1
DESCRIPTION
Demonstration Circuit DC1584A is a Simple Low-Iq Battery Charger/Protector With NTC Thermistor featuring the
LTC
®
4070EDDB.
PERFORMANCE SUMMARY
Specifications are at T
A
= 25°C
SYMBOL PARAMETER
CONDITIONS
MIN TYP
MAX
UNITS
VBUS
Input voltage
R
LIMIT
= 169
Ω
10
12
16
V
V(BAT)
Battery Float Voltage
‘VFLOAT’ jumper on 4.1V, Constant Voltage
Mode. T
NTC
= 25°C
4.059
4.141
V
I(BAT)
Battery Charge Current
Constant Current Mode, Vin = 12V, VCC =
3.8V
49.7
mA
QUICK START PROCEDURE
Refer to Figure 1 for the proper measurement
equipment setup and jumper settings and follow the
procedure below.
NOTE.
When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscilloscope
probe. Measure the input or output voltage ripple by touching the
probe tip directly across the VBUS or Vcc and GND terminals. See
Figure 2 for proper scope probe technique.
1.
Set PS1 = 12V, PS2 = 3.6V, “VFLOAT” (JP2) to
4.1V. Observe I(VBUS) (AM1). The voltage on
the battery is below the LTC4070EDDB’s float
voltage. So all the current is flowing into the bat-
tery, and that current is (12V – 3.6V) /169(R1) =
49.7mA.
2.
If “LBO” LED lit, decrease PS2 until off. Observe
BAT (VM2). The LBO output goes high when the
battery voltage is below 3.2V, but it has 200-
300mV of hysteresis. So it may not go low until
3.5V, with Vcc
↑
.
3.
Increase PS2 until LBO is lit. Observe BAT
(VM2).
4.
Increase PS2 until HBO lit. Observe BAT (VM2).
The HBO LED will light when the battery voltage
is within ~50mV of the float voltage.
5.
Disconnect PS2, AM2, and 3.6
Ω
resistor. Ob-
serve BAT (VM2). The only limit to the Vcc volt-
age now is the LTC4070, so the voltage will rise
to the float voltage.
6.
Reset the Jumpers to their default position.
QUICK START GUIDE FOR
DC1584A
LTC4070EDDB: Simple Low-Iq
Battery Charger/Protector
With NTC Thermistor Input
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