Linear Technology LTC1148CS-5, LTC1148CS-3.3, LTC1148CS, LTC1148CN-5, LTC1148CN-3.3 Datasheet

LTC1148

LTC1148-3.3/LTC1148-5

High Efficiency Synchronous

Step-Down Switching Regulators

FEATURES

■Ultrahigh Efficiency: Over 95% Possible

■Current-Mode Operation for Excellent Line and Load Transient Response

■High Efficiency Maintained Over Three Decades of Output Current

■Low 160μA Standby Current at Light Loads

■Logic Controlled Micropower Shutdown: IQ < 20μA

■Wide VIN Range: 3.5V* to 20V

■Short-Circuit Protection

■Very Low Dropout Operation: 100% Duty Cycle

■Synchronous FET Switching for High Efficiency

■Adaptive Nonoverlap Gate Drives

■Output Can Be Externally Held High in Shutdown

■Available in 14-Pin Narrow SO Package

APPLICATIOUS

■Notebook and Palmtop Computers

■Portable Instruments

■Battery-Operated Digital Devices

■Cellular Telephones

■DC Power Distribution Systems

■GPS Systems

DESCRIPTIOU

The LTC®1148 series is a family of synchronous stepdown switching regulator controllers featuring automatic Burst ModeTM operation to maintain high efficiencies at low output currents. These devices drive external complementary power MOSFETs at switching frequencies up to 250kHz using a constant off-time current-mode architecture providing constant ripple current in the inductor.

The operating current level is user-programmable via an external current sense resistor. Wide input supply range allows operation from 3.5V* to 18V (20V maximum). Constant off-time architecture provides low dropout regu-

lation limited by only the RDS(ON) of the external MOSFET and resistance of the inductor and current sense resistor.

The LTC1148 series combines synchronous switching for maximum efficiency at high currents with an automatic low currentoperatingmode,calledBurstModeoperation,which reduces switching losses. Standby power is reduced to only

2mW at VIN = 10V (at IOUT = 0). Load currents in Burst Mode operation are typically 0mA to 300mA.

For operation up to 48V input, see the LTC1149 and LTC1159 data sheets and Application Note 54.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a trademark of Linear Technology Corporation. * LTC1148L and LTC1148L-3.3 only.

TYPICAL APPLICATIOU

VIN (5.2V TO 18V)

+

1μF

+

CIN

VIN

100μF

P-DRIVE

P-CHANNEL

L*

RSENSE**

Si4431DY

0V = NORMAL

LTC1148HV-5

62μH

0.05Ω

VOUT

SHUTDOWN

>1.5V = SHUTDOWN

5V/2A

SENSE+

		ITH	SENSE–	1000pF	+
RC		CT				COUT
				N-CHANNEL
			N-DRIVE		D1
1k	CT			Si4412DY	MBRS140T3	390μF
		SGND	PGND
CC	470pF
3300pF						LT1148 • TA01
					*COILTRONICS CTX62-2-MP
					**KRL SL-1-C1-0R050J

Figure 1. High Efficiency Step-Down Converter

			LTC1148-5 Efficiency
	100
									VIN = 6V
	95
(%)									V	IN		= 10V
EFFICIENCY	90
	85
	80
			0.2																			2
	0.02

LOAD CURRENT (A)

LTC1148 • TA01

1

LTC1148 LTC1148-3.3/LTC1148-5

ABSOLUTE WAXIWUW RATIUGS

(Note 1)

Input Supply Voltage (Pin 3)
LTC1148 and LTC1148L Series	............	16V to – 0.3V
LTC1148HV Series ...............................		20V to – 0.3V
Continuous Output Current (Pins 1, ..............14)		50mA
Sense Voltages (Pins 7, 8)
LTC1148HV (Adjustable Only)
VIN ³ 12.7V ......................................		13V to – 0.3V
VIN < 12.7V .........................	(V IN + 0.3V) to – 0.3V
Operating Ambient Temperature Range ......		0°C to 70°C
Extended Commercial		– 40°C to 85°C
Temperature Range ...............................
Junction Temperature (Note 2) ............................		125°C
Storage Temperature Range ................		– 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................		300°C

PACKAGE/ORDER IUFORWATIOU

							ORDER PART
							NUMBER
				TOP VIEW
							LTC1148CN
	P-DRIVE	1			14	N-DRIVE	LTC1148HVCN
	NC	2			13	NC	LTC1148CN-3.3
	VIN	3			12	PGND
							LTC1148HVCN-3.3
	CT	4			11	SGND
							LTC1148CN-5
	INTVCC	5			10	SHUTDOWN
							LTC1148HVCN-5
	ITH	6			9	VFB*
							LTC1148CS
	SENSE–	7			8	SENSE+
							LTC1148HVCS
	N PACKAGE			S PACKAGE
							LTC1148LCS
	14-LEAD PDIP			14-LEAD PLASTIC SO
	*FIXED OUTPUT VERSIONS = NC						LTC1148CS-3.3
	TJMAX = 125°C, θJA = 70°C/ W (N)						LTC1148HVCS-3.3
	TJMAX = 125°C, θJA = 110°C/ W (S)						LTC1148LCS-3.3
							LTC1148CS-5
							LTC1148HVCS-5

Consult factory for Industrial and Military grade parts.

ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 10V, VSHUTDOWN = 0V unless otherwise noted.

SYMBOL	PARAMETER	CONDITIONS		MIN	TYP	MAX	UNITS
V9	Feedback Voltage (LTC1148, LTC1148L,	VIN = 9V	●	1.21	1.25	1.29	V
	LTC1148HV)
I9	Feedback Current (LTC1148, LTC1148L,		●		0.2	1	μA
	LTC1148HV)
VOUT	Regulated Output Voltage	VIN = 9V
	LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3	ILOAD = 700mA	●	3.23	3.33	3.43	V
	LTC1148-5, LTC1148HV-5	ILOAD = 700mA	●	4.90	5.05	5.20	V
VOUT	Output Voltage Line Regulation	VIN = 7V to 12V, ILOAD = 50mA		– 40	0	40	mV
	Output Voltage Load Regulation	5mA < ILOAD < 2A			40	65	mV
	LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3		●
	LTC1148-5, LTC1148HV-5	5mA < ILOAD < 2A	●		60	100	mV
	Output Ripple (Burst Mode)	ILOAD = 0A			50		mVP-P
IQ	Input DC Supply Current (Note 3)	(Note 7)
	LTC1148 Series	4V < VIN < 12V			1.6	2.1	mA
	Normal Mode
	Sleep Mode	4V < VIN < 12V			160	230	μA
	Sleep Mode (LTC1148-5)	6V < VIN < 12V			160	230	μA
	Shutdown	VSHUTDOWN = 2.1V, 4V < VIN < 12V			10	20	μA
	LTC1148HV Series	4V < VIN < 18V			1.6	2.3	mA
	Normal Mode
	Sleep Mode	4V < VIN < 18V			160	250	μA
	Sleep Mode (LTC1148HV-5)	6V < VIN < 18V			160	250	μA
	Shutdown	VSHUTDOWN = 2.1V, 4V < VIN < 18V			10	22	μA
	LTC1148L Series	3.5V < VIN < 12V			1.6	2.1	mA
	Normal Mode
	Sleep Mode	3.5V < VIN < 12V			160	230	μA
	Shutdown	VSHUTDOWN = 2.1V, 3.5V < VIN < 12V			10	20	μA

2

LTC1148

LTC1148-3.3/LTC1148-5

ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 10V, VSHUTDOWN = 0V, unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

V8 – V7

Current Sense Threshold Voltage

– = 5V, V

= V

/4 + 25mV (Forced)

25

mV

LTC1148, LTC1148HV, LTC1148L

V

SENSE

9

OUT

V

– = 5V, V

= V

/4 – 25mV (Forced)

●

130

150

170

mV

SENSE

9

OUT

LTC1148-3.3, LTC1148HV-3.3

V

– = V + 100mV (Forced)

25

mV

SENSE

OUT

LTC1148L-3.3

V

– = V – 100mV (Forced)

●

130

150

170

mV

SENSE

OUT

LTC1148-5, LTC1148HV-5

V

– = V + 100mV (Forced)

25

mV

SENSE

OUT

V

– = V – 100mV (Forced)

●

130

150

170

mV

SENSE

OUT

V10

Shutdown Pin Threshold

0.5

0.8

2

V

I10

Shutdown Pin Input Current

0V < VSHUTDOWN < 8V, VIN = 16V

1.2

5

μA

I

4

C Pin Discharge Current

V in Regulation, V

SENSE

– = V

OUT

50

70

90

μA

T

OUT

μA

VOUT = 0V

2

10

tOFF

Off Time (Note 5)

CT = 390pF, ILOAD = 700mA

4

5

6

μs

tR, tF

Driver Output Transition Times

CL = 3000pF (Pins 1, 14), VIN = 6V

100

200

ns

–40°C ≤ TA ≤ 85°C (Note 5), VIN = 10V, unless otherwise noted.

SYMBOL	PARAMETER	CONDITIONS					MIN	TYP	MAX	UNITS
V9	Feedback Voltage (LTC1148, LTC1148HV	VIN = 9V					1.20	1.25	1.30	V
	LTC1148L)
VOUT	Regulated Output Voltage	VIN = 9V
	LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3	ILOAD = 700mA					3.17	3.33	3.43	V
	LTC1148-5, LTC1148HV-5	ILOAD = 700mA					4.85	5.05	5.20	V
IQ	Input DC Supply Current (Note 3)	(Note 7)
	LTC1148 Series	4V < VIN < 12V						1.6	2.4	mA
	Normal Mode
	Sleep Mode	4V < VIN < 12V						160	260	μA
	Sleep Mode	6V < VIN < 12V						160	260	μA
	Shutdown	VSHUTDOWN = 2.1V, 4V < VIN < 12V						10	22	μA
	LTC1148HV Series	4V < VIN < 18V						1.6	2.6	mA
	Normal Mode
	Sleep Mode	4V < VIN < 18V						160	280	μA
	Sleep Mode	6V < VIN < 18V						160	280	μA
	Shutdown	VSHUTDOWN = 2.1V, 4V < VIN < 18V						10	24	μA
	LTC1148L Series	3.5V < VIN < 12V						1.6	2.4	mA
	Normal Mode
	Sleep Mode	3.5V < VIN < 12V						160	260	μA
	Shutdown	VSHUTDOWN = 2.1V, 3.5V < VIN < 12V						10	22	μA
V8 – V7	Current Sense Threshold Voltage		–	= 5V, V	= V /4 – 25mV (Forced)			25		mV
	LTC1148, LTC1148HV, LTC1148L (Note 4)	V
		SENSE	–	9	OUT
		V		= 5V, V	= V /4 + 25mV (Forced)		125	150	175	mV
		SENSE		9	OUT
	LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3	V	–	= V + 100mV (Forced)				25		mV
		SENSE	–	OUT
		V		= V – 100mV (Forced)			125	150	175	mV
		SENSE		OUT
	LTC1148-5, LTC1148HV-5	V	–	= V + 100mV (Forced)				25		mV
		SENSE	–	OUT
		V		= V – 100mV (Forced)			125	150	175	mV
		SENSE		OUT
V10	Shutdown Pin Threshold						0.55	0.8	2	V
tOFF	Off Time (Note 5)	CT = 390pF, ILOAD = 700mA					3.8	5	6	μs

3

LTC1148 LTC1148-3.3/LTC1148-5

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range.

Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.

Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formulas:

LTC1148CN, LTC1148CN-3.3, LTC1148CN-5: TJ = TA + (PD × 70°C/W) LTC1148CS, LTC1148CS-3.3, LTC1148CS-5: TJ = TA + (PD × 110°C/W)

Note 3: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. See Applications Information.

Note 4: The LTC1148 and LTC1148HV versions are tested with external feedback resistors resulting in a nominal output voltage of 5V. The LTC1148L version is tested with external feedback resistors resulting in a nominal output voltage of 2.5V.

Note 5: In applications where RSENSE is placed at ground potential, the off time increases approximately 40%.

Note 6: The LTC1148, LTC1148HV and LTC1148L series are not tested and not quality assurance sampled at –40°C and 85°C. These specifications are guaranteed by design and/or correlation.

Note 7: The LTC1148L and LTC1148L-3.3 allow operation to VIN = 3.5V.

TYPICAL PERFORWAUCE CHARACTERISTICS

Efficiency vs Input Voltage

	100
									FIGURE 1 CIRCUIT
	98
	96
										ILOAD = 1A
	94
(%)
	92
EFFICIENCY
	90				ILOAD =			100mA
	88
	86
	84
	82
	80
			4							16				20
	0				8			12

INPUT VOLTAGE (V)

LTC1148 • TPC01

DC Supply Current

	2.1
			NOT INCLUDING
	1.8		GATE CHARGE CURRENT
(mA)
	1.5
				ACTIVE MODE
CURRENT	1.2
SUPPLY	0.9
	0.6
	0.3
				SLEEP MODE

0

0

2

4

6

8

10

12

14

16

18

20

INPUT VOLTAGE

LTC1148 • TPC04

Line Regulation

Load Regulation

	40	FIGURE 1 CIRCUIT						20			FIGURE 1 CIRCUIT
	30	ILOAD = 1A						0			RSENSE = 0.05Ω
	20
(mV)	10						(mV)	–20		VIN = 6V
	0							–40
OUT							OUT
V	–10						V			VIN = 12V
								–60
	–20
	–30							–80
	–40		8	12			–100
	0	4			16	20		0	0.5	1	1.5	2	2.5
			INPUT VOLTAGE (V)							LOAD CURRENT (A)
					LTC1148 • TPC02							LTC1148 • TPC03

	Operating Frequency
Supply Current in Shutdown	vs (VIN – VOUT)

	20	VSHUTDOWN = 2V											1.6	VOUT = 5V
	18
													1.4
	16																0°C
												FREQUENCYNORMALIZED
A)(CURRENTSUPPLYμ													0.4
	14												1.2
																	70°C
	12												1.0
																	25°C
	10												0.8
	8												0.6
	6
	4
	2												0.2
	0	2	4	6	8	10	12	14	16	18	20		0	2	4	6	8	10	12
	0												0
				INPUT VOLTAGE (V)											(VIN – VOUT) VOLTAGE (V)
									LTC1148 • TPC05								LTC1148 • TPC06

4

LTC1148 LTC1148-3.3/LTC1148-5

TYPICAL PERFORWAUCE CHARACTERISTICS

Gate Charge Supply Current Off Time vs VOUT

	28						80			VSENSE	– = VOUT
(mA)	24						70
	20						60
CURRENTCHARGE		QN + QP = 100nC
						s)(TIMEOFFμ
							50
	16
	12						40
							30
GATE	8		QN	+ QP = 50nC			20
	4						10			LTC1148-5
	0						0	LTC1148-3.3
		80	140	200	260			1	2	3	4	5
	20						0
		OPERATING FREQUENCY (kHz)							OUTPUT VOLTAGE (V)
					LTC1148 • TPC07					LTC1148 • TPC08

Current Sense Threshold Voltage

	175
											MAXIMUM
(mV)	150									THRESHOLD
	125
VOLTAGE
	100
SENSE	75
	50
					MINIMUM
	25				THRESHOLD
	0
												80
	0		20		40					60					100

TEMPERATURE (°C)

LTC1148 • TPC09

PIU FUUCTIOUS

P-DRIVE (Pin 1): High Current Drive for Top P-Channel MOSFET. Voltage swing at this pin is from VIN to ground.

NC (Pin 2): No Connection. Can connect to power ground.

VIN (Pin 3): Main Supply Pin. Must be closely decoupled to power ground Pin 12.

CT (Pin 4): External capacitor CT from Pin 4 to ground sets the operating frequency. The actual frequency is also dependent upon the input voltage.

INTVCC (Pin 5): Internal Supply Voltage, Nominally 3.3V. Can be decoupled to signal ground. Do not externally load this pin.

ITH (Pin 6): Gain Amplifier Decoupling Point. The current comparator threshold increases with the Pin 6 voltage.

SENSE– (Pin 7): Connects to internal resistive divider which sets the output voltage in LTC1148-3.3 and LTC1148-5 versions. Pin 7 is also the (–) input for the current comparator.

SENSE+ (Pin 8): The (+) Input to the Current Comparator. A built-in offset between Pins 7 and 8 in conjunction with RSENSE sets the current trip threshold.

VFB (Pin 9): For the LTC1148 adjustable version, Pin 9 serves as the feedback pin from an external resistive divider used to set the output voltage. On LTC1148-3.3 and LTC1148-5 versions this pin is not used.

SHUTDOWN (Pin 10): When grounded, the LTC1148 series operates normally. Pulling Pin 10 high holds both MOSFETs off and puts the LTC1148 series in micropower shutdown mode. Requires CMOS logic signal with tR, tF < 1μs, should not be left floating.

SGND (Pin 11): Small-Signal Ground. Must be routed separately from other grounds to the (–) terminal of COUT.

PGND (Pin 12): Driver Power Ground. Connects to source of N-channel MOSFET and the (–) terminal of CIN.

NC (Pin 13): No Connection. Can connect to power ground.

N-DRIVE (Pin 14): High Current Drive for Bottom N-Channel MOSFET. Voltage swing at Pin 14 is from ground to VIN.

5

LTC1148

LTC1148-3.3/LTC1148-5

FUUCTIOUAL DIAGRAW Pin 9 connection shown for LTC1148-3.3 and LTC1148-5; changes create LTC1148.

SGND

11

SLEEP

+ S –

				3	VIN
				1	P-DRIVE				SENSE+		SENSE–
									8		7
									ADJUSTABLE
										VERSION
				14	N-DRIVE					VFB
											9
				12	PGND			–
							V
								+
		R			–	25mV TO 150mV
					C
		Q				–	+
		S			+						5pF
									VOS
VTH2	VTH1	–
							13k	–
		T
					ITH	6
							G
		+
								+	1.25V		100k
		OFF-TIME	VIN	–
	4	CONTROL	SENSE				SHUTDOWN 10	REFERENCE		5	INTVCC
	CT		VFB
											LTC1148 • FD

TEST CIRCUIT

+

+

VIN

IRF9Z34

1N5818

330μF

IRFZ34

1

P-DRIVE

N-DRIVE

14

1μF

2

NC

NC

13

50μH

+

LTC1148

3

12

VIN

PGND

4

CT

SGND

11

V10

5

10

INTVCC

SHUTDOWN

+

25k

100pF

6

ITH

NC (VFB)

9

440μF

390pF

10nF

3300pF

7

8

SENSE

–

SENSE+

+

+

+

V7

RSENSE

75k

1k

V7

1000pF

0.05

Ω

TO

V8

VOUT

6