S-8333CAAA-I8T1U Datasheet, PDF (18/44 Pages) Seiko Instruments Inc – PWM CONTROL SWITCHING REGULATOR CONTROLLER

STEP-UP, FOR LCD BIAS SUPPLY, 1-CHANNEL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
S-8333 Series
Rev.4.2_01
6. Short-circuit protection delay time setting capacitor (CSP)
With the S-8333 Series, the short-circuit protection delay time can be set to any value by an external capacitor.
Connect the capacitor across the CSP and VSS pins. Select the capacitance by using the following equation and
referring to Figure 14. However, the following equation and figure assume that the capacitor value is the desired
value and show the theoretical values when the IC is in the typical conditions. Note that fluctuations of capacitor
and IC are not considered.
C_SP [μF] ≅
t_PRO [ms] × 2 × 10^−3
1.0
120
100
80
60
40
20
0
0
0.05
0.10 0.15
CSP [μF]
0.20
0.25
Figure 14 CSP vs. tPRO
7. Output voltage setting resistors (RFB1, RBF2)
With the S-8333 Series, the output voltage can be set to any value by external divider resistors.
Connect the divider resistors across the VOUT and VSS pins. Because VFB = 1 V, the output voltage can be
calculated by this equation.
V_OUT
(R_FB1 + R_FB2)
=
R_FB2
Connect divider resistors RFB1 and RFB2 as close to the IC to minimize effects from of noise. If noise does have
an effect, adjust the values of RFB1 and RFB2 so that RFB1 + RFB2 < 100 kΩ.
CFB connected in parallel with RFB1 is a capacitor for phase compensation. Select the optimum value of this
capacitor at which the stable operation can be ensured from the values of the inductor and output capacitor.
8. Phase compensation setting resistor and capacitor (RZ, CZ)
The S-8333 Series needs appropriate compensation for the voltage feedback loop to prevent excessive output
ripple and unstable operation from deteriorating the efficiency. This compensation is implemented by connecting
RZ and CZ in series across the CC and VSS pins. RZ sets the high-frequency gain for a high-speed transient
response. CZ sets the pole and zero of the error amplifier and keeps the loop stable. Adjust RZ and CZ, taking
into consideration conditions such as the inductor, output capacitor, and load current, so that the optimum
transient characteristics can be obtained.
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