Service Manual
PA246Q
24
#2
Converter Circuit – L4978
The L4978 is a step down monolithic power switching regulator delivering 2A at a voltage between
3.3V and 50V (selected by a simple external divider). Realized in BCD mixed technology, the device
uses an internal power D-MOS transistor (with a typical R
DS(on)
of 0.25
Ω
) to obtain very high efficiency
and high switching speed.
A switching frequency up to 300 kHz is achievable (the maximum power dissipation of the
packages must be observed). A wide input voltage range between 8V to 55V and output voltages
regulated from 3.3V to 50V cover the majority of today’s applications.
Features of this new generation of DC/DC converter include pulse-by-pulse current limit, hiccup mode
for short circuit protection, voltage feed-forward regulation, soft-start, protection against feedback loop
disconnection, inhibit for zero current consumption and thermal shutdown.
Pin Assignment of L4978
Pin No.
Names
Function
1
GND
Ground
2
SS_INH
A logic signal (active low) disables the device (sleep mode operation).
A capacitor connected between this pin and ground determines the
soft start time. When this pin is grounded disables the device (driven
by open collector/drain).
3
OSC
An external resistor connected between the unregulated input voltage
and this pin and a capacitor connected from this pin to ground fix the
switching frequency. (Line feed forward is automatically obtained)
4
OUT
Step-down regulator output
5
V
CC
Unregulated DC input voltage
6
BOOT
A capacitor connected between this pin and OUT allows to drive the
internal DMOS Transistors
7
COMP
E/A output to be used for frequency compensation
8
FB
Step-down feedback input. Connecting directly to this pin results in an
output voltage of 3.3V. An external resistive divider is required for
higher output voltages.
Содержание PA246Q
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Страница 22: ...Service Manual PA246Q 25 5 Schematic Diagram 5 1 Power Board ...
Страница 23: ...Service Manual PA246Q 26 5 2 Control Board ...
Страница 24: ...Service Manual PA246Q 27 5 3 Interface Board ...
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Страница 29: ...Service Manual PA246Q 32 6 PCB layout 6 1 Power Board ...
Страница 30: ...Service Manual PA246Q 33 6 2 Control Board 6 3 Interface Board ...
Страница 35: ...Service Manual PA246Q 54 11 3 Check Scalar ...
Страница 36: ...Service Manual PA246Q 55 11 4 Check LCD Module ...
Страница 40: ...Service Manual PA246Q 59 11 8 Check PFC Function ...
Страница 41: ...Service Manual PA246Q 60 12 Exploded View ...
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Страница 45: ...Service Manual PA246Q 64 Photos of Recommended Parts List 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ...