MP28117DQ - Monolithic Power Systems, Inc.

MP28117

Dual 1.2MHz, 800mA Synchronous

Step-Down Converter

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The Future of Analog IC Technology

DESCRIPTION

The MP28117 contains two independent

1.2MHz constant frequency, current mode,

PWM step-down converters. Each converter

integrates a main switch and a synchronous

rectifier for high efficiency without an external

Schottky diode. The MP28117 is ideal for

powering portable equipment that runs from a

single cell Lithium-Ion (Li+) battery. Each

converter can supply 800mA of load current

from a 2.5V to 6V input voltage. The output

voltage can be regulated as low as 0.6V. The

MP28117 can also run at 100% duty cycle for

low dropout applications.

FEATURES

• Up to 95% Efficiency

• 1.2MHz Constant Switching Frequency

• 800mA Load Current on Each Channel

• 2.5V to 6V Input Voltage Range

• Output Voltage as Low as 0.6V

• 100% Duty Cycle in Dropout

• Current Mode Control

• Short Circuit Protection

• Thermal Fault Protection

• <0.1μA Shutdown Current

• Internally Compensated

• Space Saving 10-Pin QFN Package

APPLICATIONS

• Cellular and Smart Phones

• Microprocessors and DSP Core Supplies

• PDAs

• MP3 Players

• Digital Still and Video Cameras

• Portable Instruments

“MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic

Power Systems, Inc.

TYPICAL APPLICATION

MP28117

IN2IN1

GND2GND1

FB2

SW2

EN2

FB1

SW1

EN1

IN1/IN2

2.5V to 6V

OFF ONOFF ON

OUT2

1.2V

800mA

OUT1

1.8V

800mA

100

EFFICIENCY (

)

0 500 1000

LOAD CURRENT (mA)

OUT

=3.3V

MP28117 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

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PACKAGE REFERENCE

Part Number* Package Temperature

MP28117DQ QFN10

(3mm x 3mm) –40°C to +85°C

* For Tape & Reel, add suffix –Z (eg. MP28117DQ–Z)

For RoHS Compliant Packaging, add suffix –LF

(eg. MP28117DQ–LF–Z)

ABSOLUTE MAXIMUM RATINGS (1)

VIN1/IN2 to GND ............................ –0.3V to +6.5V

VSW1/SW2 to GND................... –0.3V to VIN + 0.3V

VFB1/FB2, VEN1/EN2 to GND ............. –0.3V to +6.5V

Junction Temperature.............................+150°C

Lead Temperature ..................................+260°C

Storage Temperature .............–65°C to +150°C

Recommended Operating Conditions (2)

Supply Voltage VIN1/IN2 ....................... 2.5V to 6V

Output Voltage VOUT1/OUT2 .................. 0.6V to 6V

Operating Temperature .............–40°C to +85°C

Thermal Resistance (3) θJA θJC

QFN10 (3mm x 3mm) ............. 50 ...... 12... °C/W

Notes:

1) Exceeding these ratings may damage the device.

2) The device is not guaranteed to function outside of its

operating conditions.

3) Measured on approximately 1” square of 1 oz copper.

ELECTRICAL CHARACTERISTICS (4)

VIN1/IN2 = VEN1/EN2 = 3.6V, TA = +25°C, unless otherwise noted.

Parameter Symbol Condition Min Typ Max Units

Each Converter Supply Current VEN1/EN2 = VIN1/IN2, VFB1/FB2 = 0.65V 440 600 μA

Each Converter Shutdown

Current

VEN1/EN2 = 0V, VIN1/IN2 = 6V 0.10 1 μA

IN Under Voltage Lockout

Threshold

Rising Edge 2.15 2.30 2.40 V

IN Under Voltage Lockout

Hysteresis

55 mV

TA = +25°C 0.588 0.600 0.612

Regulated FB Voltage VFB –40°C ≤ TA ≤ +85°C 0.582 0.600 0.618 V

FB Input Bias Current IFB V

FB1/FB2 = 0.65V –50 0.5 +50 nA

PFET On Resistance ISW1/SW2 = 100mA 0.42 Ω

NFET On Resistance ISW1/SW2 = –100mA 0.26 Ω

SW Leakage Current V

EN1/EN2 = 0V, VIN1/IN2 = 6V

VSW1/SW2 = 0V or 6V –2 +2 μA

PFET Current Limit Duty Cycle = 100%,

Current Pulse Width < 1ms 0.9 1.3 1.8 A

Oscillator Frequency fOSC 0.99 1.24 1.49 MHz

Thermal Shutdown Trip

Threshold

150

°C

EN Enable Threshold –40°C ≤ TA ≤ +85°C 0.3 0.96 1.5 V

EN Input Current VEN1/EN2 = 0V to 6V –1 +1 μA

Notes:

4) Production test at +25°C. Specifications over the temperature range are guaranteed by design and characterization.

TOP VIEW

EN1

FB1

IN2

GND2

SW2

SW1

GND1

IN1

FB2

EN2

EXPOSED PAD

ON BACKSIDE

MP28117 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

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TYPICAL PERFORMANCE CHARACTERISTICS

VIN1/IN2 = 3.3V, VOUT1 = 1.8V, VOUT2 = 1.2V, L1/2 = 4.7μH, CIN1/IN2 = 4.7μF, COUT1/OUT2 = 10μF, TA = +25°C,

unless otherwise noted.

Short Circuit Protection

(No Load)

Short Circuit Recovery

(No Load)

Startup from Shutdown

VOUT

1V/div

0.5A/div

VOUT

1V/div

0.5A/div

VEN

2V/div

VOUT

1V/div

0.5A/div

400ns/div

Load Transient

(IOUT=0mA to 500mA Step)

Medium Load Operation

(IOUT=400mA)

VOUT AC

100mV/div.

ILOAD

0.5A/div.

VSW

2V/div.

VOUT AC

20mV/div.

200mA/div.

VSW

2V/div.

VOUT AC

20mV/div.

500mA/div.

400ns/div

Heavy Load Operation

(IOUT=800mA)

0.606

0.604

0.602

0.600

0.598

0.596

0.594

FEEDBACK VOLTAGE (V)

-40 +200

-20 +40 +60 +80 +100

TEMPERATURE (°C)

Feedback Voltage vs

Temperature

100

EFFICIENCY (%)

0.0 0.40.2 0.6 0.8

LOAD CURRENT (A)

Efficiency vs

Load Current

VOUT1=1.8V

VOUT2=1.2V

MP28117 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

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PIN FUNCTIONS

Pin # Name Description

1 EN1

Channel 1 Enable Control Input. Drive EN1 above 1.5V to turn on the Channel 1. Drive EN1

below 0.3V to turn it off (shutdown current < 0.1μA).

2 FB1

Channel 1 Feedback Input. Connect FB1 to the center point of the external resistor divider. The

feedback voltage is 0.6V.

3 IN2 Channel 2 Supply Input. Bypass to GND with a 2.2μF or greater ceramic capacitor.

4 GND2 Ground 2.

5 SW2

Channel 2 Power Switch Output. Inductor connection to drains of the internal PFET and NFET

switches.

6 EN2

Channel 2 Enable Control Input. Drive EN2 above 1.5V to turn on the Channel 2. Drive EN2

below 0.3V to turn it off (shutdown current < 0.1μA).

7 FB2

Channel 2 Feedback Input. Connect FB2 to the center point of the external resistor divider. The

feedback voltage is 0.6V.

8 IN1 Channel 1 Supply Input. Bypass to GND with a 2.2μF or greater ceramic capacitor.

9 GND1 Ground 1.

10 SW1

Channel 1 Power Switch Output. Inductor connection to drains of the internal PFET and NFET

switches.

MP28117 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

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OPERATION

IN1/

IN2

EN1/

EN2

FB1/

FB2

GND1/

GND2

SW1/

SW2

PWMCMP

PWM

OSC

EAMP

ICS

SLOPE COMP

FEEDBACK

ERROR\

AMP

0.6V

EAO

17pF

BIAS

VOLTAGE

REFERENCE

PWM

CONTROL

LOGIC

1.0MHz

OSCILLATOR

IAMP

10X

CURRENT

SENSE

AMP

MAIN

SWITCH

(PCH)

SYNCHRONOUS

RECTIFIER

(NCH)

Figure 1—Functional Block Diagram (Diagram represents ½ of the MP28117)

The MP28117 has dual independent constant

frequency current mode PWM step-down

converters. The MP28117 is optimized for low

voltage, Li-Ion battery powered applications

where high efficiency and small size are critical.

The MP28117 uses external resistor dividers to

set two output voltages independently from

0.6V to 6V. The device integrates both main

switches and synchronous rectifiers, which

provides high efficiency and eliminates the

need for an external Schottky diode. The

MP28117 can achieve 100% duty cycle. The

duty cycle D of each step-down converter is

defined as:

%100

%100fTD

OUT

OSCON ×=××=

Where TON is the main switch on time, fOSC is

the oscillator frequency (1.2MHz), VOUT is the

output voltage and VIN is the input voltage.

Current Mode PWM Control

Slope compensated current mode PWM control

provides stable switching and cycle-by-cycle

current limit for superior load and line response

and protection of the internal main switch and

synchronous rectifier. Each channel switches at

a constant frequency (1.2MHz) and regulates

the output voltage. During each cycle the PWM

comparator modulates the power transferred to

the load by changing the inductor peak current

based on the feedback error voltage. During

normal operation, the main switch is turned on

for a certain time to ramp the inductor current at

each rising edge of the internal oscillator, and

switched off when the peak inductor current is

above the error voltage. When the main switch

is off, the synchronous rectifier will be turned on

immediately and stay on until the next cycle

starts.

MP28117 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

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Dropout Operation

Each channel of the MP28117 allows the main

switch to remain on for more than one switching

cycle and increases the duty cycle while the

input voltage is dropping close to the output

voltage. When the duty cycle reaches 100%,

the main switch is held on continuously to

deliver current to the output up to the PFET

current limit. The output voltage then is the

input voltage minus the voltage drop across the

main switch and the inductor.

Short Circuit Protection

The MP28117 has short circuit protection.

When any output is shorted to ground, the

oscillator frequency is reduced to prevent the

inductor current from increasing beyond the

PFET current limit. The PFET current limit is

also reduced to lower the short circuit current.

The frequency and current limit will return to the

normal values once the short circuit condition is

removed and the feedback voltage reaches

0.6V.

Maximum Load Current

The MP28117 can operate down to 2.5V input

voltage, however the maximum load current

decreases at lower input due to large IR drop

on the main switch and synchronous rectifier.

The slope compensation signal reduces the

peak inductor current as a function of the duty

cycle to prevent sub-harmonic oscillations at

duty cycles greater than 50%. Conversely the

current limit increases as the duty cycle

decreases.

APPLICATION INFORMATION

Output Voltage Setting

The external resistor divider sets the output

voltage. The feedback resistor R1 also sets the

feedback loop bandwidth with the internal

compensation capacitor (see Figure 1).

Choose R1 around 300kΩ for optimal transient

response. R2 is then given by:

V6.0

OUT −

Table 1—Resistor Selection vs. Output

Voltage Setting

VOUT R1 R2

1.2V 300kΩ (1%) 300kΩ (1%)

1.5V 300kΩ (1%) 200kΩ (1%)

1.8V 300kΩ (1%) 150kΩ (1%)

2.5V 300kΩ (1%) 95.3kΩ (1%)

Inductor Selection

A 1μH to 10μH inductor with DC current rating

at least 25% higher than the maximum load

current is recommended for most applications.

For best efficiency, the inductor DC resistance

shall be <200mΩ. See Table 2 for

recommended inductors and manufacturers.

For most designs, the inductance value can be

derived from the following equation:

()

OSCLIN

OUTINOUT

fIV

VVV

L×Δ×

−×

Where ΔIL is inductor ripple current. Choose

inductor ripple current approximately 30% of the

maximum load current, 800mA.

The maximum inductor peak current is:

II L

LOAD)MAX(L

Under light load conditions below 100mA, larger

inductance is recommended for improved

efficiency. Table 3 lists inductors recommended

for this purpose.

MP28117 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

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Table 2—Suggested Surface Mount Inductors

Manufacturer Part Number Inductance (μH) Max DCR (Ω)

Saturation

Current (A)

Dimensions

LxWxH (mm3)

Coilcraft LP03310-222ML 2.2 0.15 1.1 3.3 x 3.3 x 1

Toko 1002AS 2.2 0.11 1.14 4.6 x 4.6 x 1.2

Sumida CDRH3D16 2.2 0.072 1.20 4 x 4 x 1.8

Table 3—Inductors for Improved Efficiency at 25mA, 50mA, under 100mA Load.

Manufacturer Part Number Inductance (μH) Max DCR (Ω)

Saturation

Current (A) IRMS (A)

Coilcraft DO1605T-103MX 10 0.3 1.0 0.9

Murata LQH4C100K04 10 0.2 1.2 0.8

Sumida CR32-100 10 0.2 1.0 0.7

Sumida CR54-100 10 0.1 1.2 1.4

Input Capacitor Selection

The input capacitor reduces the surge current

drawn from the input and switching noise from

the device. The input capacitor impedance at

the switching frequency shall be less than input

source impedance to prevent high frequency

switching current passing to the input. Ceramic

capacitors with X5R or X7R dielectrics are

highly recommended because of their low ESR

and small temperature coefficients. For most

applications, a 4.7μF capacitor is sufficient.

Output Capacitor Selection

The output capacitor keeps output voltage

ripple small and ensures regulation loop stable.

The output capacitor impedance shall be low at

the switching frequency. Ceramic capacitors

with X5R or X7R dielectrics are recommended.

The output ripple ΔVOUT is approximately:

()

⎟

⎠

⎞

⎜

⎝

⎛

××

+×

××

−×

≤Δ 3Cf8

ESR

LfV

VVV

OSCOSCIN

OUTINOUT

OUT

Thermal Dissipation

Power dissipation shall be considered when

both channels of the MP28117 provide

maximum 800mA output current to the loads at

high ambient temperature with low input supply

voltage. If the junction temperature rises above

150°C, the MP28117 two channels will be shut

down.

The junction-to-ambient thermal resistance of

the 10-pin QFN (3mm x 3mm) RΘJA is 50°C/W.

The maximum power dissipation is about 1.6W

when the MP28117 is operating in a 70°C

ambient temperature environment.

W6.1

W/C50

C70C150

PD o

MAX =

−

PC Board Layout

The high current paths (GND1/GND2, IN1/IN2

and SW1/SW2) should be placed very close to

the device with short, direct and wide traces.

Input capacitors should be placed as close as

possible to the respective IN and GND pins.

The external feedback resistors shall be placed

next to the FB pins. Keep the switching nodes

SW1/SW2 short and away from the feedback

network.

MP28117 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third

party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not

assume any legal responsibility for any said applications.

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PACKAGE INFORMATION

QFN10 (3mm x 3mm)

SIDE VIEW

TOP VIEW

110

BOTTOM VIEW

2.90

3.10

1.45

1.75

2.90

3.10

2.25

2.55

0.50

BSC

0.18

0.30

0.80

1.00

0.00

0.05

0.20 REF

PIN 1 ID

MARKING

1.70

0.50

0.25

RECOMMENDED LAND PATTERN

2.90 NOTE:

1) ALL DIMENSIONS ARE IN MILLIMETERS.

2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH.

3) LEAD COPLANARITY SHALL BE 0.10 MILLIMETER MAX.

4) DRAWING CONFORMS TO JEDEC MO-229, VARIATION VEED-5.

5) DRAWING IS NOT TO SCALE.

PIN 1 ID

SEE DETAIL A

2.50

0.70

PIN 1 ID OPTION B

R0.20 TYP.

PIN 1 ID OPTION A

R0.20 TYP.

DETAIL A

0.30

0.50

PIN 1 ID

INDEX AREA