LMZ12010
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SNVS667H –FEBRUARY 2010–REVISED AUGUST 2015
Typical Application (continued)
For VOUT = 0.8 V the FB pin can be connected to the output directly and RFBB can be set to 8.06 kΩto provide
minimum output load.
Table 1 lists the values for RFBT , and RFBB.
Table 1. Typical Application Bill of Materials
REF DES DESCRIPTION CASE SIZE MANUFACTURER MANUFACTURER P/N
U1 SIMPLE SWITCHER PFM-11 Texas Instruments LMZ12010TZ
CIN1,6 (OPT) 0.047 µF, 50 V, X7R 1206 Yageo America CC1206KRX7R9BB473
CIN2,3,4 10 µF, 50 V, X7R 1210 Taiyo Yuden UMK325BJ106MM-T
CIN5 (OPT) CAP, AL, 150 µF, 50 V Radial G Panasonic EEE-FK1H151P
CO1,5 (OPT) 0.047 µF, 50 V, X7R 1206 Yageo America CC1206KRX7R9BB473
CO2 (OPT) 47 µF, 10 V, X7R 1210 Murata GRM32ER61A476KE20L
CO3,4 330 μF, 6.3 V, 0.015 ΩCAPSMT_6_UE Kemet T520D337M006ATE015
RFBT 3.32 kΩ0805 Panasonic ERJ-6ENF3321V
RFBB 1.07 kΩ0805 Panasonic ERJ-6ENF1071V
RENT 42.2 kΩ0805 Panasonic ERJ-6ENF4222V
RENB 12.7 kΩ0805 Panasonic ERJ-6ENF1272V
CSS 0.47 μF, ±10%, X7R, 16 V 0805 AVX 0805YC474KAT2A
D1 (OPT) 5.1 V, 0.5 W SOD-123 Diodes Inc. MMSZ5231BS-7-F
8.2.2.3 Soft-Start Capacitor Selection
Programmable soft-start permits the regulator to slowly ramp to its steady-state operating point after being
enabled, thereby reducing current inrush from the input supply and slowing the output voltage rise-time.
Upon turnon, after all UVLO conditions have been passed, an internal 1.6-ms circuit slowly ramps the SS input to
implement internal soft start. If 1.6 ms is an adequate turnon time then the Css capacitor can be left unpopulated.
Longer soft-start periods are achieved by adding an external capacitor to this input.
Soft-start duration is given by the formula:
tSS = VREF × CSS / Iss = 0.795 V × CSS / 50 µA (8)
This equation can be rearranged as follows:
CSS = tSS × 50 μA / 0.795 V (9)
Using a 0.22-μF capacitor results in 3.5-ms typical soft-start duration; and 0.47 μF results in 7.5 msec typical.
0.47 μF is a recommended initial value.
As the soft-start input exceeds 0.795 V the output of the power stage will be in regulation and the 50-μA current
is deactivated. Note that the following conditions will reset the soft-start capacitor by discharging the SS input to
ground with an internal current sink.
• The Enable input being pulled low
• A thermal shutdown condition
• VIN falling below 4.3 V (typical) and triggering the VCC UVLO
8.2.2.4 Tracking Supply Divider Option
The tracking function allows the module to be connected as a slave supply to a primary voltage rail (often the
3.3-V system rail) where the slave module output voltage is lower than that of the master. Proper configuration
allows the slave rail to power up coincident with the master rail such that the voltage difference between the rails
during ramp-up is small (that is, < 0.15 V typical). The values for the tracking resistive divider must be selected
such that the effect of the internal 50-µA current source is minimized. In most cases the ratio of the tracking
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