AS1324-BTTT-12_技术文档

Data Sheet

AS1324

1.5MHz, 600mA, DC/DC Step-Down Regulator

1 General Description

2 Key Features

ꢀ High Efficiency: Up to 96%

The AS1324 is a high-efficiency, constant-frequency

synchronous buck converter available in adjustable- and

fixed-voltage versions. The wide input voltage range

(2.7V to 5.5V), automatic powersave mode and minimal

external component requirements make the AS1324

perfect for any single Li-Ion battery-powered application.

ꢀ Output Current: 600mA

ꢀ Input Voltage Range: 2.7V to 5.5V

ꢀ Constant Frequency Operation: 1.5MHz

ꢀ Variable- and Fixed-Output Voltages

ꢀ No Schottky Diode Required

ꢀ Automatic Powersave Operation

ꢀ Low Quiescent Current: 30µA

ꢀ Internal Reference: 0.6V

Typical supply current with no load is 30µA and

decreases to ≤1µA in shutdown mode.

The AS1324 is available as the standard versions listed

in Table 1.

Table 1. Standard Versions

Model

Output Voltage

Adjustable via External Resistors

Fixed: 1.2V

AS1324-AD

AS1324-12

AS1324-15

AS1324-18

ꢀ Shutdown Mode Supply Current: ≤1µA

ꢀ Thermal Protection

Fixed: 1.5V

Fixed: 1.8V

ꢀ 5-pin TSOT-23 Package

An internal synchronous switch increases efficiency and

eliminates the need for an external Schottky diode. The

internally fixed switching frequency (1.5MHz) allows for

the use of small surface mount external components.

3 Applications

Very low output voltages can be delivered with the inter-

nal 0.6V feedback reference voltage.

The device is ideal for mobile communication devices,

laptops and PDAs, ultra-low-power systems, threshold

detectors/discriminators, telemetry and remote systems,

medical instruments, or any other space-limited applica-

tion with low power-consumption requirements.

The AS1324 is available in a 5-pin TSOT-23 package.

Figure 1. Typical Application Diagram – High Efficiency Step Down Converter

4.7µH

V^OUT= 1.8V, 600mA

V^IN= 2.7V to 5.5V

4

3

EN

1

5 VOUT

VIN

SW

CIN

10µF

COUT

10µF

AS1324-

18

AS1324-

18

GND 2

SW 3

5

1

VOUT

EN

4 VIN

GND

2

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AS1324

Data Sheet - Pinout and Packaging

4 Pinout and Packaging

Pin Assignments

Figure 2. Pin Assignments (Top View)

EN

1

2

3

5

VFB

1

2

3

5

VOUT

AS1324-12/

AS1324-15/

AS1324-18

AS1324

GND

SW

GND

SW

4

VIN

4 VIN

Pin Descriptions

Table 2. Pin Descriptions

Pin Name

Number

Description

Enable Input. Driving this pin above 1.5V enables the device. Driving this pin below 0.3V

puts the device in shutdown mode. In shutdown mode all functions are disabled while SW

goes high impedance, drawing <1µA supply current.

1

EN

Note: This pin should not be left floating.

Ground.

2

3

GND

SW

Switch Node Connection to Inductor. This pin connects to the drains of the internal main

and synchronous power MOSFET switches.

Input Supply Voltage. This pin must be closely decoupled to GND with a ≥ 4.7µF ceramic

capacitor. Connect to any supply voltage between 2.7 to 5.5V.

4

5

VIN

VFB

Feedback Pin. This pin receives the feedback voltage from the external resistor divider

across the output. (Adjustable voltage variant only.)

Output Voltage Feedback Pin. An internal resistor divider steps the output voltage down

for comparison to the internal reference voltage. (Fixed voltage variants only.)

VOUT

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AS1324

Data Sheet - Absolute Maximum Ratings

5 Absolute Maximum Ratings

Stresses beyond those listed in Table 3 may cause permanent damage to the device. These are stress ratings only,

and functional operation of the device at these or any other conditions beyond those indicated in Section 6 Electrical

Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may

affect device reliability.

Table 3. Absolute Maximum Ratings

Parameter

Min

Max

Units

Comments

VIN to GND

-0.3

7

V

VIN

+ 0.3

SW, EN, FB to GND

-0.3

V

Thermal Resistance ΘJA

ESD

207.4

ºC/W

kV

on PCB

HBM MIL-Std. 883E 3015.7 methods

JEDEC 78

2

Latch-Up

-100

-40

+100

+85

mA

ºC

Operating Temperature Range

Storage Temperature Range

-65

+125

ºC

The reflow peak soldering temperature (body

temperature) specified is in accordance with

IPC/JEDEC J-STD-020C “Moisture/Reflow

Sensitivity Classification for Non-Hermetic

Solid State Surface Mount Devices”.

The lead finish for Pb-free leaded packages

is matte tin (100% Sn).

Package Body Temperature

Junction Temperature

+260

125

ºC

Junction temperature (TJ) is calculated from

the ambient temperature (TAMB) and power

dissipation (PD) as:

TJ = TAMB + (PD)(207.4ºC/W)

(EQ 1)

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AS1324

Data Sheet - Electrical Characteristics

6 Electrical Characteristics

VIN = EN = 3.6V, VOUT < VIN - 0.5V, TAMB = -40 to +85°C, typ. values @ TAMB = +25ºC (unless otherwise specified).

Table 4. Electrical Characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Units

VIN

Input Voltage Range

2.7

5.5

V

Powersave Mode; VFB = 0.62V or VOUT =

IQ

Quiescent Current

Shutdown Current

30

35

1

103%, IOUT = 0mA,

T

AMB = +25ºC

µA

ISHDN

Shutdown Mode; VEN = 0V,

TAMB = +25ºC

0.1

Regulation

Regulated Feedback

Voltage ¹

VFB

AS1324, IOUT = 100mA

VIN = 2.7V to 5.5V

0.585

0.6

0.1

0.615

V

Reference Voltage

Line Regulation

ΔVFB

1

%/V

nA

IVFB

Feedback Current

TAMB = +25ºC

-30

30

AS1324-AD, IOUT = 100mA²

AS1324-12, IOUT = 100mA

AS1324-15, IOUT = 100mA

AS1324-18, IOUT = 100mA

VFB

1.164

1.455

1.746

1.20

1.50

1.80

1.236

1.545

1.854

Regulated Output

Voltage

VOUT

V

Output Voltage

Line Regulation

ΔVOUT

VIN = 2.7 to 5.5V

0.1

1

%/V

Output Voltage

Load Regulation

VLOADREG

IOUT = 0 to 100mA

0.02

%/mA

DC-DC Switches

VIN = 3V, VFB = 0.5V or VOUT = 90%,

TAMB = 25ºC

IPK

Peak Inductor Current

0.5

0.75

1

A

RPFET

RNFET

ILSW

P-Channel FET RDS(ON)

N-Channel FET RDS(ON)

SW Leakage

ILSW = 100mA

ILSW = -100mA

0.4

0.35

±0.01

Ω

VEN = 0V, VSW = 0V or 5V

±1

µA

Control Inputs

VEN

EN Threshold

0.3

1.2

1

1.5

±1

V

IEN

EN Leakage Current

±0.01

µA

Oscillator

VFB = 0.6V or VOUT = 100%

1.5

1.8

MHz

kHz

fOSC

Oscillator Frequency

VFB = 0V or VOUT = 0V, TAMB = 25ºC

115

1. The device is tested in a proprietary test mode where VFB is connected to the output of the error amplifier.

2. Please see Feedback Resistor Selection on page 13 for resistor values.

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AS1324

Data Sheet - Typical Operating Characteristics

7 Typical Operating Characteristics

Parts used for measurement: 4.7µH (MOS6020-472) Inductor, 10µF (GRM188R60J106ME47) CIN and COUT.

Figure 3. Efficiency vs. Input Voltage; VOUT = 1.8V

Figure 4. Efficiency vs. Output Current; VOUT = 1.2V

95

100

95

90

85

80

75

70

90

85

80

75

70

65

IOUT = 600mA

VIN =2.5V

VIN =2.7V

60

IOUT = 100mA

VIN =3.7V

VIN =4.2V

VIN = 5.5V

IOUT = 10mA

55

IOUT = 1mA

50

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

1

10

100

1000

Input Voltage (V)

Output Current (mA)

Figure 5. Efficiency vs. Output Current; VOUT = 1.5V

Figure 6. Efficiency vs. Output Current; VOUT = 1.8V

100

95

90

85

80

75

70

95

90

85

80

75

70

65

VIN =2.5V

VIN =2.7V

VIN =3.7V

VIN =2.5V

VIN =2.7V

60

VIN =3.7V

VIN =4.2V

VIN = 5.5V

55

VIN =4.2V

VIN = 5.5V

55

50

1

10

100

1000

1

10

100

1000

Output Current (mA)

Figure 7. Efficiency vs. Output Current; VOUT = 2.5V

Figure 8. Efficiency vs. Output Current; VOUT = 3.3V

100

95

90

85

80

75

70

65

95

90

85

80

75

70

65

60

VIN =3.7V

60

VIN =4.2V

55

VIN = 5.5V

50

1

10

100

1000

1

10

100

1000

Output Current (mA)

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AS1324

Data Sheet - Typical Operating Characteristics

Figure 9. Switching Frequency vs. Supply Voltage

Figure 10. Switching Frequency vs. Temperature

1.6

1.55

1.5

1.55

1.5

1.45

1.4

1.45

1.4

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

-45 -30 -15

0

15 30 45 60 75 90

Input Voltage (V)

Temperature (°C)

Figure 11. Feedback Voltage vs. Temperature

Figure 12. Output Voltage vs. Input Voltage

0.61

2

1.95

1.9

0.605

0.6

1.85

1.8

1.75

1.7

0.595

0.59

IOUT = 600mA

IOUT = 100mA

IOUT = 10mA

IOUT = 1mA

1.65

1.6

IOUT = 100µA

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

-45 -30 -15

0

15 30 45 60 75 90

Temperature (C°)

Input Voltage (V)

Figure 13. VOUT vs. IOUT; VOUTNOM = 1.2V

Figure 14. VOUT vs. IOUT; VOUTNOM = 1.5V

1.6

1.3

Vin=2.5V

Vin=2.7V

Vin=5.5V

Vin=2.5V

Vin=2.7V

Vin=5.5V

1.55

1.5

1.25

1.2

1.45

1.4

1.15

1.1

0

100

200

300

400

500

600

0

100

200

300

400

500

600

Output Current (mA)

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AS1324

Data Sheet - Typical Operating Characteristics

Figure 15. Quiescent Current vs. Input Voltage

Figure 16. Quiescent Current vs. Temperature

50

45

40

35

30

25

20

15

10

5

45

40

35

30

25

20

15

10

5

0

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

-45 -30 -15

0

15 30 45 60 75 90

Input Voltage (V)

Temperature (°C)

Figure 17. Load Step 0mA to 600mA

Figure 18. Load Step 10mA to 200mA

500µs/DIV

Figure 19. Startup

Figure 20. Powersave Mode

1ms/DIV

5µs/DIV

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AS1324

Data Sheet - Detailed Description

8 Detailed Description

The AS1324 is a high-efficiency buck converter that uses a constant-frequency current-mode architecture. The device

contains two internal MOSFET switches and is available in adjustable- and fixed-output voltage versions.

Figure 21. Block Diagram

Ramp

Compensator

–

VIN

4

ICOMP

+

OSC

VIN

CIN

10µF

OSCN

Frequency

Shift

5

AS1324

VOUT/VFB

0.6V

+

Error

R1

Amp

–

FB

R2

–

PMOS

NMOS

OVDET

+

Digital

Logic

Anti-

Shoot

Through

0.6V +

ΔVOVL

4.7µH

VOUT

3

–

+

SW

COUT

10µF

1

0.6V

Reference

0.6V -

ΔVOVL

EN

+

IRCMP

Shutdown

2

–

GND

Not applicable to AS1324

AS1324-12: R1 + R2 = 600kΩ

AS1324-15: R1 + R2 = 750kΩ

AS1324-18: R1 + R2 = 900kΩ

Main Control Loop

During PWM operation the converters use a 1.5MHz fixed-frequency, current-mode control scheme. Basis of the cur-

rent-mode PWM controller is an open-loop, multiple input comparator that compares the error-amp voltage feedback

signal against the sum of the amplified current-sense signal and the slope-compensation ramp. At the beginning of

each clock cycle, the internal high-side PMOS turns on until the PWM comparator trips. During this time the current in

the inductor ramps up, sourcing current to the output and storing energy in the inductor’s magnetic field. When the

PMOS turns off, the internal low-side NMOS turns on. Now the inductor releases the stored energy while the current

ramps down, still providing current to the output. The output capacitor stores charge when the inductor current

exceeds the load and discharges when the inductor current is lower than the load. Under overload conditions, when

the inductor current exceeds the current limit, the high-side PMOS is turned off and the low-side NMOS remains on

until the next clock cycle.

When the PMOS is off, the NMOS is turned on until the inductor current starts to reverse (as indicated by the current

reversal comparator (IRCMP)), or the next clock cycle begins. The IRCMP detects the zero crossing.

The peak inductor current (IPK) is controlled by the error amplifier. When IOUT increases, VFB decreases slightly relative

to the internal 0.6V reference, causing the error amplifier’s output voltage to increase until the average inductor current

matches the new load current.

The over-voltage detection comparator (OVDET) guards against transient overshoots by turning the main switch off

and keeping it off until the transient is removed.

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AS1324

Data Sheet - Detailed Description

Powersave Operation

The AS1324 uses an automatic powersave mode where the peak inductor current (IPK) is set to approximately 200mA

while independent of the output load. In powersave mode, load current is supplied solely from the output capacitor. As

the output voltage drops, the error amplifier output rises above the powersave threshold signaling to switch into PWM

fixed frequency mode and turn the PMOS on. This process repeats at a rate determined by the load demand.

Each burst event can last from a few cycles at light loads to almost continuous cycling (with short sleep intervals) at

moderate loads. In between bursts, the power MOSFETs are turned off, as is any unneeded circuitry, reducing quies-

cent current to 30µA.

Short-Circuit Protection

In cases where the AS1324 output is shorted to ground, the oscillator frequency (fOSC) is reduced to 1/13 the nominal

frequency (≅ 115kHz). This frequency reduction ensures that the inductor current has more time to decay, thus pre-

venting runaway conditions. fOSC will progressively increase to 1.5MHz when VFB/VOUT > 0V.

Shutdown

Connecting EN to GND or logic low places the AS1324 in shutdown mode and reduces the supply current to 0.1µA. In

shutdown the control circuitry and the internal NMOS and PMOS turn off and SW becomes high impedance discon-

necting the input from the output. The output capacitance and load current determine the voltage decay rate. For nor-

mal operation connect EN to VIN or logic high.

Note: Pin EN should not be left floating.

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AS1324

Data Sheet - Application Information

9 Application Information

The AS1324 is perfect for mobile communications equipment like cell phones and smart phones, digital cameras and

camcorders, portabel MP3 and DVD players, PDA’s and palmtop computers and any other handheld instruments.

Figure 22. Single Li-Ion 1.2V/600mA Regulator for High-Efficiency

4.7µH

VOUT

1.2V

600mA

4

3

VIN

2.7 to 4.2V

VIN

SW

CIN

2.2µF

COUT

10µF

22pF

AS1324

301kΩ

5

1

R2

EN

VFB

301kΩ

R1

GND

2

Figure 23. 5V Input to 3.3V/600mA Buck Regulator

4.7µH

VOUT

3.3V

600mA

4

3

VIN

5V

CIN

4.7µF

COUT

10µF

VIN

SW

22pF

AS1324

301kΩ

5

1

R2

EN

VFB

R1

66.5kΩ

GND

2

Figure 24. Single Li-Ion 1.5V/600mA Regulator for High-Efficiency

4.7µH

VOUT

1.5V

600mA

4

3

VIN

2.7 to 4.2V

VIN

SW

COUT

10µF

CIN

4.7µF

AS1324-

15

5

1

EN

VOUT

GND

2

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AS1324

Data Sheet - Application Information

Figure 25. Single Li-Ion 1.8V/600mA Regulator for Low Output Ripple

4.7µH

VOUT

1.8V

600mA

4

3

VIN

2.7 to 4.2V

VIN

SW

CIN

10µF

COUT

22µF

AS1324-

18

5

1

EN

VOUT

GND

2

External Component Selection

Inductor Selection

For most applications the value of the external inductor should be in the range of 2.2 to 6.8µH as the inductor value

has a direct effect on the ripple current. The selected inductor must be rated for its DC resistance and saturation cur-

rent. The inductor ripple current (ΔIL) decreases with higher inductance and increases with higher VIN or VOUT.

In Equation (EQ 2) the maximum inductor current in PWM mode under static load conditions is calculated. The satura-

tion current of the inductor should be rated higher than the maximum inductor current as calculated with Equation (EQ

3). This is recommended because the inductor current will rise above the calculated value during heavy load tran-

sients.

V_OUT

--------------

1 –

(EQ 2)

(EQ 3)

V_IN

-----------------------

×

ΔI_L= V_OUT

L × f

ΔI_L

-------

+

I_LMAX= I_OUTMAX

2

Where:

f = Switching Frequency (1.5 MHz typical)

L = Inductor Value

ILmax = Maximum Inductor current

ΔIL = Peak to Peak inductor ripple current

The recommended starting point for setting ripple current is ΔIL = 240mA (40% of 600mA).

The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current

to prevent core saturation. Thus, a 720mA rated inductor should be sufficient for most applications (600mA + 120mA).

A easy and fast approach is to select the inductor current rating fitting to the maximum switch current limit of the con-

verter.

Note: For highest efficiency, a low DC-resistance inductor is recommended.

Accepting larger values of ripple current allows the use of low inductance values, but results in higher output voltage

ripple, greater core losses, and lower output current capability.

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AS1324

Data Sheet - Application Information

The total losses of the coil have a strong impact on the efficiency of the dc/dc conversion and consist of both the losses

in the dc resistance and the following frequency-dependent components:

1. The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)

2. Additional losses in the conductor from the skin effect (current displacement at high frequencies)

3. Magnetic field losses of the neighboring windings (proximity effect)

4. Radiation losses

Table 5. Recommended Inductors

Part Number

L

DCR

97mΩ

150mΩ

175mΩ

110mΩ

35mΩ

50mΩ

72mΩ

105mΩ

Current Rating Dimensions (L/W/T)

Manufacturer

Murata

www.murata.com

LQH32CN2R2M33

LQH32CN4R7M33

LPS3008-222MLC

LPS3015-222MLC

MOS6020-222MLC

MOS6020-472MLC

CDRH3D16NP-2R2N

CDRH3D16ND-4R7N

2.2µH

4.7µH

2.2µH

4.7µH

2.2µH

4.7µH

790mA

650mA

3.2x2.5x2.0mm

3.1x3.1x0.8mm

3.1x3.1x1.5mm

6.0x6.8x2.4mm

4.0x4.0x1.8mm

Coilcraft

www.coilcraft.com

1100mA

2000mA

3260mA

1820mA

1200mA

900mA

Sumida

www.sumida.com

Figure 26. Efficiency Comparison of Different Inductors, VIN = 2.7V, VOUT = 1.8V and 1.2V

95

90

85

80

75

70

95

90

85

80

75

70

VOUT = 1.8V

VOUT = 1.2V

LQH32CN2R2

LPS3015-222

LQH32CN4R7

LPS3008-222

M OS6020-222

M OS6020-472

LQH32CN2R2

LPS3015-222

LQH32CN4R7

LPS3008-222

M OS6020-222

M OS6020-472

1

10

100

1000

1

10

100

1000

Output Current (mA)

Output Capacitor Selection

The advanced fast-response voltage mode control scheme of the AS1324 allows the use of tiny ceramic capacitors.

Because of their lowest output voltage ripple low ESR ceramic capacitors are recommended. X7R or X5R dielectric

output capacitor are recommended.

At high load currents, the device operates in PWM mode and the RMS ripple current is calculated as:

V_OUT

--------------

1 –

(EQ 4)

V_IN

----------------------- ----------------

1

I_RMSC

= V_OUT

×

OUT

L × f

2 ×

3

While operating in PWM mode the overall output voltage ripple is the sum of the voltage spike caused by the output

capacitor ESR plus the voltage ripple caused by charging and discharging the output capacitor:

V_OUT

--------------

1 –

(EQ 5)

V_IN

-----------------------

1

⎛

⎝

⎞

--------------------------------

ΔV_OUT= V_OUT

×

+ ESR

⎠

L × f

8 × C_OUT× f

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AS1324

Data Sheet - Application Information

Higher value, low cost ceramic capacitors are available in very small case sizes, and their high ripple current, high volt-

age rating, and low ESR make them ideal for switching regulator applications. Because the AS1324 control loop is not

dependant on the output capacitor ESR for stable operation, ceramic capacitors can be used to achieve very low out-

put ripple and accommodate small circuit size.

At light loads, the converter operates in powersave mode and the output voltage ripple is in direct relation to the output

capacitor and inductor value used. Larger output capacitor and inductor values minimize the voltage ripple in power-

save mode and tighten DC output accuracy in powersave mode.

Input Capacitor Selection

In continuous mode, the source current of thePMOS is a square wave of the duty cycle VOUT/VIN. To prevent large volt-

age transients while minimizing the interference with other circuits caused by high input voltage spikes, a low ESR

input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given as:

(EQ 6)

V_OUT× (V_IN– V_OUT

-----------------------------------------------------------

×

)

I_RMS= I_MAX

V_IN

where the maximum average output current IMAX equals the peak current minus half the peak-to-peak ripple current,

IMAX = ILIM - ΔIL/2

This formula has a maximum at VIN = 2VOUT where IRMS = IOUT/2. This simple worst-case condition is commonly used

for design because even significant deviations only provide negligible affects.

The input capacitor can be increased without any limit for better input voltage filtering. Take care when using small

ceramic input capacitors. When a small ceramic capacitor is used at the input, and the power is being supplied through

long wires, such as from a wall adapter, a load step at the output, or VIN step on the input, can induce ringing at the VIN

pin. This ringing can then couple to the output and be mistaken as loop instability, or could even damage the part by

exceeding the maximum ratings.

Ceramic Input and Output Capacitors

When choosing ceramic capacitors for CIN and COUT, the X5R or X7R dielectric formulations are recommended.

These dielectrics have the best temperature and voltage characteristics for a given value and size. Y5V and Z5U

dielectric capacitors, aside from their wide variation in capacitance over temperature, become resistive at high frequen-

cies and therefore should not be used.

Table 6. Recommended Input and Output Capacitor

Part Number

C

TC Code Rated Voltage Dimensions (L/W/T)

Manufacturer

Taiyo Yuden

www.t-yuden.com

JMK212BJ226MG-T

22µF

X5R

6.3V

0805

0603

0805

Murata

www.murata.com

GRM188R60J106ME47

GRM21BR71A475KA73

10µF

X5R

X7R

6.3V

10V

4.7µF

Because ceramic capacitors lose a lot of their initial capacitance at their maximum rated voltage, it is recommended

that either a higher input capacity or a capacitance with a higher rated voltage is used.

Feedback Resistor Selection

In the AS1324-AD, the output voltage is set by an external resistor divider connected to VFB (see Figure 27). This cir-

cuitry allows for remote voltage sensing and adjustment.

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AS1324

Data Sheet - Application Information

Figure 27. Setting the AS1324 Output Voltage

0.6V ≤ VOUT ≤ 5.5V

R2

5

R1<<R2

VFB

R1

AS1324

2

GND

Resistor values for the circuit shown in Figure 27 can be calculated as:

R₂

------

(EQ 7)

V_OUT= 0,6 × 1 +

R₁

The output voltage can be adjusted by selecting different values for R1 and R2. For R1 a value between 10kΩ and

500kΩ is recommended. A higher resistance of R1 and R2 will result in a lower leakage current at the output. It is rec-

ommended to keep VIN 500mV higher than VOUT.

Efficiency

The efficiency of a switching regulator is equivalent to:

Efficiency = (POUT/PIN)100%

(EQ 8)

For optimum design, an analysis of the AS1324 is needed to determine efficiency limitations and to determine design

changes for improved efficiency. Efficiency can be expressed as:

Efficiency = 100% – (L1 + L2 + L3 + ...)

(EQ 9)

Where:

L1, L2, L3, etc. are the individual losses as a percentage of input power.

Althought all dissipative elements in the circuit produce losses, those four main sources should be considered for effi-

ciency calculation:

Input Voltage Quiescent Current Losses

The VIN current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and con-

trol currents. VIN current results in a small (<0.1%) loss that increases with VIN, even at no load. The VIN quiescent cur-

rent loss dominates the efficiency loss at very low load currents.

I²R Losses

Most of the efficiency loss at medium to high load currents are attributed to I²R loss, and are calculated from the resis-

tances of the internal switches (RSW) and the external inductor (RL). In continuous mode, the average output current

flowing through inductor L is split between the internal switches. Therefore, the series resistance looking into the SW

pin is a function of both NMOS & PMOS RDS(ON) as well as the the duty cycle (DC) and can be calculated as follows:

RSW = (RDS(ON)PMOS)(DC) + (RDS(ON)NMOS)(1 – DC)

(EQ 10)

The RDS(ON) for both MOSFETs can be obtained from the Electrical Characteristics on page 4. Thus, to obtain I²R

losses calculate as follows:

I²R losses = IOUT²(RSW + RL)

(EQ 11)

Switching Losses

The switching current is the sum of the control currents and the MOSFET driver. The MOSFET driver current results

from switching the gate capacitance of the power MOSFETs. If a MOSFET gate is switched from low to high to low

again, a packet of charge dQ moves from VIN to ground. The resulting dQ/dt is a current out of VIN that is typically

much larger than the DC bias current. In continuous mode:

IGC = f(QPMOS + QNMOS)

(EQ 12)

Where: QPMOS and QNMOS are the gate charges of the internal MOSFET switches.

The losses of the gate charges are proportional to VIN and thus their effects will be more visible at higher supply volt-

ages.

Other Losses

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AS1324

Data Sheet - Application Information

Basic losses in the design of a system should also be considered. Internal battery resistances and copper trace can

account for additional efficiency degradations in battery operated systems. By making sure that CIN has adequate

charge storage and very low ESR at the given switching frequency, the internal battery and fuse resistance losses can

be minimized. CIN and COUT ESR dissipative losses and inductor core losses generally account for less than 2% total

additional loss.

Thermal Shutdown

Due to its high-efficiency design, the AS1324 will not dissipate much heat in most applications. However, in applica-

tions where the AS1324 is running at high ambient temperature, uses a low supply voltage, and runs with high duty

cycles (such as in dropout) the heat dissipated may exceed the maximum junction temperature of the device.

As soon as the junction temperature reaches approximately 150ºC the AS1324 goes in thermal shutdown. In this mode

the internal PMOS & NMOS switch are turned off. The device will power up again, as soon as the temperature falls

below +145°C again.

Checking Transient Response

The main loop response can be evaluated by examining the load transient response. Switching regulators normally

take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an

amount equivalent to:

VDROP = ΔIOUT x ESR

(EQ 13)

Where:

ESR is the effective series resistance of COUT.

ΔIOUT also begins to charge or discharge COUT, which generates a feedback error signal. The regulator loop then acts

to return VOUT to its steady-state value. During this recovery time VOUT can be monitored for overshoot or ringing that

would indicate a stability problem.

Design Example

Figure 28 shows the AS1324 used in a single lithium-ion (3.7V typ) battery-powered mobile phone application. The

load current requirement is 600mA (max) but most of the time the device will require only 2mA (standby mode current).

Figure 28. Design Example

2.2µH

4

3

VOUT

2.2V

VIN

3.7V

VIN

SW

CIN

4.7µF

CER

COUT

10µF

CER

22pF

AS1324

1MΩ

5

1

R2

EN

VFB

R1

375kΩ

GND

2

For the circuit shown in Figure 28, efficiency at low- and high-load currents is an important consideration when select-

ing the value for the external inductor, which is calculated as:

V_OUT

--------------

fΔI_L

V_OUT

--------------

V_IN

⎛

⎞

⎠

(EQ 14)

L =

× 1 –

⎝

From (EQ 14), substituting VOUT = 2.2V, VIN = 3.7V, ΔI_L= 240mA and f = 1.5MHz gives:

2,2V

⎞

⎛

(EQ 15)

----------------------------------------------------

------------

= 2,48μH

L =

× 1 –

⎝

⎠

3,7V

(1,5MHz × 240mA)

Therefore, a standard 2.2µH inductor should be used for this design.

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AS1324

Data Sheet - Application Information

For best overall efficiency use an inductor with a rating of 720mA or greater and less than 0.2Ω series resistance. CIN

will require an RMS current rating of at least 0.3A ≅ ILOAD(MAX)/2, whereas COUT will require an ESR of less than

0.25Ω. In most cases, a ceramic capacitor will satisfy this requirement.

For the feedback resistors, select the value for R1 = 375kΩ. R2 can then be calculated from (EQ 7) to be:

R2 = (VOUT/0.6 - 1)375k = 1000kΩ

Layout Considerations

The AS1324 requires proper layout and design techniques for optimum performance.

ꢀ

The power traces (GND, SW, and VIN) should be kept as short, direct, and wide as is practical.

Pin VFB (AS1324 only) should be connected directly to the feedback resistors (R1 and R2). A potentiometer as

replacement for R1 and R2 should be avoided to minimize the output voltage ripple and to maintain the stability of

the regulator.

ꢀ

The resistive divider (R1/R2) must be connected between the positive plate of COUT and ground.

The positive plate of CIN should be connected as close to VIN as is practical since CIN provides the AC current to

the internal power MOSFETs.

ꢀ

Switching node SW should be kept far away from the sensitive VFB node.

The negative plates of CIN and COUT should be kept as close to each other as is practical. A starpoint to Ground is

recommended.

Figure 29. AS1324 Basic PCB Layout

R1

VIN

Via to VIN

R2

Via to GND

Via to VOUT

1

5

AS1324

4

2

3

VOUT

L1

CFWD

SW

COUT

CIN

GND

Figure 30. AS1324 Basic Diagram

High Current Path

1

5

EN

VFB

AS1324

2

R2

R1

GND

COUT

CFWD

VOUT

3

4

L1

VIN

SW

CIN

V^IN

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AS1324

Data Sheet - Application Information

Figure 31. AS1324-18 Basic PCB Layout

Via to VIN

1

VIN

Via to VOUT

5

AS1324-

18

2

3

VOUT

L1

SW

4

COUT

CIN

GND

Figure 32. AS1324-18 Basic Diagram

High Current Path

1

5

EN

VOUT

AS1324-18

2

GND

COUT

VOUT

3

4

VIN

SW

L1

CIN

VIN

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AS1324

Data Sheet - Package Drawings and Markings

10 Package Drawings and Markings

The device is available in an 5-pin TSOT-23 package.

Figure 33. 5-pin TSOT-23 Package

Symbol

Min

Typ

Max

1.00

0.10

0.90

0.45

0.39

0.20

Notes

Symbol

Min

Typ

0.40

Max

Notes

A

A1

A2

b

L

L1

L2

N

0.30

0.50

0.01

0.84

0.30

0.31

0.12

0.05

0.87

0.60REF

0.25BSC

5

b1

c

0.35

0.15

R

0.10

R1

0.25

8º

c1

0.08

0.13

0.16

0º

4º

θ

θ1

D

E

2.90BSC

2.80BSC

1.60BSC

0.95BSC

1.90BSC

3,4

10º

12º

Tolerances of Form and Position

E1

e

aaa

bbb

ccc

ddd

0.15

0.25

0.10

0.20

e1

Notes:

1. Dimensioning and tolerancing conform to ASME Y14.5M - 1994.

2. Dimensions are in millimeters.

3. Dimension D does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, and gate burrs shall

not exceed 0.15mm per end. Dimension E1 does not include interlead flash or protrusion. Interlead flash or pro-

trusion shall not exceed 0.15mm per side. Dimensions D and E1 are determined at datum H.

4. The package top can be smaller than the package bottom. Dimensions D and E1 are determined at the outer-

most extremes of the plastic body exclusive of mold flash, tie bar burrs, gate burrs, and interlead flash, but

include any mistmatches between the top of the package body and the bottom. D and E1 are determined at

datum H.

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AS1324

Data Sheet - Ordering Information

11 Ordering Information

The device is available as the following standard versions.

Table 7. Ordering Information

Model

Marking

Description

Delivery Form

Package

Output

1.5MHz, 600mA Synchronous

DC/DC Converter

5-pin TSOT-23

AS1324-BTTT-AD

ASKR

adjustable

Tape and Reel

1.5MHz, 600mA Synchronous

DC/DC Converter

5-pin TSOT-23

AS1324-BTTT-12

AS1324-BTTT-15

AS1324-BTTT-18

ASKT

ASKU

ASKS

1.2V

1.5V

1.8V

Tape and Reel

1.5MHz, 600mA Synchronous

DC/DC Converter

1.5MHz, 600mA Synchronous

DC/DC Converter

All devices are RoHS compliant and free of halogene substances.

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AS1324

Data Sheet

Copyrights

lated, stored, or used without the prior written consent of the copyright owner.

All products and companies mentioned are trademarks or registered trademarks of their respective companies.

Disclaimer

Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing

in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding

the information set forth herein or regarding the freedom of the described devices from patent infringement. austria-

microsystems AG reserves the right to change specifications and prices at any time and without notice. Therefore,

prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for current informa-

tion. This product is intended for use in normal commercial applications. Applications requiring extended temperature

range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or life-

sustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for

each application. For shipments of less than 100 parts the manufacturing flow might show deviations from the standard

production flow, such as test flow or test location.

The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However,

austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not limited to

personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or

consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the tech-

nical data herein. No obligation or liability to recipient or any third party shall arise or flow out of

austriamicrosystems AG rendering of technical or other services.

Contact Information

Headquarters

austriamicrosystems AG

A-8141 Schloss Premstaetten, Austria

Tel: +43 (0) 3136 500 0

Fax: +43 (0) 3136 525 01

For Sales Offices, Distributors and Representatives, please visit:

http://www.austriamicrosystems.com/contact-us

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Revision 1.03

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型号：	AS1324-BTTT-12
厂家：	AMS(艾迈斯)
描述：	1.5MHz, 600mA, DC/DC Step-Down Regulator 1.5MHz的， 600毫安， DC / DC降压型稳压器稳压器
文件：	总20页 (文件大小：910K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

AS1324-BTTT-12 [AMSCO]

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