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FB6831J
FB6831J
Application Note
July-2006
Fuji Electric Device Technology Co.,Ltd.
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FB6831J
1. This Data Book contains the product specifications, characteristics, data, materials, and structures as
of July 2006. The contents are subject to change without notice for specification changes or other
reasons. When using a product listed in this Data Book, be sure to obtain the latest specifications.
2. All applications described in this Data Book exemplify the use of Fuji's products for your reference
only. No right or license, either express or implied, under any patent, copyright, trade secret or other
intellectual property right owned by Fuji Electric Co., Ltd. is (or shall be deemed) granted. Fuji makes
no representation or warranty, whether express or implied, relating to the infringement or alleged
infringement of other's intellectual property rights, which may arise from the use of the applications,
described herein.
3. Although Fuji Electric is enhancing product quality and reliability, a small percentage of
semiconductor products may become faulty. When using Fuji Electric semiconductor products in your
equipment, you are requested to take adequate safety measures to prevent the equipment from
causing a physical injury, fire, or other problem if any of the products become faulty. It is
recommended to make your design fail-safe, flame retardant, and free of malfunction.
4. The products introduced in this Data Book are intended for use in the following electronic and
electrical equipment, which has normal reliability requirements.
• Computers • OA equipment • Communications equipment (Pin devices)
• Measurement equipment • Machine tools • audiovisual equipment • electrical home appliances
• Personal equipment • Industrial robots etc.
5. If you need to use a product in this Data Book for equipment requiring higher reliability than normal,
such as for the equipment listed below, it is imperative to contact Fuji Electric to obtain prior approval.
When using these products for such equipment, take adequate measures such as a backup system
to prevent the equipment from malfunctioning even if a Fuji's product incorporated in the equipment
becomes faulty.
• Transportation equipment (mounted on cars and ships) • Trunk communications equipment
• Traffic-signal control equipment • Gas leakage detectors with an auto-shut-off feature
• Emergency equipment for responding to disasters and anti-burglary devices • Safety devices
6. Do not use products in this Data Book for the equipment requiring strict reliability such as (without
limitation)
• Space equipment • Aeronautic equipment • Atomic control equipment
• Submarine repeater equipment • Medical equipment
7. Copyright © 1995 by Fuji Electric Co., Ltd. All rights reserved. No part of this Data Book may be
reproduced in any form or by any means without the express permission of Fuji Electric.
8. If you have any question about any portion in this Data Book, ask Fuji Electric or its sales agents
before using the product. Neither Fuji nor its agents shall be liable for any injury caused by any use of
the products not in accordance with instructions set forth herein.
WARNING
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Contents
1. Overview ······················································ 4
2. Features ······················································ 4
3. External View ······················································ 4
4. Block Diagram ······················································ 5
5. Terminal Functions ······················································ 5
6. Ratings and Characteristics ············································ 6 - 8
7. Operation Illustrations and Design Guides ······················ 9 - 11
8. Examples of Application Circuit and Characteristics·········· 12
Notes:
- The contents of this material may be changed without prior notice for improvement.
- The application circuit examples and constants for parts given in this material are only
intended to assist in related design, and do not take any dispersion of parts or usage
conditions into consideration. Therefore, carefully consider such dispersion of parts and
usage conditions for actual design.
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1. Overview
FB6831J is a synchronous rectifier type step-down converter with a built-in inductor. It allows a remarkably
small-sized power supply circuit by means of applying a thin, small-sized SON-10 package (2.95mm×2.4mm and
1.0mm high) that requires no externally mounted inductor. The built-in inductor makes simplification of the circuit
design possible, since it only requires a few externally mounted resistors and capacitors. It is suitable for the
single-cell application of a lithium ion battery, and at an output setting of 1.5 V within the input range of 2.7 to 5.5
V, it can supply load current of 500 mA and also cope with low-voltage output (not less than 0.8V). The output
voltage may be set optionally by using shunt resistors and is applicable for various purposes. Under light load
operation, it transfers to a LDO operation and realizes low ripple output.
2. Features
- Input voltage range: 2.7 V to 5.5 V
- Operating frequency: 2.5 MHz (fixed)
- High efficiency operation: 90% (max.)
- Output current: 500 mA (VOUT = 1.5V)
- Providing built-in MOSFETs for switching and for synchronous side
- Providing built-in ferrite inductor
- Variable output voltage: 0.8V (min.)
- LDO operation for light load
- UVLO circuit (2.5 V start)
- Overcurrent protection circuit (controlled at each pulse)
- Short-circuit protection circuit (timer-latch type)
- Overheat protection circuit
- Standby current: 1 μA or less
- Thin, small-sized package, SON with 10 pins applied (with body size of 2.95 mm × 2.4 mm and 1.0 mm high)
3. External view
Unit: mm
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4. Block Diagram
5. Terminal Functions
Terminal
No.
Terminal
symbol Functions of terminal Remarks
1 PGND
Power ground terminal
2 GND
Control line ground terminal
3 COP
Phase compensation capacitor connection terminal (Connect a capacitor between COP and CRES.)
4 CRES
Phase compensation capacitor connection terminal (Connect a capacitor between COP and CRES.)
5 IN
Output voltage feedback terminal
6 VOUT LDO output terminal for DC-DC converter Connect a capacitor.
7 VDD
Power supply terminal
8 CE
ON/OFF control terminal Low: shut down, High: operation
9 PVDD
Driving circuit power supply and PMOS
source terminal Connect a capacitor.
10 M
Test pin not yet connected
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6. Ratings and Characteristics
These data may be changed without any prior notification. Refer to the latest specifications for details.
(1) Absolute maximum ratings
Item Symbol Condition Value Unit
Input Supply Voltage VDD 6 V
Input Voltage of Control terminal VI -0.3 to VDD+0.3 V
Maximum output current IOUT 500 mA
Power Dissipation Pd Ta≦25°C 850 mW
Junction Temperature *1 Tj 125 °C
Operating Temperature TOPR -30 to +85 °C
Storage Temperature TSTG -40 to +150 °C
*1: In the mounted condition on a epoxy-glass laminate substrate of 60 mm × 52 mm, t = 1.0
Tolerable loss reduction characteristics
(2) Recommended operating conditions
Item Symbol Condition MN. TYP. MAX. Unit
Supply Voltage VDD 2.7 5.5 V
Output Voltage range VOUT I
OUT=0 to 500mA 0.8 VDD-0.7 V
COUT 4.7 μF
CIN 4.7
μF
Connected Capacitors with Regulators
CPC (100) pF
RFB0 Variable kΩ
Connected Resistors with Regulators RFB1 100 kΩ
Refer to 4. Block Diagram for the part symbols.
Tolerable loss
0.0
0.2
0.4
0.6
0.8
1.0
-20 0 20 40 60 80 100 120
Ambient temperature Ta [°C]
Tolerable loss Pd[W]
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(3) Electrical symbols
• Unless otherwise specified, the characteristics are described under the following conditions:
VDD = VPVDD = 3.6V,VOUT = 1.5V (RFB0 = 150kΩ,RFB1 = 100kΩ), CE=VDD, NO load, CIN=4.7uF, COUT=4.7uF and
Ta=+25°C
(1) Supply Voltage Range
Item Symbol Condition Min. Typ. Max. Unit
Supply Voltage VDD 2.7 3.6 4.3 V
(2) Power consumption
Item Symbol Condition Min. Typ. Max. Unit
IVDD1 VDD Pin
CE=L 0.1 1.0 uA
IVDD2 VDD Pin
CE=H, No load 60 80 100 uA
IPVDD1 PVDD Pin
CE=L 0.1 1.0 uA
Supply current
IPVDD2
PVDD Pin
CE=H, IOUT=300 mA
VOUT=1.5V
145 165 mA
(3) DC-DC converter
Item Symbol Condition Min. Typ. Max. Unit
Output voltage range*1 V
OUT I
load=0-500mA 0.8 VDD-0.7 V
Output voltage accuracy*2 V
OUTA I
load=50mA ,VOUT=1.5V -3 +3 %
VOUT=1.5V, Iload=300mA,
Capacitor ESR<100mΩ (30) (40) mVp-p
Output ripple voltage*3 V
ripple VOUT=1.5V, Iload=500mA,
Capacitor ESR<100mΩ (40) (50) mVp-p
η1 VOUT=1.8V, Iload=200mA 90 %
Maximum Efficiency*4 η2 VOUT=1.5V, Iload=200mA 85 %
*1 Output voltage is calculated by the following formula: VOUT = ((RFB0+RFB1)/RFB1) x Vref ( = 0.6Vtyp).
*2 Excluding the precision of externally connected resistors (RFB0, RFB1)
*3 Excluding switching noise (spike noise)
*4 Representative characteristics
(4) Oscillator
Item Symbol Condition Min. Typ. Max. Unit
Oscillation frequency fOSC Io=50mA 2.3 2.5 2.7 MHz
(5) LDO
Item Symbol Condition Min. Typ. Max. Unit
Output voltage range*1 V
OUT I
load=0-30mA 0.8 VDD-0.7 V
Output voltage accuracy*2 V
OUTA I
load=0-30mA ,VOUT=1.5V -3 +3 %
*1 Output voltage is calculated by the following formula: VOUT = ((RFB0+RFB1)/RFB1) x Vref( = 0.6Vtyp).
*2 Excluding the precision of externally connected resistors (RFB0, RFB1)
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(6) Operation control
Item Symbol Condition Min. Typ. Max. Unit
IOTH1 LDO to DC-DC converter 25 30 50 mA
Threshold load current IOTH2 DC-DC converter to LDO 5 15 25 mA
DC-DC converter operation and LDO operation are switched over automatically depending on the load current
value.
(7) Logic interface
Item Symbol Condition Min. Typ. Max. Unit
Logic input voltage High VIH 1.41 VDD V
Logic input voltage Low VIL 0 0.2 V
Logic input current High IIH V
IH=3.6V 0.1 1.0 uA
Logic input current Low IIL V
IL=0V -1.0 0.1 uA
(8) Under Voltage Lock Out
Item Symbol Condition Min. Typ. Max. Unit
On threshold VUVLH 2.3 2.4 2.5 V
Off threshold VUVLL 2.2 2.3 2.4 V
(9) Over current protection
Item Symbol Condition Min. Typ. Max. Unit
High-Side Current Limit*1 I
LIM 1200 mA
*1 Design value
(10) Timer latch
Item Symbol Condition Min. Typ. Max. Unit
Shutdown time tlatch f
OSC =2.5MHz 1.5 1.9 3.0 ms
The timer latch operation operates during the PMOS ON time above, and is reset by setting the CE terminal to
Low.
(11) Thermal shutdown
Item Symbol Condition Min. Typ. Max. Unit
Thermal shutdown
threshold temperature*1 Tsd 150. degC
*1 Design value
The overheat protection circuit operates if the junction reaches the above temperature, and is reset by
setting the CE terminal to Low.
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7. Operation Illustrations and Design Guides
(1)Outp ut vol tage setting
The output voltage is set so as to make the
feedback voltage to the IN terminal 0.6 V and
calculated by the following formula:
Vref
RRR
VOUT FB
FBFB ×
+
=1
10 .6.0 VtypVref =
The output voltage precision at this time is ±3%
of the IC characteristics only. (Ta = 25°C, Iload
= 0 to 500mA, Vout = 1.5V)
The actual output voltage precision includes the
tolerances of externally mounted resistors
RFB0 and RFB1 (Figure 1).
Set the output voltage to a value between 0.8 V
and VDD-0.7V.
(2)
Switchover between PWM mode and LOD mode
This IC has a built-in function that automatically
switches the operation mode under light load
operation from PWM operation to LDO
operation to reduce the output ripple voltage
under a light load. If the load current is
increased from LDO mode (light load),
operation is switched to PWM mode when the
load current reaches 30 mA (typ.), and if the
load current is decreased from PWM mode
(heavy load), operation is switched to LDO
mode when the load current (mean value)
reaches 15 mA (typ.). This switchover cannot
be regulated externally, since it is executed
automatically within the IC (Figure 2).
In the transient state at power supply startup
and at startup by using the CE terminal, the
output voltage is established in LDO mode
irrespective of the load current value.
(3)Oscillation frequency
The oscillation frequency is fixed to 2.5 MHz
(typ.) and cannot be regulated externally.
(4)Protection function
(i) Overcurrent protection
The system has a built-in pulse-by-pulse
overcurrent limitation function for detecting and
limiting the pulse-shaped main current peak
value for each pulse.
If the peak current flowing through the built-in
MOSFET reaches 1.2 A, it is controlled so that
no more current flows by turning off the
MOSFET. This current limitation is reset for the
next cycle and the MOSFET is again turned on.
This control is repeated for every cycle to limit
overcurrent.
If the overcurrent state continues, output
voltage cannot be supplied any more due to line
impedance, etc. and the built-in MOSFET
enters the full-on state, then operation switches
to timer latch protection operation and the
system enters shutdown mode.
(ii)
Timer latch short-circuit protection circ uit
The system has a built-in timer latch
short-circuit protection circuit for shutting down
the output after the elapse of a certain time in
case there is a drop in the output voltage of the
DC-DC converter circuit due to a short-circuit,
etc.. The built-in PMOS enters the full-on state
in case there is a drop in the output voltage of
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the DC-DC converter. If this ON state of PMOS
continues for more than 1.9 msec (typ.), PMOS
enters shutdown mode (Figure 3).
Shutdown mode is reset by making the VDD
terminal of power supply voltage to UVLO
voltage (2.3 V typ.) or less, or by setting the CE
terminal to Low level.
(iii) Overheat protection
The system has a built-in overheat protection
function for stopping the switching in case of a
rise in IC temperature caused by faults
including overcurrent, etc.
The switching stops when the IC chip
temperature reaches 150°C (typ.). As a result,
the IC enters the shutdown state, which is reset
by setting the VDD terminal to the UVLO
voltage (2.3 V typ.) or less, or by setting the CE
terminal to Low level.
(5)Operation mode at startup
The system starts up in LDO mode for turning
on the power supply or for startup from the CE
terminal.
Therefore, the startup speed of output voltage
changes depending upon the load current at
startup.
Take care that the rush current charging the
output capacitor flows into the input side at
startup.
(6)Recommended wiring (pattern)
Some noise may possibly be superimposed on
PGND under a heavy load, since this IC has a
built-in MOSFET for switching. This noise may
cause abnormal motion including oscillation for
some pattern wiring.
For using this IC, separate the GND line as
shown in Figure 4 below, so that the power line
affects the control line as little as possible.
This IC has a built-in inductor and may be
affected by leakage inductance. Evade any
wiring direct under the IC.
(7)Undervoltage malfunction p revention circ uit (UVLO)
The system has a built-in undervoltage
malfunction prevention circuit (ULVO) for
preventing circuit malfunctions in case of a drop
in power supply voltage. It starts to operate at
VDD = 2.4 V (typ.) when the power supply
voltage increases from 0 V. And the output is
interrupted at VDD = 2.3V (typ.) when power
supply voltage decreases.
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(8)Phase compensation circuit
Since the IC has a built-in phase compensation
circuit, no external setting is required. However,
should any such phenomenon as oscillation be
found, connect ceramic capacitor Cpc to the
COP and CRES terminals (Figure 5).
The capacitors connected to the feedback
resistors used in general DC-DC converter
circuits (for improving transient response) are
not effective for this IC. Do not connect such
capacitors (Figure 6).
(9)ON/OFF control
ON/OFF control of output by means of external
signals using the CE terminal is possible.
For turning on the output, the power supply
circuit starts operation by externally impressing
a voltage higher than 1.41 V on the CE terminal.
The maximal voltage impressed on the CE
terminal shall not be higher than the VDD
voltage.
Reduce the CE terminal voltage to not higher
than 0.2 V for turning off the output.
The current consumption at the VDD terminal
and PVDD terminal is 1μA (max.), respectively
in OFF state.
(10)Recommended land pattern
The recommended land pattern is shown below.
600
2800
470
200
400
600
（Unit：μm）
1706.5
600 600
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8. Examples of Application Circuits and Characteristics
PMOS
NMOS
Inductor
PVDD
VOUT
IN
PGND
GND
CE
VDD
COP
CRES
M
PWM controller
/oscillator
/error amplifier
/PWM comparater
/protection
Driver
Control LOGIC
/enable control
/mode select
LDO
for light load
CPC
100pF
CＩＮ
4.7uF
RFB0
150kΩ
RFB1
100kΩ
COUT
4.7uF
VOUT
1.5V/500mA
VIN
2.7 to 5.5V
Determine the constants and parts depending on actual usage conditions.
Efficiency vs. Load current
20
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
Load current Iout Iout [mA]
Efficiency [%]
1.2Vout
1.5Vout
1.8Vout
2.4Vout
Vin=3.6V
Input voltage – Output voltage
1.40
1.45
1.50
1.55
1.60
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Input voltage [V]
Output voltage [V]
Io=0mA
Io=100mA
Io=500mA
Io=50mA
Load current – Output voltage
1.40
1.45
1.50
1.55
1.60
0 100 200 300 400 500 600
Load current [mA]
Output voltage [V]
VDD=2.5V
VDD=3.6V
VDD=5.5V
