LP3913 Datasheet, PDF (60/70 Pages) Texas Instruments – Power Management IC for Flash Memory-Based Portable Media Players

LP3913
SNVS489I – NOVEMBER 2006 – REVISED SEPTEMBER 2013
www.ti.com
The output filter capacitor of the magnetic DC/DC converter smooths out current flow from the inductor to the
load, helps maintain a steady output voltage during transient load changes and reduces output voltage ripple.
These capacitors must be selected with sufficient capacitance and sufficiently low ESD to perform these
functions.
The output voltage ripple is caused by the charging and the discharging of the output capacitor and also due to
its ESR and can be calculated as follows:
I_ripple
V_pp-c = _{4 * f * C}
Voltage peak-to-peak ripple due to ESR can be expressed as follows:
V_PP-ESR = 2 * I_RIPPLE * R_ESR
(6)
Because the V_PP-C and V_PP-ESR are out of phase, the RMS value can be used to get an approximate value of the
peak-to-peak ripple:
V_pp-rms² = V_pp-c² + V_pp-esr²
Note that the output voltage ripple is dependent on the inductor current ripple and the equivalent series
resistance of the output capacitor (R_ESR). The R_ESR is frequency dependent as well as temperature dependent.
The R_ESR should be calculated with the applicable switching frequency and ambient temperature.
Capacitor
C_VDD
C_{CHG_DET}
C_USB
C_BATT
C_LDO1
C_LDO2
C_VREFH
C_VIN2,3
CVBUCK1,2
C_SW3
C_VIN1
C_VIN4
Min Value
4.7
4.7
4.7
4.7
1.0
1.0
0.1
10
10
22
1
10
Unit
Description
Recommended Type
μF
Charger Input Capacitor Ceramic, 6.3V, X5R
μF
Charger Input Capacitor Ceramic, 6.3V, X5R
μF
USB Power (V_BUS)
Ceramic, 6.3V, X5R
Capacitor
μF
Li-ion Battery Capacitor Ceramic, 6.3V, X5R
μF
LDO Output Capacitor
Ceramic, 6.3V, X5R
μF
LDO Output Capacitor
Ceramic, 6.3V, X5R
μF
Bypass Capacitor for
Ceramic, PolyPropylene and
Internal Voltage
Polycarbonate Film
Reference
μF
Buck1, Buck2 Input
Ceramic, 6.3V, X5R
Capacitor
μF
BUCK1,2 Output
Ceramic, 6.3V, X5R
Capacitor
μF
BUCK3 Output Capacitor Ceramic, 6.3V, X5R
μF
LDO Bypass Capacitor Ceramic, 6.3V, X5R
μF
Buck Bypass Capacitor Ceramic, 6.3V, X5R
Schottky Diode on Charger Input CHG_IN
A Schottky diode is required in the external adapter path to block the reverse current from either the USB or the
battery source. The most critical parameter in the selection of the right Schottky diode is the leakage current,
which needs to be below 10 µA over the temperature range in order to prevent false detection of the presence of
an external adapter. In addition the Schottky diode should have a maximum voltage rating of 10V or higher. The
current rating depends on the current limit of the adapter. The forward voltage should be limited to 500 mV at its
maximum current. The recommended Schottky diode is MBRA210ET3 from ON Semiconductor which has a
reverse leakage current under 1 µA at room temperature and a forward voltage drop of 500 mV at their max
rated current I_F = 2A.
60
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