Linear Technology LTC1159IS-5, LTC1159IS-3.3, LTC1159IS, LTC1159CS-5, LTC1159CS-3.3 Datasheet

LTC1159

LTC1159-3.3/LTC1159-5

High Efficiency Synchronous

Step-Down Switching Regulators

FEATURES

■Operation from 4V to 40V Input Voltage

■Ultrahigh Efficiency: Up to 95%

■20 A Supply Current in Shutdown

■High Efficiency Maintained Over Wide Current Range

■Current Mode Operation for Excellent Line and Load Transient Response

■Very Low Dropout Operation: 100% Duty Cycle

■Short-Circuit Protection

■Synchronous FET Switching for High Efficiency

■Adaptive Non-Overlap Gate Drives

■Available in SSOP and SO Packages

APPLICATIOUS

■Step-Down and Inverting Regulators

■Notebook and Palmtop Computers

■Portable Instruments

■Battery-Operated Digital Devices

■Industrial Power Distribution

■Avionics Systems

■Telecom Power Supplies

DESCRIPTIOU

The LTC®1159 series is a family of synchronous step-down switching regulator controllers featuring automatic Burst ModeTM operation to maintain high efficiencies at low output currents. These devices drive external complementarypowerMOSFETsatswitchingfrequenciesupto250kHz using a constant off-time current-mode architecture.

A separate pin and on-board switch allow the MOSFET driver power to be derived from the regulated output voltage providing significant efficiency improvement when operating at high input voltages. The constant off-time current-mode architecture maintains constant ripple current in the inductor and provides excellent line and load transient response. The output current level is user programmable via an external current sense resistor.

The LTC1159 automatically switches to power saving Burst Mode operation when load current drops below approximately 15% of maximum current. Standby current is only 300 A while still regulating the output and shutdown current is a low 20 A.

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

Burst Mode is a trademark of Linear Technology Corporation.

TYPICAL APPLICATIOU

VIN

		+	CIN
	VIN	1N4148	100µF
CAP	P-GATE	Si9435DY	100V
0.15µF

+		VCC		0.1µF

3.3µF		VCC	P-DRIVE
			EXTVCC
				D1	L*	RSENSE
				MBRS140T3
		LTC1159-5			33µH	1 0.05Ω 2	VOUT
			SENSE+		3	4	5V/2A
0V = NORMAL		SHDN1		0.01µF
>2V = SHUTDOWN		SHDN2	SENSE–
		ITH				+
3300pF							COUT
		CT	N-GATE		Si9410DY
	CT						220µF
1k		S-GND	P-GND
	300pF
				LTC1159 • F01	*COILTRONICS CTX33-4-MP

Figure 1. High Efficiency Step-Down Regulator

			LTC1159-5 Efficiency
	100
		FIGURE 1 CIRCUIT										VIN =		10V
(%)	90
												VIN =		20V
EFFICIENCY	80
	70
	60
			0.2																		2
	0.02

LOAD CURRENT (A)

LTC1159 • TA01

1

LTC1159 LTC1159-3.3/LTC1159-5

ABSOLUTE

WAXIWUW

RATI GS	(Note 1)
U

Input Supply Voltage (Pin 2) .....................	– 15V to 60V
VCC Output Current (Pin 3) ..................................	50mA
Continuous Pin Currents (Any Pin) ......................	50mA
Sense Voltages .........................................	– 0.3V to 13V
Shutdown Voltages ...................................................	7V
EXTVCC Input Voltage .............................................	15V
Junction Temperature (Note 2) ............................	125°C

Operating Temperature Range	0°C to 70°C
LTC1159C ..............................................
LTC1159I ...........................................	– 40°C to 85°C
Extended Commercial	– 40°C to 85°C
Temperature Range ...............................
Storage Temperature Range ................	– 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................	300°C

PACKAGE/ORDER IUFORWATIOU

TOP VIEW

P-GATE	1	20	CAP
VIN	2	19	SHDN2
VCC	3	18	EXTVCC
P-DRIVE	4	17	PGND
P-DRIVE	5	16	N-GATE
VCC	6	15	PGND
VCC	7	14	SGND
CT	8	13	SHDN1
ITH	9	12	VFB
SENSE–	10	11	SENSE+

G PACKAGE

20-LEAD PLASTIC SSOP

TJMAX = 125°C, θJA = 135°C/ W

ORDER PART

NUMBER

LTC1159CG LTC1159CG-3.3 LTC1159CG-5

TOP VIEW

P-GATE	1	16	CAP
VIN	2	15	SHDN2
VCC	3	14	EXTVCC
P-DRIVE	4	13	N-GATE
VCC	5	12	PGND
CT	6	11	SGND
ITH	7	10	VFB (SHDN1)*
SENSE–	8	9	SENSE+

N PACKAGE	S PACKAGE
16-LEAD PDIP	16-LEAD PLASTIC SO

*FIXED OUTPUT VERSIONS

TJMAX = 125°C, θJA = 80°C/ W (N)

TJMAX = 125°C, θJA = 110°C/ W (S)

ORDER PART

NUMBER

LTC1159CN LTC1159CN-3.3 LTC1159CN-5 LTC1159CS LTC1159CS-3.3 LTC1159CS-5 LTC1159IS LTC1159IS-3.3 LTC1159IS-5

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VSHDN1 = 0V (Note 3), unless otherwise noted.

SYMBOL	PARAMETER	CONDITIONS		MIN	TYP	MAX	UNITS
VFB	Feedback Voltage (LTC1159 Only)		●	1.21	1.25	1.29	V
IFB	Feedback Current (LTC1159 Only)		●		0.2		µA
VOUT	Regulated Output Voltage	VIN = 9V
	LTC1159-3.3	ILOAD = 700mA	●	3.23	3.33	3.43	V
	LTC1159-5	ILOAD = 700mA	●	4.90	5.05	5.20	V
VOUT	Output Voltage Line Regulation	VIN = 9V to 40V		– 40	0	40	mV
	Output Voltage Load Regulation	5mA < ILOAD < 2A			40	65	mV
	LTC1159-3.3		●
	LTC1159-5	5mA < ILOAD < 2A	●		60	100	mV
	Burst Mode Output Ripple	ILOAD = 0A			50		mVP-P
IIN	VIN Pin Current (Note 4)	VIN = 12V, EXTVCC = 5V			200		µA
	Normal Mode
		VIN = 40V, EXTVCC = 5V			300		µA
	Shutdown	VIN = 12V, VSHDN2 = 2V			15		µA
		VIN = 40V, VSHDN2 = 2V			25		µA
IEXTVCC	EXTVCC Pin Current (Note 4)	EXTVCC = 5V, Sleep Mode			250		µA

2

LTC1159

LTC1159-3.3/LTC1159-5

ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VSHDN1 = 0V (Note 3), unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

VCC

Internal Regulator Voltage

VIN = 12V to 40V, EXTVCC = 0V, ICC = 10mA

●

4.25

4.5

4.75

V

VIN – VCC

VCC Dropout Voltage

VIN = 4V, EXTVCC = Open, ICC = 10mA

300

400

mV

VEXT – VCC

EXTVCC Switch Drop

VIN = 12V, EXTVCC = 5V, ISWITCH = 10mA

250

350

mV

VP-GATE – VIN

P-Gate to Source Voltage (Off)

VIN = 12V

– 0.2

0

V

VIN = 40V

– 0.2

0

V

VSENSE+ –

Current Sense Threshold Voltage

V

= 5V, V

= 1.32V (Forced)

25

mV

V

SENSE

–

LTC1159

SENSE

–

FB

V

–

= 5V, V

= 1.15V (Forced)

130

150

170

mV

SENSE

FB

●

LTC1159-3.3

VSENSE– = 3.4V (Forced)

25

mV

VSENSE– = 3.1V (Forced)

●

130

150

170

mV

LTC1159-5

VSENSE– = 5.2V (Forced)

25

mV

VSENSE– = 4.7V (Forced)

●

130

150

170

mV

VSNDN1

SHDN1 Threshold

0.5

0.8

2

V

LTC1159CG, LTC1159-3.3, LTC1159-5

VSHDN2

SHDN2 Threshold

0.8

1.4

2

V

ISHDN2

Shutdown 2 Input Current

VSHDN2 = 5V

12

20

A

ICT

CT Pin Discharge Current

VOUT in Regulation

50

70

90

A

VOUT = 0V

2

10

A

tOFF

Off-Time (Note 5)

CT = 390pF, ILOAD = 700mA, VIN = 10V

4

5

6

s

tr, tf

Driver Output Transition Times

CL = 3000pF (Pins P-Drive and N-Gate), VIN = 6V

100

200

ns

– 40°C ≤ TA ≤ 85°C (Note 6)

SYMBOL	PARAMETER	CONDITIONS	MIN	TYP	MAX	UNITS
VFB	Feedback Voltage (LTC1159 Only)		1.2	1.25	1.3	V
VOUT	Regulated Output Voltage	VIN = 9V
	LTC1159-3.3	ILOAD = 700mA	3.17	3.30	3.43	V
	LTC1159-5	ILOAD = 700mA	4.85	5.05	5.25	V
IIN	VIN Pin Current (Note 4)	VIN = 12V, EXTVCC = 5V		200		A
	Normal
		VIN = 40V, EXTVCC = 5V		300		A
	Shutdown	VIN = 12V, VSHDN2 = 2V		15		A
		VIN = 40V, VSHDN2 = 2V		25		A
IEXTVCC	EXTVCC Pin Current (Note 4)	EXTVCC = 5V, Sleep Mode		250		A
VCC	Internal Regulator Voltage	VIN = 12V to 40V, EXTVCC = 0V, ICC = 10mA		4.5		V
VSENSE+ –	Current Sense Threshold Voltage	Low Threshold (Forced)		25		mV
VSENSE–		High Threshold (Forced)	125	150	175	mV
VSHDN2	SHDN2 Threshold		0.8	1.4	2	V
tOFF	Off-Time (Note 5)	CT = 390pF, ILOAD = 700mA, VIN = 10V	3.5	5	6.5	s

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:

LTC1159CG, LTC1159CG-3.3, LTC1159CG-5: TJ = TA + (PD • 135°C/W) LTC1159CN, LTC1159CN-3.3, LTC1159CN-5: TJ = TA + (PD • 80°C/W) LTC1159CS, LTC1159CS-3.3, LTC1159CS-5: TJ = TA + (PD • 110°C/W)

Note 3: On LTC1159 versions which have a SHDN1 pin, it must be at ground potential for testing.

Note 4: The LTC1159 VIN and EXTVCC current measurements exclude MOSFET driver currents. When VCC power is derived from the output via

EXTVCC, the input current increases by (IGATECHG • Duty Cycle)/(Efficiency). See Typical Performance Characteristics and Applications Information.

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

3

LTC1159 LTC1159-3.3/LTC1159-5

ELECTRICAL CHARACTERISTICS

Note 6: The LTC1159C, LTC1159C-3.3, and LTC1159C-5 are not tested and not quality assurance sampled at – 40°C and 85°C. These specifications are guaranteed by design and/or correlation. The LTC1159I, LTC1159I-3.3 and LTC1159I-5 are guaranteed and tested over the – 40°C to 85°C operating temperature range.

Note 7: The logic-level power MOSFETs shown in Figure 1 are rated for

VDS(MAX) = 30V. For operation at VIN > 30V, use standard threshold MOSFETs with EXTVCC powered from a 12V supply. See Applications

Information.

TYPICAL PERFORWAUCE CHARACTERISTICS

Efficiency vs Input Voltage

	100	FIGURE 1 CIRCUIT
		ILOAD = 1A
	95
(%)
EFFICIENCY	90							NOTE 6
	85
	80	5	10	15	20	25	30	35	40
	0

INPUT VOLTAGE (V)

LTC1159 • TPC01

Line Regulation

Load Regulation

	60	FIGURE 1 CIRCUIT									20			FIGURE 1 CIRCUIT
		ILOAD = 1A
	40										0			VIN = 24V
(mV)	20									(mV)	–20
	0							NOTE 6			–40
OUT										OUT
V										V
	–20										–60
	–40										–80
	–60	5	10	15	20	25	30	35	40	–100		0.5	1.0	1.5	2.0	2.5
	0										0
				INPUT VOLTAGE (V)									LOAD CURRENT (A)
								LT1159 • TPC02							LTC1159 • TPC03

		Operating Frequency
EXTVCC Pin Current	VIN Pin Current	vs (VIN – VOUT)

	10	FIGURE 1 CIRCUIT								500
CURRENT (mA)	8								CURRENT (µA)	400
				ILOAD = 1A
	6									300
								NOTE 6
CC	4								SUPPLY	200
EXTV				ILOAD = 100mA
	2									100
				ILOAD = 0
	0	5	10	15	20	25	30	35	40	0
	0
				INPUT VOLTAGE (V)

	FIGURE 1 CIRCUIT								2.0
										VOUT = 5V
												T = 0°C
								FREQUENCY
									1.5
												T = 70°C	T = 25°C
			NORMAL				NOTE 6	NORMALIZED	1.0
									0.5
			VSHDN2 = 2V
0	5	10	15	20	25	30	35	40	0	5	10	15	20	25
									0
			INPUT VOLTAGE (V)								(VIN – VOUT) VOLTAGE (V)

LTC1159 • TPC04

LTC1159 • TPC05

LTC1159 • TPC06

4

LTC1159 LTC1159-3.3/LTC1159-5

TYPICAL PERFORWAUCE CHARACTERISTICS

	EXTVCC Switch Drop												Off-Time vs VOUT
	600										80
	500										70
(mV)											60
	400									s)
											50
CC										(
										TIME-
CC
V–	300									OFF	40
EXTV	200										30
	100										20
											10											LTC1159-5
	0										0				LTC1159-3.3
			5		10		15		20
												0		1		2				3		4				5
	0
			SWITCH CURRENT (mA)													OUTPUT VOLTAGE (V)

LTC1159 • TPC07

LTC1159 • TPC08

SENSE VOLTAGE (mV)

Current Sense Threshold Voltage

160
140
								MAXIMUM
120							THRESHOLD
100
80
60
40
								MINIMUM
20							THRESHOLD
0
		20		40		60			80			100
0

TEMPERATURE (°C)

LTC1159 • TPC09

PIU FUUCTIOUS

VIN: Main Supply Input Pin.

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

PGND: Driver Power Grounds. Connect to source of N- channel MOSFET and the (–) terminal of CIN.

VCC: Outputs of internal 4.5V linear regulator, EXTVCC switch, and supply inputs for driver and control circuits. The driver and control circuits are powered from the higher of the 4.5V regulator or EXTVCC voltage. Must be closely decoupled to power ground.

CT: External capacitor CT from this pin to ground sets the operating frequency. (The frequency is also dependent on the ratio VOUT/VIN.)

ITH: Gain Amplifier Decoupling Point. The current comparator threshold increases with the ITH pin voltage.

VFB: For the LTC1159 adjustable version, the VFB pin receives the feedback voltage from an external resistive divider used to set the output voltage.

SENSE–: Connects to internal resistive divider which sets the output voltage in fixed output versions. The SENSE– pin is also the (–) input of the current comparator.

SENSE+: The (+) Input for the Current Comparator. A builtin offset between the SENSE+ and SENSE– pins, in conjunction with RSENSE, sets the current trip threshold.

N-Gate: High Current Drive for the Bottom N-Channel MOSFET. The N-Gate pin swings from ground to VCC.

P-Gate: Level-Shifted Gate Drive Signal for the Top P-Channel MOSFET. The voltage swing at the P-gate pin is from VIN to VIN – VCC.

P-Drive: High Current Gate Drive for the Top P-Channel MOSFET. The P-drive pin(s) swing(s) from VCC to ground.

CAP: Charge Compensation Pin. A capacitor to VCC provides charge required by the P-gate level-shift capacitor during supply transitions. The charge compensation capacitor must be larger than the gate drive capacitor.

SHDN1: This pin shuts down the control circuitry only (VCC is not affected). Taking SHDN1 pin high turns off the control circuitry and holds both MOSFETs off. This pin must be at ground potential for normal operation.

SHDN2: Master Shutdown Pin. Taking SHDN2 high shuts down VCC and all control circuitry.

5

LTC1159

LTC1159-3.3/LTC1159-5

FUUCTIOUAL DIAGRAW Internal divider broken at VFB for adjustable versions.

VIN

SHDN2 LOW DROPOUT 4.5V REGULATOR

LOW DROP SWITCH

EXTVCC

SLEEP

+
S
–		VTH2

CT

CAP

VCC 550k

R

Q

S

VTH1 –

T

+

OFF-TIME SENSE–

CONTROL

VCC			P-GATE

550k

P-DRIVE

N-GATE

SENSE+ SENSE–

PGND

	–
	V
–	+
C	25mV TO 150mV
+
						VOS

13k	–
	G		100k
	+
	1.25V	VFB	LTC1159 • FD
SGND	REFERENCE	SHDN1
ITH

OPERATIOU (Refer to Functional Diagram)

The LTC1159 uses a current mode, constant off-time architecture to synchronously switch an external pair of complementary power MOSFETs. Operating frequency is set by an external capacitor at the CT pin.

The output voltage is sensed either by an internal voltage divider connected to the SENSE – pin (LTC1159-3.3 and LTC1159-5) or an external divider returned to the VFB pin (LTC1159). A voltage comparator V, and a gain block G, compare the divided output voltage with a reference voltage of 1.25V. To optimize efficiency, the LTC1159 automatically switches between two modes of operation, burst and continuous.

A low dropout 4.5V regulator provides the operating voltage VCC for the MOSFET drivers and control circuitry during start-up. During normal operation, the LTC1159 family powers the drivers and control from the output via the EXTVCC pin to improve efficiency. The N-GATE pin is referenced to ground and drives the N-channel MOSFET gate directly. The P-channel gate drive must be referenced to the main supply input VIN, which is accomplished by

level-shifting the P-drive signal via an internal 550k resistor and external capacitor.

During the switch “ON” cycle in continuous mode, current comparator C monitors the voltage between the SENSE+ and SENSE– pins connected across an external shunt in series with the inductor. When the voltage across the shunt reaches its threshold value, the P-gate output is switched to VIN, turning off the P-channel MOSFET. The timing capacitor CT is now allowed to discharge at a rate determined by the off-time controller. The discharge current is made proportional to the output voltage to model the inductor current, which decays at a rate which is also proportional to the output voltage. While the timing capacitor is discharging, the N-gate output is high, turning on the N-channel MOSFET.

WhenthevoltageonCT hasdischargedpastVTH1,compara- torTtrips,settingtheflip-flop.ThiscausestheN-gateoutput to go low (turning off the N-channel MOSFET) and the P- gate output to also go low (turning the P-channel MOSFET back on). The cycle then repeats. As the load current

6