LTC4001-1_15 Datasheet, PDF (5/20 Pages) Linear Technology – 2A Synchronous Buck Li-Ion Charger

TYPICAL PERFORMANCE CHARACTERISTICS
LTC4001-1
Soft-Start (PWM Mode)
INPUT
CURRENT (I_IN)
0.5A/DIV
0
INDUCTOR
CURRENT (I_L)
0.5A/DIV
SOFT-START
0
VOLTAGE (V_SS)
1V/DIV ₀
EN PIN (V_EN)
5V/DIV ₀
V_BAT = 3.5V
V_IN = 5V
2ms/DIV
40011 G09
IDET Threshold vs R_IDET for
R_PROG = 549Ω
400
CHRG Pin Temperature Fault
Behavior (Detail)
350
300
250
CHRG
1V/DIV
200
150
100
50
TIME (20μs/DIV)
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0
300 400 500 600 700 800 900 100011001200
R_IDET (Ω)
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PIN FUNCTIONS
BAT (Pin 1): Battery Charger Output Terminal. Connect a
10μF ceramic chip capacitor between BAT and PGND to
keep the ripple voltage small.
SENSE (Pin 2): Internal Sense Resistor. Connect to ex-
ternal inductor.
PGND (Pin 3): Power Ground.
GNDSENS (Pin 4): Ground Sense. Connect this pin to the
negative battery terminal. GNDSENS provides a Kelvin
connection for PGND and must be connected to PGND
schematically.
SW (Pin 5): Switch Node Connection. This pin connects
to the drains of the internal main and synchronous power
MOSFET switches. Connect to external inductor.
EN (Pin 6): Enable Input Pin. Pulling the EN pin high
places the LTC4001-1 into a low power state where the
BAT drain current drops to less than 3μA and the supply
current is reduced to less than 50μA. For normal opera-
tion, pull the pin low.
CHRG (Pin 7): Open-Drain Charge Status Output. When the
battery is being charged, CHRG is pulled low by an internal
N-channel MOSFET. When the charge current drops below
the IDET threshold (set by the R_IDET programming resistor)
for more than 5milliseconds, the N-channel MOSFET turns
off and a 30μA current source is connected from CHRG to
ground. (This signal is latched and is reset by initiating a
new charge cycle.) When the timer runs out or the input
supply is removed, the current source will be disconnected
and the CHRG pin is forced to a high impedance state. A
temperature fault causes this pin to blink.
PV_IN (Pin 8): Positive Supply Voltage Input. This pin con-
nects to the power devices inside the chip. V_IN ranges
from 4V to 5.5V for normal operation. Operation down to
the undervoltage lockout threshold is allowed with cur-
rent limited wall adapters. Decouple with a 10μF or larger
surface mounted ceramic capacitor.
V_INSENSE (Pin 9): Positive Supply Sense Input. This pin
connects to the inputs of all input comparators (UVL, V_IN
to V_BAT). It also supplies power to the controller portion
of this chip. When the BATSENS pin rises to within 30mV
of V_INSENSE, the LTC4001-1 enters sleep mode, dropping
I_IN to 50μA. Tie this pin directly to the terminal of the PV_IN
decoupling capacitor.
FAULT (Pin 10): Battery Fault. This pin is a logic high if
a shorted battery is detected or if a temperature fault is
detected. A temperature fault occurs with the temperature
monitor circuit enabled and the thermistor temperature is
either below 0°C or above 50°C (typical).
40011fa
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