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HA17384SPS Datasheet(PDF) 12 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) 12 Page - Hitachi Semiconductor

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HA17384SPS/SRP, HA17384HPS/HRP, HA17385HPS/HRP
12
Operation (Description of Timing Chart)
From Power ON to Turn On
After the power is switched ON, the power supply terminal voltage (V
IN) of this IC rises by charging
through bleeder resistor R
B.
At this time, when the power voltage is in the range of 2 V to 16 V*
1. The
low-voltage, lock out UVL1 operates and accordingly the OUT voltage, that is, the gate voltage of the
power MOSFET, is fixed at 1.3 V or a lower value, resulting in the power MOSFET remaining in the OFF
state.
When the power supply voltage reaches 16 V, UVL1 of this IC is reset and the reference voltage (Vref)
generating part turns ON. However, until Vref becomes 4.7 V, the low-voltage, lock out UVL2 operates to
keep the OUT terminal voltage low. After Vref terminal voltage becomes 4.7 V or higher, OUT terminal
outputs a PWM pulse.
Note: 1. The value is for the HA17384S/H.
The value is 8.4 V for the HA17385H.
Generation of Triangular Wave and PWM Pulse
After the output of the Vref, each blocks begins to operate. The triangular wave is generated on the R
T/CT
terminal. For PWM pulses, the triangular wave rise time is taken as the variable on-duty on-time. The
triangular wave fall time is taken as the dead-band time. The initial rise of the triangular wave starts from 0
V, and to prevent a large on-duty at this time, the initial PWM pulse is masked and not output. PWM
pulses are outputted after the second triangular wave. The above operation is enabled by the charge energy
which is charged through the bleeder resistor R
B into the capacitor CB of VIN.
Stationary Operation
PWM pulses are outputted after the second wave of the triangular wave and stationary operation as the
switching power supply starts.
By switching operation from ON/OFF to OFF/ON in the switching device (power MOSFET), the
transformer converts the voltage. The power supply of IC V
IN is fed by the back-up winding of the
transformer.
In the current mode of the IC, the current in the switcing device is always monitored by a source resistor
R
CS.
Then the current limiter level is varied according to the error voltage (COMP terminal voltage) for
PWM control. One third of the error voltage level, which is divided by resistors “2R” and “R” in the IC, is
used to sense the current (R = 25 k
Ω).
Two diodes between the error output and the 2R-R circuit act only as a DC level shifter. Actually, these
diodes are connected between the 2R-R circuit and GND, and, the current sensing comparator and GND,
respectively. Therefore, these blocks operate 1.4 V higher than the GND level. Accordingly, the error of the
current sensing level caused by the switching noise on the GND voltage level is eliminated. The zener
diode of 1 V symbolically indicates that the maximum sensing voltage level of the CS terminal is 1 V.


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