S-8337AAAA-P8T1G Datasheet, PDF (21/51 Pages) Seiko Instruments Inc – SWITCHING REGULATOR CONTROLLER

STEP-UP, 1.2 MHz HIGH-FREQUENCY, PWM CONTROL SWITCHING REGULATOR CONTROLLER
Rev.4.0_01
S-8337/8338 Series
6. Short-circuit protection delay time setting capacitor (CSP)
With the S-8337/8338 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
1.0
•
10^−3
120
100
80
60
40
20
0
0
0.05
0.10 0.15
C_SP [μF]
0.20
0.25
Figure 14 CSP vs. tPRO
7. Output voltage setting resistors (RFB1, RBF2)
With the S-8337/8338 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-8337/8338 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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