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FUJITSU SEMICONDUCTOR DATA SHEET
DS04-27228-2E
ASSP
For Power Supply Applications (General Purpose DC/DC Converter)
2-Channel DC/DC Converter IC
with Overcurrent Protection Symmetrical-Phase Type
MB3886
s DESCRIPTION
The MB3886 is a symmetrical-phase type of two-channel, DC/DC converter IC using pulse width modulation (PWM) , incorporating an overcurrent protection circuit (requiring no current sense resistor) and an overvoltage protection circuit. Providing high output driving capabilities, the MB3886 is suitable for down-conversion. The MB3886 adopts both synchronous rectification to provide high efficiency and symmetrical phasing (two antiphase triangular waves) which contributes to making the input capacitor small. The MB3886 contains a 5-volt regulator resulting in a reduced number of components used. It also contains a variety of protection features which output the protection status upon detection of an overvoltage or overcurrent while reducing the number of external protective devices required. The result is an ideal built-in power supply for driving products with high speed CPU’s such as home TV game devices and notebook PC’s. This product is covered by US Patent Number 6,147,477.
s FEATURES
• • • • Overcurrent protection circuit (requiring no current sense resistor) and overvoltage protection circuit Power-supply voltage range : 5.5 V to 18 V Synchronous rectification system providing high efficiency PSIG pins (open-drain) to output the protection status (Continued)
s PACKAGE
30-pin plastic SSOP
(FPT-30P-M02)
MB3886
(Continued) • Symmetrical-phase system reducing the input capacitor loss • Built-in channel control function • Reference voltage : 3.5 V ± 1% • Error amplifier threshold voltage : 1.25 V ± 1% (0 °C to 85 °C) • Oscillator frequency range : 10 kHz to 500 kHz • Built-in circuit for load-independent soft-start and discharge control • Totem-pole type output for N-ch MOSFET
s PIN ASSIGNMENT
(TOP VIEW)
PSIG1 : 1 CTL1 : 2 ILIM1 : 3 CT : 4 RT : 5 SGND : 6 CS1 : 7 −INE1 : 8 FB1 : 9 +INC1 : 10 OUT1-1 : 11 VS1 : 12 CB1 : 13 OUT2-1 : 14 PGND : 15
30 : PSIG2 29 : CTL2 28 : ILIM2 27 : VREF 26 : VCC 25 : CSCP 24 : CS2 23 : −INE2 22 : FB2 21 : +INC2 20 : OUT1-2 19 : VS2 18 : CB2 17 : OUT2-2 16 : VB
(FPT-30P-M02)
2
MB3886
s PIN DESCRIPTION
Pin No. Pin name I/O 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 PSIG1 CTL1 ILIM1 CT RT SGND CS1 −INE1 FB1 +INC1 OUT1-1 VS1 CB1 OUT2-1 PGND VB OUT2-2 CB2 VS2 OUT1-2 +INC2 FB2 −INE2 CS2 CSCP VCC VREF ILIM2 CTL2 PSIG2 O I I Description CH1 protection status output terminal CH1 control terminal “H” level : CH1 ON state “L” level : CH1 OFF state and protection status reset CH1 overcurrent detection resistor connection terminal
Triangular waveform oscillation frequency setting capacitor connection terminal Triangular waveform oscillation frequency setting resistor connection terminal Ground terminal CH1 soft-start capacitor connection terminal I O I O CH1 error amp. inverting input terminal CH1 error amp. output terminal CH1 overvoltage comparator noninverting input terminal CH1 totem-pole output terminal (External main-side FET gate drive) CH1 boot capacitor connection terminal Connect a capacitor between the CB1 and VS1 terminals. CH1 totem-pole output terminal (External synchronous-rectification-side FET gate drive) Output circuit bias output terminal CH2 totem-pole output terminal (External synchronous-rectification-side FET gate drive) CH2 boot capacitor connection terminal Connect a capacitor between the CB2 and VS2 terminals. CH2 totem-pole output terminal (External main-side FET gate drive) CH2 error amp. output terminal CH2 error amp. inverting input terminal
CH1 external main-side FET source connection terminal O
Ground terminal O O
CH2 external main-side FET source connection terminal O O I CH2 overvoltage comparator noninverting input terminal
CH2 soft-start capacitor connection terminal Timer-latch short-circuit protection capacitor connection terminal Reference voltage, control circuit power supply terminal O I I O Reference voltage output terminal CH2 overcurrent detection resistor connection terminal CH2 control terminal “H” level : CH2 ON state “L” level : CH2 OFF state and protection status reset CH2 protection status output terminal 3
MB3886
s BLOCK DIAGRAM
VCC 26 5 V Reg. FB1 9 −INE1 8 CS1 7 VREF 10 µA +INC1 10 CTL1 2
1.47 V CTL1 3.8 kΩ
16 VB
10 µA
< CH1 > Error Amp.1 − + + 1.25 V OVP Comp.1 + −
Latch1-1
13 CB1 PWM Comp.1 + −
Drive1-1
11 OUT1-1 12 VS1
R SQ
Dead Time Modulation1
Latch2-1
Drive2-1
14 OUT2-1
CTL1 R QS
Current Protection Logic
PSIG1 1
− + 3 ILIM1
FB2 22
10 µA
< CH2 > Error Amp.2 − + + 18 CB2 PWM Comp.2 + −
Drive1-2
−INE2 23 CS2 24 VREF 10 µA +INC2 21 CTL2 29
3.8 kΩ
1.25 V OVP Comp.2 + −
Latch1-2
20 OUT1-2 19 VS2
1.47 V CTL2 R
Dead Time Modulation2
Latch2-2
Drive2-2
17 OUT2-2 15 PGND
SQ PSIG2 30
CTL2
Current Protec.