RP9 0 1 K SERI ES

Synchronous Step-down DC/DC Converter with VD and VR

NO.EA-156-121225

OUTLINE

The RP901xxxx is a CMOS-based current mode PWM control synchronous step-down DC/DC converter with a voltage detector (VD) and an LDO regulator (VR).

Each of Step-down DC/DC converters is composed of an oscillator, a voltage reference unit, an error amplifier, a switching control circuit, a soft-start circuit, a protection circuit, a UVLO circuit, a switching transistor. Due to the switching elements are built in and synchronous control, a high efficiency step-down DC/DC converter can be made with an inductor and capacitors. To realize high efficiency at light load, automatic PWM/VFM alternative mode can be selected other than the PWM fixed control mode.

As protection circuits, a current limit circuit which limits Lx peak current cycle by cycle and a hiccup mode protection circuit which works if the load current over the limit continues for a certain time

*1 are built in. The output voltage can be preset with 0.05V step in the factory due to the built-in feed back resistance, and the tolerance is

±2%. Since the package is DFN (PLP) 2527-10, high density mounting on board is possible.

Built-in LDO regulator (VR) is composed of a voltage reference unit, a voltage detecting resistor-network, an error amplifier, a short current limit circuit, and a driver transistor. After the soft-start time of the DC/DC converter is over and a specified delay time, LDO starts up. The sequence function is fixed internally

*2

.

Built-in voltage detector (VD) supervises the input voltage or the output of the VR (The reset function works for

UVLO and over-current of the DC/DC converter). The option is preset in the factory. The output type is N-channel open drain. The released delay time is built-in, typ.50ms.

If the junction temperature of the IC is over the limit, the system is reset by the built-in thermal shut-down circuit.

*1) A version: As soon as the load current is over the limit, the system restarts by the protection.

*2) C, D versions: No sequence function

FEATURES

• Input Voltage Range ················································· 4.5V to 5.5V

• Supply Current·························································· Typ. 460µA (at PWM mode)

Typ. 170µA (at light load applied to B, C, D versions)

Step-down DC/DC Converter

• Output Voltage Range ·············································· 1.2V to 1.8V, preset is possible by user’s request

• Output Voltage Tolerance ········································· ±2%

• Oscillator Frequency················································· Typ. 1.2MHz

• Built-in driver ON resistance····································· Typ. P-channel 0.25 , N-channel 0.25 (at V

IN

=5V)

• Soft-start function······················································ Typ. 1ms

• Lx peak current limit function···································· Typ. 1.4A (D version: 1.5A)

• Output Current·························································· Min. 800mA (D version: 900mA)

• Protection Delay Time ·············································· Typ. 0.1ms (applied to B, C, D versions)

• UVLO function ·························································· Typ. 3.5V

• Chip enable function················································· ”H” active

Ver. 1.0

1

RP901K

LDO Regulator

• Output Voltage Range ·············································· 2.5V to 3.3V, preset is possible by user’s request

• Output Voltage Tolerance ········································· ±1.0%

• Output Current ·························································· Min. 600mA

• Start-up delay time···················································· Typ. 2ms (applied to A, B versions)

• Auto-Discharge function at turning off ······················ Discharge resistance Typ.50 (at V

IN

=5V)

VD

• Voltage Detector Threshold Range ·························· 2.0V to 3.0V, preset is possible by user’s request

(A version: VR output voltage is supervised),

3.0V to 5.0V, preset is possible by user’s request

(B, C, D versions: Input voltage is supervised

• Released Delay Time················································ Typ.50ms

• Thermal shutdown circuit·········································· Detecting Temperature: Typ. 165°C,

Released temperature: Typ. 110

°C

• Package···································································· DFN(PLP)2527-10

• External Components ··············································· C

IN

=10.0µF, C

OUT1

=10.0µF, L=4.7µH (DC/DC),

C

OUT2

=2.2µF(VR)

APPLICATION

• Optical Disk Equipment

Ver. 2.5

2

BLOCK DIAGRAMS

A version

PVDD

CE

CHIP

ENABLE

VREF

SOFT

START

RAMP

COMPENSATION

OSCILLATOR

PWM

AVDD

VREF

V

OUT2

CURRENT

PROTECTION

VREF

CURRENT

FEEDBACK

CURRENT

PROTECTION

SWITCHING

CONTROL

UVLO

CE

DELAY CIRCUIT

B/C/D version

PVDD

CE

CHIP

ENABLE

VREF

SOFT

START

RAMP

COMPENSATION

CURRENT

FEEDBACK

OSCILLATOR

CURRENT

PROTECTION

PWM VFM

SWITCHING

CONTROL

UVLO

AVDD

VREF

DELAY CIRCUIT

VREF

V

OUT2

CURRENT

PROTECTION

CE

L

X

V

OUT1

PGND

AGND

V

DOUT

L

X

V

OUT1

PGND

AGND

V

DOUT

RP901K

Ver. 2.5

2

RP901K

SELECTION GUIDE

In the RP901 series, the output voltage combination and function can be designated.

The selection can be made by the alphanumeric serial number as the next example.

Product Code Package Units/ 1 reel

RP901Kxxx

∗-TR

DFN(PLP)2527-10 5,000pcs

Pb free

Yes

Halogen free

Yes xxx: Serial number to describe the voltage combination of DC/DC converter, voltage regulator, and voltage detector.

∗: Function version

A version: DC/DC control type is PWM-fixed, without protection delay time, output current Min.

800mA, VR has start-up delay time to make a sequence. VD supervises the output of VR (Reset is output at UVLO and over current of DC/DC)

B version: DC/DC control type is PWM/VFM automatic mode shift, with protection delay time, output current Min. 800mA, VR has start-up delay time to make a sequence. VD supervises the input voltage.

C version: DC/DC control type is PWM/VFM automatic mode shift, with protection delay time, output current Min. 800mA, VR: without delay time to make a sequence, VD supervises the input voltage.

D version: DC/DC control type is PWM/VFM automatic mode shift, with protection delay time, output current Min. 900mA, VR: without delay time to make a sequence, VD supervises the input voltage.

PIN CONFIGURATION

DFN(PLP)2527-10

10

9

Mark Side

8 7 6

Bottom Side

6 7 8 9 10

1

2 3 4 5

5

4 3 2 1

Steam via

Ver. 2.5

2

RP901K

PIN DESCRIPTIONS

Pin No. Symbol

1 CE

2 V

DOUT

3 AGND

4 PGND

5 L

X

6 PVDD

Chip Enable Pin (”H” active)

Description

VD Output Pin (N-channel open drain output)

Analog Ground Pin

Power Ground Pin

DC/DC Switching Pin

Power Supply Input Pin

8 V

OUT1

9 AVDD

10 V

OUT2

DC/DC Output Pin

Analog Power Supply Input Pin

VR Output Pin

The backside of the package tab is connected to the substrate of the IC (GND). Connect to GND pin

(Recommendation), or solder the tab and left open electrically.

Make short 3pin and 4pin, and make short 6pin and 9pin.

ABSOLUTE MAXIMUM RATINGS

Rating

(GND=0V)

Unit Symbol Item

V

V

IN

CE

PVDD Pin Voltage

AVDD Pin Voltage

CE Pin Voltage

6.5 V

-0.3 to 6.5 V

V

LX

V

OUT1

V

L

X

OUT

Pin Voltage

1 Pin Voltage

-0.3 to V

-0.3 to V

IN

IN

+ 0.3

+ 0.3

V

V

V

V

OUT2

DOUT

Tstg

V

V

OUT

2 Pin Voltage

DOUT

Pin Voltage

P

D

Power

(1)

Dissipation*

(2)

Ta

Operating

Temperature

Storage Temperature

-0.3 to V

IN

+ 0.3

-0.3 to 6.5

1750 (Ta=25

1138 (Ta=25

°C, Tjmax=150°C)

°C, Tjmax=150°C)

-40 to +85

-55 to +125

V

V mW

°C

°C

*

For more information about Power Dissipation and Standard Land Pattern, refer to

PACKAGE INFORMATION

.

ABSOLUTE MAXIMUM RATINGS

Electronic and mechanical stress momentarily exceeded absolute maximum ratings may cause the permanent damages and may degrade the life time and safety for both device and system using the device in the field. The functional operation at or over these absolute maximum ratings is not assured.

RECOMMENDED OPERATING CONDITIONS (ELECTRICAL CHARACTERISTICS)

All of electronic equipment should be designed that the mounted semiconductor devices operate within the recommended operating conditions. The semiconductor devices cannot operate normally over the recommended operating conditions, even if when they are used over such conditions by momentary electronic noise or surge. And the semiconductor devices may receive serious damage when they continue to operate over the recommended operating conditions.

Ver. 2.5

2

RP901K

ELECTRICAL CHARACTERISTICS

Unless otherwise specified, the measurement is done by an open loop circuit. Unless otherwise specified, V

IN

=V

CE

=5V,

AGND=PGND=0V.

RP901xxx

Symbol Parameter Conditions Min. Max.

Unit

V

IN

4.5 5.5 V

I

I

SS1

SS2

Operating Input Voltage

Supply Current 1

Supply Current 2

(applied to B/C/D version)

V

IN

=V

CE

=5.5V

V

OUT

1=V

SET

x 0.8

V

IN

=V

CE

=5.5V

V

OUT

1=V

SET

x 1.2

V

IN

=5.5V

V

CE

=0V

A version

B/C/D version

460

170

1.0

2.0

5.0

μA

μA

μA

V

CEH

CE Input Voltage ”H”

V

CEL

CE Input Voltage ”L”

T

T

TSD

TSR

Thermal Shutdown

Detector Temperature

Thermal Shutdown

Release Temperature

Junction Temperature

Junction Temperature

1.0

165

110

0.3

V

V

°C

°C

DC/DC SECTION

(Ta=25

°C)

Symbol Parameter Conditions Min. Max.

Unit

I

V

OUT1

Output Voltage 1

ΔV

OUT1

/

ΔTa

Output Voltage 1

Temperature Coefficient

V

IN

-40

°C ≤ Ta ≤ 85°C

±150 ppm/

°C fosc Oscillator V

IN

=5V -20%

LXLEAKH

L

X

leakage Current “H”

I

LXLEAKL

L

X

leakage Current “L”

R

R

ONP

ONN

P-channel transistor

ON resistance

N-channel transistor

ON resistance

Maxduty Maximum Duty Cycle

V

IN

=V

LX

=5.5V, V

CE

V

IN

=5.5V, V

CE

=V

LX

V

V

IN

IN

=5V, I

=5V, I

LX

LX

100 %

I

LXLIM

L

X

Current Limit

V

IN

=V

CE

=5V

A/B/C version

V

IN

=V

CE

=5V

D version

1.0 ms

1.0

1.1

1.4

1.5

A

IN

=V

CE

=5V

0.0 ms

V

UVLO1

V

IN

=V

CE

3.40 3.50 3.60

V

V

UVLO2

Voltage V

IN

=V

CE

3.63 3.73 3.83

V

All test items listed under

ELECTRICAL CHARACTERISTICS

are done under the pulse load condition (Tj

≈Ta=25ºC) except Thermal Shutdown.

Ver. 2.5

2

RP901K

VR SECTION

(Ta=25

°C)

Symbol Parameter Conditions Min. Max.

Unit

I

V

OUT2

LIM2

Output Voltage 2

Current Limit 2

I

SS3

Supply Current 3

ΔV

OUT2

/

ΔI

OUT2

ΔV

OUT2

/

ΔTa

Load Regulation

Output Voltage 2

Temperature Coefficient

I

SC

Short Current Limit

T

VR

(A/B version)

Start-up Timing Delay

T

VR

(C/D Version)

Start-up Delay

R

LOW

For auto discharge at off, N-channel Tr.

ON resistance

V

IN

=5V, I

OUT

=1mA -1.0% V

V

IN

=V

CE

=5.5V

600 mA

60

μA

1mA

-40

V

V

≤ 400mA

°C ≤ Ta ≤ 85°C

OUT2

IN

≤ I

OUT2

=0V

Start from the finish moment of soft start-time of DC/DC converter

Start from UVLO release moment of DC/DC converter

=5V, V

CE

=0V

40 80

±50 mV

Ppm

/

°C

70 mA

2.0 ms

50

μs

50

VD SECTION

(Ta=25

°C)

Symbol Parameter Conditions Min. Max.

Unit

-V

V

DET

Δ-V

DET

/

ΔTa

HYS

VD Detector Threshold

Temperature Coefficient

-40

°C ≤ Ta ≤ 85°C

-2.0% +2.0% V

±40 ppm

/

°C

-V

DET x 0.05

V

50 ms T

PLH

VD Release Delay Time

I

DOUTL

V

DOUT

”L” Output Current V

IN

=2.0V , V

DOUT

All test items listed under

ELECTRICAL CHARACTERISTICS

are done under the pulse load condition (Tj

≈Ta=25ºC) except Thermal Shutdown.

Ver. 2.5

2

TYPICAL APPLICATION AND TECHNICAL NOTES

RP901K

External Components Recommendation

Inductor L1: 4.7

μH (A/B/C Version VLF4014AT-4R7M1R1 TDK

4.7

μH (D Version VLF4014ST-4R7M1R4 TDK

Pull-up Resistance R1: 50k

Capacitors C1: 10

μF Ceramic capacitor (C2012JB0J106K TDK)

C2: 2.2

μF Ceramic capacitor

C3: 10

μF Ceramic capacitor (C2012JB0J106K TDK)

TECHNICAL NOTES ON EXTERNAL COMPONENTS

Place all the external components as close as possible to the IC and make the wiring length as short as possible. Especially, the capacitor between V

IN and GND must be as close as possible to the IC. If the impedance of the power supply and ground is high, the power level of the IC may shift by the switching current and the operation may unstable. Make the power line and the ground line sufficient. Through the power line, the ground line, inductor, L

X

pin, V

OUT line, large current may flow by switching, therefore fully consideration is necessary. The wiring between V

OUT

pin and the inductor, and load and V

OUT

pin must be separated.

PVDD and AVDD must be short and make them close as possible. Place a capacitor as close as possible to

PVDD. If the distance between AVDD and PVDD is long, add another 0.1

μF capacitor between AVDD and

GND.

Capacitance value between VDD and GND should be 10

μF or more and use a low ESR ceramic capacitor.

Use a ceramic capacitor for V

V

OUT2

OUT1

pin, and the capacitor should be 10

μF or more. Use a ceramic capacitor for

pin, and the ceramic capacitor should be 2.2

μF or more.

Choose an inductor with low DCR, and enough permissible current and which is hard to reach magnetic saturation. If the inductance value is too small, at the maximum load, the current flows through Lx transistor and inductor may be beyond the absolute maximum rating. Choose an appropriate inductance value.

If the spike noise of Lx pin is large, place a snubber circuit between Lx and GND (CR serial connection, etc.) to reduce the spike noise. Time constants of CR depend on the actual PCB and decide with the evaluation of the

PCB.

º The performance of the power circuit with the IC depends on the peripheral circuits. In terms of the external components, PCB pattern, and IC, the peripheral circuit should be designed not to exceed beyond ratings

(voltage, current, power).

Ver. 2.5

3

RP901K

STEP-DOWN DC/DC CONVERTERS’ OPERATION AND OUTPUT CURRENT

This explanation is about the general step-down DC/DC converters’ operation.

In the step-down DC/DC converter, when the Lx transistor turns on, at the same time, energy is accumulated into an inductor and when the transistor turns off, the current accumulated in the inductor is released and averaged, then make the energy loss reduced and the output voltage lower than the input voltage is supplied.

Basic Circuit Current flows L

IL

ILmax i1

V

IN

Pch Tr

L

V

OUT

ILmin topen i1 i2

Nch Tr i2

CL

GND ton toff

T 1/fosc

Step1. P-channel transistor turns on, current IL=i1, energy is charged into L, CL is charged and the output current I

OUT is supplied. While the P-channel transistor turns on (t

ON

), and in proportion to IL=i1 is from

IL=ILmin=0 increases and reaches to ILmax.

Step2. P-channel transistor turns off, L keeps IL=ILmax, and turns on the N-channel transistor, current IL=i2 flows.

Step3. IL=i2 decreases gradually, after t

OPEN,

IL=ILmin=0 and N-channel transistor turns off.

However, if the cycle is continuous mode, before IL=ILmin=0, t

OFF time becomes nothing, the next cycle starts and the P-channel transistor turns on, and the N-channel transistor turns off. In this case, ILmin

>0 and charge is remained, and charge is increased from IL=ILmin >0.

In the PWM control, the number of switching in a second (f

OSC

) is fixed, and t

ON is controlled and the output voltage is constantly maintained.

The step-down operation is constant and stable, the current flows through the inductor’s maximum value (ILmax) and the minimum value (ILmin) is same as when the P-channel transistor turns on and off as described above.

Supposed that the difference between ILmax and ILmin is

ΔI,

∆I = ILmax – ILmin = V

OUT

x t

OPEN

/ L = (VIN – VOUT) x t

ON

/ L ···································· Formula 1

Thus,

T = 1 / f

OSC

= t

ON

+ t

OFF duty (%) = t

ON

/ T x 100 = t

ON

x f

OSC

x 100 t

OPEN t

OFF

The left side of the equation describes the current level at turning on, and the right side of the equation describes the current level at turning off.

Ver. 2.5

4

RP901K

OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENS

In the general step-down DC/DC converters, the relation between the output current and external components is described as below:

(Supposed that the peak to peak value of the ripple current is “ I

RP

“, On resistance of the L

X transistor, P-channel transistor, N-channel transistor is respectively described as “R

ONP

“ and “R

ONN

“, inductor’s DCR is described as

“ R

L

“)

Supposed that the time when L

X

P-channel transistor turns on is described as “ t

ON

“,

V

IN

= V

OUT

+ (R

ONP

+ R

L

) x I

OUT

+ L x I

RP

/ t

ON

································································ Formula 1

Supposed that the time when L

X

P-channel transistor turns off (N-channel transistor turns on) is described as

“ t

OFF

“,

L x I

RP

/ t

OFF

= (R

ONN

+ R

L

) x I

OUT

+ V

OUT

······································································ Formula 2

Using Formula 1 and Formula 2, and On duty of the P-channel transistor, t

ON

/(t

ON

+ t

OFF

)= D

ON

is solved,

D

ON

=(V

OUT

+ R

ONN

x I

OUT

+ R

L

x I

OUT

) / (V

IN

– R

ONP

x I

OUT

+ R

ONN

x I

OUT

) ···················· Formula 3

Ripple current is

I

RP

= (V

IN

– V

OUT

– R

ONP

x I

OUT

– R

L

x I

OUT

) x D

ON

/ f

OSC

/ L············································ Formula 4

Then the peak current through the inductor and L

X transistor,

ILmax = I

OUT

+ I

RP

/ 2 ····································································································· Formula 5

Decide the peripheral circuits with considering ILmax and input and output conditions.

º The calculation is based on the ideal operation of the PWM continuous mode.

Ver. 2.5

2