Rainbow Electronics MAX863 User Manual

_______________General Description

The MAX863 dual-output DC-DC converter contains
two independent step-up controllers in a single com­pact package. This monolithic Bi-CMOS design draws
only 85µA when both controllers are on. The input
range extends down to 1.5V, permitting use in organiz­ers, translators, and other low-power hand-held prod­ucts. The MAX863 provides 90% efficiency at output
loads from 20mA to over 1A. This space-saving device
is supplied in a 16-pin QSOP package that fits in the
same area as an 8-pin SOIC.

The device uses a current-limited, pulse-frequency­modulated (PFM) control architecture that reduces start­up surge currents and maintains low quiescent currents
for excellent low-current efficiency. Each controller
drives a low-cost, external, N-channel MOSFET switch,
whose size can be optimized for any output current or
voltage.

In larger systems, two MAX863s can be used to gener­ate 5V, 3.3V, 12V, and 28V from just two or three bat­tery cells. An evaluation kit (MAX863EVKIT) is available
to speed designs. For a single-output controller, refer to
the MAX608 and MAX1771 data sheets.

________________________Applications

2- and 3-Cell Portable Equipment

Organizers

Translators

Hand-Held Instruments

Palmtop Computers

Personal Digital Assistants (PDAs)

Dual Supply (Logic and LCD)

____________________________Features

♦ Smallest Dual Step-Up Converter: 16-Pin QSOP

♦ 90% Efficiency

♦ 1.5V Start-Up Voltage

♦ 85µA Max Total Quiescent Supply Current

♦ 1µA Shutdown Mode

♦ Independent Shutdown Inputs

♦ Drives Surface-Mount, Dual N-Channel MOSFETs

♦ Low-Battery Input/Output Comparator

♦ Step-Up/Down Configurable

MAX863

Dual, High-Efficiency, PFM, Step-Up

DC-DC Controller

________________________________________________________________ Maxim Integrated Products 1

__________________Pin Configuration

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

SENSE1 REF

SHDN2

LBI

LBO

FB2

SHDN1

CS2

EXT2

TOP VIEW

MAX863

QSOP

V

DD

FB1

EXT1

BOOT

CS1

GND

PGND

__________Typical Operating Circuit

19-1218; Rev 2; 2/98

PART

MAX863C/D

MAX863EEE -40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*

16 QSOP

EVALUATION KIT MANUAL

AVAILABLE

______________Ordering Information

*Dice are tested at TA= +25°C.

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

V

IN

OUT1

SENSE1 V

N

EXT1

CS1

BOOT

DD

EXT2

CS2

OUT2

N

MAX863

PGND

FB2

SHDN1

SHDN2

REF

GND

ON/OFF

LOW-BATTERY
DETECTOR OUTPUT

LBO

LBI

FB1

MAX863

Dual, High-Efficiency, PFM, Step-Up
DC-DC Controller

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= +5V, I

LOAD

= 0mA, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” 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 the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

VDDto GND............................................................-0.3V to +12V

PGND to GND .......................................................-0.3V to +0.3V

SHDN1, SHDN2, SENSE1, LBO to GND ................-0.3V to +12V

EXT1, EXT2 to PGND..................................-0.3V to (V

DD

+ 0.3V)

FB1, FB2, CS1, CS2, SEL,

LBI, BOOT to GND.................................-0.3V to (V

DD

+ 0.3V)

LBO Continuous Output Current.........................................15mA

EXT1, EXT2 Continuous Output Current .............................50mA

Continuous Power Dissipation (T

A

= +70°C)

QSOP (derate 8.30mW/°C above +70°C) ...................667mW

Operating Temperature Range

MAX863EEE ....................................................-40°C to +85°C

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

Storage Temperature Range .............................-65°C to +160°C

Lead Temperature (soldering, 10sec) .............................+300°C

V

DD

= OUT1 = BOOT (Note 1)

CONDITIONS

1.5 11

UNITSMIN TYP MAXSYMBOLPARAMETER

(Note 2)

V

2.7 11

V

DD

VDDInput Voltage

SHDN1 = VDD, SHDN2 = GND,
measured from V

DD

µA

35 60

I

DD

Quiescent Current

SHDN1 = SHDN2 = VDD, measured from V

DD

50 85

VIN= 2.7V to 5V, V

OUT1

= 5V,

I

LOAD

= 300mA, Figure 2

mV/V8Line Regulation

VIN= 3.3V, V

OUT1

= 5V,

I

LOAD

= 0mA to 500mA, Figure 2

mV/A40Load Regulation

nA210IFB, I

LBI

FB1, FB2, LBI Input Current

VDD= 1.5V

V

0.7 x V

DD

V

IH

2.7V < VDD< 11V 1.6

SHDN1, SHDN2, SEL, BOOT
Input High Voltage

mV85 100 115V

CS

CS1, CS2 Threshold Voltage

µs14 17.5 22

Logic input = VDDor GND

t

ON

Maximum Switch On-Time

µA125CS1, CS2 Input Current

µA1I

I

SHDN1, SHDN2, SEL, BOOT
Input Current

V1.225 1.25 1.275VFB, V

LBI

FB1, FB2, LBI
Threshold Voltage (Note 4)

C

LOAD

= 1nF, 10% to 90% ns50EXT Rise/Fall Time (Note 5)

µs1.6 2 2.4t

OFF

Minimum Switch Off-Time

FB1 = GND

V

4.85 5 5.15

V

OUT1

OUT1 Output Voltage
(Note 3)

FB1 = V

DD

3.2 3.3 3.4

VDD= 1.5V

V

0.2 x V

DD

V

IL

2.7V < VDD< 11V 0.4

SHDN1, SHDN2, SEL, BOOT
Input Low Voltage

SHDN1 = SHDN2 = GND

µA1I

DD, SHDN

Shutdown Current

Ω

5EXT On-Resistance

V

LBO

= 11V, V

LBI

> 1.275V µA1I

LBO

LBO Leakage Current

I

LBO,SINK

= 1mA, V

LBI

< 1.225V V0.1 0.4V

LBO,L

LBO Low Level

MAX863

Dual, High-Efficiency, PFM, Step-Up

DC-DC Controller

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS

(VDD= +5V, I

LOAD

= 0mA, TA= -40°C to +85°C, unless otherwise noted.) (Note 6)

Note 1: When bootstrapped, an internal low-voltage oscillator drives the EXT1 pin rail-to-rail for low supply voltages.
Note 2: For non-bootstrapped operation, V

DD

> 2.7V is required to allow valid operation of all internal circuitry.

Note 3: For adjustable output voltages, see the Set the Output Voltage section.
Note 4: Measured with LBI falling. Typical hysteresis is 15mV.
Note 5: EXT1 and EXT2 swing from V

DD

to GND.

Note 6: Specifications to -40°C are guaranteed by design and not production tested.

VDD= OUT1 (Note 1) 1.6 11

CONDITIONS

VDDInput Voltage

(Note 2)

V

2.8 11

V

DD

V1.21 1.285V

FB

FB1, FB2 Threshold Voltage

60

mV85 115V

CS

CS1, CS2 Threshold Voltage

UNITSMIN TYP MAXSYMBOLPARAMETER

FB1 = V

DD

3.15 3.45

OUT1 Output Voltage
(Note 3)

FB1 = GND

V

4.8 5.2

V

OUT1

SHDN1 = SHDN2 = VDD, measured from V

DD

85

Quiescent Current

SHDN1 = VDD, SHDN2 = GND,
measured from V

DD

µAI

DD

SHDN1 = SHDN2 = GND

µA1I

DD, SHDN

Shutdown Current

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

0.01 0.1 1 10 100 1000

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT1

= 3.3V, BOOTSTRAPPED)

MAX863 toc01

OUTPUT CURRENT (mA)

EFFICIENCY (%)

B

C

A

10

0

30

20

50

40

70

60

90

80

100

V

OUT1

= 3.3V

A: V

IN

= 1.5V

B: V

IN

= 2.4V

C: V

IN

= 2.7V

0.01 0.1

10

0

30

20

50

40

70

60

90

80

100

1 10 100 1000

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT1

= 5.0V, BOOTSTRAPPED)

MAX863 toc02

OUTPUT CURRENT (mA)

EFFICIENCY (%)

V

OUT1

= 5.0V

A: V

IN

= 1.5V

B: V

IN

= 2.4V

C: V

IN

= 2.7V

D: V

IN

= 3.3V

E: V

IN

= 3.6V

F: V

IN

= 4.0V

B

C

A

D

E

F

0.01 0.1

0

10

20

30

40

50

60

70

80

90

100

1 10 100 1000

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT1

= 5.0V, NON-BOOTSTRAPPED)

MAX863 toc03

OUTPUT CURRENT (mA)

EFFICIENCY (%)

V

OUT1

= 5.0V

A: V

IN

= 2.7V

B: V

IN

= 3.3V

C: V

IN

= 3.6V

D: V

IN

= 4.0V

A

B

C

D

MAX863

Dual, High-Efficiency, PFM, Step-Up
DC-DC Controller

4 _______________________________________________________________________________________

____________________________Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

0.01 0.1

10

20

30

40

50

60

70

80

90

100

0

1 10 100 1000

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT1

= 12V, NON-BOOTSTRAPPED)

MAX863 toc04

OUTPUT CURRENT (mA)

EFFICIENCY (%)

V

OUT1

= 5.0V

A: V

IN

= 2.7V

B: V

IN

= 3.3V

C: V

IN

= 3.6V

D: V

IN

= 4.0V

E: V

IN

= 6.0V

A

B

C

D

E

3.5

1

1 10 1000

BOOTSTRAPPED-MODE MINIMUM

START-UP INPUT VOLTAGE

vs. OUTPUT CURRENT

0.5

1.0

1.5

2.0

2.5

3.0

MAX863toc05

OUTPUT CURRENT (mA)

START-UP INPUT VOLTAGE (V)

100

V

OUT1

= 3.3V

V

OUT1

= 5V

0

012

VDD CURRENT

vs. V

DD

VOLTAGE

10

20

60

MAX863 toc15

VDD VOLTAGE (V)

V

DD

CURRENT (µA)

40

30

8

50

10

24 6

Cond: Single +5V

BOTH ON

CONVERTER 1 ON

CONVERTER 2 ON

LOAD-TRANSIENT RESPONSE

A

MAX863 toc08

B

100µs/div

V

OUT1

= 3.3V, I

OUT1

= 100mA TO 600mA

A: V

OUT1

, 100mV/div, 3.3V DC OFFSET

B: I

OUT1

, 200mA/div

RESPONSE ENTERING/

EXITING SHUTDOWN (BOOTSTRAPPED)

B

A

MAX863 toc09

C 3.3V

200µs/div

V

OUT1

= 3.3V, I

OUT1

= 100mA, VIN = 2.4V
A: SHDN1, 5V/div
B: INDUCTOR CURRENT, 2A/div
C: V

OUT1

, 3.3V OFFSET, 500mV/div

LINE-TRANSIENT RESPONSE

B

A

MAX863 toc10

C0A

500µs/div

V

OUT1

= 5V, I

OUT1

= 800mA

A: V

IN

= 2.7V TO 3.7V, 500mV/div

B: V

OUT1

, AC COUPLED, 50mV/div

C: INDUCTOR CURRENT, 2A/div

0

012

EXT RISE AND FALL TIMES vs.

SUPPLY VOLTAGE AND MOSFET CAPACITANCE

20

140

MAX863 toc07

SUPPLY VOLTAGE (V)

RISE/FALL TIME (ns)

6

60

80

40

24 8

120

100

C,1

C,2

B,1

B,2

A,1

A,2

10

A: 470pF
B: 1.0nF
C: 2.2nF
1: RISE
2: FALL

MAX863

Dual, High-Efficiency, PFM, Step-Up

DC-DC Controller

_______________________________________________________________________________________ 5

_______________Detailed Description

The MAX863 dual, bi-CMOS, step-up, switch-mode
power-supply controller provides preset 3.3V, 5V, or
adjustable outputs. Its pulse-frequency-modulated
(PFM) control scheme combines the advantages of low
supply current at light loads and high efficiency with
heavy loads. These attributes make the MAX863 ideal
for use in portable battery-powered systems where
small size and low cost are extremely important, and
where low quiescent current and high efficiency are
needed to maximize operational battery life. Use of
external current-sense resistors and MOSFETs allows
the designer to tailor the output current and voltage
capability for a diverse range of applications.

PFM Control Scheme

Each DC-DC controller in the MAX863 uses a one-shot­sequenced, current-limited PFM design, as shown in
Figure 1. Referring to the Typical Operating Circuit
(Figure 2) and the switching waveforms (Figures 3a–3f),
the circuit works as follows. Output voltage is sensed
by the error comparator using either an internal voltage
divider connected to SENSE1 or an external voltage
divider connected to FB1. When the output voltage
drops, the error comparator sets an internal flip-flop.
The flip-flop turns on an external MOSFET, which allows
inductor current to ramp-up, storing energy in a mag­netic field.

______________________________________________________________Pin Description

PIN

Feedback Input for DC-DC Controller 1 in Fixed-Output ModeSENSE11

FUNCTIONNAME

IC Power-Supply InputV

DD

2

Bootstrap Low-Voltage-Oscillator Enable Input. BOOT is an active-high, logic-level input. It enables the
low-voltage oscillator to allow start-up from input voltages down to 1.5V while in a bootstrapped circuit
configuration. Connect BOOT to GND when in a non-bootstrapped configuration. If BOOT is high, V

DD

must be connected to OUT1.

BOOT4

Adjustable Feedback and Preset Output Voltage Selection Input for DC-DC Controller 1. Connect to V

DD

for 3.3V preset output or to GND for 5V output. Connect a resistor voltage divider to adjust the output volt­age. See the section Set the Output Voltage.

FB13

Gate-Drive Output of DC-DC Controller 1. Drives an external N-channel power MOSFET.EXT16

High-Current Ground Return for Internal MOSFET DriversPGND8

Analog Ground for Internal Reference, Feedback, and Control CircuitsGND7

Input to the Current-Sense Comparator of DC-DC Controller 1CS15

Input to the Current-Sense Amplifier of DC-DC Controller 2CS210

Adjustable Feedback Input for DC-DC Controller 2. Connect a resistor voltage divider to adjust the output
voltage. See the section Set the Output Voltage.

FB212

Active-Low Shutdown Input for DC-DC Controller 1. Connect to VDDfor normal operation.

SHDN1

11

Low-Battery Comparator Input. When the voltage on LBI drops below 1.25V, LBO sinks current. If unused,
connect to GND.

LBI14

Reference Bypass Input. Connect a 0.1µF ceramic capacitor from REF to GND.REF16

Active-Low Shutdown Input for DC-DC Controller 2. Connect to VDDfor normal operation.

SHDN2

15

Low-Battery Output. An open-drain N-channel MOSFET output. Sinks current when the voltage on LBI
drops below 1.25V. If unused, connect to GND.

LBO13

Gate-Drive Output of DC-DC Controller 2. Drives an external N-channel power MOSFET.EXT29