410
Optical disc ICs
4-channel H-bridge type BTL driver for
CD players
BA5950FP
The BA5950FP is a 4-channel H-bridge BTL power driver for CD players. Input is PWM, and gain and the filter constant
can be changed with an attached resistor and capacitor.
FApplications
CD players, CD-ROM drives and other optical disc devices
FFeatures
1) 4-channel BTL driver on a HSOP 28-pin power pack-
age, allowing for application miniaturization.
2) Direct PWM input.
3) Filter constants can be changed with an attached re-
sistor and capacitor.
4) Internal thermal shutdown circuit with hysteresis ca-
pabilities.
5) Internal mute circuit.
FAbsolute maximum ratings (Ta = 25_C)
FRecommended operating conditions (Ta = 25_C)
411
Optical disc ICs BA5950FP
Block diagram
412
Optical disc ICs BA5950FP
Pin descriptions
413
Optical disc ICs BA5950FP
Input / output circuits
414
Optical disc ICs BA5950FP
FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 8V, RL = 8Ω)
415
Optical disc ICs BA5950FP
Measurement circuits
416
Optical disc ICs BA5950FP
417
Optical disc ICs BA5950FP
Switch table
Circuit operation
(1) Overview
Fig. 6 shows the inputs from the digital servo IC. SW1
turns on when the forward input signal is received (HIGH
level, above 2.0V). SW2 turns on when the reverse input
signal is received (Fig. 3). When this happens, the
constant current enters resistor R1 and the capacitor,
generating an integral waveform based on the duty of the
input waveform. This is increased by a factor of 3 by the
driver and output (Fig. 5).
When forward or reverse input remains at the HIGH level,
the DC voltage generated at point A is :
I R1 [V] (reverse : –1 R1 [V])
This is the voltage generated relative Vref. The width set-
ting is such that the following driver buffer output is gen-
erated :
3IR1 [V] (reverse : –3IR1 [V]) 1
The time constant is :
R1 (C)30p)
This can be changed with an attached capacitor.
Dead zone width is set by input duty ratio according to the
following equation :
(2) Settings
The constant current is determined by the resistor (R0)
connected between pin 28 and pin 1 (GND).
I = 1.25 / R0 [A]
Consequently, equations 1 and 2 are as follows.
The ratio of R0 and R1 determine everything. R0 must stay
between 10kΩ and 40kΩ, R1 below 100kΩ.
Example : When R 0 = 30kΩ, R1 = 40kΩ, input HIGH level
= 5V
1!5V (0dB relative to input)
2!0.6% (input equivalent = 30mV)
I R1 100 [%] (one side)
10.0 [kΩ] 1.0 [µA] 2
1.25
10.0 [kΩ] 1.0 [µA]
3 1.25 [V]
R0
R1
100 [%]
R1
R0
1
2
’
’
418
Optical disc ICs BA5950FP
419
Optical disc ICs BA5950FP
Application example
420
Optical disc ICs BA5950FP
FOperation notes
(1) The BA5950FP has an internal thermal shutdown
circuit with hysteresis. Output current is muted when the
chip temperature exceeds 175_C (typically) and restored
when the chip temperature falls to 150_C (typically).
(2) Output current can be muted by raising the mute pin
(pin19) voltage above 2.0V. The mute pin must be kept
below 0.5V during normal operation.
(3) All four driver output channels are muted during
thermal shutdown, muting and a drop in bias pin voltage.
No other components are muted.
(4) Connect a stabilizing capacitor (roughly 1µF) to the
internal reference voltage output pin (pin10).
(5) Connect the IC to a 0.1µF bypass capacitor to the
power supply, at the base of the IC.
(6) Connect the radiating fin to an external ground.
FElectrical characteristic curves
421
Optical disc ICs BA5950FP
External dimensions (Units: mm)
