MAX1757 Maxim, MAX1757 Datasheet - Page 13

• Manufacturer Part Number: MAX1757
• Description: Stand-Alone / Switch-Mode Li Battery Charger with Internal 14V Switch
• Manufacturer: Maxim

When choosing the current-sense resistor, note that the
voltage drop across this resistor adds to the power
loss, reducing efficiency. Reducing the voltage across
the current-sense resistor may degrade input current
limit accuracy due to the input offset of the input cur-
rent-sense amplifier.
The input current error amplifier (GMS) is compensated
at CCS. A 0.1µF capacitor at CCS provides suitable
performance for most applications.
The PWM controller drives the internal high-side MOS-
FET to control charging current or voltage. The input to
the PWM controller is the lowest of CCI, CCV, or CCS.
An internal clamp limits the noncontrolling signals to
within 200mV of the controlling signal to prevent delay
when switching between regulation loops.
Figure 4. State Diagram
Li+ Battery Charger with Internal 14V Switch
______________________________________________________________________________________
V
BATT
NOT OK
TEMP
THRESHOLD
< UNDERVOLTAGE
NOT OK
TEMP
TEMP
QUAL
V
FULLCHG = HIGH
FASTCHG = LOW
DCIN
FAULT = HIGH
PREQUAL
V
PWM Controller
DCIN
> V
TEMP
TEMP
OK
BATT
OK
ONCE PER
< BATT
SECOND
TEMP
OK
ONCE PER
SECOND
FASTCHG = HIGH
FULLCHG = HIGH
FAULT = HIGH
V
PREQUAL
NOT OK
TIMEOUT
BATT
TEMP
RESET
TEMP
OK
> 2.5V
FULLCHG = HIGH
FULL CHARGE
FASTCHG = HIGH
FULLCHG = LOW
FASTCHG = HIGH
FULLCHG = HIGH
FAST CHARGE
FASTCHG = LOW
FAULT = HIGH
FAULT = HIGH
FAULT = HIGH
Stand-Alone, Switch-Mode
TOP-OFF
SHDN HIGH
REGULATION VOLTAGE (V
FASTCHG = HIGH
FULLCHG = HIGH
I
SHUTDOWN
V
FAULT = HIGH
CHARGE
BATT
FULL-CHARGE
FASTCHG = HIGH
FULLCHG = HIGH
FAST-CHARGE
FAULT = LOW
TIMEOUT
The current mode PWM controller measures the induc-
tor current to regulate the output voltage or current,
simplifying stabilization of the regulation loops.
Separate compensation of the regulation circuits allows
each to be optimally stabilized. Internal slope compen-
sation is included, ensuring stable operation over a
wide range of duty cycles.
The controller drives an internal N-channel MOSFET
switch to step the input voltage down to the battery
voltage. The high-side MOSFET gate is driven to a volt-
age higher than the input source voltage by a bootstrap
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 high-
side MOSFET gate is driven from BST, supplying suffi-
TIMEOUT
FAULT
= BATTERY
< I
TIMEOUT
MIN
TOP-OFF
OR
V
BATT
ENTERED FROM ALL STATES
< 0.95 × V
BATTR
WHEN SHDN IS LOW.
SHUTDOWN IS
FASTCHG = HIGH
FULLCHG = HIGH
)
FAULT = HIGH
BATTR
DONE
V
BATT
< 0.95 × V
BATTR
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