 103  
1.20 A  
21  
 
MB39A105  
Peak-to-peak value:  
VIN (Min)  
IL =  
ton  
L
4 × (9 4)  
1
=
6.8 × 106 × 9 × 500 × 103  
=: 0.654 A  
• Flyback diode  
The flyback diode is generally used as a Shottky barrier diode (SBD) when the reverse voltage to the diode is  
less than 40V. The SBD has the characteristics of higher speed in terms of faster reverse recovery time, and  
lower forward voltage, and is ideal for achieving high efficiency. As long as the DC reverse voltage is sufficiently  
higher than the output voltage, the average current flowing through the diode is within the mean output current  
level, and peak current is within peak surge current limits, there is no problem. In this application the SANYO  
SBS004 is used. The diode mean current and diode peak current can be calculated by the following formulas.  
Diode mean current : IDi  
VOVIN(Min)  
IDi IO × (1 −  
)
VO  
Diode peak current : IDip  
VO × IO  
VIN (Min)  
VIN (Min)  
2L  
IDip  
+
ton  
Example: Using the SANYO SBS004  
VR (DC reverse voltage) = 15 V, mean output current = 1.0 A, peak surge current = 10 A,  
VF (forward voltage) = 0.40 V, IF = 1.0 A  
VOVIN (Min)  
IDi IO × (1 −  
)
VO  
0.25 × (1 0.733)  
66.8 mA  
VO × IO  
VIN (Min)  
VIN (Min)  
2L  
IDip  
+
ton  
1.20 A  
22  
 
MB39A105  
• Smoothing Capacitor  
The smoothing capacitor is an indispensable element for reducing ripple voltage in output. In selecting a smooth-  
ing capacitor it is essential to consider equivalent series resistance (ESR) and allowable ripple current. Higher  
ESR means higher ripple voltage, so that to reduce ripple voltage it is necessary to select a capacitor with low  
ESR. However, the use of a capacitor with low ESR can have substantial effects on loop phase characteristics,  
and therefore requires attention to system stability. Care should also be taken to use a capacity with sufficient  
margin for allowable ripple current. This application uses the TEPSLA21A475M8R (NEC/TOKIN) . The ESR,  
capacitance value, and ripple current can be calculated from the following formulas.  
Equivalent Series Resistance : ESR  
VO  
IL  
1
ESR ≤  
2πfCL  
Capacitance value : CL  
IL  
CL  
2πf (VO IL × ESR)  
Ripple current : ICL  
VIN  
L
ICL  
ton  
Example: Using the TEPSLA21A475M8R (Three piecies are parallel.)  
Rated voltage = 10 V, ESR = 500 m, maximum allowable ripple current = 1 App  
Equivalent series resistance  
VO  
IL  
1
ESR ≤  
2πfCL  
0.18  
0.654  
1
2π × 500 × 103 × 14.1 × 106  
252.7 mΩ  
Capacitance value : CL  
IL  
CL  
2πf (VO IL × ESR)  
0.39  
2π × 500 × 103 × (0.18 0.654 × 0.167)  
2.94 µF  
Ripple current : ICL  
VIN  
L
ICL  
ton  
4 × (9 4)  
1
×
6.8 × 106 × 9  
500 × 103  
0.654 App  
23  
 
MB39A105  
REFERENCE DATA  
Conversion Efficiency vs. Load current  
100  
Ta = +25 °C  
9 V output  
90  
80  
70  
60  
50  
40  
30  
Vin = 1.8 V  
Vin = 3.3 V  
Vin = 6.0 V  
1 m  
10 m  
100 m  
1
Load current IL (A)  
Switching Wave Form  
VG (V)  
10  
Ta = +25 °C  
VIN = 3.3 V  
VO = 9 V  
5
0
IO = 100 mA  
VD (V)  
15  
10  
5
0
0
1
2
3
4
5
6
7
8
9
10  
t (µs)  
24  
 
MB39A105  
USAGE PRECAUTION  
Printed circuit board ground lines should be set up with consideration for common impedance.  
Take appropriate static electricity measures.  
• Containers for semiconductor materials should have anti-static protection or be made of conductive material.  
• After mounting, printed circuit boards should be stored and shipped in conductive bags or containers.  
• Work platforms, tools, and instruments should be properly grounded.  
• Working personnel should be grounded with resistance of 250 kto 1 Mbetween body and ground.  
Do not apply negative voltages.  
The use of negative voltages below –0.3 V may create parasitic transistors on LSI lines, which can cause  
abnormal operation.  
ORDERING INFORMATION  
Part number  
Package  
Remarks  
8-pin plastic TSSOP  
(FPT-8P-M05)  
MB39A105PFT  
25  
 
MB39A105  
PACKAGE DIMENSION  
8-pin plastic TSSOP  
(FPT-8P-M05)  
0.127±0.03  
3.00±0.10(.118±.004)  
(.0050±.001)  
8
5
4.40±0.10 6.40±0.20  
(.173±.004) (.252±.008)  
INDEX  
Details of "A" part  
1.10(.043)MAX  
4
1
"A"  
0~8˚  
0.65(.026)  
0.22±0.10  
(.009±.004)  
0.54(.021)  
0.10±0.10  
(.004±.004)  
0.10(.004)  
1.95(.077)  
C
2002 FUJITSU LIMITED F08013Sc-1-1  
Dimensions in mm (inches)  
26  
 
MB39A105  
FUJITSU LIMITED  
All Rights Reserved.  
The contents of this document are subject to change without notice.  
Customers are advised to consult with FUJITSU sales  
representatives before ordering.  
The information and circuit diagrams in this document are  
presented as examples of semiconductor device applications, and  
are not intended to be incorporated in devices for actual use. Also,  
FUJITSU is unable to assume responsibility for infringement of  
any patent rights or other rights of third parties arising from the use  
of this information or circuit diagrams.  
The products described in this document are designed, developed  
and manufactured as contemplated for general use, including  
without limitation, ordinary industrial use, general office use,  
personal use, and household use, but are not designed, developed  
and manufactured as contemplated (1) for use accompanying fatal  
risks or dangers that, unless extremely high safety is secured, could  
have a serious effect to the public, and could lead directly to death,  
personal injury, severe physical damage or other loss (i.e., nuclear  
reaction control in nuclear facility, aircraft flight control, air traffic  
control, mass transport control, medical life support system, missile  
launch control in weapon system), or (2) for use requiring  
extremely high reliability (i.e., submersible repeater and artificial  
satellite).  
Please note that Fujitsu will not be liable against you and/or any  
third party for any claims or damages arising in connection with  
above-mentioned uses of the products.  
Any semiconductor devices have an inherent chance of failure. You  
must protect against injury, damage or loss from such failures by  
incorporating safety design measures into your facility and  
equipment such as redundancy, fire protection, and prevention of  
over-current levels and other abnormal operating conditions.  
If any products described in this document represent goods or  
technologies subject to certain restrictions on export under the  
Foreign Exchange and Foreign Trade Law of Japan, the prior  
authorization by Japanese government will be required for export  
of those products from Japan.  
F0209  
FUJITSU LIMITED Printed in Japan  
 

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