RICOH R1224N Technical data

R1224N SERIES

PWM/VFM step-down DC/DC Controller

NO.EA-096-111123

OUTLINE

The R1224N Series are CMOS-based PWM step-down DC/DC Converter controllers with low supply current. Each of these ICs consists of an oscillator, a PWM control circuit, a reference voltage unit, an error amplifier, a phase compensation circuit, a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip enable circuit, resistors for output voltage detect, and input voltage detect circuit. A low ripple, high efficiency step-down DC/DC converter can be easily composed of this IC with only several external components, or a power-transistor, an inductor, a diode and capacitors. Output Voltage is fixed or can be adjusted with external resistors (Adjustable types are without PWM/VFM alternative circuit).

With a PWM/VFM alternative circuit, when the load current is small, the operation is automatically switching into the VFM oscillator from PWM oscillator. Therefore, the efficiency at small load current is improved. Several types of the R1224Nxxx, which are without a PWM/VFM alternative circuit, are also available.

If the term of maximum duty cycle keeps on a certain time, the embedded protection circuit works. The protection circuit is Reset-type protection circuit, and it works to restart the operation with soft-start and repeat this operation until maximum duty cycle condition is released. When the cause of large load current or something else is removed, the operation is automatically released and returns to normal operation. Further, built-in UVLO function works when the input voltage is equal or less than UVLO threshold, it makes this IC be standby and suppresses the consumption current and avoid an unstable operation.

FEATURES

• Supply Current ................................................................		Typ. 20μA (R1224Nxx2E/F/M/L, R1224N102M)
		Typ. 30μA (R1224Nxx2G, R1224N102G)
		Typ. 40μA (R1224Nxx2H, R1224N102H)
• Standby Current ..............................................................		Typ. 0μA
•	Input Voltage Range .......................................................	2.3V to 18.5V
•	Output Voltage Range.....................................................	1.2V to 6.0V (0.1V steps; R1224Nxx2x)
		1.0V to VIN (R1224N102x)
• Output Voltage Accuracy.................................................		±2.0%
•	Oscillator Frequency .......................................................	Typ. 180kHz (R1224Nxx2L/M, R1224N102M)
		Typ. 300kHz (R1224Nxx2E/G, R1224N102G)
		Typ. 500kHz (R1224Nxx2F/H, R1224N102H)
•	Efficiency.........................................................................	Typ. 90%
• Low Temperature-Drift Coefficient of Output Voltage......		Typ. ±100ppm/°C
•	Package ..........................................................................	SOT-23-5
•	Built-in Soft-start Function...............................................	Typ. 10ms
•	Built-in Current Limit Circuit

APPLICATIONS

•Power source for hand-held communication equipment, cameras, video instruments such as VCRs, camcorders.

•Power source for battery-powered equipment.

•Power source for household electrical appliances.

1

R1224N

BLOCK DIAGRAM

			Fixed Output Voltage Type
	VIN	5	OSC
			3	VOUT

EXT

4

	Amp	Vref
PWM/VFM		Soft Start
CONTROL
	Protection	Chip Enable	1	CE
	UVLO	Vref

2

GND

Adjustable Output Voltage Type

VIN 5

EXT 4

OSC

3 VFB

Amp	Vref
	Soft Start
Protection	Chip Enable	1	CE
UVLO	Vref

2

GND

2

R1224N

SELECTION GUIDE

The output voltage, the oscillator frequency, the modulation method and the output voltage adjustment for the ICs can be selected at the user’s request.

Product Name	Package	Quantity per Reel	Pb Free	Halogen Free
R1224Nxx2 -TR-FE	SOT-23-5	3,000 pcs	Yes	Yes

xx: The output voltage can be designated in the range from 1.2V(12) to 6.0V(60) in 0.1V steps. (For externally adjustable output voltage type, feedback voltage of 1.0V(10).)

: The oscillator frequency, the modulation method and the output voltage adjustment are options as follows.

	Code	Oscillator frequency	PWM/VFM	Output voltage
			alternative circuit	adjustment
	E	300kHz	Yes	No
	F	500kHz	Yes	No
	G	300kHz	No	Yes
	H	500kHz	No	Yes
	L	180kHz	Yes	No
	M	180kHz	No	Yes

PIN CONFIGURATION

• SOT-23-5

		5								4
					(mark side)
					1		2			3
PIN DESCRIPTION
Pin No	Symbol												Pin Description
1	CE	Chip Enable Pin ("H" Active)
2	GND	Ground Pin
3	VOUT (VFB)	Pin for Monitoring Output Voltage (Feedback Voltage)
4	EXT	External Transistor Drive Pin (CMOS Output)
5	VIN	Power Supply Pin

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R1224N

ABSOLUTE MAXIMUM RATINGS			GND=0V
Symbol	Item	Rating	Unit
VIN	VIN Supply Voltage	−0.3 to 20	V
VEXT	EXT Pin Output Voltage	−0.3 to VIN+0.3	V
VCE	CE Pin Input Voltage	−0.3 to VIN+0.3	V
VOUT/VFB	VOUT/VFB Pin Input Voltage	−0.3 to VIN+0.3	V
IEXT	EXT Pin Inductor Drive Output Current	± 50	mA
PD	Power Dissipation (SOT-23-5)	420	mW
Topt	Operating Temperature Range	−40 to 85	°C
Tstg	Storage Temperature Range	−55 to 125	°C

) For Power Dissipation, please 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.

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R1224N

ELECTRICAL CHARACTERISTICS

• R1224Nxx2x (x=E/F/G/H/L/M) except R1224N102x						Topt=25°C
	Symbol	Item	Conditions	Min.	Typ.	Max.	Unit
	VIN	Operating Input Voltage		2.3		18.5	V
	VOUT	Step-down Output Voltage	VIN=VCE=VSET+1.5V, IOUT=−100mA	VSET	VSET	VSET	V
			When VSET≤1.5V, VIN=VCE=3.0V	×0.98		×1.02
	VOUT/	Step-down Output Voltage	−40°C≤Topt≤85°C		±100		ppm/°C
	Topt	Temperature Coefficient
			VIN=VCE=VSET+1.5V, IOUT=−100mA
	fosc	Oscillator Frequency	L/M Version	144	180	216	kHz
			E/G Version
				240	300	360
			F/H Version
				400	500	600
	fosc/	Oscillator Frequency	−40°C≤Topt≤85°C		±0.2		%/°C
	Topt	Temperature Coefficient
			VIN=VCE=VOUT=18.5V		20	50
	IDD1	Supply Current 1	E/F/L/M Version				μA
			G version		30	60
			H version		40	80
	Istandby	Standby Current	VIN=18.5V, VCE=0V, VOUT=0V		0	0.5	μA
	IEXTH	EXT "H" Output Current	VIN=8V, VEXT=7.9V, VOUT=8V,		−17	−10	mA
			VCE=8V
	IEXTL	EXT "L" Output Current	VIN=8V, VEXT=0.1V, VOUT=0V,	20	30		mA
			VCE=8V
	ICEH	CE "H" Input Current	VIN=VCE=VOUT=18.5V		0	0.5	μA
	ICEL	CE "L" Input Current	VIN=VOUT=18.5V, VCE=0V	−0.5	0		μA
	VCEH	CE "H" Input Voltage	VIN=8V, IOUT=−10mA	1.5			V
	VCEL	CE "L" Input Voltage	VIN=8V, IOUT=−10mA			0.3	V
	Maxduty	Oscillator Maximum		100			%
		Duty Cycle
	VFMdty	VFM Duty Cycle	E/F/L Version		35		%
	VUVLO1	UVLO Voltage	VIN=VCE=2.5V to 1.5V, VOUT=0V	1.8	2.0	2.2	V
	VUVLO2	UVLO Release Voltage	VIN=VCE=1.5V to 2.5V, VOUT=0V		VUVLO1	2.3	V
					+0.1
	tstart	Delay Time by Soft-Start function	VIN=VSET+1.5V, IOUT=−10mA	5	10	20	ms
			VCE=0V→VSET+1.5V
	tprot	Delay Time for protection circuit	VIN=VCE=VSET+1.5V	5	15	30	ms
			VOUT=VSET+1.5V→0V
		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.

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R1224N

• R1224N102x (x=G/H/M)						Topt=25°C
	Symbol	Item	Conditions	Min.	Typ.	Max.	Unit
	VIN	Operating Input Voltage		2.3		18.5	V
	VFB	Feedback Voltage	VIN=VCE=3.0V, IOUT=−100mA	0.98	1.00	1.02	V
	VFB/	Feedback Voltage	−40°C≤Topt≤85°C		±100		ppm/°C
	Topt	Temperature Coefficient
			VIN=VCE=2.5V, IOUT=−100mA	144	180	216
	fosc	Oscillator Frequency	M Version				kHz
			G Version	240	300	360
			H Version	400	500	600
	fosc/	Oscillator Frequency	−40°C≤Topt≤85°C		±0.2		%/°C
	Topt	Temperature Coefficient
			VIN=VCE=VFB=18.5V		20	50
	IDD1	Supply Current 1	M Version				μA
			G Version		30	60
			H Version		40	80
	Istandby	Standby Current	VIN=18.5V, VCE=0V, VFB=0V		0	0.5	μA
	IEXTH	EXT "H" Output Current	VIN=8V, VEXT=7.9V, VFB=8V,		−17	−10	mA
			VCE=8V
	IEXTL	EXT "L" Output Current	VIN=8V, VEXT=0.1V, VFB=0V,	20	30		mA
			VCE=8V
	ICEH	CE "H" Input Current	VIN=VCE=VFB=18.5V		0	0.5	μA
	ICEL	CE "L" Input Current	VIN=VFB=18.5V, VCE=0V	−0.5	0		μA
	VCEH	CE "H" Input Voltage	VIN=8V, IOUT=−10mA	1.5			V
	VCEL	CE "L" Input Voltage	VIN=8V, IOUT=−10mA			0.3	V
	Maxduty	Oscillator Maximum Duty Cycle		100			%
	VUVLO1	UVLO Voltage	VIN=VCE=2.5V to 1.5V, VFB=0V	1.8	2.0	2.2	V
	VUVLO2	UVLO Release Voltage	VIN=VCE=1.5V to 2.5V, VFB=0V		VUVLO1	2.3	V
					+0.1
	tstart	Delay Time by Soft-Start function	VIN=2.5V, IOUT=−10mA	5	10	20	ms
			VCE=0V→2.5V
	tprot	Delay Time for protection circuit	VIN=VCE=2.5V	5	15	30	ms
			VFB=2.5V→0V
		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.

6

R1224N

TYPICAL APPLICATION AND APPLICATION HINTS

(1) Fixed Output Voltage Type (R1224Nxx2E/F/G/H/L/M except xx=10)

C1

R1

5	VIN
1	CE
C2

L

PMOS

4

EXT	VOUT	3
R1224N		C3
GND		SD
2		LOAD

			CE CONTROL		: CR105-270MC (Sumida, 27μH)
PMOS: HAT1044M (Hitachi)				L
SD1	: RB063L-30 (Rohm)			C3	: 47μF (Tantalum Type)
C1	: 10μF (Ceramic Type)			C2 : 0.1μF (Ceramic Type)
R1	: 10Ω

(2) Adjustable Output Type (R1224N102G/H/M) Example: Output Voltage=3.2V

				L
C1		PMOS		R4	C4
		4			R3
R1	VIN	EXT	VFB	3
5
1		R1224N			C3
	CE			SD
		GND			R2
C2		2			LOAD

			CE CONTROL		: CR105-270MC (Sumida, 27μH)
PMOS: HAT1044M (Hitachi)				L
SD1	: RB063L-30 (Rohm)			C3	: 47μF (Tantalum Type)
C1	: 10μF (Ceramic Type)			C2 : 0.1μF (Ceramic Type) C4: 1000pF (Ceramic Type)
R1	: 10Ω, R2=22kΩ, R3=2.7kΩ, R4=33kΩ

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R1224N

When you use these ICs, consider the following issues;

As shown in the block diagram, a parasitic diode is formed in each terminal, each of these diodes is not formed for load current, therefore do not use it in such a way. When you control the CE pin by another power supply, do not make its “H” level more than the voltage level of VIN pin.

Set external components as close as possible to the IC and minimize the connection between the components and the IC. In particular, a capacitor should be connected to VIN pin with the minimum connection. Make sufficient ground and reinforce supplying. A large switching current could flow through the connection of power supply, an inductor and the connection of VIN. If the impedance of the connection of power supply is high, the voltage level of power supply of the IC fluctuates with the switching current. This may cause unstable operation of the IC.

Protection circuit may work if the maximum duty cycle continue for the time defined in the electrical characteristics. Once after stopping the output voltage, output will restart with soft-start operation. If the difference between input voltage and output voltage is small, the protection circuit may work.

Use capacitors with a capacity of 22μF or more for VOUT pin, and with good high frequency characteristics such as tantalum capacitors. We recommend you to use output capacitors with an allowable voltage at least twice as much as setting output voltage. This is because there may be a case where a spike-shaped high voltage is generated by an inductor when an external transistor is on and off.

Choose an inductor that has sufficiently small D.C. resistance and large allowable current and is hard to reach magnetic saturation. And if the value of inductance of an inductor is extremely small, the ILX may exceed the absolute maximum rating at the maximum loading.

Use an inductor with appropriate inductance.

Use a diode of a Schottky type with high switching speed, and also pay attention to its current capacity.

Do not use this IC under the condition with VIN voltage at equal or less than minimum operating voltage.

When the threshold level of an external power MOSFET is rather low and the drive-ability of voltage supplier is small, if the output pin is short circuit, input voltage may be equal or less than UVLO detector threshold. In this case, the devise is reset with UVLO function that is different from the reset-protection function caused by maximum duty cycle.

With the PWM/VFM alternative circuit, when the on duty cycle of switching is 35% or less, the R1224N alters from PWM mode to VFM mode (Pulse skip mode). The purpose of this circuit is raising the efficiency with a light load by skipping the frequency and suppressing the consumption current. However, the ratio of output voltage against input voltage is 35% or less, (ex. VIN>8.6V and VOUT=3.0V) even if the large current may be loaded, the IC keeps its VFM mode. As a result, frequency might be decreased, and oscillation waveform might be unstable. These phenomena are the typical characteristics of the IC with PWM/VFM alternative circuit.

If the input voltage is equal or more than 6V, R1 and C2 in the typical application are necessary as a VIN filter to prevent unstable operation.

ÌThe performance of power source circuits using these ICs extremely depends upon the peripheral circuits. Pay attention in the selection of the peripheral circuits. In particular, design the peripheral circuits in a way that the values such as voltage, current, and power of each component, PCB patterns and the IC do not exceed their respected rated values.

8

R1224N

How to Adjust Output Voltage and about Phase Compensation

As for Adjustable Output type, feedback pin (VFB) voltage is controlled to maintain 1.0V. Output Voltage, VOUT is as following equation:

VOUT: R2+R4=VFB: R2

VOUT=VFB×(R2+R4)/R2

Thus, with changing the value of R2 and R4, output voltage can be set in the specified range.

In the DC/DC converter, with the load current and external components such as L and C, phase might be behind 180 degree. In this case, the phase margin of the system will be less and stability will be worse. To prevent this, phase margin should be secured with proceeding the phase. A pole is formed with external components L and C3.

Fpole ~1/2π L ×C3

A zero (signal back to zero) is formed with R4 and C4.

Fzero~1/(2π×R4×C4)

For example, if L=27μH, C3=47µF, the cut off frequency of the pole is approximately 4.5kHz. To make the cut off frequency of the pole as much as 4.5kHz, set R4=33kΩ and C4=1000pF. If VOUT is set at 2.5V, R2=22kΩ is appropriate.

R3 prevents feedback of the noise to VFB pin, about 2.7kΩ is appropriate value.

				L
C1		PMOS		R4	C4
		4			R3
R1	VIN	EXT	VFB	3
5
1		R1224N			C3
	CE			SD
		GND			R2
C2		2			LOAD
	CE CONTROL

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R1224N

OPERATION of step-down DC/DC converter and Output Current

The step-down DC/DC converter charges energy in the inductor when Lx transistor is ON, and discharges the energy from the inductor when Lx transistor is OFF and controls with less energy loss, so that a lower output voltage than the input voltage is obtained. The operation will be explained with reference to the following diagrams:

	<Basic Circuits>			<Current through L>
			i1	IL	ILmax
			IOUT
VIN	Lx Tr	L	VOUT	ILmin	topen
	SD	i2
			CL
GND				ton	toff
					T=1/fosc

Step 1: Lx Tr. turns on and current IL (=i1) flows, and energy is charged into CL. At this moment, IL increases from ILmin. (=0) to reach ILmax. in proportion to the on-time period (ton) of Lx Tr.

Step 2: When Lx Tr. turns off, Schottky diode (SD) turns on in order that L maintains IL at ILmax, and current IL (=i2) flows.

Step 3: IL decreases gradually and reaches ILmin. after a time period of topen, and SD turns off, provided that in the continuous mode, next cycle starts before IL becomes to 0 because toff time is not enough. In this case, IL value is from this ILmin (>0).

In the case of PWM control system, the output voltage is maintained by controlling the on-time period (ton), with the oscillator frequency (fosc) being maintained constant.

Discontinuous Conduction Mode and Continuous Conduction Mode

The maximum value (ILmax) and the minimum value (ILmin) current which flow through the inductor is the same as those when Lx Tr. is ON and when it is OFF.

The difference between ILmax and ILmin, which is represented by	I;
I=ILmax-ILmin=VOUT×topen/L=(VIN-VOUT)×ton/L ...................................	Equation 1

wherein, T=1/fosc=ton+toff

duty (%)=ton/T×100=ton×fosc×100

topen < toff

=

In Equation 1, VOUT×topen/L and (VIN-VOUT)×ton/L are respectively shown the change of the current at ON, and the change of the current at OFF.

When the output current (IOUT) is relatively small, topen<toff as illustrated in the above diagram. In this case, the energy is charged in the inductor during the time period of ton and is discharged in its entirely during the time period of toff, therefore ILmin becomes to zero (ILmin=0). When Iout is gradually increased, eventually, topen becomes to toff (topen=toff), and when IOUT is further increased, ILmin becomes larger than zero (ILmin>0). The former mode is referred to as the discontinuous mode and the latter mode is referred to as continuous mode.

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R1224N

In the continuous mode, when Equation 1 is solved for ton and assumed that the solution is tonc,

tonc=T×VOUT/VIN.....................................................................................

Equation 2

When ton<tonc, the mode is the discontinuous mode, and when ton=tonc, the mode is the continuous mode.

OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENTS

When Lx Tr. is ON:

(Wherein, Ripple Current P-P value is described as IRP, ON resistance of Lx Tr. is described as Rp the direct current of the inductor is described as RL.)

VIN=VOUT+(Rp+RL)×IOUT+L×IRP/ton .................................................	Equation 3
When Lx Tr. is OFF:
L×IRP/toff=VF+VOUT+RL×IOUT ............................................................	Equation 4
Put Equation 4 to Equation 3 and solve for ON duty, ton/(toff+ton)=DON,
DON=(VOUT+VF+RL×IOUT)/(VIN+VF−Rp×IOUT) ......................................	Equation 5
Ripple Current is as follows;
IRP=(VIN−VOUT−Rp×IOUT−RL×IOUT)×DON/f/L........................................	Equation 6
Wherein, peak current that flows through L, Lx Tr., and SD is as follows;
ILmax=IOUT+IRP/2............................................................................	Equation 7

Consider ILmax, condition of input and output and select external components.

Ì The above explanation is directed to the calculation in an ideal case in continuous mode.

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R1224N

External Components

1.Inductor

Select an inductor that peak current does not exceed ILmax. If larger current than allowable current flows, magnetic saturation occurs and make transform efficiency worse.

When the load current is definite, the smaller value of L, the larger the ripple current.

Provided that the allowable current is large in that case and DC current is small, therefore, for large output current, efficiency is better than using an inductor with a large value of L and vice versa.

2.Diode

Use a diode with low VF (Schottky type is recommended.) and high switching speed.

Reverse voltage rating should be more than VIN and current rating should be equal or more than ILmax.

3.Capacitors

As for CIN, use a capacitor with low ESR (Equivalent Series Resistance) and a capacity of at least 10µF for stable operation.

COUT can reduce ripple of Output Voltage, therefore 47µF or more value of tantalum type capacitor is recommended.

4.Lx Transistor

Pch Power MOSFET is required for this IC.

Its breakdown voltage between gate and source should be a few V higher than Input Voltage.

In the case of Input Voltage is low, to turn on MOSFET completely, to use a MOSFET with low threshold voltage is effective.

If a large load current is necessary for your application and important, choose a MOSFET with low ON resistance for good efficiency.

If a small load current is mainly necessary for your application, choose a MOSFET with low gate capacity for good efficiency.

Maximum continuous drain current of MOSFET should be larger than peak current, ILmax.

12