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LTC3388-1/LTC3388-3

338813f

TYPICAL APPLICATION

FEATURES DESCRIPTION

20V High Efficiency

Nanopower

Step-Down Regulator

The LTC

3388-1/LTC3388-3 are high efficiency step-down

DC/DC converters with internal high side and synchronous

power switches that draw only 720nA typical DC sup-

ply current at no load while maintaining output voltage

regulation.

Capable of supplying 50mA of load current, the LTC3388-1/

LTC3388-3 also incorporate an accurate undervoltage lock-

out (UVLO) feature to disable the converter and maintain

a low quiescent current state when the input voltage falls

below 2.3V. In regulation, the LTC3388-1/LTC3388-3 enter

a sleep state in which both input and output quiescent cur-

rents are minimal. The buck converter turns on and off as

needed to maintain regulation. An additional standby mode

disables buck switching while the output is in regulation

for short duration loads requiring low ripple.

Output voltages of 1.2V, 1.5V, 1.8V, 2.5V (LTC3388-1) and

2.8V, 3.0V, 3.3V, 5.0V (LTC3388-3) are pin selectable. The

LTC3388-1/LTC3388-3 can operate with V

up to 20V while

the no load quiescent current remains below 1µA.

L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks

of Linear Technology Corporation. All other trademarks are the property of their respective

owners.

50mA Step-Down Converter

APPLICATIONS

720nA Input I

in Regulation (No Load), V

= 4V

820nA Input I

in Regulation (No Load), V

= 20V

400nA Input I

in UVLO

2.7V to 20V Input Operating Range

Up to 50mA of Output Current

Pin Selectable Output Voltages:

1.2V, 1.5V, 1.8V, 2.5V (LTC3388-1)

2.8V, 3.0V, 3.3V, 5.0V (LTC3388-3)

High Efficiency Hysteretic Synchronous

DC/DC Conversion

Standby Mode Disables Buck Switching

Available in 10-Lead MSE and 3mm × 3mm

DFN Packages

Keep Alive Power for Portable Products

Industrial Control Supplies

Distributed Power Systems

Battery-Operated Devices

338813 TA01a

CAP

IN2

STBY

OUT

PGOOD

D0, D1

LTC3388-1/

LTC3388-3

GND

1µF

4.7µF

2.2µF

25V

2.7V TO 20V

47µF

OUTPUT

VOLTAGE

SELECT

OUT

100µH

Efficiency vs Load Current

LOAD CURRENT (A)

EFFICIENCY (%)

100

338813 TA01b

100µ 1m 10m1µ 10µ

OUT

= 1.8V, L = 100µH

= 3.0V

= 10V

= 20V

Summary of content (20 pages)

PAGE 1
LTC3388-1/LTC3388-3 20V High Efficiency Nanopower Step-Down Regulator DESCRIPTION FEATURES n n n n n n n n n 720nA Input IQ in Regulation (No Load), VIN = 4V 820nA Input IQ in Regulation (No Load), VIN = 20V 400nA Input IQ in UVLO 2.7V to 20V Input Operating Range Up to 50mA of Output Current Pin Selectable Output Voltages: 1.2V, 1.5V, 1.8V, 2.5V (LTC3388-1) 2.8V, 3.0V, 3.3V, 5.
PAGE 2
LTC3388-1/LTC3388-3 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN ............................................................. –0.3V to 22V D0, D1 ..............–0.3V to [Lesser of (VIN2 + 0.3V) or 6V] CAP ......................[Higher of –0.3V or (VIN – 6V)] to VIN VIN2, VOUT ......... –0.3V to [Lesser of (VIN + 0.3V) or 6V] EN, STBY ..................................................... –0.3V to 6V PGOOD......................................................... –0.3V to 6V ISW ..................................
PAGE 3
LTC3388-1/LTC3388-3 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are for TA = 25°C (Note 2). Unless otherwise noted, VIN = 5.5V.
PAGE 4
LTC3388-1/LTC3388-3 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are for TA = 25°C (Note 2). Unless otherwise noted, VIN = 5.5V. SYMBOL PARAMETER VIH D0/D1/EN/STBY Input High Voltage CONDITIONS l VIL(D0, D1) D0/D1 Input Low Voltage l 0.
PAGE 5
LTC3388-1/LTC3388-3 TYPICAL PERFORMANCE CHARACTERISTICS UVLO vs Temperature RP,BUCK /RN,BUCK vs Temperature IPEAK vs Temperature 2.8 180 2.0 170 1.8 160 1.6 2.6 IPEAK (mA) VUVLO (V) 2.4 UVLO FALLING RDS(ON) (Ω) NMOS UVLO RISING 150 1.4 PMOS 140 1.2 130 1.0 2.2 2.0 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 120 –50 125 –25 0 25 50 75 TEMPERATURE (°C) 100 0.8 –55 –35 –15 125 338813 G05 338813 G04 338813 G06 1.2V Output vs Temperature (LTC3388-1) Operating Waveforms 1.
PAGE 6
LTC3388-1/LTC3388-3 TYPICAL PERFORMANCE CHARACTERISTICS 3.0V Output vs Temperature (LTC3388-3) 3.3V Output vs Temperature (LTC3388-3) 3.10 3.40 3.05 WAKE-UP THRESHOLD 5.0 2.90 4.9 VOUT (V) 2.95 WAKE-UP THRESHOLD WAKE-UP THRESHOLD 3.25 2.85 3.20 3.15 3.10 2.80 4.8 4.7 PGOOD FALLING 3.05 PGOOD FALLING PGOOD FALLING 4.6 2.75 3.00 2.70 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 2.95 –50 125 –25 0 25 50 75 TEMPERATURE (°C) 338813 G13 1.56 100 4.5 –50 125 3.36 VIN = 5.
PAGE 7
LTC3388-1/LTC3388-3 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs ILOAD, L = 22μH (LTC3388-1) 100 100 VIN = 3.0V 90 80 80 70 70 60 50 40 30 60 50 40 30 VOUT = 2.5V VOUT = 1.8V VOUT = 1.5V VOUT = 1.2V 20 10 0 VIN = 3.0V 90 EFFICIENCY (%) EFFICIENCY (%) Efficiency vs ILOAD, L = 100μH (LTC3388-1) 1μ 10μ 100μ 1m LOAD CURRENT (A) VOUT = 2.5V VOUT = 1.8V VOUT = 1.5V VOUT = 1.
PAGE 8
LTC3388-1/LTC3388-3 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs ILOAD, L = 22μH (LTC3388-3) 100 100 VIN = 6.0V 90 80 80 70 70 60 50 40 VOUT = 5.0V VOUT = 3.3V VOUT = 3.0V VOUT = 2.8V 20 10 50 40 1μ 10μ 100μ 1m LOAD CURRENT (A) 10 0 10m 1μ 10μ 100μ 1m LOAD CURRENT (A) 10m 338813 G28 338813 G29 Efficiency vs VIN for ILOAD = 50mA, L = 22μH (LTC3388-3) Efficiency vs VIN for ILOAD = 50mA, L = 100μH (LTC3388-3) 100 100 95 95 90 90 85 80 VOUT = 5.0V VOUT = 3.3V VOUT = 3.
PAGE 9
LTC3388-1/LTC3388-3 PIN FUNCTIONS EN (Pin 1): Enable Input. Logic level input referenced to VIN2. A logic high on EN will enable the buck converter. Driving EN to VIN2 will result in no additional quiescent current on VIN. However, if EN is driven near VIH or VIL 40nA of additional quiescent current can appear on VIN. STBY (Pin 2): Standby Input. Logic level input referenced to VIN2. A logic high on STBY will place the part in standby mode.
PAGE 10
LTC3388-1/LTC3388-3 BLOCK DIAGRAM VIN 4 INTERNAL RAIL GENERATION VIN2 40nA 3 CAP 5 SW 7 VIN2 UVLO EN 1 VIN2 BUCK CONTROL 40nA 11 GND STBY 2 SLEEP 6 BANDGAP REFERENCE 8, 9 D1, D0 VOUT 10 PGOOD 2 REF – PGOOD + 338813 BD 338813f 10
PAGE 11
LTC3388-1/LTC3388-3 OPERATION The LTC3388-1/LTC3388-3 is an ultralow quiescent current power supply designed to maintain a regulated output voltage by means of a nanopower high efficiency synchronous buck regulator. Undervoltage Lockout (UVLO) When the voltage on VIN rises above the UVLO rising threshold the buck converter is enabled and charge is transferred from the input capacitor to the output capacitor. If VIN falls below the UVLO falling threshold the part will re-enter UVLO.
PAGE 12
LTC3388-1/LTC3388-3 OPERATION Four selectable voltages are available by tying the output select bits, D0 and D1, to GND or VIN2. Table 1 shows the four D0/D1 codes and their corresponding output voltages as well as the difference in output voltages between the LTC3388-1 and LTC3388-3. Table 1. LTC3388-1/LTC3388-3 Output Voltage Selection D1 D0 VOUT VOUT Quiescent Current (I VOUT) 0 0 1.2V/2.8V 28nA/66nA 0 1 1.5V/3.0V 36nA/72nA 1 0 1.8V/3.3V 43nA/78nA 1 1 2.5V/5.
PAGE 13
LTC3388-1/LTC3388-3 OPERATION Enable and Standby Modes Two logic pins, EN and STBY, determine the operating mode of the LTC3388-1/LTC3388-3. When EN is high and STBY is low the synchronous buck converter is enabled and will regulate the output if the input voltage is above the programmed output voltage and above the UVLO threshold. If EN is low the buck converter circuitry is powered down to save quiescent current.
PAGE 14
LTC3388-1/LTC3388-3 APPLICATIONS INFORMATION Introduction The basic LTC3388-1/LTC3388-3 application circuit is shown on the front page. External components are selected based on the performance requirements of the application. Input Capacitor Selection The input capacitor at VIN should be selected to adequately bypass the LTC3388-1/LTC3388-3 and filter the switching current presented by the buck regulator. The VIN capacitor should be rated to withstand the highest voltage ever present at VIN.
PAGE 15
LTC3388-1/LTC3388-3 APPLICATIONS INFORMATION If transient load currents above 50mA are required then a larger capacitor can be used at the output. This capacitor will be continuously discharged during a load condition and the capacitor can be sized for an acceptable drop in VOUT: ILOAD −IBUCK COUT = VOUT + – VOUT – t LOAD ( current rating greater than 200mA. The DCR of the inductor can have an impact on efficiency as it is a source of loss. Trade-offs between price, size, and DCR should be evaluated.
PAGE 16
LTC3388-1/LTC3388-3 APPLICATIONS INFORMATION Efficiency Considerations The efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Efficiency can be expressed as: Efficiency = 100% – (η1 + η 2 + η 3 + ...) where η1, η2, etc. are the individual losses as a percentage of input power.
PAGE 17
LTC3388-1/LTC3388-3 APPLICATIONS INFORMATION Interfacing with a Microprocessor ripple in the output voltage of the LTC3388-1/LTC3388-3 will cease and the output capacitor will support the load of the microprocessor and other circuitry. While in standby the output voltage will decrease as it’s loaded. The output capacitor should be sized to minimize the decline. The PGOOD, STBY, and EN pins can be useful when powering a microprocessor from the LTC3388-1/LTC3388-3.
PAGE 18
LTC3388-1/LTC3388-3 PACKAGE DESCRIPTION DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 p0.05 3.55 p0.05 1.65 p0.05 2.15 p0.05 (2 SIDES) PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 2.38 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p0.10 (4 SIDES) R = 0.125 TYP 6 0.40 p 0.10 10 1.65 p 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 s 45o CHAMFER PIN 1 TOP MARK (SEE NOTE 6) (DD) DFN REV C 0310 5 0.200 REF 1 0.25 p 0.05 0.50 BSC 0.75 p0.05 0.00 – 0.
PAGE 19
LTC3388-1/LTC3388-3 PACKAGE DESCRIPTION MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev D) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 p 0.102 (.074 p .004) 5.23 (.206) MIN 0.889 p 0.127 (.035 p .005) 1.68 p 0.102 (.066 p .004) 1 0.05 REF 10 3.00 p 0.102 (.118 p .004) (NOTE 3) DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 10 9 8 7 6 DETAIL “A” 0o – 6o TYP 1 2 3 4 5 GAUGE PLANE 0.53 p 0.152 (.021 p .
PAGE 20
LTC3388-1/LTC3388-3 TYPICAL APPLICATION Piezoelectric Energy Harvester with Dual, ±3.3V Outputs PZ1 PZ2 VIN PGOOD 1μF 6V 10μF 25V 4.7μF 6V LTC3588-1 22μH CAP SW VIN2 VOUT 3.3V D1 D0 1μF 6V 47μF 6V 2.2μF 10V GND VIN PGOOD CAP LTC3388-3 * SW VIN2 VOUT EN 4.7μF 6V 22μH D1 D0 GND STBY 47μF 6V –3.3V 338813 TA02 * EXPOSED PAD MUST BE ELECTRICALLY ISOLATED FROM SYSTEM GROUND AND CONNECTED TO THE –3.3V RAIL.