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HA17384SPS Datasheet(PDF) 23 Page - Hitachi Semiconductor

Part No. HA17384SPS
Description  High Speed Current Mode PWM Control IC for Switching Power Supply
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Maker  HITACHI [Hitachi Semiconductor]
Homepage  http://www.renesas.com/eng
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HA17384SPS Datasheet(HTML) 23 Page - Hitachi Semiconductor

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HA17384SPS/SRP, HA17384HPS/HRP, HA17385HPS/HRP
23
Triangular wave
PWM maximum
ON pulse
Dumax is the ratio of
maximum ON time of
PWM to one cycle time.
In the above case,
Dumax = 95%
Calculation of operation parameters
1. Maximum ON duty Du max (Refer to the right figure.)
Du max =
1
1 + 1.78
× In 1 +
190
RT − 440Ω
(
)
RT =
+ 440
190
0.56 (1/Du max
− 1)
CT = 1.78 ×
Du max
fosc
× R
T
IDmax =
VTHCS
fosc =
1
CT × RT ×
0.56 + In 1 +
190
()
{}
2. Oscillation frequency fosc
From the above two equations, the following two equations are
obtained.
3. Equalization to device RT from Du max
e
(e = 2.71828.base of natural logarithm)
4. Equation to device CT from fosc and RT
5. Operating current IIN
IIN = IQ + IsinkCT × (1 − Du max) + Ciss × VIN × fosc
providing that IQ = 8.4mA Typ (Supply current when oscillation in IC stops.)
Ciss is the input gate capacitance of the power MOSFET which is connected and VIN is
the supply voltage of the IC.
Note that the actual value may differ from the calculated one because of the internal
delay in operation and input characteristics of the POWER MOS FET. Check the
value when mounting.
Additionally a small Dumax leads to a large supply current, even if the frequency is
not changed, and start up may become difficult. In such a case, the following
measure is recommended.
Example 1: Calculation when RT = 10kΩ and CT = 3300pF
fosc = 52kHz, Du max = 95%, IIN = 9.7mA
Example 2: Calculation for 50% of Du max and 200 kHz of fosc
RT = 693Ω, CT = 6360pF, IIN = 12.5mA
(1) For an AC/DC converter, a small bleeder resistance is required.
(2) The large capacitance between Vref and GND is required.
(3) Use a large Dumax with a triangular wave and raise the current limit of the
switching device to around the maximum value (1.0V Typ).
The current limit is expressed as
RT − 440Ω
However, Ciss = 1000pF, VIN = 18V
RCS
− 1
Figure 11 Calculation of Operation Parameters


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