ROHM BD9853AFV Technical data

Large Current External FET Controller Type Switching Regulators

Single/Dual-output High-frequency
Step-down Switching Regulator(Controller type)

BD9853AFV

●Description

The BD9853AFV is a 2-ch synchronous DC/DC controller that can operate at a maximum switching frequency of 2MHz,
enabling the use of a smaller external coil than conventional lower-frequency switching regulators. This makes the
BD9853AFV a suitable choice for downsizing applications.

●Features

1) Synchronous Switching Regulator Controller 2channels

2) FET(Pch/Nch) Direct Drive

3) Adjustable Oscillator Frequency with External Resistor (Max. 2MHz)

4) Under Voltage Lockout Function (UVLO)

5) Thermal Shut Down Function (TSD)

6) Short Circuit Protection (SCP)

7) Independent ON/OFF Function in Each Channel with Soft Start Pin

8) SSOP-B16 Package

●Applications
TVSTB, PC, Portable CD・DVD,DVC etc.

●Absolute Maximum Ratings (Ta = 25℃)

Parameter Symbol Limits Unit

Supply Voltage (VCC-GND) Vcc 18 V

VREGA-GND Voltage VREGA 7 V

VCC-VREGB Voltage VREGB 7 V

Power Dissipation Pd 562(*1) mW
Operating Temperature Range Topr -40 to +85 ℃
Junction Temperature Tjmax +150 ℃
Storage Temperature Range Tstg -55 to +150 ℃

* Reduced by 4.49mW for each increase in Ta of 1℃ over 25℃ (When mounted on a board 70×70×1.6tmm grass-epoxy PCB)

●Recommended Operating Conditions

Parameter Symbol

Supply Voltage Vcc 4.5 12 16 V

Oscillator Frequency fosc 100 1000 2000 KHz

SSOPB16

Limits

Min. Typ. Max.

No.09028EAT05

Unit

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© 2009 ROHM Co., Ltd. All rights reserved.

1/16

2009.05 - Rev.A

BD9853AFV

Technical Note

●Electrical Characteristics (Unless otherwise specified Ta=25℃,Vcc=12V,fosc=1000kHz,STB=3V)

Parameter Symbol

Min. Typ. Max.

Limits

Unit Conditions

【Whole Device】

Standby Current Iccst － 0 5 μASTB=0V
Circuit Current Icc － 3.2 5.2 mA INV1,INV2=2.5V

【Regulator for Driver REGA】

Output Voltage Vrega 4.5 5.0 5.5 V
Output Current Capability Irega － － -100 mA Vrega > 4.5V

【Regulator for Driver REGB】

Output Voltage Vregb VCC-5.5 VCC-5.0 VCC-4.5 V
Output Current Capability Iregb 100 － － mA Vregb < Vcc-4.5V

【Oscillator】

Oscillator Frequency fosc 900 1000 1100 kHz

RRT=8.2kΩ
OUTH=2200pF,OUTL=1000pF

Oscillator Frequency Coefficient1 Dfosc1 -2 0 2 % Vcc=4.5 to 5V

Oscillator Frequency Coefficient2 Dfosc2 -2 0 2 % Vcc=5 to 18V

【Error Amplifier】

Threshold Voltage Vthea 0.79 0.80 0.81 V
Input Bias Current Ibias -230 -115 － nA

Voltage Gain Av 60 80 100 dB DC GAIN
Max. Output Voltage Vfbh Vrega-0.85 － － V
Min. Output Voltage Vfbl － － 0.85 V

Output Sink Current Isink 2 11 - mA INV=2.5V, FB=2.5V

Output Source Current Isource - -15 -2 mA INV=0V, FB=2.5V

【PWM Comparator】

0% Threshold Voltage Vth0 1.4 1.5 1.6 V FB Voltage

100% Threshold Voltage Vth100 2.4 2.5 2.6 V FB Voltage

* This product is not designed for the protection against radioactive rays.

ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM ROHM

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2/16

2009.05 - Rev.A

BD9853AFV

Technical Note

●Electrical Characteristics (Unless otherwise specified, Ta=25℃,Vcc=12V,fosc=1000kHz,STB=3V)

Parameter Symbol

Min. Typ. Max.

Limits

Unit Conditions

【FET Driver】

On Resistance (OUT1H)

On Resistance (OUT1L)

On Resistance (OUT2H)

On Resistance (OUT2L)

RonP 1.6 3.2 4.8 Ω OUT=Hi
RonN 1.7 3.4 5.1 Ω OUT=Lo
RonP 1.6 3.2 4.8 Ω OUT=Hi
RonN 1.7 3.4 5.1 Ω OUT=Lo
RonP 1.6 3.2 4.5 Ω OUT=Hi
RonN 1.7 3.4 5.1 Ω OUT=Lo
RonP 1.6 3.2 4.8 Ω OUT=Hi

RonN 1.7 3.4 5.1 Ω OUT=Lo
Dead Time(Turn ON) tdtON 30 70 120 ns *OUTH,L H→L,OUTH=2200pF,OUTL=1000pF
Dead Time(Turn OFF) tdtOFF 25 60 115 ns *OUTH,L H→L,OUTH=2200pF,OUTL=1000pF

【Control Block】

Threshold Voltage Vstb 0.6 1.5 2.4 V
Sink Current Istb 6 15 30 μA

【Soft Start Block】

Soft Start Start-yo Voltage Vstasoft 0.2 0.3 0.4 V Output OFF when Vscp/SOFT＜Vstass
Standby Voltage Vstsoft － － 40 mV SCP/SOFT Voltage
Source Current Isosoft -3.2 -2.3 -1.4 μA Vscp/SOFT=0.6V

【Short Circuit Protection (SCP)】

Timer Start Voltage Vtime 0.50 0.56 0.62 V INV Voltage

Threshold Voltage Vthscp 2.2 2.3 2.4 V SCP/SOFT Voltage

Standby Voltage Vstscp 1.21 1.35 1.49 V SCP/SOFT Voltage (When soft start ends)
Source Current Isoscp -3.2 -2.3 -1.4 μA SCP/SOFT=1.8V

【Under Voltage Lockout (UVLO)】

Threshold Voltage Vuvlo 4.0 4.15 4.30 V Vcc sweep down

Hysteresis Voltage DVuvlo 0.05 0.1 0.15 V

* This product is not designed for the protection against radioactive rays.
* Measurement of dead time

Turn ON Turn OFF

OUTH

OUTL

2.5V

tdtON

VCC-2.5V

VCC-2.5V

OUTH

2.5V

OUTL

tdtOFF

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3/16

2009.05 - Rev.A

BD9853AFV

●Characteristic Data

100

90

80

70

60

50

ONDUTY[%]

40

30

20

10

0

1.31.41.51.61.71.81.92.02.12.22.32.42.52.6

OUTL

OUTH

FB VOLTAGE:VFB[V]

Fig.1 FB VOLTAGE VS ON DUTY

0

-1

-2

-3

-4

-5

-6

-7

-8

-9

-10

-11

-12

-13

-14

FB SOURCE CURRENT[mA]

-15

-16

-17

-18

-19

-20
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4

OUTL SINK CURRENT:IOUT[mA]

Fig.4 FB SOURCE CURRENT

1000

950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100

50

0

0.00.20.40.60.81.01.21.41.61.82.02.22.42.62.83.03.23.43.63.84.0

Fig.7 OUTL SINK CURRENT

FB VOLTAGE[V]

VCC=12V,18V

VCC=4.5V

(OU TL-GN D) VO LTAGE [V]

180
160
140
120
100

80
60
40
20

0

-20

-40

-60

-80

GAIN[dB]、PHASE[deg]

-100

-120

-140

-160

-180

0.01 0.1 1 10 100 1000 10000 100000

Phase

Gain

FREQUENCY[KHz]

Fig.2 ERROR AMP OPEN LOOP

1000

950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150

OUTH SINK CURRENT:IOUT[mA]

100

50

0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0

VCC=12V,18V

4

VCC=4.5V

(REGB-OUTH) VOLTAGE[V]

Fig.5 OUTH SINK CURRENT

1000

950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100

OUTL SOURCE CURRENT:IOUT[mA]

50

0

0.0 0.2 0.4 0.6 0.8 1. 0 1.2 1.4 1.6 1. 8 2.0 2.2 2.4 2.6 2.8 3. 0 3.2 3.4 3. 6 3.8 4.0

VCC=12V,18V

VCC=4.5V

(REGA-OUTL) VOLTAGE[V]

Fig.8 OUTL SOURCE CURRENT

Technical Note

20
19
18
17
16
15
14
13
12
11
10

9
8
7
6
5

FB SINK CURRENT[mA]

4
3
2
1
0

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

Fig.3 FB SINK CURRENT

1000

950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100

50

OUTH SOURCE CURRENT:IOUT[mA]

0

0.00.20.40.60.81.01.21.41.61.82.02.22.42.62.83.03.23.43.63.84.0

Fig.6 OUTH SOURCE CURRENT

FB VOLTAGE[V]

VCC=12V,18V

VCC=4.5V

(VCC-OUTH) VOLTAGE:[V]

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4/16

2009.05 - Rev.A

BD9853AFV

●Block Diagram

VOUT1

VCC

VCC

FB1

REGA

REGB

both channel

ON/OFF

5V

VCC-5V

Technical Note

STB

REGA

VCC

REGB

SCP/SOFT1

VOUT2

SCP/SOFT2

INV1

FB2

INV2

RT

SOFT1

0.8V

(Push-Pull)

SOFT2

0.8V

(Push-Pull)

OSC

Timer
Latch

0.56V

TSD

⊿ ｔ

⊿ ｔ

VREF

REGA

REGA

GND

REGB

GND

REGB

VCC

VCC

OUT1H

OUT1L

OUT2H

OUT2L

GND

VCC

Pch

VOUT1

Nch

VCC

Pch

VOUT2

Nch

Fig. 9

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5/16

2009.05 - Rev.A

BD9853AFV

●Pin Configuration

Fig. 10

●Pin Description

Pin Number Pin Name Pin Descriptions

Technical Note

1 VCC Input Supply Voltage

2 OUT1H High Side (Main) FET Driver Output Pin (CH1)

3 OUT1L Low Side (Synchronous) FET Driver Output Pin (CH1)

4 REGA Internal Regulator Output Pin (5V Output, 1uF Ceramic Capacitor necessary)

5 RT Oscillator Frequency Adjustment Pin with external Resistor

6 FB1 Error Amplifier Output Pin (CH1)

7 INV1 Error Amplifer Negative Input Pin (CH1)
8 SCP/SOFT1 Short Circuit Protection・Soft Start Delay Time Setting Pin with External Capacitor (CH1)
9 SCP/SOFT2 Short Circuit Protection・Soft Start Delay Time Setting Pin with External Capacitor (CH2)

10 INV2 Error Amplifer Negative Input Pin (CH2)

11 FB2 Error Amplifier Output Pin (CH2)

12 GND Ground Pin

13 STB ON/OFF Control Pin

14 OUT2L Low Side (Synchronous) FET Driver Output Pin (CH2)

15 OUT2H High Side (Main) FET Driver Output Pin (CH2)

16 REGB Internal Regulator Output Pin (VCC-5V Output, 1uF Ceramic Capacitor necessary)

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6/16

2009.05 - Rev.A

BD9853AFV

●Block functional descriptions
・Triangular wave oscillator

Connecting the resistor that sets the triangular wave oscillation frequency at the RT terminal generates the triangular wave,
which is input into the CH1 and CH2 PWM comparator.

・Error amp

The INV pin detects the output voltage, compares it to the programmed output voltage and amplifies the difference for
output by the FB pin. (The 0.8V reference is the comparison voltage. The tolerance is 1.25%.)

・PWM comparator

The PWM comparator converts the error amp (FB) voltage into a pulse width modulated waveform that goes to the FET
driver and turns FET output ON.

・FET driver

The push-pull FET driver directly drives the external MOSFET,providing high-side(OUT1H,OUT2H) switching at voltages
between Vcc⇔REGB, and low-side switching in the 0⇔REGA voltage range. (REGA = 5V; REGB= VCC -5V internal power)

・Standby function

The standby function enables output ON/OFF control by the STB pin. Output is ON when STB voltage is HIGH.
With the STB pin set HIGH, the output ON/OFF for each channel can be independently controlled by one of the
SCP/SOFT1, 2 pins.

・Soft Start/Short Circuit Protection (SCP)

Connecting the external capacitor on the SCP/SOFT1, 2 pins sets the SCP delay time and soft start time.
When STB is HIGH and the IC starts up, the capacitors on the SCP/SOFT1, 2 pins charge up at 2uA, stabilizing when the
system reaches 1.3V.
If load conditions change rapidly, causing the output voltage in either channel to fall to 70% or less of the set output voltage
(INV voltage 0.56 or lower), the SCP/SOFT1, 2 external capacitors will charge further until output for both channels
switches OFF at 2.3V.

・Under Voltage Lockout (UVLO)

Under Voltage lockout prevents IC malfunctions that could otherwise occur due to intermittent or fluctuating power supply
voltage, or insufficient voltage during start-up.When the VCC voltage falls to 4.1V or below, both channel outputs are
turned OFF, while the SCP/SOFT1, 2 pins are simultaneously set LOW.
The UVLO detection voltage includes 0.1V hysteresis width to prevent malfunctions from input voltage fluctuations.

・Thermal Shutdown (TSD)

The TSD circuit protects the IC against thermal runaway and heat damage.

・The TSD thermal sensor detects junction temperature. When the temperature reaches the TSD threshold (175℃), the

circuit switches the output of both channels OFF, and also switches REGA and REGB OFF. At the same time, it sets the
SCP/SOFT1, 2 pins LOW. The hysteresis width (15℃) provided between the TSD function start temperature (threshold)
and the stop temperature serves to prevent malfunctions from temperature fluctuations.

Technical Note

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7/16

2009.05 - Rev.A

BD9853AFV

●Timing Chart

STB

STB ON

Technical Note

STB OFF

Vo1(solid line)

INV1

(dotted line)

SCP/SOFT1

Vo2

(solid line)

INV2

(dotted line)

SCP/SOFT2

0.3V

0.3V

0.8V

1.3V

0.8V

1.3V

Output OFF at

SCP/SOFT<0.3V

External GND short

(independent control)

Sort removed

SCP protection OFF

Output short

2.3V

End SCP delay

Fig. 11

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8/16

2009.05 - Rev.A

BD9853AFV

●Application component selection and settings

Determining output voltage

Output voltage is determined by dividing the resistance of the

external resistors.
VOUT＝0.8V×(1 + R2/R1)

determining the oscillation frequency

The oscillation pin is set by the resistor connected to the RT terminal (5 PIN).

10.000

INV

⑦　⑩

Technical Note

OUT

V

R2

R1

1.000

RT

⑤

0.100

0.010

Oscillating Frequency(MHz)

0.001
1 10 100 1000

Timing Resistance(kΩ)

RRT

Selecting the external MOSFET

In the BD9853AFV design, the main side (OUT1H, OUT2H) is provided with an external PCH FET, while an NCH FET is
used on the synchronous rectification side (OUT1L, OUT 2L) .

FET selection should be made in conformance with the following relative configurations for maximum drain voltage (VDSS),
maximum gate source voltage (VGS), maximum output current, on-resistance RDS (ON) and gate capacitance (Ciss) loss:

・Maximum drain voltage (VDSS) is higher than the IC’s maximum input voltage (VIN).
・Maximum gate source voltage is higher than the IC gate driving voltage (REGA, VCC-REGB).
・Maximum output current is higher than the combined maximum load current and coil ripple current (⊿I

).

L

・The sum of on-resistance RDS (ON) and gate capacitance (Ciss) conduction loss, together with the switching loss,

must not exceed the power dissipation (pd) for the package.

FET conduction loss Phigh and Plow are defined as follows:

Phigh=Iout
Plow=Iout

2

×RDS(ON)×VOUT/VIN (PMOS conduction loss)

2

×RDS(ON)×(1-VOUT/VIN) (NMOS conduction loss)

Iout：output load current, RDS(ON) : FET ON resistance value, VIN : input voltage, Vout : output voltage

FET switching loss PSW is calculated as follows:

PSW=VIN/2×(tr + tf)×fosc×Iout
VIN : input voltage, tr : drain waveform rise time, tf : drain waveform fall time, fosc : oscillation frequency, lout : load current
In addition to the criteria for selecting individual MOSFET components, consideration must also be given to the
combination of the PMOS (main side) and NMOS (synchronous side) to be used. The configuration must not generate
any through current with PMOS and NMOS both ON at the same time. In order to meet this condition, the following
formula must be satisfied, where PCH, NCH MOSFET turn-on delay time is represented as tdON, MOSFET turn-off delay
time is tdOFF, and dead time is tdt.

tdt > tdON - tdOFF
The tdt turn-on is (OUTH,OUTL：H→L)70ns typ. Turn-off is OUTH,OUTL：L→H)70ns typ. Be sure to confirm that the
process delay time does not pose problem in terms of the overall MOSFET delay.
The following MOSFETs meet all of the selection criteria outlined above, and are recommended for use. Both are
manufactured by ROHM.

PCH: RSS040PO3 NCH: RSS065P03

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2009.05 - Rev.A

yp)

BD9853AFV

Technical Note

Selecting the synchronous diode

An extremely low forward voltage Schottky barrier diode should be employed as the synchronous diode.

Selection of the specific diode to be used should be made in conformance with the following relative configurations for
maximum forward current, reverse voltage and diode power dissipation.

・The maximum current rating is higher than the combined maximum load current and coil ripple current (⊿I
・The reverse voltage rating is higher than the VIN value.
・Power dissipation for the selected diode must be within the rated level.

Synchronous diode power dissipation (Pdi) is expressed in the following formula:

Pdi=Iout(MAX)×tdt×fosc×Vf

Iout(MAX) : maximum load current, tdt： dead time 60ns typ,fosc : oscillation frequency, Vf：forward voltage

Selecting the output/input coil

The output coil and the output capacitor together form a second-order smoothing filter for the switch waveform and provide
the DC output voltage.
If a coil’s inductor value is low, its physical size is minimized, but the penalty is higher ripple current, with lowered efficiency
and an increase in output noise. Conversely, a higher inductor value increases the size of the coil, but lowers the ripple
current and, consequently. the output ripple current.
Generally speaking, ripple current should be between 20% and 50% of output load current. The following equation is used
to calculate the inductor value that corresponds to the ripple current value being employed.

(V

L=

L：inductor value, V
fosc：oscillation frequency, I

IN－VOUT)

⊿I

L

：maximum input voltage, V

IN

V

OUT

××

V

IN

：output load current

OUT

f

OSC

OUT

1

=(0.2 to 0.5)×I

⊿I

L

,

OUT

：output voltage, ⊿IL：coil ripple current value

Note that the current rating for the coil should be higher than I

Selecting the input capacitor

The input capacitor is the source of current that flows to the coil via the FET whenever the high side MOSFET is ON. In
selecting an input capacitor, sufficient margin must be provided to accommodate capacitor pressure and the permissible
ripple current.
The expression below defines the effective value of the ripple current to the input capacitor. It should be used in
determining the suitability of the capacitor in providing sufficient margin for the permissible ripple current.

I
I

I

RMS＝IOUT

: effective value of the ripple current to the input capacitor

RMS

: output load current

OUT

×√

(1－V

OUT/VIN

)×V

OUT/VIN

Selecting the output capacitor

The output capacitor should confine ESR and permissible ripple current within a stable region.
Although incorporating a low-ESR capacitor will limit ripple voltage and load fluctuation, it can also hurt the stability of the
feedback network. Therefore, in order to maintain a stable feedback loop when ceramic or other low-ESR capacitors are
employed, special attention must be paid to providing an appropriate phase compensation scheme.
A suitable output capacitor will satisfy the following formula for ESR.

ESR≦⊿V

⊿V

/⊿IL

L

: permissible ripple voltage, ⊿IL : coil ripple current

L

In addition, use the following formula to determine the effective value of the output capacitance permissible ripple current,
and select a capacitor that allows sufficient margin to accommodate this value.

=⊿IL/2√3

I

RMS

: effective value of ripple current to the output condenser, ⊿IL : coil ripple current

I

RMS

Setting the soft start time

To prevent output voltage startup overshoot on either channel, the capacitors connected to the SCP/SOFT 1, 2 pins – in a
discharged state at power-on – are gradually charged during a delay interval, thus providing a soft start. The soft start
period is the time from when the standby pins go from LOW to HIGH, starting the charge, to the time that the output
voltage reaches the programmed setting. The soft start time is calculated in the following equation:

tsoft＝

0.8[V] (t

×Cscp/soft［F］

Isosoft (typ: 2.3μA)[A]

tsoft : soft start time, Cscp/soft : SCP/SOFT pin connection capacitance, Isosoft : charge current

(MAX)＋⊿IL.

OUT

).

L

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10/16

2009.05 - Rev.A

BD9853AFV

Technical Note

Setting the Short Circuit Protection (SCP) delay time

When the soft start is complete for each channel, the output voltage stabilizes at the set value 1.35V(typ) for the
SCP/SOFT1, 2 pins.
When any type of short circuit occurs, the voltage at the point of the fault is reduced. In this case, when voltage at the INV
pin falls to 0.56V(typ) or below, the SCP comparator sensor detects the short and further charges the SCP/SOFT pins for
the shorted channel from the 1.35V(typ) level. When the SCP/SOFT pins are charged to 2.3V(typ), the Pch/Nch MOSFET
is switched OFF.
The elapsed time from the occurrence of the output short to the point the external FET switches OFF is calculated with the
following formula:

tscp

0.95[V](typ)×Cscp/soft［F］

＝

Isosofc (typ: 2.3μA)[A]

tscp : SCP delay time, Cscp/soft : SCP/SOFT pin connection capacitance,Isoscp : charge current

* If the current more than the capacity of power supply when the short between VOUT and GND occurs, input voltage starts to fall and under voltage lockout

(UVLO) is activated at Vin < 4.15 V (typ.). The UVLO has FET driver output (OUT1H, OUT2H, OUT1L, OUT2L) off and external FETs become off. When
external FETs are not operating, input voltage returns because of the short between VOUT and GND and the UVLO is canceled. But input voltage starts to
fall again because the UVLO is not activated.
There is possibility that a series of behavior “output short → input voltage fall → UVLO activated → external FETs off → input voltage returns → UVLO
canceled → output short”. So please make provision like inserting FUSE in input line.

Pin conditions with the only single channel use

Pin conditions are shown in the following, when the only single channel out of 2 channels is used.

Use only CH1 Use only CH2

・SCP/SOFT2, INV2 ⇒ GND short ・SCP/SOFT1, INV1 ⇒ GND short
・FB2, OUT2H, OUT2L ⇒ OPEN ・FB1, OUT1H, OUT1L ⇒ OPEN

●Application example

VCC

VCC

VCC

VCC

OUT1H

OUT1L

REGA

RT

FB1

INV1

SCP/SOFT1

1μF

REGB

OUT2H

OUT2L

STB

GND

FB2

INV2

SCP/SOFT2

4.7μF

16

15

14

13

12

11

220pF

10

9

3.3kΩ

RSS040P03

(ROHM)

VCC

RSS065

(ROHM)

NO3

4.7μH

C6-K3L

(MITSUMI)

RB081

L-20

(ROHM)

10μF

(ceramic）

10kΩ

120pF

VOUT1

(3.3V)

22kΩ

100kΩ

39kΩ

10μF

(ceramic）

4.7μF

4.7μH

C6-K3L

(MITSUMI)

RB081

L-20

(ROHM)

0.1μF

1μF

8.2kΩ

680pF

1

2

3

4

5

6

7

8

RSS040P03

(ROHM)

10kΩ

RSS065

NO3

(ROHM)

0.015μF 0.015μF

100kΩ

47kΩ

VOUT2

(2.5V)

15kΩ

68pF

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© 2009 ROHM Co., Ltd. All rights reserved.

11/ 16

2009.05 - Rev.A

BD9853AFV

Technical Note

●I/O Equivalent Circuit

OUT1H(2),OUT2H(15) OUT1L(3),OUT2L(14) REGA(4)
Max ratings：7V(from VCC or REGB) Max ratings：7V Max ratings：7V

VCC

VCCREGA

VCC

REGA

REGB

OUT1H
OUT2H

OUT1L
OUT2L

RT(5) FB1(6),FB2(11) INV1(7),INV2(10)
Max ratings：7V Max ratings：7V Max ratings：10V

REGA

REGA

VCC

VCC

VCC

INV1
INV2

RT

SCP/SOFT1(8),SCP/SOFT2(9) STB(13) REGB(16)
Max ratings：7V Max ratings：18V Max ratings：7V(fromVCC)

VREF

REGA

VCC

SCP/SOFT1
SCP/SOFT2

STB

VCC

VCC

REGB

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© 2009 ROHM Co., Ltd. All rights reserved.

12/16

2009.05 - Rev.A

BD9853AFV

Technical Note

●Recommended Board Patterns

P

MOS

V

OUT

C

IN

N

MOS

SBD

C

OUT

GND(IC)

INV

GND(others)

There are two current loops at the behavior of switching regulator. When laying a pattern on the board, put these elements
near to minimize these current loops and make the lines as short and wide as possible. And connect all GND lines at one
point to reduce effects caused by above current noise to other lines.

a pattern example of switching part

OUT

C

L

SBD

MOS

MOS

N

P

IN

C

Place following parts with attention about patterns

VCC REGB

CREGB

GND

CVCC

1

REGB

16VCC

GND

CREGA

RRT

2

3

4

REGA

5

RT

6

7

8

15

14

13

12

11

10

9

・Place CVCC, CREGA, RRT, CREGB as near to the pin as possible.
・Pattern area has to be small enough to reduce parasitic capacitance with RT terminal.

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© 2009 ROHM Co., Ltd. All rights reserved.

13/16

2009.05 - Rev.A

BD9853AFV

Technical Note

●Notes for use

1) Absolute maximum ratings
Use of the IC in excess of absolute maximum ratings such as the applied voltage or operating temperature range may
result in IC deterioration or damage. Assumptions should not be made regarding the state of the IC (short mode or open
mode) when such damage is suffered. A physical safety measure such as a fuse should be implemented when use of the
IC in a special mode where the absolute maximum ratings may be exceeded is anticipated.

2) GND potential
Ensure a minimum GND pin potential in all operating conditions. In addition, ensure that no pins other than the GND pin
carry a voltage lower than or equal to the GND pin, including during actual transient phenomena.

3) Thermal design
Use a thermal design that allows for a sufficient margin in light of the power dissipation (Pd) in actual operating conditions.

4) Inter-pin shorts and mounting errors
Use caution when orienting and positioning the IC for mounting on printed circuit boards. Improper mounting may result in
damage to the IC. Shorts between output pins or between output pins and the power supply and GND pin caused by the
presence of a foreign object may result in damage to the IC.

5) Operation in a strong electromagnetic field
Use caution when using the IC in the presence of a strong electromagnetic field as doing so may cause the IC to
malfunction.

6) Thermal shutdown circuit (TSD circuit)
This IC incorporates a built-in thermal shutdown circuit (TSD circuit). The TSD circuit is designed only to shut the IC off to
prevent runaway thermal operation. Do not continue to use the IC after operating this circuit or use the IC in an
environment where the operation of the thermal shutdown circuit is assumed.

7) Testing on application boards
When testing the IC on an application board, connecting a capacitor to a pin with low impedance subjects the IC to stress.
Always discharge capacitors after each process or step. Ground the IC during assembly steps as an antistatic measure,
and use similar caution when transporting or storing the IC. Always turn the IC's power supply off before connecting it to or
removing it from a jig or fixture during the inspection process.

8) Common impedance
Power supply and ground wiring should reflect consideration of the need to lower common impedance and minimize ripple
as much as possible
(by making wiring as short and thick as possible or rejecting ripple by incorporating inductance and capacitance).

9) Applications with modes that reverse VCC and pin potentials may cause damage to internal IC circuits.
For example, such damage might occur when VCC is shorted with the GND pin while an external capacitor is charged.
It is recommended to insert a diode for preventing back current flow in series with VCC or bypass diodes between VCC
and each pin.

Bypass diode

Back current prevention diode

VCC

Output Pin

10) Pin short and mistake fitting
Do not short-circuit between OUT pin and VCC pin, OUT pin and GND pin, or VCC pin and GND pin.
When soldering the IC on circuit board,
please be unusually cautious about the orientation and the position of the IC.

11) Timing resistor and capacitor
Timing resistor connected between RT and GND, has to be placed near RT terminal. And pattern has to be short enough.

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© 2009 ROHM Co., Ltd. All rights reserved.

14/16

2009.05 - Rev.A

BD9853AFV

Technical Note

12) IC pin input
This monolithic IC contains P+ isolation and PCB layers between adjacent elements in order to keep them isolated.
P/N junctions are formed at the intersection of these P layers with the N layers of other elements to create a variety of
parasitic elements. For example, when a resistor and transistor are connected to pins as shown in following chart,

 the P/N junction functions as a parasitic diode

when GND > (Pin A) for the resistor or GND > (Pin B) for the transistor (NPN).

 Similarly, when GND > (Pin B) for the transistor (NPN),

the parasitic diode described above combines with the N layer of other adjacent elements to operate as a parasitic

NPN transistor.
The formation of parasitic elements as a result of the relationships of the potentials of different pins is an inevitable result
of the IC's architecture. The operation of parasitic elements can cause interference with circuit operation as well as IC
malfunction and damage. For these reasons, it is necessary to use caution so that the IC is not used in a way that will
trigger the operation of parasitic elements, such as by the application of voltages lower than the GND (PCB) voltage to
input and output pins.

Resistance

＋

Ｐ

Ｎ

Parasitic diode

Ｐ

Ｎ

P substrate

ＧＮＤ

Transistor (NPN)

(PinB)(PinA)

＋

Ｐ

Ｎ

Parasitic elementals

Ｎ

Ｂ

Ｎ

Ｐ

Ｎ

P substrate

ＧＮＤ

Ｅ

ＧＮＤ

＋

Ｐ

Ｎ

Other adiacent components

Ｃ

＋

Ｐ

(PinA)

(PinB)

Parasitic diode

ＧＮＤ

Ｂ

ＧＮＤ

Ｃ

Ｅ

Parasitic diode

●Power Dissipation Reduction

1000

800

600

400

200

POWER DISSIPATION ： Pd(mW)

0

※IC mounted on a ROHM standard board
(70mm X 70mm X 1.6mm, glass epoxy)

0 25 50 75 100 125 150 175

AMBIENT TEMPERATURE：Ta (℃)

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© 2009 ROHM Co., Ltd. All rights reserved.

15/16

2009.05 - Rev.A

BD9853AFV

●Ordering part number

B D 9 8 5 3 A F V - E 2

Part No.

SSOP-B16

Part No.

5.0±0.2

16

4.4±0.2

6.4±0.3

1

1.15±0.1

0.10

0.65

9

0.3Min.

8

0.15±0.1

0.1

0.22±0.1

(Unit : mm)

Package

FV:

SSOP-B16

<Tape and Reel information>

Embossed carrier tapeTape

Quantity

Direction
of feed

2500pcs
E2

The direction is the 1pin of product is at the upper left when you hold

()

reel on the left hand and you pull out the tape on the right hand

Reel

Packaging and forming specification
E2: Embossed tape and reel

1pin

Order quantity needs to be multiple of the minimum quantity.

∗

Direction of feed

Technical Note

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© 2009 ROHM Co., Ltd. All rights reserved.

16/16

2009.05 - Rev.A

Notes

No copying or reproduction of this document, in part or in whole, is permitted without the
consent of ROHM Co.,Ltd.

The content specied herein is subject to change for improvement without notice.

The content specied herein is for the purpose of introducing ROHM's products (hereinafter
"Products"). If you wish to use any such Product, please be sure to refer to the specications,
which can be obtained from ROHM upon request.

Examples of application circuits, circuit constants and any other information contained herein
illustrate the standard usage and operations of the Products. The peripheral conditions must
be taken into account when designing circuits for mass production.

Great care was taken in ensuring the accuracy of the information specied in this document.
However, should you incur any damage arising from any inaccuracy or misprint of such
information, ROHM shall bear no responsibility for such damage.

The technical information specied herein is intended only to show the typical functions of and
examples of application circuits for the Products. ROHM does not grant you, explicitly or
implicitly, any license to use or exercise intellectual property or other rights held by ROHM and
other par ties. ROHM shall bear no responsibility whatsoever for any dispute arising from the
use of such technical information.

Notice

The Products specied in this document are intended to be used with general-use electronic
equipment or devices (such as audio visual equipment, ofce-automation equipment, commu­nication devices, electronic appliances and amusement devices).

The Products specied in this document are not designed to be radiation tolerant.

While ROHM always makes efforts to enhance the quality and reliability of its Products, a
Product may fail or malfunction for a variety of reasons.

Please be sure to implement in your equipment using the Products safety measures to guard
against the possibility of physical injury, re or any other damage caused in the event of the
failure of any Product, such as derating, redundancy, re control and fail-safe designs. ROHM
shall bear no responsibility whatsoever for your use of any Product outside of the prescribed
scope or not in accordance with the instruction manual.

The Products are not designed or manufactured to be used with any equipment, device or
system which requires an extremely high level of reliability the failure or malfunction of which
may result in a direct threat to human life or create a risk of human injury (such as a medical
instrument, transportation equipment, aerospace machinery, nuclear-reactor controller,
fuel-controller or other safety device). ROHM shall bear no responsibility in any way for use of
any of the Products for the above special purposes. If a Product is intended to be used for any
such special purpose, please contact a ROHM sales representative before purchasing.

If you intend to export or ship overseas any Product or technology specied herein that may
be controlled under the Foreign Exchange and the Foreign Trade Law, you will be required to
obtain a license or permit under the Law.

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Thank you for your accessing to ROHM product informations.
More detail product informations and catalogs are available, please contact us.

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A