tca5600 Freescale Semiconductor, Inc, tca5600 Datasheet - Page 9

• Manufacturer Part Number: tca5600
• Description: Universal Microprocessor Power Supply/controllers
• Manufacturer: Freescale Semiconductor, Inc

Voltage Reference (V ref )
bandgap voltage reference and is accessible on Pin 5 for
additional tasks. This circuit part has its own supply
connection on Pin 3 and is, therefore, able to operate in
standby mode. The RC network R3, C6 improves the ripple
rejection on both regulators.
DC/DC Converter
principle and does not need a time base circuit. The
maximum coil current is well defined by means of the current
sensing resistor R1 under all working conditions (startup
phase, circuit overload, wide supply voltage range and
extreme load current change). Figure 13 shows the Simplified
Converter Schematic.
A simplified method on “how to calculate the coil inductance”
is given below. The operation point at minimum supply
voltage (V CC2 ) and max. output current (I out2 ) for a fixed
output voltage (V out2 ) determines the coil data. Figure 14
shows the typical voltage and current waveforms on the coil
L1 (coil losses neglected).
Equations (1) and (2) yield the respective coil voltage
V L – and V L + (see Figure 14):
2.5 V typical]
[V F , V CE(sat) , V 12(H) : see Electrical Characteristics Table]
The time ratio
defined by Equation (3):
V 12(H)
V 12(L)
V L + = V out2 +
MOTOROLA ANALOG IC DEVICE DATA
V (Pin 9 – Pin 8) : input/output voltage drop of the regulator,
The voltage reference V ref is based upon a highly stable
The dc/dc converter performs according to the flyback
+
Figure 13. Simplified Converter Schematic
Control Feedback
V L – = V CC2 – V CE(sat) – V 12(H)
Comp
V CC2
0.68
for the charging time to dumping time is
V (Pin 9 – Pin 8) + V F – V CC2
R1
12
10
=
V CE(sat)
C2
100
L1
300 H
VF
t 1
t 2
+
F
=
9
C7
0.22 F
V L +
V L –
Regulator
Prog.
APPLICATIONS INFORMATION
8
7
10k
R5
TCA5600 TCF5600
85K
R4
(See Figure 18)
C3
47nF
V out2
(1)
(2)
(3)
The coil charging time t 1 is found using Equation (4):
[f : minimum oscillation frequency which should be chosen
above the audio frequency band (e.g. 20 kHz)]
Knowing the dc output current I out2 of the programmable
regulator, the peak coil current I L(peak) can now be calculated:
The coil inductance L1 of the nonsaturated coil is given by
Equation (6):
The formula (6a) yields the current sensing resistor R1 for a
defined peak coil current I L(peak) :
In order to limit the by–pass current through capacitor C7
during the energy dumping phase the value C2>>C7 should
be implemented.
For all other operation conditions, the feedback signal from
the programmable voltage regulator controls the activity of
the converter.
Coil
Current
I Lpeak
Figure 14. Voltage and Current Waveform
Coil
Voltage
V CC2
I L(peak) = 2 (I out2 ) (1 + )
on the Coil (not to scale)
É É É
É É É
L1 =
t 1 =
R1 =
t 1
I L(peak)
(1 +
É É É É
É É
É É
I L(peak)
t 1
V 12(H)
t 2
1
1
(V L –)
) f
t
t
(6a)
9
(5)
(4)
(6)