BQ24250C_15 Datasheet, PDF (21/46 Pages) Texas Instruments – bq24250C 2A Single Input I2C, Standalone Switch-Mode Li-Ion Battery Charger with Power-Path Management

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bq24250C
SLUSBY7 – JULY 2014
Where I_IC is the desired input current limit in Amperes.
Based on the application diagram reference designators, the resistor R1 and R2 can be calculated as follows to
set V_{IN_DPM}:
V_{IN _ DPM}
=
V_{REF _ DPM}
´
R₁ + R₂
R₂
= 1.2V ´ ^{R1 + R2}
R₂
(3)
V_{IN_DPM} should be chosen first along with R₁. Choosing R₁ first will ensure that R₂ will be greater than the
resistance chosen. This is the case since V_{IN_DPM} should be chosen to be greater than 2x V_{REF_DPM}.
If external resistors are not desired in order to reduce the BOM count, the VDPM and the ILIM pins can be
shorted to set the internal defaults. The ISET resistor cannot be shorted in order to avoid an unstable charging
state.Note that floating the ILIM pin will result in zero charge current if the external ISET is configured via the I²C
register. Table 2 summarizes the settings when the ILIM, ISET, and V_{IN_DPM} pins are shorted to GND:
Table 2. ILIM, VDPM, and ISET Short Behaviors
PIN SHORTED
ILIM
VDPM
ISET
BEHAVIOR
Input current limit = 2A
V_{IN_DPM} = 4.68V
Fault—Charging Suspended
8.4.5 Transient Response
The bq24250C includes an advanced hybrid switch mode control architecture. When the device is regulating the
charge current (fast-charge), a traditional voltage mode control loop is used with a Type-3 compensation
network. However, the bq24250C switches to a current mode control loop when the device enters voltage
regulation. Voltage regulation occurs in three charging conditions: 1) Minimum system voltage regulation (battery
below MINSYS), 2) Battery voltage regulation (I_BAT < I_CHG), and 3) Charge Done (V_SYS = V_BAT + 3.5%). This
architecture allows for superior transient performance when regulating the voltage due to the simplification of the
compensation when using current mode control. The below transient response plot illustrates a 0A to 2A load
step with 4.7ms full cycle and 12% duty cycle. A 3.9V Li-Ion battery is used. The input voltage is set to 5V,
charge current is set to 0.5A and the input current is limited to 0.5A. Note that a high line impedance input supply
was used to indicate a realistic input scenario (adapter and cable). This is illustrated by the change in V_IN seen at
the input of the IC.
Figure 19 shows a ringing at both the input voltage and the input current. This is caused by the input current limit
speed up comparator.
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