Rainbow Electronics MAX781 User Manual

19-0205; Rev 0; 7/94

EVALUATION KIT

AVAILABLE

PDA/Hand-Held Computer Power Controller

_______________General Description

The MAX781 is a system-engineered power-supply con­troller for subnotebook computers, PDAs, or similar bat­tery-powered equipment. It provides high-performance,
step-down (buck), pulse-width modulated (PWM) control
for generating +3.3V and constant-current battery charg­ing. Dual PCMCIA VPP outputs are powered by a regulat­ed flyback winding. Five high-side gate drivers and a
buffered analog multiplexer are also included. All func­tions are controlled by an SPI/Microwire™ compatible
four-wire serial interface.

The MAX781 generates +3.3V with high efficiency through
synchronous rectification and PWM operation at heavy
loads. It uses Idle Mode™ operation at light loads. Only
small external components are required because of the
device’s high switching frequency (300kHz) and advanced
current-mode PWM architecture that allows for output
capacitance as low as 50µF per ampere of load.

The MAX781 is configured by 32 bits of serial data. These
bits select the operating mode, set the switch-mode bat­tery charger current level, select one of eight analog multi­plexer channels, and turn on/off the five high-side gate
drivers. A status byte read from the serial interface indi­cates if the battery has been removed, if the DC charging
source has been connected, or if there is a fault condition
on the +3.3V output. An interrupt output signals the CPU if
a status signal changes.

____________________________Features

♦ +3.3V Step-Down Controller
♦ Dual PCMCIA 2.0 Compatible VPP Outputs

(0V/3.3V/5V/12V)

♦ Digitally Adjustable Switching Current Source for

Battery Charging

♦ 5 High-Side Switch Gate-Driver Outputs
♦ SPI Serial Interface
♦ 300kHz Switching Frequency
♦ Oscillator SYNC Input
♦ 2.5V ±1.5% Reference Output
♦ 36-Pin SSOP Package

________________________Applications

Subnotebook Computers
PDAs
Communicating Computers
Handy-Terminals

______________Ordering Information

PART

MAX781CBX
MAX781EBX -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

0°C to +70°C

36 SSOP
36 SSOP

________________________________________________Typical Application Diagram

(up to 18V)

5 to 8

NiCd/NiMH

CELLS 

or
2 LION
CELLS

DCIN

DIGITALLY

ADJUSTABLE

SWITCHING

CURRENT

SOURCE

MAX781

HIGH-SIDE GATE DRIVERS


5



+3.3V AT 1A OR MORE


SERIAL INTERFACE

4

INTERRUPT

VPPA

VPPB

ANALOG MULTIPLEXER OUTPUT

SUBSYSTEMS

LOAD 

SWITCHES

SELF REFRESH

DRAM

CPU

PCMCIA
SLOT A

PCMCIA
SLOT B

ADC

MAX781

Pin Configuration on last page.

™

SPI is a trademark of Motorola Inc. Microwire is a trademark of National Semiconductor Corp.

Idle Mode is a trademark of Maxim Integrated Porducts.

________________________________________________________________

Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

1

PDA/Hand-Held Computer Power Controller

ABSOLUTE MAXIMUM RATINGS

BATT, VCHG, VHI to AGND.........................................-0.3V, 20V

VPPA, VPPB to AGND..................................................-0.3V, 20V

FAST, GD1, GD2, GD3, GD4, GD5 to AGND..............-0.3V, 20V

BST to AGND...............................................................-0.3V, 30V

BST to LX.......................................................................-0.3V, 7V

DHI to LX.......................................................-0.3V, (BST + 0.3V)

PGND to AGND........................................................-0.3V, +0.3V

MAX781

All Other Pins to AGND or PGND ..................................-0.3V, 7V

VPPA, VPPB Current.........................................................100mA

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.

ELECTRICAL CHARACTERISTICS

(BATT = 6V, power-on reset state, TA= T

MIN

to T

, unless otherwise noted.)

MAX

5OUT Current....................................................................100mA

3OUT Current......................................................................40mA

Continuous Power Dissipation (T

SSOP (derate 11.76mW/°C above +70°C) ....................941mW

Operating Temperature Ranges

MAX781CBX .........................................................0°C to +70°C

MAX781EBX......................................................-40°C to +85°C

Storage Temperature Range.............................-65°C to +150°C

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

= +70°C)

A

SUPPLY AND REFERENCE

BATT Quiescent Supply Current

5OUT Output Voltage

Internal Undervoltage Lockout
Threshold (measured at 5OUT,
UVLO = AGND)

UVLO Threshold
(measured at UVLO)

INTERNAL OSCILLATOR

Internal Oscillator Frequency

CONDITIONS

Shutdown mode, –S—H—D—N–= 0V
Low-power mode, –S—H—D—N–= BATT = 18V
Standby mode, –S—H—D—N–= BATT = 18V
Operate mode, –S—H—D—N–= BATT = 18V
No load
I

= -20µA to 100µA

SOURCE

Operate or standby mode, 5.5V < BATT < 18V,
0mA < I

Low-power mode, 5.5V < BATT < 18V,
0mA < I

V

5OUT

V

5OUT

V

UVLO

V

UVLO

SYNC = REF
SYNC = AGND or 5OUT

5OUT

5OUT

rising
falling

rising
falling

< 25mA

< 10mA

10

60 120

250 750

4.8 5.2

4.8 5.2

4.30 4.60 4.80

4.10 4.35 4.50
97 103

90 96

270 300 340
170 230 260

UNITSMIN TYP MAXPARAMETER

µA

mA12

V2.463 2.5 2.537REF Output Voltage

mV-20 20REF Load Regulation

V

V

%REF

nA50UVLO Input Bias Current

kHz
kHz270 350SYNC Capture Range (Note 1)

ns500SYNC Minimum Pulse Width (Note1)
ns200SYNC Fall Time (Note 1)
µs1SYNC Rise Time (Note 1)

V0.75SYNC Input Voltage Low
V3.8SYNC Input Voltage High

nA-100 100SYNC Leakage Current

2 _______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

ELECTRICAL CHARACTERISTICS (continued)

(BATT = 6V, power-on reset state, TA= T

3.3V OUTPUT

DLO On-Resistance

BATTINT Battery-Detect
Threshold (measured at TEMP)

VPP REGULATOR

VPP_Output Voltage

HIGH-SIDE GATE DRIVERS

to T

MIN

Low-power mode, 4V < BATT < 18V, 0mA < I
Standby mode, 4V < BATT < 18V, 0mA < I

Operate mode, 4V < BATT < 18V,
CS to 3OUT = 0mV to 80mV

3OUT falling

High, 5OUT = 4.75V
Low, 5OUT = 4.75V
High or low, BST - LX = 4.5V
TEMP falling
TEMP rising

Operate mode V12.8 13.5 14.2VHI Regulation Threshold

Operate mode,
I

SINK

VPPA1 = VPPA0 = 0,
VPPB1 = VPPB0 = 0,
GDSEL1 to GDSEL5 = 0

VHI = 20V
Operate mode,

VHI = 18V,
VPPA1 = VPPA0 = 0,
VPPB1 = VPPB0 = 0,
GDSEL1 to GDSEL5 = 0

I

SINK

VPP_1 = 0, VPP_0 = 0

14.2V < VHI < 18V, VPP_1 = 0, VPP_0 = 1,
0mA < IVPP_ < 60mA

14.2V < VHI < 18V, VPP_1 = 1, VPP_0 = 0,
0mA < IVPP_ < 60mA

14.2V < VHI < 18V, VPP_1 = 1, VPP_0 = 1,
0mA < IVPP_ < 60mA

VHI = 14.2V, GDSEL_ = 1,
I

SOURCE

VHI = 14.2V, GDSEL_ = 0,
I

SINK

GD_ = 2.5V, GDSEL_ = 1,
VHI = 14.2V

GD_ = 2.5V, GDSEL_ = 0,
VHI = 14.2V

, unless otherwise noted.)

MAX

= 200µA,

= 1mA,

= 1µA

= 20µA

CONDITIONS

3OUT

3OUT

< 1mA

< 10mA

3.17 3.43

3.17 3.43

3.17 3.43

15
10

75 81

83 89

0.25

4.75 5.0 5.25

11.4 12.0 12.6

3.14 3.3 3.49

MAX781

UNITSMIN TYP MAXPARAMETER

V3OUT Output Voltage

mV80 100 130CS to 3OUT Current-Limit Threshold

V2.9 3.0 3.13VINT Fault-Detect Threshold

mV1503VINT Fault-Detect Hysteresis

Ω
Ω10DHI On-Resistance

%3OUT

V20VHI Clamp Voltage

mA1VHI Clamp Current

µA45VHI Input Bias Current

V

V14GD_ Output High Voltage

V0.25GD_ Output Low Voltage

µA61018GD_ Source Current

µA200 450 900GD_ Sink Current

_______________________________________________________________________________________ 3

PDA/Hand-Held Computer Power Controller

ELECTRICAL CHARACTERISTICS (continued)

(BATT = 6V, power-on reset state, TA= T

ANALOG MULTIPLEXER

MAX781

AOUT Output Voltage

SERIAL INTERFACE

CE, SCLK, DIN Logic Input High
Voltage

CE, SCLK, DIN Logic Input Low
Voltage

DOUT, INT Logic Output High
Voltage

DOUT, INT Logic Output Low
Voltage

CE, SCLK, DIN Logic Input
Rise/Fall Time (Note 1)

BATTERY CHARGER

CSBAT Full-Scale Current-Sense
Voltage

COMP Current-Sense Amplifier
Offset Voltage

Current-Sense Amplifier CSBAT to
COMP Transconductance (gm)

FAST OUTPUT

Output Sink Current

to T

MIN

MUX2 = 0, MUX1 = 0, MUX0 = 0
MUX2 = 0, MUX1 = 0, MUX0 = 1
MUX2 = 0, MUX1 = 1, MUX0 = 0
MUX2 = 0, MUX1 = 1, MUX0 = 1
MUX2 = 1, MUX1 = 0, MUX0 = 0
MUX2 = 1, MUX1 = 0, MUX0 = 1
MUX2 = 1, MUX1 = 1, MUX0 = 0
MUX2 = 1, MUX1 = 1, MUX0 = 1
I

SINK

I

SOURCE

I

SINK

High or low, 5OUT = 4.75V
CHG6 to CHG0 = 1,

CHARGE = 1

CSBAT = 0V mV-2 0 2

FAST = 3V, FASTON = 1
FAST = 18V, FASTON = 0

, unless otherwise noted.)

MAX

= 10µA

= 1mA

= 1.6mA

CONDITIONS

UNITSMIN TYP MAXPARAMETER

%3OUT65.33 66.67 68.00
%5OUT44.54 45.45 46.36

%BATT19.90 20.00 20.10

%TEMP65.33 66.67 68.00

%VPPA18.49 18.87 19.25
%VPPB18.49 18.87 19.25
%VREF99.8 100 100.2

%AUXIN65.33 66.67 68.00

mV10AOUT Output Low

V2

V0.8

nA-100 100SCLK, DIN Leakage Current
kΩ60 100 140CE Internal Pull-Down Resistance

V2.7

V0.4

ns50

Ω10DCHG On Resistance

mV190 200 210

µmho400 600 750

mA1.0 2.0

nA±1.0

4 _______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

TIMING CHARACTERISTICS (Note 1)

PARAMETER MIN TYP MAX UNITS

DIN to SCLK Data Setup Time 125 ns
DIN to SCLK Data Hold Time
SCLK to DOUT Valid Propagation Delay 30 200 ns
SCLK Clock Period 400 ns
SCLK High Pulse Width 125 ns
SCLK Low Pulse Width 125 ns
CE Assertion to DOUT Enable 120 ns
CE Deassertion to DOUT Disable 120 ns

CE Assertion to SCLK Rising-Edge
Setup Time

SCLK Rising Edge to CE Deassertion 200 ns
CE High Pulse Width 300 ns
SCLK Rising Edge to CE Assertion 200 ns
CE Deassertion to SCLK Rising Edge 200 nst

Note 1: Guaranteed by design.

SYMBOL

t

DS

t

DH

t

DO

t

CP

t

CH

t

CL

t

DV

t

TR

t

CSS

t

CSH

t

CSW

t

CS0
CS1

0 ns

200 ns

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

MAX781

NO LOAD SUPPLY CURRENT

10

1

0.1

(I

=0mA)

3OUT

SYNC=UVLO=AGND,
CHARGE=0
GDSEL_=0

0.01

QUIESCENT CURRENT (mA)

MUX_=0
5ON=1
VPP_=0

0.001
2 4 6 8 10 12 14 16 18



OPERATE MODE (IDLE = 0)

OPERATE MODE (IDLE = 1)

STANDBY MODE

LOW-POWER MODE

SHUTDOWN MODE

BATT INPUT VOLTAGE (V)

MAX781-01

CHARGER OUTPUT CURRENT

1000

100

CURRENT INTO BATT (mA)

10

1

3 7 15 31 12763

CHARGER CODE (CHG6–CHG0 VALUE)



%

mA

R4 = 0.2Ω
SYNC = AGND
BATT = 7V TO 8V
VCHG = 12V

100
90

MAX781-03

80
70

60
50
40
30
20

10

_______________________________________________________________________________________ 5

EFFICIENCY (%)

PDA/Hand-Held Computer Power Controller

____________________________Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

VPPA AND VPPB OUTPUT POWER

VPPA SHORTED TO VPPB AND

400

MAX781

350

300
250

200

CURRENT (mA)

150

100

CLAMPED TO 11.5V

VPPA + VPPB CURRENT

CONFIGURATION = $FF, $00, $02, $6A,
SYNC = AGND, NO 3OUT LOAD
T1 TURNS RATIO (SECONDARY
TURNS / PRIMARY TURNS) = 3.5

50

4

6 8 10 12 14 16 18

VHI VOLTAGE

BATT INPUT CURRENT

BATT VOLTAGE (V)

14.0

MAX781-02

13.5

13.0

12.5

12.0

11.5

11.0

10.5

DCHG DUTY CYCLE vs. COMP VOLTAGE

90

AT 0% DUTY CYCLE,

80

DCHG = 5OUT

70
60
50
40

VHI VOLTAGE (V)

30

DCHG DUTY CYCLE (%)

20
10

0

0.5 1.0 1.5 2.0 2.5 3.0

0



COMP VOLTAGE (V)

MAX781-04

3OUT OPERATE MODE POWER EFFICIENCY

(FIXED 300kHz SWITCHING FREQUENCY)

100

BATT = 5.5V

90

SYNC = REF
IDLE = 0

80

MODE1 = 1
MODE0 = 0

70
60

50
40

POWER EFFICIENCY (%)

30
20

10

1 10 100 1000

3OUT OUTPUT CURRENT (mA)

MAX781-05

3OUT OPERATE MODE POWER EFFICIENCY

(FIXED 230kHz SWITCHING FREQUENCY)

100

BATT = 5.5V

90

SYNC = AGND
IDLE = 0

80

MODE1 = 1
MODE0 = 0

70
60

50
40

POWER EFFICIENCY (%)

30
20

10

1 10 100 1000

3OUT OUTPUT CURRENT (mA)

3OUT OPERATE MODE POWER EFFICIENCY

(FIXED 300kHz SWITCHING FREQUENCY)

100

BATT = 7.5V

90

SYNC = REF
IDLE = 0

80

MODE1 = 1
MODE0 = 0

70
60

50
40

POWER EFFICIENCY (%)

30
20

10

1 10 100 1000

3OUT OUTPUT CURRENT (mA)

MAX781-06

MAX781-08

3OUT OPERATE MODE POWER EFFICIENCY

(VARIABLE SWITCHING FREQUENCY)

100

BATT = 5.5V

90

SYNC = REF
IDLE = 1

80

MODE1 = 1
MODE0 = 0

70
60
50
40

POWER EFFICIENCY (%)

30
20

10

100

90
80

70
60

50
40

POWER EFFICIENCY (%)

30
20

10

%

1 10 100 1000

3OUT OUTPUT CURRENT (mA)

3OUT OPERATE MODE POWER EFFICIENCY

(FIXED 230kHz SWITCHING FREQUENCY)

BATT = 7.5V
SYNC = AGND
IDLE = 0
MODE1 = 1
MODE0 = 0

1 10 100 1000

3OUT OUTPUT CURRENT (mA)

3OUT OPERATE MODE POWER EFFICIENCY

(VARIABLE SWITCHING FREQUENCY)

450
400

MAX781-12

350
300
250

kHz

200
150
100
50

0

MAX781-07

100

BATT = 5.5V

90

SYNC = AGND
IDLE = 1

80

MODE1 = 1
MODE0 = 0

70
60
50
40

POWER EFFICIENCY (%)

30

SWITCHING FREQUENCY (kHz)

20
10

100

90
80
70
60
50
40

POWER EFFICIENCY (%)

30
20

10

%

1 10 100 1000

3OUT OUTPUT CURRENT (mA)

3OUT OPERATE MODE POWER EFFICIENCY

(VARIABLE SWITCHING FREQUENCY)

BATT = 7.5V
SYNC = REF
IDLE = 1
MODE1 = 1
MODE0 = 0

%

1 10 100 1000

3OUT OUTPUT CURRENT (mA)

kHz

450
400

MAX781-10

350
300
250
200

kHz

150
100

SWITCHING FREQUENCY (kHz)

50
0

450
400

MAX781-11

350
300
250
200
150
100

SWITCHING FREQUENCY (kHz)

50
0

6 _______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

____________________________Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

3OUT OPERATE MODE POWER EFFICIENCY

VARIABLE SWITCHING FREQUENCY

100

BATT = 7.5V

90

SYNC = AGND
IDLE = 1

80

MODE1 = 1
MODE0 = 0

70
60
50
40

POWER EFFICIENCY (%)

30
20

10

%

1 10 100 1000

3OUT OUTPUT CURRENT (mA)

kHz

450
400

MAX781-09

350
300
250
200
150
100

SWITCHING EFFICIENCY (kHz)
50
0

USING THE BATTERY CHARGER TO DRIVE

A CCFL BACKLIGHT ROYER OSCILLATOR

2.5
SYNC = REF

VCHG = 7V

2.0
BATT = VCHG - DIODE DROP

R4 = 0.47Ω

1.5

1.0

0.5

CCFL TUBE CURRENT (mA, rms)

0

0

mV

mA, rms

10 20 30 40 50 60 70

CHG6–CHG0 BITS VALUE

110
100

MAX781-01

90
80
70
60
50
40
30

CSBAT AVERAGE VOLTAGE (mV)

20
10

______________________________________________________________Pin Description

PIN

1–4 GD2–GD5 High-Side Gate-Driver Outputs

5 VPPA VPP-Programming Voltage Output A
6 VHI VPPA, VPPB Linear-Regulator Input Power
7 VPPB VPP-Programming Voltage Output B
8 AGND Analog Ground

9 SYNC Oscillator Frequency Control and Synchronization Input
10 CE Serial-Interface Chip-Enable Input—active high
11 SCLK Serial-Interface Clock Input
12 DOUT Serial-Interface Data Output
13 DIN Serial-Interface Data Input
14 INT Interrupt Output
15 FAST General-purpose open-drain output
16 COMP Battery-Charger Compensation
17 CSBAT Battery-Charger Current-Sense Input
18 5OUT Linear-Regulated +5V Output
19 DCHG Battery-Charger MOSFET Gate-Driver Output
20 PGND Power Ground
21 DLO +3.3V Regulator, Synchronous Rectifier, Gate-Driver Output
22 BST +3.3V Regulator Boost Capacitor Connection (0.1µF to LX)
23 DHI +3.3V Regulator High-Side Gate-Driver Output
24 LX +3.3V Regulator Inductor Connection

NAME FUNCTION

MAX781

_______________________________________________________________________________________

7

PDA/Hand-Held Computer Power Controller

_________________________________________________Pin Description (continued)

25 3OUT +3.3V Regulator Feedback Connection and Linear-Regulated + 3.3V Output
26 CS +3.3V Regulator Current-Sense Input
27 SS +3.3V Regulator Soft-Start Capacitor Connection
28 BATT Battery Voltage Input
29 VCHG Charger Voltage Input

MAX781

30 UVLO Undervoltage Lockout Threshold Input
31 REF +2.5V Reference Output
32 AOUT Analog Multiplexer Buffered Output
33 TEMP Analog Multiplexer Input and Battery Sense Input
34 AUXIN Analog Multiplexer Input
35
36 GD1 High-Side Gate-Driver Output

BATTERY
CHARGER
DC INPUT

C10

–S—H—D—N–

D3

R4

Shutdown-Mode Control Input

C14 D1

L1

R8

T

D2

COMPATIBLE

INTERFACE

M3

SPI

SERIAL 

R1

C1

BATTERY
CHARGER
SECTION

C3 C2

VCHG

DCHG

REF
SYNC
TEMP

COMP

CSBAT

CE
SCLK
DIN
DOUT
INT

FAST
AUXIN
AOUT

SHDN

MAX781

UVLO SS

C5

5OUT

BATT

BST

DLO

PGND

3OUT

AGND

VPPA
VPPB

GD1

GD5

VHI

DHI

+5V LOW 
CURRENT OUTPUT


C12

D7

M1

C7

LX

M2

CS

GATE DRIVERS
FOR POWER
SWITCHING

D6

T1

D5

C8

C11

R7

C9

+14V OUTPUT

PCMCIA 2.0
CARD SLOT
VPPs

C6

+3.3V
OUTPUT

Figure 1. Typical Operating Circuit

8 _______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

MAX781

VCHG

BATT

UVLO

SHDN

AGND

SCLK

DIN

+3.3V LINEAR 

REGULATOR

2.5V

REFERENCE

+5V LINEAR 
REGULATOR

+3.3V SWITCHING

CHGSTAT

50N

CE

UNDERVOLTAGE

BIAS
GEN

MODE1

MODE0

SERIAL INTERFACE

IDLE

REGULATOR

3VSTAT

AVPP1

INREG

VPP LINEAR

REGULATORS

AVPP0

BVPP1

BVPP0

3OUT

REF

CS3

SS
BST
DHI
LX
DLO

PGND

SYNC

VHI
VPPA
VPPB

INT
DOUT
FAST

MUX_

BATTSTAT

AUXIN

AOUT

TEMP

ANALOG

MULTIPLEXER

Figure 2. MAX781 Block Diagram

_______________________________________________________________________________________ 9

CHG_

BATTERY
CHARGER

CHGON

DCHG
COMP

CSBAT

GATE

DRIVERS

GDON

5

MUXON

37

GDSEL_

5

PDA/Hand-Held Computer Power Controller

_______________Detailed Description

Table 1 describes the MAX781’s four modes of opera­tion, and Table 2 shows how to select the desired
mode. MODE1 and MODE0 are the two bits, out of a
total of 32 bits of configuration data, which select the
operational mode. See Table 3 for a complete list of

MAX781

the 32 bits of configuration data.

Table 1. MAX781 Modes of Operation

MODE DESCRIPTION

• Entire chip shut down

Shutdown

Low
Power

Standby

Operate

With –S—H—D—N–pulled up to the battery voltage, the
MAX781 powers on in low-power mode. After power­up, pulling CE high temporaily places the MAX781 into
operate mode and allows data to be shifted into the
internal shift register. As soon as CE goes low, the
MAX781 enters the mode programmed by the MODE1
and MODE0 bits.

• All blocks turned off

• I

< 10µA

Q

• 3OUT, 5OUT, REF off

• Default on power-up

• 3OUT supplies 10mA at +3.3V linear

regulated from BATT

• VPP outputs off (VPPA = VPPB = High-Z)

• Analog multiplexer off (AOUT = High-Z)

• High-side gate drivers off

(GD1 = GD2 = GD3 = GD4 = GD5 = 0V)

• Battery-charging current source off
(DCHG = 5OUT)

• 3OUT supplies 10mA at +3.3V linear
regulated from BATT

• VPP outputs off (VPPA = VPPB = High-Z)

• Analog multiplexer enabled

• High-side gate drivers off

• Battery-charging current source enabled

• Buck switching regulator on

• 3OUT regulated to +3.3V

• VPP outputs enabled

• VHI regulated to +14V

• Analog multiplexer enabled

• High-side gate drivers enabled

• Battery-charging current source enabled

Modes of Operation

Table 2. Operating Modes

–S—H—D—N–

MODE1 MODE0

0 x x
1 1 1

1 1 1 0
1 0 1

1 0 1
1 0 0
1 1 0

CE

x

Shutdown

1

Operate
Low Power (default

on power-up)

1

Standby

0

Low Power

x

Standby

x

Operate

Resulting Mode

Serial Interface

The MAX781 is controlled by 32 bits of configuration
data. These 32 bits must be written, MSB first, into the
MAX781 using a synchronous serial interface. Table 3
describes the function of each bit of configuration data.
To turn the gate drivers on/off, select VPP voltages or
program the analog multiplexer. CE, SCLK, DIN, and
DOUT are the synchronous serial-interface pins. Figure
3 shows an example of the signal timing necessary to
send 32 bits of data to the MAX781. The first six bits
clocked out of DOUT are the status bits, and the
remaining 26 bits clocked out of DOUT should be
ignored. Figure 4 shows the detailed timing require­ments of the synchronous serial interface.

To write the last eight bits of the configuration data
without affecting the rest of the configuration bits, clock
eight bits instead of 32 into DIN. This allows the
CHARGE, IDLE, MODE1, MODE0, and VPP control bits
to be updated in only eight serial clock cycles. As the
eight bits are clocked into DIN, the status bits are
clocked out of DOUT. Figure 5 shows an example of
such a quick access. If eight zeros are sent in a quick
access, no configuration data is updated. This allows
the status bits to be read quickly without affecting the
last byte of configuration data.

Status Bits

As the 32 bits of serial-configuration data are written
into the MAX781, 32 bits of data are read out of DOUT.
The first six bits contain status information, and the
remaining 26 bits should be ignored.

BATTINT and BATTSTAT (Table 3) indicate battery sta­tus. It is assumed that the battery pack used with the
MAX781 has a thermistor attached to its negative termi-

10 ______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

Table 3. Configuration Data-Bit Assignments

NAME

BIT

*

0
0
0
0
0
0

0
0
0
0
1
0
1
0
0
0
0
0
0
1
0
1
0
1
1
1
1
0
0
0
0

BATTINT

BATTSTAT

3VINT

3VSTAT

CHGINT

CHGSTAT

GDSEL5
GDSEL4
GDSEL3
GDSEL2
GDSEL1

MUX2
MUX1
MUX0
CHG6
CHG5
CHG4
CHG3
CHG2
CHG1
CHG0

50N

FASTON

CHARGE

IDLE
MODE1
MODE0

VPPB1
VPPB0
VPPA1
VPPA0

1 = TEMP pin voltage crossed 0.82* 3OUTR/W31
1 = TEMP > 0.82*3OUT, 0 = TEMP < 0.82*3OUTR30
1 = 3OUT fault detectedR/W29
1 = 3OUT out of regulation, 0 = in regulationR28
1 = VCHG > BATT detectedR/W27
1 = VCHG > BATT, 0 = VCHG < BATTR26
Unused25
1 = GD5 sources from VHI, 0 = GD5 sinks to AGNDW24
1 = GD4 sources from VHI, 0 = GD4 sinks to AGNDW23
1 = GD3 sources from VHI, 0 = GD3 sinks to AGNDW22
1 = GD2 sources from VHI, 0 = GD2 sinks to AGNDW21
1 = GD1 sources from VHI, 0 = GD1 sinks to AGNDW20
Analog multiplexer bit 2W19
Analog multiplexer bit 1W18
Analog multiplexer bit 0W17
Charger current setting DAC bit 6W16
Charger current setting DAC bit 5W15
Charger current setting DAC bit 4W14
Charger current setting DAC bit 3W13
Charger current setting DAC bit 2W12
Charger current setting DAC bit 1W11
Charger current setting DAC bit 0W10
1 = 5OUT linear regulator on, 0 = offW9
1 = FAST sinks current, 0 = FAST open drainW8
1 = DCHG switching current source on, 0 = offW7
1 = Idle regulation, 0 = PWM regulationW6
Operating mode select bit, 1, see Table 2W5
Operating mode select bit, 0, see Table 2W4
VPPB voltage select bit 1, see Table 5W3
VPPB voltage select bit 0, see Table 5W2
VPPA voltage select bit 1, see Table 5W1
VPPA voltage select bit 0, see Table 5W0

MAX781

DESCRIPTIONR/W

* = Power-on reset default state

nal, causing the battery pack to need at least three ter­minals: BATT+, BATT,- and THERM. The MAX781’s
TEMP pin connects to the battery pack’s thermistor
(Figure 6). Without the battery pack installed, R8 pulls
the MAX781’s TEMP pin up to 3OUT, and BATTSTAT =

1. When the battery pack is inserted, the resistive
divider formed by the thermistor and R8 pulls the TEMP
pin below 3OUT, forcing BATTSTAT = 0. Any transition
of BATTSTAT sets BATTINT. Clear BATTINT by writting
a logic 1 in bit 31 of the serial-configuration data. The

______________________________________________________________________________________ 11

BATTSTAT comparator is disabled in low-power and
shutdown modes, and outputs a logic zero regardless
of the state of its inputs.

3VINT and 3VSTAT indicate the status of the 3OUT
output (+3.3V ±4%). 3OUT is out of regulation when
its output voltage falls below +3.1V. 3VSTAT = 0 when
3OUT is in regulation, and 3VSTAT = 1 when 3OUT is
out of regulation. A rising edge on 3VSTAT sets
3VINT; thus, 3OUT going out of regulation sets 3VINT.

PDA/Hand-Held Computer Power Controller

TIME

OUTPUT FROM CPU

INPUT TO MAX781

OUTPUT FROM CPU

INPUT TO MAX781

CE

SCLK

MAX781

OUTPUT FROM CPU

INPUT TO MAX781

INPUT TO CPU

OUTPUT FROM MAX781

DATA CLOCKED INTO MAX781 

ON RISING EDGE OF SCLK

DIN

DATA CLOCKED OUT OF MAX781

ON FALLING EDGE OF SCLK

DOUT

Figure 3. Serial Configuration Data Example Timing

CE

SCLK

DOUT

DIN

t

CSO

t

CSS

t

DV

Figure 4. Detailed Timing Diagram

CE

SCLK

BATTINT 3VINT VPPA1 VPPA0

BATTSTATBATTINT 3VINT

XXX XXX XXX

• • •

t

CP

t

CH

t

CSH

• • •

t

DS

t

DH

t

CL

• • •

t

DO

t

TR

• • •

TIME

t

CSW

t

CS1

DIN

DOUT

CHARGE MODE1 MODE0IDLE VPPA1VPPB0VPPB1 VPPA0

BATTSTAT 3VSTAT CHGINT CHGSTATBATTINT 3VINT

XXX XXX XXX

Figure 5. Quick-Access Example Timing

12 ______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

The 3VSTAT comparator is disabled in the low-power,
standby, and shutdown modes, and outputs a logic
zero regardless of the state of its inputs. The MAX781
serial-interface outputs are powered from 3OUT. If
3OUT is short circuited to ground, then neither DOUT
nor INT will be able to source current.

CHGINT and CHGSTAT indicate the status of the
charging voltage applied to VCHG. The MAX781 pow­ers itself from either BATT or VCHG, whichever has the
higher voltage. CHGSTAT = 0 when BATT is approxi­mately 200mV greater than VCHG. CHGSTAT = 1
when BATT falls below VCHG plus approximately
200mV. Any transition on CHGSTAT sets CHGINT.
The CHGSTAT comparator is disabled only in shut­down mode.

At power-up, BATTINT is set if the charger is not con­nected, CHGINT is set if the charger is connected.

Table 4. Status Detection in the Four Operating
Modes

Low

Power

R

TEMP

MODE

Standby

Enabled
Enabled
Enabled

BATT

3OUT

TEMP

Operate

Enabled
Enabled
Enabled

83kR8

STATUS

BIT

BATTSTAT Disabled Disabled

3VSTAT Disabled Disabled

CHGSTAT Disabled Enabled

BATT+

Shutdown

BATTERY

PACK

THERM

T

The INT pin outputs the logical OR of the BATTINT,
3VINT, and CHGINT status bits. The INT pin generates
an interrupt on the CPU that controls the MAX781.

Supply and Reference

5OUT outputs +5V, linear regulated from either BATT or
VCHG, in all modes except shutdown. 5OUT can
source up to 25mA. Power comes from BATT as long
as the BATT voltage is greater than the VCHG voltage.
When the VCHG voltage exceeds BATT, VCHG sup­plies the 5OUT linear regulator.

The MAX781’s internal circuitry is powered from 5OUT.
When the DLO pin drives high, it sources current from
5OUT. The DOUT and INT pin output drivers are pow­ered from 3OUT. If an external 5V supply is available
and connected to the 5OUT pin, the 5OUT linear regu­lator can be disabled by clearing the 5ON bit. If 5ON is
cleared without an external +5V supply connected to
5OUT, or if 5OUT is shorted to ground, the MAX781
internal registers will be cleared to their power-on state.

3.3V Output

3OUT outputs +3.3V in all modes except for shutdown.
In low-power and standby modes, 3OUT is linear regu­lated from either BATT or VCHG, whichever has the
higher voltage. In operate mode, the switch-mode
buck (step-down) converter is activated to regulate
3OUT to 3.3V. In operate mode, the 3OUT linear regu­lator is off.

WRITING A "1" TO BATTINT

CLEARS THE FLIP FLOP



TO ANALOG MULTIPLEXER

COMPARATOR DISABLED IN

LOW-POWER MODE; OUTPUTS "0"

REGARDLESS OF STATE OF INPUTS

CLR

D
>
>

BATTINT

Q

BATTSTAT

MAX781

BATT-

R4

Figure 6. BATTINT, BATTSTAT Status Circuitry

______________________________________________________________________________________ 13

1µF

AGND,
PGND

14.1k

MAX781

402k

PDA/Hand-Held Computer Power Controller

DHI high-side drives an external N-channel power
MOSFET, M1. Inside the MAX781, the DHI driver is
well-isolated so it can be powered separately from the
rest of the chip. The DHI driver is powered by current
that flows into BST and out of LX. Thus, BST is the
“power” connection and LX is the “ground” connection
for the DHI driver. An internal level shifter allows the
MAX781 internal circuitry to communicate with the DHI

MAX781

driver.
R

, connected from CS to 3OUT, senses current in

SENSE

the primary of transformer T1. With no load on VHI, the
primary of T1 can be treated as the inductor in a cur­rent-mode buck converter. R
the primary and turns off M1 when the current limit is
reached. The current limit is adjusted to ensure that
3OUT stays at 3.3V. With M1 off, M2 stays on until the
voltage on R
current limit that protects the output in the event 3OUT
is short circuited to ground. When the voltage from
3OUT to CS reaches 100mV, M1 is turned off whether
or not 3OUT is in regulation.

A capacitor (C5) on the soft-start (SS) pin allows the
current limit to slowly ramp up when power is first
applied. A 4µA current source from 3OUT feeds the SS
pin. The ramp time to full current limit is approximately
1ms for every nanofarad of capacitance on SS, with a
minimum value of 10ns. Once the SS pin reaches 3.3V,
the maximum peak current is available.

UVLO prevents the buck regulator and battery charger
from switching if 5OUT is out of regulation. The voltage
on UVLO is compared to REF. If UVLO is greater than
REF, the buck regulator and battery charger will func­tion normally. With UVLO less than REF, the buck regu­lator and battery charger stay off and the low-power
mode linear regulator supplies 3OUT, whether or not
operate mode has been set. Tying UVLO to AGND
allows an internal resistive divider to feed the UVLO com­parator, preventing operation of the buck regulator and
battery charger for 5OUT voltages less than approximately

4.35V (see the
The MAX781 3.3V buck regulator is similar to the 3.3V

buck regulator on the MAX783. For further information,
refer to the MAX783 data sheet

reaches zero. There is an absolute

SENSE

Electrical Characteristics

detects current in

SENSE

).

Idle Regulation vs. PWM Regulation

In operate mode, 3OUT can be regulated using pulse­skipping (Idle-Mode™ regulation) or pulse-width-modu­lation (PWM) regulation. The IDLE bit selects the

regulation scheme used for load current below about
25% of current limit.

Idle-Mode™ regulation pulses M1 until 25% of the
absolute current limit is reached, at which point M1
turns off. M1 does not turn on again until 3OUT falls
below 3.3V. This scheme improves light-load efficiency
by minimizing the number of times M1 needs to be
turned on to keep 3OUT in regulation. However, the
operating frequency varies with load. At load currents
above 25% of current limit, the regulator uses resonant
frequency PWM regulation independent of the idle bit.

PWM regulation turns M1 on at a constant frequency
and modulates M1’s duty cycle to maintain the current
required to keep 3OUT in regulation. The switching fre­quency remains constant regardless of the load cur­rent. Operating with a constant frequency results in
lower amplitude and more easily filtered output ripple.

The SYNC pin either sets the internal switching fre­quency or synchronizes the MAX781 to an external
oscillator. Tying SYNC to REF sets a switching fre­quency of 300kHz. Tying SYNC to 5V or AGND sets a
230kHz switching frequency. Driving SYNC with an
external oscillator synchronizes the PWM switching with
the external oscillator.

VPP Regulator

VPPA and VPPB linear regulate VHI down to
0V/+3.3V/+5V/+12V for use as a PCMCIA VPP voltage.
The VPPB0, VPPB1, VPPA0, VPPA1 bits control the
VPPB and VPPA output voltage. Programming VPPA or
VPPB to 0V shuts off the linear regulator and saves qui­escient supply current. Table 5 shows how to program
the VPPA and VPPB control bits.

During the flyback phase of the buck converter (DLO
on), VHI loads 3OUT. As long as DLO is on, power can
be supplied to VHI. When 3OUT has a light load, DLO
may not stay on long enough to supply power to VHI.
To prevent VHI from sagging, an internal comparator
checks VHI. If VHI sags below 12.8V, DLO is turned on
for 1µs to provide power to VHI, regardless of the volt­age on RSENSE. Power can only be delivered to VHI in
operate mode when the buck switching regulator is
active.

The VHI pin includes an overvoltage clamp that sinks
current if VHI exceeds 19V.

This prevents the parasitic capacitance in transformer
T1 from causing the VHI voltage to climb without limit.

™Idle-Mode is a trademark of Maxim Integrated Products.

14 ______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

Table 5. VPPA and VPPB Control Bits

VPPA1

0 0
0 1
1 0
1 1

VPPB1 VPPB0

0 0
0
1
1 1 3.3

VPPA0

1
0

VPPA Voltage (V)

0
5

12

3.3

VPPB Voltage (V)

0
5

12

Gate Drivers

GD1 through GD5 are gate-driver outputs that high­side drive external N-channel power MOSFETs. Loads
connected to 3OUT can be connected or disconnected
by using the circuitry shown in Figure 7. Clearing
GDSEL1 (GDSEL1 = 0) causes GD1 to sink up to
450µA to AGND. Setting GDSEL1 (GDSEL = 1) causes
GD1 to source up to 10µA from VHI. GD2–GD5 oper­ate the same way. VHI is active (i.e., regulated to at
least 12.8V) only in operate mode, so the gate drivers
also only function in operate mode. GDSEL1 defaults
to a 1 on power-up. GDSEL2 through GDSEL5 default
to 0 on power-up.

FAST is a general-purpose output pin that sinks current
when FASTON = 1 and goes open drain when FASTON
= 0. FAST can be pulled up to any voltage up to 19V.
To use FAST as a general-purpose 3.3V logic output,
pull it up to 3OUT with a 100kΩ resistor. FAST may be
used to pull the gate of M3 down to connect the battery
to the input supply. The MAX781 does not limit the bat­tery current when FAST is used in this way.

...TO REST OF 3OUT CIRCUIT

3OUT

GD_

MAX781

NEEDS TO BE TURNED

AGND

...TO REST OF AGND CONNECTIONS

Figure 7. Using the Gate Drivers for High-Side Load Switching

N-CHANNEL 
POWER MOSFET

3.3V LOAD THAT
ON/OFF

The battery charger is a voltage-mode average current

Battery Charger

regulator. Figure 8 shows a functional diagram of the
battery charger circuitry. The GMAMP is a transcon­ductance amplifer with approximately 62dB of open­loop DC gain. Set the GMAMP bandwidth with the
capacitor on COMP.

GMAMP bandwidth in hertz = gm / C

where gm = 0.0006 mho (mho = 1/Ω) and C = capaci­tance on COMP in farads.

Average the current-sense signal by setting the
GMAMP bandwidth much lower than the battery-charg­er switching frequency. The voltage output of the
GMAMP at COMP is converted to a duty cycle, which is
driven out of DCHG.

Serial-configuration bits CHG6–CHG0 set the average
current level. When CHG6–CHG0 are all set (1111111),
CSBAT is regulated to an average of 200mV. When
CHG6–CHG0 equals binary 0111111, CSBAT is regulat­ed to an average of 100mV.

CHG6–CHG0

DACOUT

(0mV TO 200mV)

GMAMP

CSBAT

Figure 8. Battery-Charger Block Diagram

7-BIT DAC

AT 0% DUTY CYCLE, DCHG = 5OUT

VOLTAGE TO
DUTY CYCLE
CONVERTER

5OUT

DCHG = 5OUT 
EXTERNAL SWITCH OFF

DCHG = AGND
EXTERNAL SWITCH ON

PGNDCOMP

DCHG

Analog Multiplexer

The MAX781’s built-in buffered analog multiplexer
selects one of eight different signal sources to be out­put from the AOUT pin. Figure 9 shows the analog mul­tiplexer circuitry. The AOUT buffer amplifier is disabled
in the shutdown and low-power modes, leaving the

89.7kΩ resistor to pull AOUT down to ground. Program
the MUX0, MUX1, MUX2 bits in the serial-configuration
data to select the analog multiplexer channel (Table 6).
Resistive dividers in the signal paths scale the chan­nels to ensure that AOUT is scaled to REF. The AOUT
buffer amplifier can sink or source 1mA.

MAX781

______________________________________________________________________________________ 15

PDA/Hand-Held Computer Power Controller

Table 6. Analog Multiplexer Channel Selection

MUX2

MAX781

0
0

AUXIN

REF

VPPB

VPPA

TEMP

BATT

5OUT

3OUT

MUX0

MUX1

MUX2

Figure 9. Analog Multiplexer Circuitry

A0

A1

A2

MUX1

3-to-8

DECODER

11

11

01

10
10
0
0

498.4k

116k

498.4k

116k

500k

125k359k

200k

183.3k

150k

300k

Y0
Y1
Y2
Y3
Y4
Y5
Y6
Y7

MUX0

1
0
1
0
1
0
1
0

AOUT

OUTPUTS

AUXIN/1.5

REF
VPPB/5.3
VPPA/5.301

TEMP/1.5

BATT/5
5OUT/2.2
3OUT/1.5

89.7k

AOUT

_Component Selection and Layout

3.3V Output

Input and Output Bypass Capacitors

Capacitor C15 ensures that the buck regulator has a
low AC-impedance power source. C15’s root mean
square ripple-current rating must be greater than 0.5 x
(maximum power output capability of the system) /

3.3V. Capacitor C6 keeps 3OUT output ripple low and
stabilizes the regulation loop. C15 and C6 must have
low equivalent series resistance (ESR), preferably with
less than 0.2Ω of ESR at 200kHz. Tantalum capacitors
typically have the lowest ESR. C15’s ground connec­tion must be as close as possible to C6’s ground con­nection; ideally, the two capacitors will be grounded at
the same point. The MAX781’s AGND pin should only
connect to system ground at the ground connection of
C15 and C6. If the PC board has a ground plane, a
separate trace should directly connect AGND to the
ground connections of C15 and C6. Likewise, the
BATT pin should only connect to the battery at C15’s
positive terminal.

The capacitance and ESR of C6 determine loop stabili­ty. To ensure loop stability, the minimum capacitance
and maximum ESR values are:

C6 > 2.5V / (3.3V x R7 x 2 x p x GBWP)

with C6 specified in Farads, R7 specified in ohms,
GBWP = gain bandwidth product of 60,000Hz, and:

C6 ESR < (3.3V x R7) / 2.5V

with C6 ESR specified in ohms, and R7 specified in
ohms.

In order to achieve the required low ESR, it may be
appropriate to select a value greater than the minimum
for C6, or to construct a composite C6 by paralleling
several smaller capacitors.

Current-Sense Resistor

Current-sense resistor R7 sets the maximum peak cur­rent through power switch M1 and the primary of trans­former T1. The MAX781’s maximum peak current limit
is 120mV / R, where R is the minimum possible resis­tance for R7, and 120mV is the maximum electrical
specification for the current-limit threshold. For exam­ple, selecting a 0.082Ω ±1% resistor for R7 yields a
maximum peak current limit of 120mV / 0.082Ω x 0.99 =

1.478A. The maximum peak current limit must be less
than or equal to the maximum allowed continuous DC
current through either M1 or the primary of T1.

R7 also determines how much power 3OUT, VPPA, and
VPPB can deliver. The current-limit threshold can be
as small as 80mV and, using a 0.082Ω ±1% resistor,

16 ______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

R7 can be as large as 0.082Ω x 1.01 = 0.0828Ω, yield­ing a minimum peak current limit of 80mV / 0.0828Ω =

0.966A.
Use the spreadsheet in Listings 1 and 2 to calculate the

power available at 3OUT as a function of the current­sense resistor choice.

Listing 1. Spreadsheet for Calculating 3OUT
Current Capability

Parameter Min Max Units
(Cell A1) (Cell B1) (Cell C1)

Current-Limit Threshold 80 120 mV
Current Sense R7 81 83 mΩ
Current Limit 0.964 1.481 A
Switching Frequency 270 340 kHz
Switching Period 2.941 3.704 µs
T1 Primary Inductance 16 24 µH
3OUT Regulation Point 3.170 3.430 V
BATT Input Range 5.000 17.500 V
(Cell A10)
Current Limit 0.964 A
Switching Period 3.704 µs
T1 Primary Inductance 16 µH
3OUT 3.430
BATT 17.500
VHI Load Current 60 mA
T1 Turns Ratio 3.5
T1 Coupling Loss 80 %
(Cell A20)
T1 Ripple Current 0.638 A
T1 Continuous Current 0.325 A
3OUT Current, No VHI load 0.645 A
VHI Load Power 0.926 W
3OUT Guaranteed Current 0.307 A
(Cell A26) (Cell B26) (Cell C26)

Listing 2. Calculating 3OUT Current-Capability
Formulas

B4: +B2/C3
C4: +C2/B3
B6: 1/C5*1000
C6: 1/B5*1000
B12: +B4

C13: +C6
B14: +B7
C15: +C8
C16: +C9
C21: @MIN(+C15/C16*C13*(C16-C15)/B14,B12)
C22: +B12-C21
C23: @IF(C22=0,0.5*(B14/1000000)*C21^2*1000000/

C13/C15,C22+C21/2)
C24: +C15*(C18+1)*C17/1000
C25: +C23-C24/(C19/100)/C15

R7 must have as little series inductance as possible
and be as physically small as possible. 3OUT and CS3
need to Kelvin sense R7. A pair of traces running in
parallel should leave 3OUT and CS3 and diverge only
when they meet R7. Minimize the distance between
R7 and the positive terminal of C6.

Power MOSFETs

M1 and M2 must be logic level, low r

DS(ON)

, N-channel
power MOSFETs. M1’s drain should be as close as
possible to C15’s positive terminal and M2’s source
should be as close as possible to C15’s ground con­nection point.

Transformer T1

T1’s primary inductance must be between 10µH and
100µH. The peak current allowed through the primary
with the secondary open circuited must be greater than
the worst-case peak current set by R7. T1’s turns ratio
(number of turns on secondary / number of turns on pri­mary) should be 3.5. If VHI rises up to 20V when 3OUT
is loaded in operate mode, T1 may have too much
interwinding capacitance. Minimize interwinding
capacitance to prevent energy waste in the VHI clamp
(which clamps VHI to 19V to protect the MAX781).

__________Applications Information

Table 7 shows the targets for a typical design require­ment. Since both PCMCIA slots will not be pro­grammed at the same time, VPPA and VPPB will never
be at +12V at the same time; thus the worst case for
power consumption is when both 3.3V and VPPA or
VPPB is fully loaded.

Total power consumption = (max 3OUT voltage) x (max
3OUT load current) + (VHI voltage) x (max VPP or load
current) / (transformer efficiency).

Design Example

MAX781

______________________________________________________________________________________ 17

PDA/Hand-Held Computer Power Controller

Table 7. Specifications for a Typical Design

PARAMETER

Input Power

3.3V Output

MAX781

Current

VPPA Output
Current

VPPB Output
Current

Charge Current

VPPA and VPPB are linear regulated from VHI, so the
power consumed by loads on VPPA or VPPB equals
the VHI voltage times the load current. Barring a
Schottky diode drop, VHI equals the 3OUT voltage x (1
+ turns ratio). With the specifications of Table 7 and
an 80% transformer efficiency, the total power con­sumption works out to 2.037W; thus the average cur­rent through the primary of T1 is 594mA. The peak
current through the primary of T1 will depend on the
minimum primary inductance. As a rule of thumb, the
peak current will be about 1.5 times the average cur­rent. For an average current of 594mA, the peak cur­rent would be about 900mA. To achieve a 900mA peak
current, select R7 to be 80mV / 900mA = 0.088Ω. The
closest comercially available value would be 0.082Ω
±1%. The spreadsheet in Listing 1 calculates how high
a guaranteed output current can be, given commercial­ly available component values, and taking component
tolerances into account.

Table 8 shows the electrical specifications for a trans­former that meets the requirements of Listing 1.

Power MOSFETs M1 and M2 should have an on-resis­tance at logic-level gate drive (r

DESIGNATION

5 NiCD cells
15V DC adapter

+12V output when
programming flash
memory in Slot A

+12V output when
programming flash
memory in Slot A

Digitally
programmable

DS(ON)

MIN

MAX

5

17.5

300

60

60 mA

0

1

at VGS= 4.5V)

UNITS

V

mA

mA

A

Table 8. Dale Electronics M/N LPE-6562-A070
Specifications

PARAMETER

Primary Inductance 20
Leakage Inductance

(at 0.1V
Primary Continuous

DC Current
Primary DC Resistance
Secondary DC Resistance
Turns Ratio

(secondary/primary)

RMS

, 100kHz)

of the same order as T1’s primary DC resistance. The
Siliconix Si9955DY dual N-channel MOSFET satisfies
this requirement with a 0.2Ω maximum on-resistance
per device.

Table 9 lists the bill of materials for an example circuit
that fulfills the requirements of Table 7.

MIN

16

TYP

3.5

MAX

24

2.6

0.075

0.51

UNITS

µH
µH0.03

A

Ω
Ω

Driving a CCFL Backlight Royer Oscillator

The digitally adjustable current from the battery charger
can be used to drive a Royer oscillator. The Royer
oscillator is a resonant circuit fed by a constant current.
The root mean square current out of the secondary
winding of the Royer transformer is proportional to the
current fed into the center tap of the Royer transformer.
Figure 10 shows the application circuit. The diode from
VCHG to BATT keeps BATT from dropping too far
below 5OUT, which causes excess supply current.
Figure 11 shows how the programmed current corre­sponds to the CCFL root mean square tube current.

The NPN transistor connected to COMP and the zener
diode protects the transformer from an open-tube con­dition by shutting off the Si9953DY if pin 2 of the
CTX110606 exceeds 0.6V + 10V + 0.6V. This limits the
voltage on the secondary to 11.2 x 171 x 2 = 3830.4V
peak-to-peak = 1354V

, which is well within the

RMS

CTX110606 maximum secondary voltage specification
of 2010V

RMS

.

18 ______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

Table 9. Design Example Bill of Materials

SYMBOL

T1 M/N LPE-6562-A070
L1 CDR125-470

M1, M2 Si9955DY

M3 Si9953DY
R1
R4
R7
R8
C1
C2
C3
C5
C6 195D127X06R3R2T
C7
C8

C9
C10 195D226X0025R2T
C11
C12
C14 195D226X0025R2T

D1 CMPD4150

D2 EC10QS03

D3 EC15QS03

D5 EC10QS03

D6 EC10QS05

D7 CMPD4150

transformer
47µH, 1.5A IDC inductor
N-Channel MOSFETs
P-Channel MOSFET
100kΩ, ±20% resistor

0.2Ω, ±1% resistor

0.082Ω, ±1% resistor
10kΩ, ±1% resistor

0.1µF, 20V capacitor

0.33µF, 6V capacitor
1µF, 6V capacitor

0.01µF, 6V capacitor
120µF, 6.3V capacitor, 0.09Ω ESR at 100kHz

0.1µF, 10V capacitor
1µF, 16V capacitor
1µF, 16V capacitor
22µF, 25V capacitor

2.2µF, 25V capacitor
1µF, 6V capacitor
22µF, 25V capacitor
20V 1N4150 type diode
20V Schottky diode
20V Schottky diode
20V Schottky diode
50V Schottky diode
20V 1N4150 type diode

DESCRIPTION

PART No.

MAX781

MANUFACTURER

Dale
Sumida
Siliconix
Siliconix

IRC
IRC

Sprague

Sprague

Sprague
Central
Nihon
Nihon
Nihon
Nihon
Central

Table 10. Component Suppliers

SUPPLIER

[phone]Central Semiconductor
[phone]Coiltronics
[phone]Dale
[phone]IRC

Nihon
Rep: Quantum Marketing

Siliconix

Wilhelm Westerman
Rep: Inter-Technical Group

Zetex

______________________________________________________________________________________ 19

Japan 81-3-3494-7411
USA [phone]

[phone]

[phone]Sumida
Germany 0621-408012

USA [phone]
USA [phone]

UK 061-627-4963

PHONE

FAX

[phone]
[phone]
[phone]
[phone]
81-3-3494-7414

[phone]
[phone]

[phone](603) 224-1961Sprague
[phone]

0621 403538
[phone]

[phone]
061-627-5467

PDA/Hand-Held Computer Power Controller

MAX781

MAX781

BATT

VCHG

COMP

DCHG

CSBAT

0.1µF

CMPD4448

0.33µF

10k

CMPT3904

CMPD4448

22µF

20V

CMPZ5240B

10k

CMPD4448

Si9953DY

CTX150-4

EC10QS02L

15pF 2kV

2

1

MKS01-SMD

CCFL

FMMT619

M1 DRAIN

CCFL

CTX110606

2345

710Ω

0.1µF

0.47Ω

10

FMMT619

AGND

NOTE: SEE TABLE 10 FOR COMPONENT SUPPLIER INFORMATION.
CM = CENTRAL SEMICONDUCTOR

CT = COILTRONICS
EQ = NIHON INTER ELECTRIC CORP.
FM = ZETEX
MK = WILHELM WESTERMANN

Figure 10. Digitally Adjustable CCFL Backlight Circuit

20 ______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

Interfacing the MAX781 to an

IBM Compatible PC

Figure 1 shows the MAX781 typical operating circuit.
On power-up, with 4.8V < BATT < 18V and CE = SCLK
= DIN = 0V, the MAX781 is in low-power mode. 3OUT
outputs +3.3V linear regulated from BATT, and REF
outputs +2.5V. INT should output a 3.3V logic high.
Neither DHI nor DLO should be switching. Serial data
must be sent to the MAX781 in order to change modes.
The parallel printer interface on a personal computer
can be used to send serial control data to the MAX781.
Listing 3 shows a simple Microsoft Quick Basic pro­gram for communicating with the MAX781 over the
LPT1 parallel interface port.

MAX781

______________________________________________________________________________________ 21

PDA/Hand-Held Computer Power Controller

Listing 3. MAX781 Control Program in QBasic

MAX781

22 ______________________________________________________________________________________

PDA/Hand-Held Computer Power Controller

TOP VIEW

GD2
GD3
GD4
GD5

VPPA

VHI

VPPB
AGND
SYNC

SCLK
DOUT

DIN

FAST

COMP

CSBAT

5OUT

___________________Chip Topography__________________Pin Configuration

GD4

VHI

DIN
INT

CE

GD5 GD3 GD1

FAST

COMP

36

1
2
3
4
5

MAX781

6
7
8
9

CE

10
11
12
13

INT

14
15
16
17
18

GD1
SHDN

35

AUXIN

34

TEMP

33

AOUT

32

REF

31
30

UVLO
VCHG

29
28

BATT

27

SS

26

CS
3OUT

25

LX

24
23

DHI
BST

22

DLO

21

PGND

20
19

DCHG

VPPA

VPPB

AGND

SYNC

SCLK

DOUT

SSOP

GD2 SHDN

DCHG

5OUT

0.152"

(3.861mm)

TEMP

AUXIN

DLOCSBAT

PGND BST

AOUT
REF

UVLO

VCHG
BATT

0.219"

(5.563mm)

SS
CS

3OUT

LX

DHI

MAX781

TRANSISTOR COUNT: 2661
SUBSTRATE CONNECTED TO AGND.

______________________________________________________________________________________ 23

PDA/Hand-Held Computer Power Controller

________________________________________________________Package Information

INCHES MILLIMETERS

DIM

MAX781



A

A1

B
C

HE

D
E
e
H
L

α

MIN

0.094

0.004

0.011

0.009

0.604

0.292


0.398

0.020

0˚

MAX

0.104

0.011

0.017

0.012

0.610

0.298

0.416

0.035
8˚

MIN

2.39

0.10

0.30

0.23

15.34

7.42

0.80 BSC0.032 BSC





10.10

0.51
0˚

MAX

2.64

0.28

0.44

0.32

15.49

7.57


10.57

0.89

8˚

21-0032A

D

α

A

0.127mm

0.004in.

A1

e

B

C

L

36-PIN PLASTIC

SHRINK

SMALL-OUTLINE

PACKAGE

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

24

__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 [phone]

24

__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 [phone]

© 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

© 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.