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FUJITSU SEMICONDUCTOR
DS04-27233-2E
DATA SHEET
ASSP For Power Supply Applications
(General Purpose DC/DC Converter)
1-ch DC/DC Converter IC
for low voltage
MB39A105
nnnn 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/out
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MB39A105 nnnn PIN ASSIGNMENT (TOP VIEW) - INE 1 8 FB CSCP 2 7 RT VCC 3 6 GND SCPOD 4 5 OUT (FPT-8P-M05) 2
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MB39A105 nn PIN DESCRIPTION nn Pin No. Symbol I/O Descriptions 1 - INE I Error amplifiers (Error Amp) inverted input terminal 2CSCP Timer-latch short-circuit protection capacitor connection terminal 3VCC Power supply terminal Open drain output terminal for short-circuit protection detection 4SCPOD O During timer-latch short-circuit protection operation : Output “High-Z” During normal operation : Output “L” 5 OUT O External Nch FET gate drive terminal 6GND Ground terminal 7RT Triangular w
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MB39A105 nnnn BLOCK DIAGRAM VCC SCPOD 3 4 - INE 1 VREF Error Amp PWM - Comp. Drive + + + Nch 5 OUT - (0.5 V – 1%) FB 8 VREF IO = 400 mA 6 GND (0.7 V) at VCC = 3.3 V SCP Comp. (0.3 V) - (0.9 V) + CSCP 2 SQ - (1.0 V) RT Current R OSC bias Power UVLO VREF ON/OFF VREF CTL (1.27 V) L : UVLO release – 10% 7 RT 4 +
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MB39A105 nnnn ABSOLUTE MAXIMUM RATINGS Rating Parameter Symbol Condition Unit Min Max Power supply voltage VCC VCC terminal 7V Output current IO OUT terminal 35 mA Output peak current IOP Duty £ 5% (t = 1/fOSC· Duty) 700 mA Power dissipation PD Ta £ +25 C 490* mW Storage temperature TSTG - 55 +125 C * : 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.)
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MB39A105 nnnn ELECTRICAL CHARACTERISTICS (VCC = 3.3 V, Ta = +25 C) Value Pin Symbol Parameter Conditions Unit No Min Typ Max 1. Under voltage lockout Threshold voltage VTLH 3VCC = 1.151.351.55V protection circuit block [UVLO] Threshold voltage VTH 2 0.95 1.00 1.05 V Short-circuit detection time D VCSCP 2 0.15 0.20 0.25 V setting difference voltage Input source current ICSCP 2CSCP = 0.85 V - 1.76 - 0.88 - 0.44 m A 2. Short-circuit protection block Reset voltage VRST 3VCC = 1.11.31.
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MB39A105 nnnn TYPICAL CHARACTERISTICS Power Supply Current vs. Power Supply Voltage Power Supply Current vs. RT Terminal Current 5 5.0 Ta = +25 C Ta = +25 C 4.5 RT = 7.5 kW VCC = 3.3 V 4 4.0 3.5 3 3.0 2.5 2 2.0 ICC 1.5 1 1.0 0.5 0 0.0 02 46 8 10 0 10 2030 4050 Power supply voltage VCC (V) RT terminal current IRT (m A) Error Amplifier Threshold Voltage vs. Power Supply Voltage 1.0 Ta = +25 C 0.9 VCC = 3.3 V 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 02 46 8 10 Power supply voltage VCC (V) Error A
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MB39A105 Triangular Wave Oscillation Frequency Triangular Wave Oscillation Frequency vs. Ambient Temperature vs. Timing Resistor 600 10000 Ta = +25 C VCC = 3.3 V VCC = 3.3 V RT = 7.5 kW 550 1000 500 100 450 400 10 - 40 - 20 0 20 40 60 80 100 1 10 100 Timing resistor RT (kW ) 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
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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 Power dissipation PD (mW)
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MB39A105 nnnn 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
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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 Power L OFF (standby) ON/OFF CTL H ON (operating) (L : OFF, H : ON) 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, th
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MB39A105 nnnn SETTING THE OUTPUT VOLTAGE • Output Voltage Setting Circuit VO R1 Error Amp 1 - 0.5 VO (V) = (R1 + R2) + R2 - INE + R2 (0.5 V) CSCP 2 nnnn 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 (kW ) 12
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MB39A105 nnnn 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 m A. 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 re
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MB39A105 nnnn SETTING TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PROTECTION CIRCUIT 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 t
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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 Short-circuit detection time t tS tCSCP 15
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MB39A105 nnnn I/O EQUIVALENT CIRCUIT ÆÆ Soft-start block (CS) Short-circuit protection circuit block (SCP) ææ 3 VCC VCC ESD protection CSCP + element 4 SCPOD ESD - 1.0 V 2 CSCP protection element ESD protection GND element 6 GND ÆÆ Triangular wave oscillator block (RT) ææ ÆÆ Error amplifier blockææ VCC VCC (1.27 V) 0.33 V + - CS - INE 1 7 RT 0.5 V FB 8 GND GND Output blockææ VCC OUT 5 GND 16 ÆÆ ÆÆ ææ
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+ MB39A105 nnnn APPLICATION EXAMPLE m m m m m W m m W m - W – - – - - - W W m m W W 17 C1 C2 C3 R8 0.1 F 4.7 F4.7 F 100 k Q1 SCPOD 3 4 VCC R5 R6 L1 43 k 330 k INE VO A 6.8 H A 1 (9.0 V) VREF R7 PWM Error Amp 22 k Comp. Drive + + D1 OUT R4 + Nch 5 51 k Q2 (0.5 V 1%) C4 C5 C6 C7 C9 4.7 F 4.7 F 4.7 F 0.1 F 0.1 F 8 IO = 400 mA VREF GND FB (0.7 V) at VCC = 3.3 V 6 SCP Comp. (0.3 V) (0.9 V) CSCP + 2 VIN SQ C8 RT Current (1.8 V to (1.0 V) 0.22 F 6.0 V) R OSC bias Power UVLO VREF ON/OFF VREF CTL (1
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MB39A105 nnnn PARTS LIST COMPONENT ITEM SPECIFICATION VENDOR PARTS No. Q1 Pch FET VDS = 20 V, ID = - 2 A (Max) SANYO MCH3306 Q2, Q3 Nch FET VDS = 20 V, Qg = 4.5 nC (Typ) SANYO MCH3405 D1 Diode VF = 0.40 V (Max) , at IF = 1 A SANYO SBS004 L1 Inductor 6.8 m H 1.4 A, 144 mW SUMIDA CMD5D13-6R8 C1, C7, C9 Ceramics Condenser 0.1 m F 50 V TDK C1608JB1H104K C2 to C6 NeoCapacitor 4.7 m F 10 V NEC/TOKIN TEPSLA21A475M8R C8 Ceramics Condenser 0.22 m F 10 V TDK C1608JB1A224K R1 Resistor 7.5 kW 0.5 % ssm RR08
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MB39A105 nnnn 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 determi
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MB39A105 2 PC = ID · RDS (ON) · Duty 9- 2.4 2 = 0.94 · 0.16 · 9 := 0.104 W VD (Max) · ID · tr · fOSC PS (ON) = 6 - 9 3 9 · 0.94 · 18 · 10 · 500 · 10 = 6 : = 0.013 W VD (Max) · ID (Max) · tf · fOSC PS (OFF) = 6 - 9 3 9 · 1.20 · 8 · 10 · 500 · 10 = 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 es
