Datasheet

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19-1752; Rev 1; 1/01

MAX1758

Stand-Alone, Switch-Mode

Li+ Battery Charger with Internal 28V Switch

EVALUATION KIT AVAILABLE

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

General Description

The MAX1758 is a switch-mode lithium-ion (Li+) battery

charger that charges one-to-four cells. It provides a reg-

ulated charging current accurate to ±10% and a regu-

lated voltage with only a ±0.8% total voltage error at the

battery terminals. The internal high-side switch delivers

a programmable current of up to 1.5A to charge the bat-

tery. The built-in safety timer automatically terminates

charging once the adjustable time limit has been

reached.

The MAX1758 regulates the voltage set point and

charging current using two loops that work together to

transition smoothly between voltage and current regula-

tion. An additional control loop monitors the total cur-

rent drawn from the input source (charging + system),

and automatically reduces battery-charging current,

preventing overload of the input supply and allowing

the use of a low-cost wall adapter.

The per-cell battery regulation voltage is set between

4.0V and 4.4V using standard 1% resistors. The num-

ber of cells is set from 1-to-4 by pin strapping. Battery

temperature is monitored by an external thermistor to

prevent charging outside the acceptable temperature

range.

The MAX1758 is available in a space-saving 28-pin

SSOP package. Use the MAX1758EVKIT to help reduce

design time. For a stand-alone charger with a 14V

switch, refer to the MAX1757 data sheet. For a charger

controller capable of up to 4A charging current, refer to

the MAX1737 data sheet.

________________________Applications

Features

o Stand-Alone Charger for Up to 4 Li+ Batteries

o ±0.8% Battery Regulation Voltage Accuracy

o Low-Dropout 98% Duty Cycle

o Safely Precharges Near-Dead Cells

o Continuous Voltage and Temperature Monitoring

o 0.1µA Shutdown Battery Current

o Input Voltage Up to 28V

o Up to 1.5A Programmable Charge Current

o Safety Timer Prevents Overcharging

o Input Current Limiting

o Space-Saving 28-Pin SSOP

o 300kHz PWM Oscillator Reduces Noise

DCIN

CSSP

CSSN

CCV

CCI

CCS

FASTCHG

BST

PGND

SHDN

FULLCHG

FAULT

TIMER2

TIMER1

CELL

HSD

BATT

VADJ

GND

REF

THM

ISETOUT

ISETIN

SSOP

TOP VIEW

MAX1758

Ordering Information

28 SSOP

PIN-PACKAGETEMP. RANGE

-40°C to +85°CMAX1758EAI

PART

Li+ Battery Packs

Notebook Computers

Hand-Held Instruments

Desktop Cradle Chargers

Pin Configuration

GND

DCIN

6V TO 28V

CSSP

CSSN

BST

PGND

BATT

THM

THERM

FASTCHG

FULLCHG

FAULT

HSD

SYSTEM

LOAD

Li+ BATTERY

1 TO 4 CELLS

MAX1758

ISETOUT

ISETIN

VADJ

CCS

CCI

CCV

REF

TIMER1

TIMER2

SHDN

OFF

CELL

Typical Operating Circuit

Summary of content (17 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch General Description The MAX1758 is a switch-mode lithium-ion (Li+) battery charger that charges one-to-four cells. It provides a regulated charging current accurate to ±10% and a regulated voltage with only a ±0.8% total voltage error at the battery terminals. The internal high-side switch delivers a programmable current of up to 1.5A to charge the battery.
PAGE 2
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch ABSOLUTE MAXIMUM RATINGS DCIN, CSSP, CSSN, HSD to GND..........................-0.3V to +30V CSSP to CSSN.......................................................-0.6V to +0.6V BST to GND ............................................................-0.3V to +36V BST to LX..................................................................-0.3V to +6V LX to PGND ..............................................-0.6V to (VHSD + 0.
PAGE 3
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CS to BATT Hard Current Limit CONDITIONS Instantaneous peak current limit BATT, CS Input Voltage Range MIN TYP MAX UNITS 2.4 2.
PAGE 4
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS BATT Undervoltage Threshold (Note 3) 2.4 2.5 2.6 V/cell BATT Overvoltage Threshold (Note 4) 4.
PAGE 5
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 6
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = -40°C to +85°C, unless otherwise noted.) (Note 7) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS BATT Undervoltage Threshold (Note 3) 2.4 2.6 V/cell BATT Overvoltage Threshold (Note 4) 4.55 4.
PAGE 7
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch Typical Operating Characteristics (Circuit of Figure 1, VDCIN = 18V, V SHDN = VVL, VCELL = GND, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, TA = +25°C, unless otherwise noted.) BATTERY VOLTAGE vs. CHARGING CURRENT CHARGING CURRENT vs. ISETOUT VOLTAGE 2.0 1.5 0.8 0.6 1.0 0.4 0.5 0.2 0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0 CHARGING CURRENT (A) ISETOUT VOLTAGE (V) VOLTAGE LIMIT vs. VADJ VOLTAGE REFERENCE VOLTAGE vs.
PAGE 8
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch Pin Description 8 PIN NAME FUNCTION 1 VL Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL to GND with 2.2µF or larger ceramic capacitor. 2 ISETIN Input Current Limit Adjust. Use a voltage-divider to set the voltage between 0 and VREF. See Input Current Regulator section. 3 ISETOUT 4 THM Thermistor Input. Connect a thermistor from THM to GND to set qualification temperature range.
PAGE 9
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MBRS340 D1 INPUT SUPPLY D2 28 DCIN CSSP 27 C7 0.1μF C8 0.1μF R1 0.05Ω MAX1758 CSSN 26 C9 0.1μF 17 TO VL 5 2 R4 3 C3 1μF 7 11 R5 VL ISETIN ISETOUT VADJ CELL R6 10k 25 C17 1nF C1 0.1μF 24 CCI BST HSD HSD 12 FAULT 9 20 C14 0.1μF L1 22μH 19 D4 MBRS340 PGND CS CCS BATT 18 21 TIMER1 THM 13 15 16 14 8 C18 0.1μF C5 1nF FULL CHARGE 10 C16 0.
PAGE 10
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch Table 1.
PAGE 11
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch The MAX1758 includes a state machine that controls the charging algorithm. Figure 4 shows the state diagram. Table 1 is the charging state table. When power is applied, or SHDN input is driven high, the part goes into the reset state where the timers are reset to zero to prepare for charging. From the reset state, it enters the prequalification state.
PAGE 12
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch DCIN TO BATT CSS LEVEL SHIFT AND GAIN OF 10 CSSP CSSN ENABLE VL 5.
PAGE 13
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch SHUTDOWN SHUTDOWN IS ENTERED FROM ALL STATES WHEN SHDN IS LOW. FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH VDCIN < BATT SHDN HIGH RESET VBATT < UNDERVOLTAGE THRESHOLD VDCIN > VBATT FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH PREQUAL FAULT PREQUAL TIMEOUT FASTCHG = LOW FULLCHG = HIGH FAULT = HIGH FASTCHG = HIGH FULLCHG = HIGH FAULT = LOW VBATT > 2.
PAGE 14
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch capacitor. This capacitor (between BST and LX) is charged through a diode from VL when LX is low. An internal N-channel MOSFET turns on momentarily after the high-side switch turns off, pulling LX to PGND to ensure that the bootstrap capacitor charges. The highside MOSFET gate is driven from BST, supplying sufficient voltage to fully drive the MOSFET gate even when its source is near the input voltage.
PAGE 15
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch cell voltage limit battery regulation voltage is determined, the VADJ voltage is calculated by the equation: VVADJ = (9.5 VBATTR / N) - (9.0 x VREF) CELL is the programming input for selecting cell count N. Table 2 shows how CELL is connected to charge 1, 2, 3, or 4 cells. Setting the Charging Current Limit A resistor-divider from REF to GND sets the voltage at ISETOUT (VISETOUT).
PAGE 16
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch dissipation ratings more critical when using tantalum capacitors. The output filter capacitor is used to absorb the inductor ripple current. The output capacitor impedance must be significantly less than that of the battery to ensure that it will absorb the ripple current. Both the capacitance and ESR rating of the capacitor are important for its effectiveness as a filter and to ensure stability of the PWM circuit.
PAGE 17
MAX1758 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch Package Information Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed.