Diodes PAM2321 User Manual

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PAM2321

3MHz, FAST TRANSIENT 2A STEP-DOWN CONVERTER

Description

The PAM2321 is a 2A step-down converter with a typical input

voltage of 3.3V and a fixed output voltage of 1.2V or an adjustable

output. The 3MHz switching frequency enables the use of small

external components. The ultra-small 3mmx3mm footprint and high

efficiency make the PAM2321 an ideal choice for portable

applications.

The PAM2321 delivers 2A maximum output current while consuming

only 55µA no-load quiescent current. Low R

MOSFETs and 100% duty cycle operation make the PAM2321 the

ideal choice for high output voltage, high current applications which

require a low dropout threshold.

The PAM2321 provides excellent transient response and output

accuracy across the operating range.

The PAM2321 maintains high efficiency throughout the load range.

The PAM2321 automatically optimizes efficiency during light load

mode (PSM) and maintains constant frequency and low output ripple

during PWM mode.

Over-temperature and short circuit protection safeguard the PAM2321

and system components from damage.

The PAM2321 are available in Pb-free, ultrasmall, low profile,

TDFN3X3-10 package. The product is rated over a temperature range

of -40°C to +85°C.

DS(ON)

integrated

Features

• 2A Maximum Output Current

• Tiny 0.47µH Chip Inductor

• Excellent Transient Response

• Input Voltage: 2.7V to 5.5V

• Fixed or Adjustable Output Voltage Options:

 Fixed Output Voltage: 1.2V

 Adjustable Output Voltage: 1.0V to V

• High Efficiency with 3MHz Switching Frequency

• 55µA No Load Quiescent Current

• 100% Duty Cycle Low-Dropout Operation

• Internal Soft-Start

• Over-Temperature and Current Limit Protection

• <1µA Shutdown Current

• -40°C to +85°C Temperature Range

• Pb-Free/Halogen Free Package

Pin Assignments

Applications

• Cellular Phone

• Digital Cameras

• Hard Disk Drives

• MP3 Players

• PDAs and Handheld Computers

• Portable Media Players

• USB Devices

• Wireless Network Cards

• RoHS/REACH Compliant

PAM2321

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(

Typical Applications Circuit

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PAM2321

Pin Descriptions

Name

PGND

PVIN

AGND

Main power ground return pin. Connect to the output and input capacitor return.

Input power supply tied to the source of the high side P-Channel MOSFET.

Power supply; supplies power for the internal circuitry.

VIN

Feedback input pin. This pin is connected directly to the converter output for the 1.2V fixed output version, or connected to an

external resistor divider for the adjustable output version. Analog ground. This pin is internally connected to the analog ground of the control circuitry. Enable pin. A logic low disables the converter and it consumes less than 1μA of current. When connected high, it resumes normal

operation. Switching node. Connect the inductor to this pin. It is internally connected to the drain of both high and low side MOSFETs.

Exposed pad of the package provides both electrical contact to the ground and good thermal

contact to the PCB. This pad must be soldered to the PCB for proper operation.

Functional Block Diagram

OUT

Function

)

2R/1R1*6.0

PAM2321

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PAM2321

Absolute Maximum Ratings (@T

These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground.

Parameter Rating Unit

Input Voltage -0.3 to +6.5 V

EN, FB Pin Voltage

SW Pin Voltage

Junction Temperature 150 °C

Storage Temperature Range -65 to +150 °C

Soldering Temperature 300, 5sec °C

Recommended Operating Conditions (@T

Parameter Rating Unit

Supply Voltage 2.5 to 5.5 V

Operation Temperature Range -40 to +85

Junction Temperature Range -40 to +125

= +25°C, unless otherwise specified.)

-0.3 to V

-0.3 to (V

+0.3)

= +25°C, unless otherwise specified.)

°C

Thermal Information

Parameter Symbol Package Max Unit

Thermal Resistance (Junction to Case)

Thermal Resistance (Junction to Ambient)

Internal Power Dissipation

TDFN3x3-10 8.5

TDFN3x3-10 60

TDFN3x3-10 1.66 W

°C/W

PAM2321

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PAM2321

Electrical Characteristics

(@TA = +25°C, VIN = 3.3V, V

Parameter Symbol Test Conditions Min Typ Max Units

Input Voltage Range

UVLO Threshold

Output Voltage Range

Output Voltage Accuracy

Regulated Feedback Voltage

PMOS Current Limit

Output Voltage Line Regulation LNR

Output Voltage Load Regulation LDR

Quiescent Current

Shutdown Current

Oscillator Frequency

Drain-Source On-State Resisitance

SW Leakage Current

Start-Up Time

PSM Threshold

EN Threshold High

EN Threshold Low

EN Leakage Current

Over Temperature Protection OTP 150 °C

OTP Hysteresis OTH 30 °C

PAM2321

Document number: DSxxxxx Rev. 2 - 1

= 1.2V, CIN = 10µF, CO = 10µF, L = 0.47µH, unless otherwise specified.)

OUT

Rising

Hysteresis 250 mV

UVLO

VIN Falling

DS(ON)

OUT

LIM

OSC

LSW

IO = 0mA

No Load 0.588 0.600 0.612 V

= 3.3V to 4V

= 1mA to 2A

No Load 55 90 µA

VEN = 0V

IDS = 100mA

1 µA

VIN = 3.3V, VO = 1.2V

200 mA

1.4 V

0.4 V

±0.01 µA

P MOSFET 130 mΩ

N MOSFET 90 mΩ

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2.7 3.3 5.5 V

2.6 2.7 V

2 V

1 1.2

VIN

-3.0 +3.0 %

3.0 A

0.3 %/V

1 %/A

1 µA

3 MHz

200 µs

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Typical Performance Characteristics (@T

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PAM2321

= +25°C, CIN = 10µF, CO = 10µF, L = 0.47µH unless otherwise specified.)

PAM2321

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Typical Performance Characteristics (cont.) (@T

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PAM2321

= +25°C, CIN = 10µF, CO = 10µF, L = 0.47µH unless otherwise specified.)

PAM2321

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PAM2321

Application Information

The basic PAM2321 application circuit is shown in Page 2. External component selection is determined by the load requirement, selecting L first

and then C

and C

Inductor Selection

For most applications, the value of the inductor will fall in the range of 1μH to 4.7μH. Its value is chosen based on the desired ripple current and

efficiency. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V

the ripple current as shown in equation 3.0. A reasonable starting point for setting ripple current is ΔI

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 2.8A rated inductor should be enough for most applications (2A + 800mA). For better efficiency, choose a low DC-resistance inductor.

CIN and C

In continuous mode, the source current of the top MOSFET is a square wave of duty cycle V

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

This formula has a maximum at V

significant deviations do not offer much relief. Note that the capacitor manufacturer's ripple current ratings are often based on 2000 hours of life.

This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Consult the

manufacturer if there is any question.

The selection of C

Typically, once the ESR requirement for C

output ripple ΔV

OUT

()()

⎛ ⎜

−=

OUTL

⎜ ⎝

⎞

OUT

⎟

Equation (1)

⎟

⎠

Selection

[]

()

−

required

OUT

is determined by:

OUT

≈

≅

OMAXRMS

= 2V

OUT

is driven by the required effective series resistance (ESR).

OUT

⎛ ⎜

ESR

LOUT

⎜ ⎝

⎞

⎟ ⎟

fC8

OUT

⎠

VVV

, where I

RMS

has been met, the RMS current rating generally far exceeds the I

2/1

OUTINOUT

= I

/2. This simple worst-case condition is commonly used for design because even

OUT

or V

OUT

= 800mA (40% of 2A).

. To prevent large voltage transients, a low

OUT/VIN

(P-P) requirement. The

RIPPLE

also increases

Where f = operating frequency, C

highest at maximum input voltage since ΔI

= output capacitance and ΔIL = ripple current in the inductor. For a fixed output voltage, the output ripple is

OUT

increases with input voltage.

Using Ceramic Input and Output Capacitors

Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and

low ESR make them ideal for switching regulator applications. Using ceramic capacitors can achieve very low output ripple and small circuit size.

When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formul ations. These dielectrics have the best

temperature and voltage characteristics of all the ceramics for a given value and size.

Thermal Consideration

Thermal protection limits power dissipation in the PAM2321. When the junction temperature exceeds +150°C, the OTP (Over Temperature

Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature

drops below +120°C.

For continuous operation, the junction temperature should be maintained below +125°C. The power dissipation is defined as:

()

−+

is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses.

RVVRV

PAM2321

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L)ON(DSOINH)ON(DSO

()

VIIF

INQOS

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Application Information (cont.)

For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:

VIRIP

INQH)ON(DS

PAM2321

Since R

voltage range. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surrounding airflow

and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula:

Where T

junction to the ambient. Based on the standard JEDEC for a two layers thermal test board, the thermal resistance θ

60°C/W. The maximum power dissipation at T

, quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input

DS(ON)

−

is the maximum allowable junction temperature +125°C. TA is the ambient temperature and θJA is the thermal resistance from the

J(MAX)

= (125°C - 25°C) /60°C/W = 1.66W

A)MAX(J

of TDFN3x3 package is

= +25°C can be calculated by following formula:

Setting the Output Voltage

The internal reference is 0.6V (Typical). The output voltage is calculated as below:

The output voltage is given by Table 1.

Table 1: Resistor selection for output voltage setting.

1.2V 100k 100k

1.5V 150k 100k

1.8V 200k 100k

2.5V 380k 120k

3.3V 540k 120k

⎛ ⎜

⎝

⎞

1x6.0

⎟

⎠

R1 R2

Pulse Skipping Mode (PSM) Description

When load current decreases, the peak switch current in Power-PMOS will be lower than skip current threshold and the device will enter into

Pulse Skipping Mode.

In this mode, the device has two states, working state and idle state. First, the device enters into working state control led by internal error

amplifier.When the feedback voltage gets higher than internal reference voltage, the device will enter into low I

blocks disabled. The output voltage will be reduced by loading or leakage current. When the feedback voltage gets lower than the internal

reference voltage, the convertor will start a working state again.

idle state with most of internal

100% Duty Cycle Operation

As the input voltage approaches the output voltage, the converter turns the P-Channel transistor continuously on. In this mode the output voltage

is equal to the input voltage minus the voltage drop across the P-Channel transistor:

where R

= P-Channel switch ON resistance, I

DS(ON)

()

+−=

RRIVV

LDSONLOADINOUT

= Output Current, RL = Inductor DC Resistance

LOAD

UVLO and Soft-Start

The reference and the circuit remain reset until the VIN crosses its UVLO threshold. The PAM2321 has an internal soft-start circuit that limits the

in-rush current during start-up. This prevents possible voltage drops of the input voltage and eliminates the output voltage overshoot.

PAM2321

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Application Information (cont.)

Short Circuit Protection

When the converter output is shorted or the device is overloaded, each high-side MOSFET current-limit event (3A typ) turns off the high-side

MOSFET and turns on the low-side MOSFET. An internal counter is used to count the each current-limit event. The counter is reset after

consecutive high-side MOSFETs turn on without reaching current limit. If the current-limit condition persists, the counter fills up. The control logic

then stops both high-side and lowside MOSFETs and waits for a hiccup period, before attemping a new soft-start sequence. The counter bits is

decided by V

1.7%. The hiccup mode is disable during soft-start time.

voltage. If ≤VFB 0 2, the counter is 3-bit counter; if VFB >0.2 the counter is 6-bit counter. The typical hicuup made duty cycle is

Thermal Shutdown

When the die temperature exceeds +150°C, a reset occurs and the reset remains until the temperature decrease to +120°C, at which time the

circuit can be restarted.

PCB Layout Check List

When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the PAM2321. Check the following

in your layout:

1. The input capacitor should be close to IC as close as possible.

2. Must put a small decoupling capacitor between VIN PIN and AGND Pin.

3. Minimize the switching loop area to avoid excessive switching noise.

4. AGND and PGND should connect at input capacitor GND.

5. For the good thermal dissipation, PAM2321 has a heat dissipate pad in the bottom side, it should be soldered to PCB surface. For the copper

area can't be large in the component side, so we can use mu ltiple vias connect to other side of the PCB.

Ordering Information

Part Number Output Voltage Part Type Standard Package

PAM2321AYMADJ

PAM2321

Document number: DSxxxxx Rev. 2 - 1

P2321A

XXXYW

T-DFN3x3-10 3000 Units/Tape & Reel

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Marking Information

Package Outline Dimensions (All dimensions in mm.)

TDFN3x3-10

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PAM2321

A/B : Pin Configuration X : Internal Code Y : Year W : Week

PAM2321

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PAM2321

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PAM2321

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