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S-85S1AB27-I6T1U Datasheet(PDF) 11 Page - Seiko Instruments Inc |
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S-85S1AB27-I6T1U Datasheet(HTML) 11 Page - Seiko Instruments Inc |
11 / 30 page 5.5 V INPUT, 200 mA SYNCHRONOUS STEP-DOWN SWITCHING REGULATOR WITH 260 nA QUIESCENT CURRENT Rev.1.2_00 S-85S1A Series 11 9. Pre-bias compatible soft-start function The S-85S1A Series has a built-in pre-bias compatible soft-start circuit. If the pre-bias compatible soft-start circuit starts when electrical charge remains in the output voltage (VOUT) as a result of power supply restart, etc., or when VOUT is biased beforehand (pre-bias status), switching operation is stopped until the soft-start voltage exceeds the internal feedback voltage, and then VOUT is maintained. If the soft-start voltage exceeds the internal feedback voltage, switching operation will restart and VOUT will rise to the output voltage setting value (VOUT(S)). This allows VOUT(S) to be reached without lowering the pre-biased VOUT. In soft-start circuits which are not pre-bias compatible, a large current flows as a result of the discharge of the residual electric charge through the low side power MOS FET when switching operation starts, which could cause damage, however in a pre-bias compatible soft-start circuit, the IC is protected from the large current when switching operation starts, and it makes power supply design for the application circuit simpler. In the S-85S1A Series, VOUT reaches VOUT(S) gradually due to the soft-start circuit. In the following cases, rush current and VOUT overshoot are reduced. • At power-on • When the EN pin changes from "L" to "H". • When UVLO operation is released. • When thermal shutdown is released. • At short-circuit recovery In addition, the soft-start circuit operates under the following conditions. The soft-start circuit starts operating after "H" is input to the EN pin and the soft-start wait time (tSSW) = 1.5 ms typ. elapses. The soft-start time (tSS) is set to 1.0 ms typ. • At power supply restart (the IC restart) • At UVLO detection (after UVLO release) • At thermal shutdown detection (after thermal shutdown release) • After Hiccup control VEN (tSSW)(tSS) VOUT VSW Soft-start operation during pre-bias Soft-start wait time Soft-start time Figure 6 |
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