MB3885

Manufacturer Part NumberMB3885
Description1-channel Dc/dc Converter Ic With Synchronous Rectifier
ManufacturerFujitsu Microelectronics, Inc.
MB3885 datasheet
 


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FUJITSU SEMICONDUCTOR
DATA SHEET
ASSP For Power Management Applications
1-channel DC/DC Converter IC
with Synchronous Rectifier
MB3885
DESCRIPTION
The MB3885 is a 1-channel DC/DC converter IC using pulse width modulation (PWM) and synchronous rectifi-
cation, designed for down conversion applications.
This device is a power supply with high output drive capacity. Synchronous rectification also provides for high
efficiency.
In addition, a 5 V regulator is built in to reduce the number of system components. 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.
FEATURES
• Synchronous rectification for high efficiency
• Supply voltage range : 5.5 V to 18 V
• Built-in high-precision reference voltage circuit : 2.5 V
• Error Amp. threshold voltage : 1.25 V
• Oscillator frequency range : 10 kHz to 500 kHz
• Built-in soft-start circuit with error Amp. input control
• Totem pole type output for N-ch MOSFET
PACKAGE
1
1
(0 C to 85 C)
20-pin Plastic SSOP
(FPT-20P-M03)
DS04-27227-2E

MB3885 Summary of contents

  • Page 1

    ... Synchronous Rectifier MB3885 DESCRIPTION The MB3885 is a 1-channel DC/DC converter IC using pulse width modulation (PWM) and synchronous rectifi- cation, designed for down conversion applications. This device is a power supply with high output drive capacity. Synchronous rectification also provides for high efficiency. ...

  • Page 2

    ... MB3885 PIN ASSIGNMENTS N. N. CSCP : INE : 8 INE : 9 VCC : 10 2 (TOP VIEW N. N. VREF 17 : SGND 16 : PGND 15 : OUT2 OUT1 (FPT-20P-M03) ...

  • Page 3

    ... Totem pole output terminal (External main side FET gate drive External main side FET source connection terminal Totem pole output terminal. (External synchronous rectifier side FET gate 15 OUT2 O drive) 16 PGND Ground terminal 17 SGND Ground terminal 18 VREF O Reference voltage output terminal 19 N.C. No connection 20 N.C. No connection MB3885 Description 3 ...

  • Page 4

    ... MB3885 BLOCK DIAGRAM Error Amp. INE 1.25 V OVP Comp. 9 INC VCC 1.47 V SCP Comp CSCP 4 VCC 10 PWM Comp.1 DTC PWM Comp.2 Latch 2.1 V bias S R UVLO OSC Latch Reg Drive1 13 OUT1 14 VS ...

  • Page 5

    ... 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. Conditions CC CB terminal Duty Duty) OSC 10cm). MB3885 Rating Unit Min Max 120 mA 800 mA 555 125 C 5 ...

  • Page 6

    ... MB3885 RECOMMENDED OPERATING CONDITIONS Parameter Supply voltage Boot voltage Reference voltage output current Bias output current Input voltage Output current Peak output current Oscillator frequency Timing resistor Timing capacitor Boot capacitor Reference voltage output capacitor Bias output capacitor Soft-start capacitor Short detection capacitor ...

  • Page 7

    ... CSCP 0. 470 1 TH1 1 TH2 INE MB3885 0 mA, VREF 0 mA Value Unit Min Typ Max 2.475 2.500 2.525 V 0. 4.95 5.05 5.15 V 2.6 2 ...

  • Page 8

    ... MB3885 Parameter Symbol Pin No. Frequency band width 7. Output voltage Error Amp Block Output source [Error Amp.] current Output sink current 8. PWM Comparator Threshold Block voltage [PWM Comp.1, PWM Comp.2] 9. Dead time Maximum Adjustment duty cycle Block [DTC] Output current (main side) ...

  • Page 9

    ... OUT1 OUT2 OPEN OUT2 : OUT1 : 13 470 pF OUT1 OUT2 OPEN OUT1 : OUT2 : 9 INC TH 9 INC MB3885 0 mA, VREF 0 mA Value Unit Min Typ Max 100 200 ns 100 250 ns 1.44 1.47 1.50 V 200 30 nA 6.5 9 ...

  • Page 10

    ... MB3885 TYPICAL CHARACTERISTICS Supply Current vs. Supply Voltage Supply voltage V Reference Voltage vs. Ambient Temperature 2.0 1.5 1.0 0.5 0.0 0.5 1.0 1.5 2 Ambient temperature Triangular Wave Upper/Lower Limit Voltage vs. Triangular Wave Oscillator Frequency 2.5 2.0 1.5 1.0 0 Triangular wave oscillator frequency fosc (Hz) 10 Reference Voltage vs. Supply Voltage ...

  • Page 11

    ... Ambient temperature 180 90 4 4.7 k 1.5 V 180 10 M MB3885 VCC 12 V CTL 5 V CTL 150 pF CTL 470 pF CTL 15000 100 VCC 470 pF 20 ...

  • Page 12

    ... MB3885 (Continued) 12 Power Dissipation vs. Ambient Temperature 600 555 500 400 300 200 100 Ambient temperature 100 ...

  • Page 13

    ... The output block has totem pole configuration on both the main side and synchronous rectifier side, and can drive an external N-ch MOSFET. Also, the high output drive capability (700 mA Max : duty the use of low on-resistor FET devices. MB3885 5 ) provides high gate-source capacitor, enabling 13 ...

  • Page 14

    ... MB3885 2. Control Functions Output ON/OFF control is provided by using the CS terminal (pin 6) setting functions. CS terminal voltage level GND Hi-Z 3. Protective Functions (1) Timer Latch Short Circuit Protection (SCP) The short circuit protection comparators read the output voltage levels. If the output voltage falls below the short detection voltage, the timer circuit is activated to start charging the external capacitor Cscp connected to the CSCP terminal (pin 3) ...

  • Page 15

    ... INE SCP Comp CSCP 3 S Latch C SCP Q1 Q4 Timer Latch Short Circuit Protection Circuit : 0. latch is set, turning the external TH Error Amp. 2.1 V bias R UVLO MB3885 13 Drive OUT1 15 Drive OUT2 15 ...

  • Page 16

    ... MB3885 PROCESSING WITHOUT USING THE CSCP TERMINAL When the timer latch short circuit protection circuit is not used, the CSCP terminal (pin 3) should be shorted to SGND using the shortest possible connection. Operation Without Using the CSCP Terminal 16 17 SGND CSCP 3 ...

  • Page 17

    ... Thus the DC/DC converter output voltage is in proportion to the rise in the CS terminal voltage as the soft-start capacitor connected to the CS terminal charges. The soft-start time is determined by the following formula. Soft-start time (time to output 100 ) ts ( 0.125 2 Soft start time ts MB3885 CS terminal voltage Error. amp block comparison voltage to INE voltage 17 ...

  • Page 18

    ... MB3885 VREF FB INE Error Amp 1. Soft-start Block UVLO ...

  • Page 19

    ... The oscillator frequency can be set by connecting a timing capacitor (C resistor ( the RT terminal (pin Oscillator frequency 893000 fosc (kHz (pF OUTPUT VOLTAGE SETTING INE the CT terminal (pin 4) and a timing Error Amp. 1.25 V MB3885 R2) 19 ...

  • Page 20

    ... MB3885 OVERVOLTAGE PROTECTION CIRCUIT VOTAGE SETTING Overvoltage conditions in the DC/DC converter output voltage can be detected by connecting external resistance from the DC/DC converter output voltage to the INC terminal (pin 9) on the respective overvoltage protection comparator circuits (OVP comp.) . When the output voltage of the DC/DC converter rises above the detection voltage, the overvoltage protection comparator (OVP Comp.) output goes to “ ...

  • Page 21

    ... Because IC current consumption other than I following formula. Power consumption : 0.0065 the external FET Q1, Q2, by the following formula (Ibias Ibias 6.5 mA, power consumption can be determined from the MB3885 , Qg , charged from the mA) 21 ...

  • Page 22

    ... MB3885 Vin VCC 10 VOUT1 VOUT2 Using the above formulas to determine power consumption, settings should be made with reference to the “Power Consumption vs. Input Voltage” on the following page, as well as the “Power dissipation vs. Ambient Temperature.” ...

  • Page 23

    ... Input voltage Vin (V) Power Consumption vs. Input Voltage (fosc Parameters 0.80 SW1 OFF 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0. Input voltage Vin (V) MB3885 25 C 200 kHz ...

  • Page 24

    ... MB3885 APPLICATION CIRCUIT 24 ...

  • Page 25

    ... 0.022 0 0. 470 6.3 V 2.2 F 6 1/4 W 3 1/4 W 6 1/4 W 2 1/4 W MB3885 VENDOR PARTS No. IR IRF7811 ROHM RB051L-40 ROHM RB495D RLF12545T TDK -2R7N8R7 25 ...

  • Page 26

    ... MB3885 REFERENCE DATA Conversion Efficiency vs. Load Current Characteristics 100 Load current IL ( output SW1 OFF Vin 6 V Vin 8.5 V Vin ...

  • Page 27

    ... Persons handling semiconductors should be grounded directly with resistance of 250 k • Do not apply negative voltages. • Application of negative voltage of 0 greater can create parasitic transistor effects on an LSI device, leading to abnormal operation. ORDERING INFORMATION Part Number MB3885PFV Package Plastic SSOP 20-pin (FPT-20P-M03) MB3885 Remarks 27 ...

  • Page 28

    ... MB3885 PACKAGE DIMENSION 20-pin, Plastic SSOP (FPT-20P-M03) * 6.50±0.10(.256±.004) 20 INDEX LEAD No. 1 0.65(.026) 0.10(.004) 1999 FUJITSU LIMITED F20012S-3C Note These dimensions do not include resin protrusion. Note 2 ) Pins width and pins thickness include plating thickness. 0.17±0.03 (.007±.001) ...

  • Page 29

    ... MB3885 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, ...