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| 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 package, allowing for application miniaturization. 2) Direct PWM input. 3) Filter constants can be changed with an attached resistor and capacitor. 4) Internal thermal shutdown circuit with hysteresis capabilities. 5) Internal mute circuit. FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 410 Optical disc ICs FBlock diagram BA5950FP 411 Optical disc ICs FPin descriptions BA5950FP 412 Optical disc ICs FInput / output circuits BA5950FP 413 Optical disc ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 8V, RL = 8) BA5950FP 414 Optical disc ICs FMeasurement circuits BA5950FP 415 Optical disc ICs BA5950FP 416 Optical disc ICs FSwitch table BA5950FP FCircuit 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 : R1 [V]) I R1 [V] (reverse : -1 This is the voltage generated relative Vref. The width setting is such that the following driver buffer output is generated : 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 : 10.0 [k] 1.0 [A] I R1 100 [%] (one side) 2 (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. 3 1.25 R1 [V] R0 1.0 [A] 1' 10.0 [k] 1.25 R0 R1 100 [%] 2' The ratio of R0 and R1 determine everything. R0 must stay between 10k and 40k, R1 below 100k. Example : When R0 = 30k, R1 = 40k, input HIGH level = 5V 1 !5V (0dB relative to input) 2 !0.6% (input equivalent = 30mV) 417 Optical disc ICs BA5950FP 418 Optical disc ICs FApplication example BA5950FP 419 Optical disc ICs 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. BA5950FP (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 1F) to the internal reference voltage output pin (pin10). (5) Connect the IC to a 0.1F bypass capacitor to the power supply, at the base of the IC. (6) Connect the radiating fin to an external ground. FElectrical characteristic curves 420 Optical disc ICs FExternal dimensions (Units: mm) BA5950FP 421 |
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