LM2757TMX/NOPB - NATIONAL SEMICONDUCTOR

LM2757

LM2757 Switched Capacitor Boost Regulator with High Impedance Output in

Shutdown

Literature Number: SNVS536D

LM2757

August 26, 2009

Switched Capacitor Boost Regulator with High Impedance

Output in Shutdown

General Description

The LM2757 is a constant frequency pre-regulated switched-

capacitor charge pump that operates at 1.25 MHz to produce

a low-noise regulated output voltage. The device can be con-

figured to provide up to 100 mA at 4.1V, 110 mA at 4.5V, or

180 mA at 5V. Excellent efficiency is achieved without the use

of an inductor by operating the charge pump in a gain of either

3/2 or 2 according to the input voltage and output voltage op-

tion selection.

The LM2757 presents a high impedance at the VOUT pin when

shut down. This allows for use in applications that require the

regulated output bus to be driven by another supply while the

LM2757 is shut down.

A perfect fit for space-constrained, battery-operated applica-

tions, the LM2757 requires only 4 small, inexpensive ceramic

capacitors. LM2757 is a tiny 1.2 mm X 1.6 mm 12–bump micro

SMD device. Built in soft-start, over-current protection, and

thermal shutdown features are also included in this device.

Features

■Dual gain converter (2x, 3/2x) with up to 93% Efficiency.

■Inductorless solution uses only 4 small ceramic

capacitors.

■Total solution area < 12mm2.

■True input-output and output-input disconnect.

■Up to 180 mA output current capability (5V).

■Selectable 4.1V, 4.5V or 5.0V output.

■Pre-regulation minimizes input current ripple.

■1.24 MHz switching frequency for a low-noise, low-ripple

output voltage.

■Integrated Over Current and Thermal Shutdown

Protection.

■Tiny 1.2 mm X 1.6 mm X 0.4 mm pitch, 12–bump micro

SMD package.

Applications

■USB/USB-OTG/HDMI Power

■Supercapacitor Charger

■Keypad LED Drive

■Audio amplifier power supply

■Low-current Camera Flash

■General Purpose Li-Ion-to-5V Conversion

■Cellular Phone SIM cards

Typical Application Circuit

30033701

30033723

LM2757 Switched Capacitor Boost Regulator with High Impedance Output in Shutdown

Connection Diagram and Package Mark Information

12–Bump Micro SMD Package, 0.4mm Pitch

National Semiconductor Package Number TMD12

30033702

Note 1: The actual physical placement of the package marking will vary from part to part. The package marking "X" designates the single digit date code. "V" is

a NSC internal code for die traceability. Both will vary considerably. "DL" identifies the device (part number, option, etc.).

Pin Descriptions

Pin # Name Description

A1 C2+ Flying Capacitor C2 Connection

A2 VOUT Regulated Output Voltage

A3 C1+ Flying Capacitor C1 Connection

B1 C1− Flying Capacitor C1 Connection

B2 VIN Input Voltage Connection

B3 VIN Input Voltage Connection

C1 GND Ground Connection

C2 GND Ground Connection

C3 C2− Flying Capacitor C2 Connection

D1 NC No Connect — Do not connect this pin to any node, voltage or GND. Must be left floating.

D2 M1 Mode select pin 1

D3 M0 Mode select pin 0

Mode Selection Definition

M0 M1 Output Voltage Mode

0 0 Device Shutdown, Output High

Impedance

0 1 5.0V

1 0 4.5V

1 1 4.1V

Order Information

Order Number Package Mark ID Package Supplied as:

LM2757TM XV

(A1 Bump Marking) DL

12–Bump µSMD

0.4mm pitch

250 Units, Tape & Reel

LM2757TMX 3000 Units, Tape & Reel

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LM2757

Absolute Maximum Ratings (Notes 2, 3)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

VIN Pin: Voltage to GND -0.3V to 6.0V

M0, M1 pins: Voltage to GND -0.3V to 6.0V

Continuous Power Dissipation

(Note 4)

Internally Limited

Junction Temperature (TJ-MAX) 150ºC

Storage Temperature Range -65ºC to +150º C

Maximum Lead Temperature

(Soldering, 10 sec.)

265ºC

ESD Rating (Note 5)

Human Body Model:

2.5 kV

Operating Ratings

(Notes 2, 3)

Input Voltage Range 2.7V to 5.5V

Junction Temperature (TJ) Range -30°C to +110°C

Ambient Temperature (TA) Range

(Note 6) -30°C to +85°C

Thermal Properties

Junction-to-Ambient Thermal

Resistance (θJA), micro SMD Package

(Note 7)

75°C/W

Electrical Characteristics (Notes 3, 8)

Limits in standard typeface are for TA = 25ºC. Limits in boldface type apply over the full operating ambient temperature range

(-30°C ≤ TA ≤ +85°C) . Unless otherwise noted, specifications apply to the Typical Application Circuit (pg. 1) with: VIN = 3.6V, V

(M0) = 0V, V(M1) = VIN,CIN = C2 = 0.47 µF, CIN= COUT = 1.0 µF (Note 9).

Symbol Parameter Condition Min Typ Max Units

VOUT Output Voltage

3.2V ≤ VIN ≤ 5.5V

–30°C ≤ TA ≤ +60°C

IOUT = 0 to 180 mA

V(M0) = 0V, V(M1) = VIN

4.870

(−2.6%) 5.0 5.130

(+2.6%)

3.0V ≤ VIN ≤ 5.5V

–30°C ≤ TA ≤ +85°C

IOUT = 0 to 150 mA

V(M0) = 0V, V(M1) = VIN

4.865

(−2.7%) 5.0 5.130

(+2.6%)

3.0V ≤ VIN ≤ 5.5V

IOUT = 0 to 110 mA

V(M0) = VIN, V(M1) = 0V

4.406

(–2.1%) 4.5 4.613

(+2.5%)

3.0V ≤ VIN ≤ 5.5V

IOUT = 0 to 100 mA

V(M0) = VIN, V(M1) = VIN

3.985

(–2.8%) 4.1 4.223

(+3.0%)

IQQuiescent Supply Current

V(M0) = 0V, V(M1) = VIN (5.0V)

IOUT = 0 mA

VIN = 3.6V

2.4 2.79

V(M0) = VIN, V(M1) = 0V (4.5V)

IOUT = 0 mA

VIN = 3.6V

1.5 1.80

V(M0) = VIN, V(M1) = VIN (4.1V)

IOUT = 0 mA

VIN = 3.6V

1.3 1.65

ISD Shutdown Supply Current V(M0) = 0V, V(M1) = 0V

VIN = 3.6V 1.1 2.0 µA

VROutput Voltage Ripple

IOUT = 150 mA

V(M0) = 0V, V(M1) = VIN (5.0V)

3.0V ≤ VIN ≤ 5.5V

20 mVp–p

fSW Switching Frequency 3.0V ≤ VIN ≤ 5.5V 0.932

(-25%) 1.242 1.552

(+25%) MHz

VIN Logic Input High Input pins: M1, M0

3.0V ≤ VIN ≤ 5.5V 1.0 VIN V

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LM2757

Symbol Parameter Condition Min Typ Max Units

VIL Logic Input Low Input pins: M1, M0

3.0V ≤ VIN ≤ 5.5V 0 0.40 V

RPULLDOWN

Logic Input Pulldown

Resistance (M0, M1) V(M1, M0) = 5.5V 324 457 kΩ

IIH Logic Input High Current Input Pins: M1, M0

V(M1, M0) = 1.8V(Note 11) 5 µA

IIL Logic Input Low Current Input Pins: M1, M0

V(M1, M0) = 0V 10 nA

VGGain Transition Voltage

1.5X to 2X, V(M0) = VIN, V(M1)=0V 3.333 V

2X to 1.5X, V(M0) = VIN, V(M1)=0V 3.413 V

Hysteresis, V(M0) = VIN, V(M1)=0V 80 mV

1.5X to 2X, V(M0) = 0V, V(M1)=VIN 3.87 V

2X to 1.5X, V(M0) = 0V, V(M1)=VIN 3.93 V

Hysteresis, V(M0) = 0V, V(M1)=VIN 60 mV

ISC Short Circuit Output Current VOUT = 0V 250 mA

ION

VOUT Turn-On Time from

Shutdown (Note 10) 300 µs

Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation

of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions,

see the Electrical Characteristics tables.

Note 3: All voltages are with respect to the potential at the GND pins.

Note 4: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=145°C (typ.) and disengages at

TJ=135°C (typ.).

Note 5: The Human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 6: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be

derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJMAX-OP=125°C), the maximum power dissipation

of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the part/package in the application (θJA), as given by the following

equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).

Note 7: Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set forth in the

JEDEC standard JESD51-7. The test board is a 4–layer FR-4 board measuring 102 mm x 76 mm x 1.6 mm with a 2x1 array of thermal vias. The ground plane

on the board is 50 mm x 50 mm. Thickness of copper layers are 36 µm/18 µm/18 µm/36 µm (1.5 oz./1 oz./1 oz./1.5 oz.). Ambient temperature in simulation is 22°

C, still air. Power dissipation is 1W.

The value of θJA in LM2757 in micro SMD-12 could fall in a range as wide as 50°C/W to 150°C/W (if not wider), depending on PWB material, layout and

environmental conditions. In applications where high maximum power dissipation exists (high VIN, high IOUT), special care must be paid to thermal dissipation

issues. For more information on these topics, please refer to Application Note 1112: Micro SMD Wafer Level Chip Scale Package (µSMD).

Note 8: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.

Note 9: CIN, COUT, C1, C2: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.

Note 10: Turn-on time is measured from when the M0 or M1 signal is pulled high until the output voltage crosses 90% of its final value.

Note 11: There is a 450 kΩ (typ.) pull-down resistor connected internally to each logic input.

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LM2757

Block Diagram

30033703

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LM2757

Typical Performance Characteristics Unless otherwise specified: VIN = 3.6V, V(M0) = 0V, V(M1) =

VIN, C1 = C2 = 0.47µF, CIN = COUT = 1.0µF, TA = 25ºC. Capacitors are low-ESR multi-layer ceramic capacitors (MLCC's).

Efficiency vs. Input Voltage, 5V Mode

30033704

Efficiency vs. Input Voltage, 4.5V Mode

30033705

Efficiency vs. Input Voltage, 4.1V Mode

30033706

Output Voltage vs. Output Current, 5V Mode

30033707

Output Voltage vs. Output Current, 4.5V Mode

30033708

Output Voltage vs. Output Current, 4.1V Mode

30033709

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LM2757

Output Voltage Ripple vs. Output Current, 5V Mode

30033710

Output Voltage vs. Input Voltage, 5V Mode

30033711

Output Voltage vs. Input Voltage, 4.5V Mode

30033712

Output Voltage vs. Input Voltage, 4.1V Mode

30033713

Output Leakage Current, Device Shutdown

30033714

Output Leakage Current, Device Shutdown

30033727

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LM2757

Current Limit vs. Input Voltage

30033715

Oscillator Frequency vs. Input Voltage

30033716

Operating Current vs. Input Voltage

30033717

Shutdown Supply Current vs. Input Voltage

30033718

Startup Behavior, 5V Mode

30033719

VIN = 3.6V, Load = 200mA

CH2: VOUT; Scale: 1V/Div, DC Coupled

CH4: IIN; Scale: 200mA/Div, DC Coupled

Time scale: 100µs/Div

Line Step (3.5V to 4V)

30033720

Load = 200mA, VOUT = 5V Mode

CH1: VIN; Scale: 1V/Div, DC Coupled

CH2: VOUT; Scale: 100mV/Div, AC Coupled

Time scale: 100µs/Div

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LM2757

Load Step with a Li-Ion Battery, 10mA to 200mA

30033721

VBATT = 4V, VOUT = 5V Mode

CH1: VOUT; Scale: 50mV/Div, AC Coupled

CH4: IOUT; Scale: 100mA/Div, DC Coupled

Time scale: 10µs/Div

Load Step with a Li-Ion Battery 200mA to 10mA

30033722

VBATT = 4V, VOUT = 5V Mode

CH1: VOUT; Scale: 50mV/Div, AC Coupled

CH4: IOUT; Scale: 100mA/Div, DC Coupled

Time scale: 10µs/Div

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LM2757

Operation Description

OVERVIEW

The LM2757 is a switched capacitor converter that produces

a regulated output voltage of either 5V, 4.5V or 4.1V depend-

ing on the mode selected. The core of the part is a highly

efficient charge pump that utilizes fixed frequency pre-regu-

lation to minimize ripple and power losses over wide input

voltage and output current ranges. A description of the prin-

cipal operational characteristics of the LM2757 is detailed in

the Circuit Description, and Efficiency Performance sec-

tions. These sections refer to details in the Block Diagram.

CIRCUIT DESCRIPTION

The core of the LM2757 is a two-phase charge pump con-

trolled by an internally generated non-overlapping clock. The

charge pump operates by using external flying capacitors

C1, C2 to transfer charge from the input to the output. At input

voltages below 3.9V (typ.) for the 5V mode, the LM2757 op-

erates in a 2x gain, with the input current being equal to 2x

the load current. At input voltages above 3.9V (typ.) for the

5V mode, the part utilizes a gain of 3/2x, resulting in an input

current equal to 3/2 times the load current. For the 4.5V mode,

the LM2757 operates in a 2x gain when the input voltage is

below 3.35V (typ.) and transitions to a 3/2x gain when the

input voltage is above 3.35V (typ.). For the 4.1V mode, the

device utilizes the 3/2x gain for the entire input voltage range.

The two phases of the switched capacitor switching cycle will

be referred to as the "phase one" and the "phase two". During

phase one, one flying capacitor is charged by the input supply

while the other flying capacitor is connected to the output and

delivers charge to the load . After half of the switching cycle

[ t = 1/(2×FSW) ], the LM2757 switches to phase two. In this

configuration, the capacitor that supplied charge to the load

in phase one is connected to the input to be recharged while

the capacitor that had been charged in the previous phase is

connected to the output to deliver charge. With this topology,

output ripple is reduced by delivering charge to the output in

every phase.

The LM2757 uses fixed frequency pre-regulation to regulate

the output voltage. The input and output connections of the

flying capacitors are made with internal MOS switches. Pre-

regulation limits the gate drive of the MOS switch connected

between the voltage input and the flying capacitors. Control-

ling the on resistance of this switch limits the amount of charge

transferred into and out of each flying capacitor during the

charge and discharge phases, and in turn helps to keep the

output ripple very low.

EFFICIENCY PERFORMANCE

Charge-pump efficiency is derived in the following two ideal

equations (supply current and other losses are neglected for

simplicity):

IIN = G × IOUT

E = (VOUT × IOUT) ÷ (VIN × IIN) = VOUT ÷ (G × VIN)

In the equations, G represents the charge pump gain. Effi-

ciency is at its highest as G×VIN approaches VOUT. Refer to

the efficiency graph in the Typical Performance Character-

istics section for detailed efficiency data. The transition be-

tween gains of 3/2, and 2 are clearly distinguished by the

sharp discontinuity in the efficiency curve.

ENABLE AND VOLTAGE MODE SELECTION

The LM2757 is enabled when either one of the mode select

pins (M0, M1) has a logic High voltage applied to it. There are

450kΩ pulldown resistors connected internally to each of the

mode select pins. The voltage mode is selected according to

the following table.

M0 M1 Output Voltage Mode

0 0 Device Shutdown, Output High

Impedance

0 1 5V

1 0 4.5V

1 1 4.1V

SHUTDOWN WITH OUTPUT HIGH IMPEDANCE

The LM2757 is in shutdown mode when there is a logic Low

voltage on both mode select pins (M0, M1). There are also

450kΩ pulldown resistors connected to both mode select

pins, pulling the nodes down to ground when there is no signal

present. When in shutdown, the output of the LM2757 is high

impedance, allowing an external supply to drive the output

line such as in USB OTG or mobile HDMI applications. Refer

to the output leakage current graphs in the Typical Perfor-

mance Characteristics section for typical leakage currents

into the VOUT pin, when driven by a separate supply during

shutdown. Output leakage increases with temperature, with

the lowest leakage occurring at -30°C and the highest leakage

at 85°C (on which the graph is based). It should be noted

when looking at the graphs, as the input voltage falls the leak-

age peaks at around an input voltage of 1.5V, and then goes

down as the input voltage goes to 0V. The leakage at an input

voltage of 0V is the same as the leakage current when the

battery is disconnected from the circuit.

SOFT START

The LM2757 employs soft start circuitry to prevent excessive

input inrush currents during startup. At startup, the output

voltage gradually rises from 0V to the nominal output voltage.

This occurs in 300µs (typ.). Soft-start is engaged when the

part is enabled.

THERMAL SHUTDOWN

Protection from damage related to overheating is achieved

with a thermal shutdown feature. When the junction temper-

ature rises to 145ºC (typ.), the part switches into shutdown

mode. The LM2757 disengages thermal shutdown when the

junction temperature of the part is reduced to 135ºC (typ.).

Due to the high efficiency of the LM2757, thermal shutdown

and/or thermal cycling should not be encountered when the

part is operated within specified input voltage, output current,

and ambient temperature operating ratings. If thermal cycling

is seen under these conditions, the most likely cause is an

inadequate PCB layout that does not allow heat to be suffi-

ciently dissipated out of the device.

CURRENT LIMIT PROTECTION

The LM2757 charge pump contains current limit protection

circuitry that protects the device during VOUT fault conditions

where excessive current is drawn. Output current is limited to

250mA (typ).

Application Information

RECOMMENDED CAPACITOR TYPES

The LM2757 requires 4 external capacitors for proper opera-

tion. Surface-mount multi-layer ceramic capacitors are rec-

ommended. These capacitors are small, inexpensive and

have very low equivalent series resistance (ESR, ≤ 15mΩ

typ.). Tantalum capacitors, OS-CON capacitors, and alu-

minum electrolytic capacitors generally are not recommended

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LM2757

for use with the LM2757 due to their high ESR, as compared

to ceramic capacitors.

For most applications, ceramic capacitors with an X7R or X5R

temperature characteristic are preferred for use with the

LM2757. These capacitors have tight capacitance tolerance

(as good as ±10%) and hold their value over temperature

(X7R: ±15% over -55ºC to 125ºC; X5R: ±15% over -55ºC to

85ºC).

Capacitors with a Y5V or Z5U temperature characteristic are

generally not recommended for use with the LM2757. These

types of capacitors typically have wide capacitance tolerance

(+80%, -20%) and vary significantly over temperature (Y5V:

+22%, -82% over -30ºC to +85ºC range; Z5U: +22%, -56%

over +10ºC to +85ºC range). Under some conditions, a 1µF-

rated Y5V or Z5U capacitor could have a capacitance as low

as 0.1µF. Such detrimental deviation is likely to cause Y5V

and Z5U capacitors to fail to meet the minimum capacitance

requirements of the LM2757.

Net capacitance of a ceramic capacitor decreases with in-

creased DC bias. This degradation can result in lower capac-

itance than expected on the input and/or output, resulting in

higher ripple voltages and currents. Using capacitors at DC

bias voltages significantly below the capacitor voltage rating

will usually minimize DC bias effects. Consult capacitor man-

ufacturers for information on capacitor DC bias characteris-

tics.

Capacitance characteristics can vary quite dramatically with

different application conditions, capacitor types, and capaci-

tor manufacturers. It is strongly recommended that the

LM2757 circuit be thoroughly evaluated early in the design-in

process with the mass-production capacitors of choice. This

will help ensure that any such variability in capacitance does

not negatively impact circuit performance.

The voltage rating of the output capacitor should be 10V or

more. For example, a 10V 0603 1.0µF is acceptable for use

with the LM2757, as long as the capacitance does not fall

below a minimum of 0.5µF in the intended application. All

other capacitors should have a voltage rating at or above the

maximum input voltage of the application. The capacitors

should be selected such that the capacitance on the input

does not fall below 0.7µF, and the capacitance of the flying

capacitors does not fall below 0.2µF.

The table below lists some leading ceramic capacitor manu-

facturers.

Manufacturer Contact Information

AVX www.avx.com

Murata www.murata.com

Taiyo-Yuden www.t-yuden.com

TDK www.component.tdk.com

Vishay-Vitramon www.vishay.com

OUTPUT CAPACITOR AND OUTPUT VOLTAGE RIPPLE

The output capacitor in the LM2757 circuit (COUT) directly im-

pacts the magnitude of output voltage ripple. Other prominent

factors also affecting output voltage ripple include input volt-

age, output current and flying capacitance. Due to the com-

plexity of the regulation topology, providing equations or

models to approximate the magnitude of the ripple can not be

easily accomplished. But one important generalization can be

made: increasing (decreasing) the output capacitance will re-

sult in a proportional decrease (increase) in output voltage

ripple.

In typical high-current applications, a 1.0µF low-ESR ceramic

output capacitor is recommended. Different output capaci-

tance values can be used to reduce ripple, shrink the solution

size, and/or cut the cost of the solution. But changing the out-

put capacitor may also require changing the flying capacitor

and/or input capacitor to maintain good overall circuit perfor-

mance. Performance of the LM2757 with different capacitor

setups in discussed in the section Recommended Capacitor

Configurations.

High ESR in the output capacitor increases output voltage

ripple. If a ceramic capacitor is used at the output, this is usu-

ally not a concern because the ESR of a ceramic capacitor is

typically very low and has only a minimal impact on ripple

magnitudes. If a different capacitor type with higher ESR is

used (tantalum, for example), the ESR could result in high

ripple. To eliminate this effect, the net output ESR can be sig-

nificantly reduced by placing a low-ESR ceramic capacitor in

parallel with the primary output capacitor. The low ESR of the

ceramic capacitor will be in parallel with the higher ESR, re-

sulting in a low net ESR based on the principles of parallel

resistance reduction.

INPUT CAPACITOR AND INPUT VOLTAGE RIPPLE

The input capacitor (CIN) is a reservoir of charge that aids a

quick transfer of charge from the supply to the flying capaci-

tors during the charge phase of operation. The input capacitor

helps to keep the input voltage from drooping at the start of

the charge phase when the flying capacitors are connected

to the input. It also filters noise on the input pin, keeping this

noise out of sensitive internal analog circuitry that is biased

off the input line.

Much like the relationship between the output capacitance

and output voltage ripple, input capacitance has a dominant

and first-order effect on input ripple magnitude. Increasing

(decreasing) the input capacitance will result in a proportional

decrease (increase) in input voltage ripple. Input voltage, out-

put current, and flying capacitance also will affect input ripple

levels to some degree.

In typical high-current applications, a 1.0µF low-ESR ceramic

capacitor is recommended on the input. Different input ca-

pacitance values can be used to reduce ripple, shrink the

solution size, and/or cut the cost of the solution. But changing

the input capacitor may also require changing the flying ca-

pacitor and/or output capacitor to maintain good overall circuit

performance. Performance of the LM2757 with different ca-

pacitor setups is discussed below in Recommended Capac-

itor Configurations.

FLYING CAPACITORS

The flying capacitors (C1, C2) transfer charge from the input

to the output. Flying capacitance can impact both output cur-

rent capability and ripple magnitudes. If flying capacitance is

too small, the LM2757 may not be able to regulate the output

voltage when load currents are high. On the other hand, if the

flying capacitance is too large, the flying capacitor might over-

whelm the input and output capacitors, resulting in increased

input and output ripple.

In typical high-current applications, 0.47µF low-ESR ceramic

capacitors are recommended for the flying capacitors. Polar-

ized capacitors (tantalum, aluminum electrolytic, etc.) must

not be used for the flying capacitor, as they could become

reverse-biased during LM2757 operation.

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LM2757

RECOMMENDED CAPACITANCE

The data in Table 1 can be used to assist in the selection of

capacitance for each node that best balances solution size

and cost with the electrical requirements of the application.

As previously discussed, input and output ripple voltages will

vary with output current and input voltage. The numbers pro-

vided show expected ripple voltage with VIN = 3.6V and a load

current of 200mA at 5V output, 100mA at 4.5V output, and

100mA at 4.1V output. The table offers a first look at approx-

imate ripple levels and provides a comparison of different

capacitance configurations, but is not intended to be a guar-

antee of performance. With any capacitance configuration

chosen, always verify that the performance of the ripple wave-

forms are suitable for the intended application. The same

capacitance value must be used for all the flying capacitors.

For output regulation performance with different capacitor

configurations, please refer to the Output Voltage vs. Input

Voltage graphs in the Typical Performance Characteris-

tics section of this datasheet. The output voltage regulation

is typically better when using capacitors with a higher capac-

itance value and a higher voltage bias rating than the nominal

voltage applied to them, as can be seen in the graphs, but this

may have an impact in capacitor case size. For typical high-

current small solution size applications, 1µF capacitance X5R

temperature characteristic rating 0402 (C1005) case size and

10V bias or higher capacitors can be used for the Input, Out-

put and Flying capacitors. According to current capacitor

offerings, there are no capacitors in the 0201 (C0603) case

size that satisfy the minimum capacitance requirements of the

LM2757 circuit. When selecting capacitors, it is preferred to

use the ones with the highest voltage bias rating available

from the capacitor supplier.

TABLE 1. LM2757 Performance with Different Capacitor

Configurations (Note 12)

Capacitor

Configuration

(VIN = 3.6V)

Typical

5.0V,

200mA

Output

Ripple

Typical

4.5V,

100mA

Output

Ripple

Typical

4.1V,

100mA

Output

Ripple

CIN = 1µF,

COUT = 1µF,

C1, C2 = 0.47µF

32mV 12mV 11mV

CIN = 0.68µF,

COUT = 1µF,

C1, C2 = 0.47µF

32mV 11mV 11mV

CIN = 0.68µF,

COUT = 0.47µF,

C1, C2 = 0.47µF

51mV 15mV 15mV

CIN = 0.68µF,

COUT = 0.47µF,

C1, C2 = 0.22µF

53mV 18mV 18mV

Note 12: Refer to the text in the Recommended Capacitor Configurations

section for detailed information on the data in this table

Layout Guidelines

Proper board layout will help to ensure optimal performance

of the LM2757 circuit. The following guidelines are recom-

mended:

•Place capacitors as close to the LM2757 as possible, and

preferably on the same side of the board as the IC.

•Use short, wide traces to connect the external capacitors

to the LM2757 to minimize trace resistance and

inductance.

•Use a low resistance connection between ground and the

GND pin of the LM2757. Using wide traces and/or multiple

vias to connect GND to a ground plane on the board is

most advantageous.

www.national.com 12

LM2757

Application Circuits

USB OTG / Mobile HDMI POWER SUPPLY

30033724

The 5V output mode will normally be used for the USB OTG /

Mobile HDMI application. Therefore the LM2757 can be en-

abled/disabled by applying a logic signal on only the M1 pin

while grounding the M0 pin. Depending on the USB/HDMI

mode of the application, the LM2757 can be enabled to drive

the power bus line (Host), or disabled to put its output in high

impedance allowing an external supply to drive the bus line

(Slave). In addition to the high impedance-backdrive protec-

tion, the output current limit protection is 250mA (typ.), well

within the USB OTG and HDMI requirements.

SUPERCAPACITOR FLASH DRIVER

30033725

Using the 5V output voltage mode, the LM2757 can be used

to charge a Supercapacitor for LED Flash applications while

limiting the peak current drawn off the battery during the

charge cycle. The LM2757 can be disabled for the Flash

event, placing its output in high impedance with the input. In

this way, all charge for the Flash LED(s) will come directly off

the Supercapacitor and not load the main battery line. The

LM2757 can be enabled/disabled by applying a logic signal

on only the M1 pin while grounding the M0 pin.

Special consideration must be taken when using Supercapi-

cators for LED flash applications where the voltage on the

capacitor is charged to a fixed value. This is due to the pos-

sible power management issues that could arise as a result

of the high flash current and wide tolerance ranges (V–I char-

acteristics) of typical Flash LEDs. If the voltage across the

Flash LED(s) is not managed, damage could occur where a

relatively low Vf LED is overdriven or places excessive volt-

age across the bottom control FET. To help reduce this issue,

the use of a high power current sink is advised in applications

where the forward voltage specification of the Flash LED has

a wide range.

13 www.national.com

LM2757

LED DRIVER

30033726

The 5.0V, 4.5V, or the 4.1V mode can be used depending on

the forward voltage and load requirements of the LED appli-

cation. The LM2757 can be enabled/disabled by applying the

appropriate combination of logic signals on the M1 and M0

pins. LED current for each string in this application is limited

by the voltage across the string's ballast resistor, which is de-

pendent on the output voltage mode selected and the V-I

profile of each LED used.

www.national.com 14

LM2757

Physical Dimensions inches (millimeters) unless otherwise noted

NSC Package TMD12AAA

Micro SMD Wafer Level Package

X1: 1215 µm +/- 30 µm

X2: 1615 µm +/- 30 µm

X3: 600 µm +/- 75 µm

Bump pitch: 0.4 mm

15 www.national.com

LM2757

Notes

LM2757 Switched Capacitor Boost Regulator with High Impedance Output in Shutdown

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