Specifications
OBSOLETE
LM3647
SNOS517H –MARCH 2000–REVISED APRIL 2013
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ADVANCED PIN DESCRIPTIONS
SEL1 is a selection pin to control the LM3647 discharge and maintenance charge modes. The pin has three
states: tied to V
CC
, GND, or unconnected (Hi-Z). When the charger is configured to charge Ni-Cd or Ni-MH
batteries, this pin determines if the charger discharges the battery before charging or if the charger shall only
maintenance charge the battery. When the charger is configured for Li-Ion batteries, this pin determines how the
charger behaves during maintenance charge.
Charge mode
SEL1
condition SEL2 = GND (NiCd) or V
CC
(NiMH)
V
CC
No discharge before charge
GND Maintenance charge only (no fast charge)
Open Discharge before charge
Charge mode
SEL1
condition SEL2 = Open (Li-Ion)
V
CC
Maintenance charge indefinite
GND Maintenance charge indefinite, restart fast-charge if battery gets discharged (load connected)
Open No maintenance charge, restart fast charge if battery becomes discharged
SEL2 is a selection pin to determine the battery type to be charged. The pin has three states: tied to V
CC
(Ni-
MH), GND (Ni-Cd), or unconnected (Li-Ion).
SEL2 Battery Type Select
V
CC
Ni-MH
GND NiCd
Open Li-Ion
SEL3 is a selection pin used to set charger hardware modes. The pin has two states: tied to V
CC
or GND. When
the LM3647 is configured for Ni-Cd/Ni-MH batteries, this pin selects between a power supply with current
feedback when tied to V
CC
(PWM “fast” frequency) or a constant current source when tied to GND (PWM “slow”
frequency). When configured for Li-Ion batteries, SEL3 switches between 4.1V cells or 4.2V cells.
NOTE
SEL3 must be hard wired to V
CC
if a charger that supports both Li-Ion and Ni-Cd/Ni-MH is
implemented.
PWM Output Frequency Select
SEL3
output SEL2 = V
CC
(NiMH) or GND (NiCd)
V
CC
Current feedback (“fast” PWM frequency)
GND No current feedback (external constant current source) (“slow” PWM frequency)
Li-Ion Cell Voltage Select
SEL3
output SEL2 = Open (Li-Ion)
V
CC
4.2V/cell
GND 4.1V/cell
NOTE
Current feedback is automatically selected, if LM3647 is configured for Li-Ion charging (pin
SEL2 open).
SEL4 is connected to a RC-network that determines the charge time-outs. This RC-network is also connected to
the output LED1. (See CHARGE TIMEOUT for details).
RCIN is a high-speed timing pin connected to a RC-network, used to drive the charger at the right operating
frequency.
GND is the ground pin.
V
CC
is the power-supply pin. This pin should have a 100 nF decoupling capacitor tied to GND.
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