Maxim MAX798ESE Datasheet

19-1175; Rev 0; 12/96

with Synchronous Rectifier for CPU Power

High-Accuracy Step-Down Controller

_______________General Description

The MAX798†high-performance, step-down DC-DC
converter provides main CPU power in battery-powered
systems. This buck controller achieves 96% efficiency
by using synchronous rectification and Maxim’s propri­etary Idle Mode™ control scheme to extend battery life
at full-load (up to 10A) and no-load outputs. The
MAX798’s high accuracy meets the demanding require­ments of the latest-generation CPUs. Excellent dynamic
response corrects output transients caused by the latest
dynamic-clock CPUs within five 300kHz clock cycles.
Unique bootstrap circuitry drives inexpensive N-channel
MOSFETs, reducing system cost and eliminating the crow­bar switching currents found in some PMOS/NMOS switch
designs.

The MAX798 has a logic-controlled and synchronizable
fixed-frequency pulse-width-modulating (PWM) operating
mode, which reduces noise and RF interference in sensi­tive mobile-communications and pen-entry applications.
The SKIP override input allows automatic switchover to
idle-mode operation (for high-efficiency pulse skipping) at
light loads, or forces fixed-frequency mode for lowest noise
at all loads.

________________________Applications

____________________________Features

♦ 96% Efficiency
♦ 4.5V to 30V Input Range
♦ 1.6V to 6V Adjustable Precision Output
♦ ±0.4% Max Total Load-Regulation Error
♦ 0.06%/V Max Line-Regulation Error
♦ 5V Linear-Regulator Output
♦ Precision 2.505V Reference Output
♦ Automatic Bootstrap Circuit
♦ 150kHz/300kHz Fixed-Frequency PWM Operation
♦ Programmable Soft-Start
♦ 1.2mA Typical Quiescent Current

(VIN= 12V, V

OUT

= 2.5V)

♦ 1µA Typical Shutdown Current

______________Ordering Information

PIN-PACKAGETEMP. RANGEPART

16 Narrow SO-40°C to +85°CMAX798ESE

MAX798

Notebook and Subnotebook Computers
PDAs and Mobile Communicators

__________________Pin Configuration

TOP VIEW

SS

1
2

SKIP

REF

3

GND
SYNC
SHDN

FB

CSH

Idle Mode is a trademark of Maxim Integrated Products.

†

U.S. and foreign patents pending.

MAX798

4
5
6
7
8

SO

DH

16

LX

15

BST

14

DL

13

PGND

12

VL

11

V+

10

9

CSL

__________Typical Operating Circuit

INPUT

4.5V TO 30V
5V, 25mA

4.7µF

V+ VL

BST

DH

MAX798

ON

OFF

SHDN

GND

LX

DL

PGND

CSH

CSL

FB

0.1µF

N

R

SENSE

N

V

OUT

________________________________________________________________

Maxim Integrated Products

1

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone]

High-Accuracy Step-Down Controller
with Synchronous Rectifier for CPU Power

ABSOLUTE MAXIMUM RATINGS

V+ to GND.................................................................-0.3V, +36V

GND to PGND........................................................................±2V

VL to GND ...................................................................-0.3V, +7V

BST to GND...............................................................-0.3V, +36V

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

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

SHDN to GND............................................................-0.3V, +36V

MAX798

SYNC, SS, REF, SKIP, DL to GND...................-0.3V, (VL + 0.3V)

CSH, CSL to GND .......................................................-0.3V, +7V

VL Short Circuit to GND..............................................Momentary

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

(V+ = +15V, GND = PGND = 0V, IVL= I

STEP-DOWN CONTROLLER

Nominal Adjustable Output
Voltage Range

Current-Limit Voltage

INTERNAL REGULATOR AND REFERENCE

= 0A, TA= 0°C to +85°C, unless otherwise noted.)

REF

CONDITIONS

External resistor divider
CSH - CSL = 40mV, SKIP = VL

0mV < (CSH - CSL) < 80mV, SKIP = VL
6V < V+ < 30V
CSH - CSL, positive
CSH - CSL, negative

SHDN = 2V, 0mA <IVL< 25mA, 5.5V < V+ < 30V
Rising edge, hysteresis = 15mV
Rising edge, hysteresis = 25mV
No external load (Note 1) V2.463 2.505 2.537Reference Output Voltage
Falling edge V1.8 2.3Reference Fault Lockout Voltage
0µA < I

SHDN = 0V, CSL = 6V, V+ = 0V or 30V, VL = 0V
SHDN = 0V, V+ = 30V, CSL = 0V or 6V

FB = CSH = CSL = 6V, VL switched over to CSL µA15V+ Off-State Leakage Current
V+ = 4V, CSL = 0V (Note 2) mW6.6 10.5Dropout Power Consumption
CSH = CSL = 6V mW6.4 8.5Quiescent Power Consumption

REF

< 100µA mV20Reference Load Regulation

REF Short Circuit to GND...........................................Continuous

VL Output Current...............................................................50mA

Continuous Power Dissipation (T

SO (derate 8.70mW/°C above +70°C)........................696mW

Operating Temperature Range

MAX798ESE....................................................-40°C to +85°C

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

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

= +70°C)

A

80 100 120

-40 -100 -160

UNITSMIN TYP MAXPARAMETER

V4.5 30Input Supply Range
V1.6 6
V1.576 1.6 1.624Feedback Voltage

%±0.4Load Regulation

%/V0.04 0.05Line Regulation

mV

µA2.0 4.0 6.5SS Source Current

mA2.0SS Fault Sink Current

V4.75 5.25VL Output Voltage
V3.8 4.0VL Fault Lockout Voltage
V4.2 4.7VL/CSL Switchover Voltage

µA0.1 1CSL Shutdown Leakage Current
µA15V+ Shutdown Current

2 _______________________________________________________________________________________

High-Accuracy Step-Down Controller

with Synchronous Rectifier for CPU Power

ELECTRICAL CHARACTERISTICS (continued)

(V+ = +15V, GND = PGND = 0V, IVL= I

Oscillator Frequency

Maximum Duty Cycle

Input High Voltage

Input Low Voltage

Input Current

= 0A, TA= 0°C to +85°C, unless otherwise noted.)

REF

CONDITIONS UNITSMIN TYP MAXPARAMETER

SYNC = REF
SYNC = 0V or 5V

Guaranteed by design

SYNC = REF
SYNC = 0V or 5V
SYNC
SHDN, SKIP
SYNC

SHDN, SKIP
SHDN, 0V or 30V

SYNC, SKIP
CSH, CSL, CSH = CSL = 4V, device not shut down
FB, FB = 1.6V ±100 nA
DL forced to 2V
DH forced to 2V, BST - LX = 4.5V A1DH Sink/Source Current
High or low
High or low, BST - LX = 4.5V

270 300 330
125 150 175

89 91
93 96

VL - 0.5

2.0

0.8

0.5
2
1

50

kHz

ns200SYNC High Pulse Width
ns200SYNC Low Pulse Width
ns200SYNC Rise/Fall Time

kHz195 340Oscillator Sync Range

%

V

V

µA
µA

A1DL Sink/Source Current

Ω7DL On-Resistance
Ω7DH On-Resistance

MAX798

_______________________________________________________________________________________ 3

High-Accuracy Step-Down Controller
with Synchronous Rectifier for CPU Power

ELECTRICAL CHARACTERISTICS

(V+ = +15V, GND = PGND = 0V, IVL= I

STEP-DOWN CONTROLLER

Nominal Adjustable Output

MAX798

Voltage Range

Current-Limit Voltage

INTERNAL REGULATOR AND REFERENCE

OSCILLATOR AND INPUTS/OUTPUTS

Oscillator Frequency

Maximum Duty Cycle

= 0A, TA= -40°C to +85°C, unless otherwise noted.) (Note 3)

REF

CONDITIONS UNITSMIN TYP MAXPARAMETER

External resistor divider V1.6 6.0
CSH - CSL = 40mV, SKIP = VL

0mV < (CSH - CSL) < 80mV, SKIP = VL
6V < V+ < 30V %/ V0.04 0.06Line Regulation
CSH - CSL, positive
CSH - CSL, negative -40 -100 -160

SHDN = 2V, 0mA < IVL< 25mA, 5.5V < V+ < 30V
Rising edge, hysteresis = 15mV
Rising edge, hysteresis = 25mV
No external load (Note 1)
0µA < I
SHDN = 0V, V+ = 30V, CSL = 0V or 6V
FB = CSH = CSL = 6V, VL switched over to CSL
CSH = CSL = 6V

SYNC = REF
SYNC = 0V or 5V

SYNC = REF
SYNC = 0V or 5V
High or low
High or low, BST - LX = 4.5V

REF

< 100µA

70 130

4.15 4.75VL/CSL Switchover Voltage

250 300 350
110 150 190

250SYNC Low Pulse Width

88 91
92 96

V5.0 30Input Supply Range

V1.560 1.6 1.640Feedback Voltage

%±1Load Regulation

mV

V4.7 5.3VL Output Voltage
V3.75 4.05VL Fault Lockout Voltage
V
V2.438 2.505 2.562Reference Output Voltage

mV30Reference Load Regulation

µA110V+ Shutdown Current
µA110V+ Off-State Leakage Current

mW6.4 9.1Quiescent Power Consumption

kHz

ns250SYNC High Pulse Width
ns

kHz210 320Oscillator Sync Range

%

Ω7DL On-Resistance
Ω7DH On-Resistance

Note 1: Since the reference uses VL as its supply, V+ line-regulation error is insignificant.
Note 2: At very low input voltages, quiescent supply current can increase due to excess PNP base current in the VL linear

regulator. This occurs only if V+ falls below the preset VL regulation point (5V nominal). The typical maximum quiescent
current in dropout will not exceed 16mA.

Note 3: All -40°C to +85°C specifications above are guaranteed by design.

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