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BD88420GUL-E2

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22
Technical Note
13/21
BD88400GUL,BD88410GUL,BD88415GUL,BD88420GUL
www.rohm.com
2011.03 – Rev. A
© 2011 ROHM Co., Ltd. All rights reserved.
[CHARGE PUMP / CHARGE PUMP CONTROL]
The negative power supply circuit is composed of the regulated charge-pump. This circuit outputs the regulated negative
voltage (PVSS) directly from power-supply voltage (PVDD). Therefore, it doesn't depend on the power-supply voltage, and
a constant voltage is output (PVSS=-2.4V
@Typ.
, refer to Fig.4). Moreover, there is not swinging of the power supply by the
output current of the headphone amplifier, and it doesn't influence the headphone amplifier characteristic.
Fig.59 Characteristics of load current regulation of PVSS (Reference data)
・Power control
The power control is a logical sum of SHDNLB and SHDNRB. The negative power supply circuit starts when H level is
input to either of SHDNLB or SHDNRB, and power is downed at the SHDNLB=SHDNRB=L level.
Table.1 Control of the charge pump
SHDNLB SHDNRB Control
L L Power down
L H Power on
H L Power on
H H Power on
・Operating Frequency
The operating frequency of the negative power supply charge pump is designed for the temperature and the voltage
dependence may decrease. The reference data (measurements) is occupied to Fig.60. Please note the interference with
the frequency in the application board.
Fig.60 Temperature characteristic and Voltage characteristic of operating frequency (Reference data)
・The flying capacitor and the hold capacitor
The flying capacitor (CF) and the hold capacitor (CH) greatly influence the characteristic of the charge pump. Therefore,
please connect the capacitor with an excellent temperature characteristic and voltage characteristic of 2.2µF as much as
possible near IC.
-3
-2.5
-2
-1.5
-1
-0.5
0
0 20406080
Load Current [mA]
VSS Voltage [V]
Ta=25
℃
VDD=3.3V
SHDN_B=SVDD
CF=CH=2.2uF
200
220
240
260
280
300
320
340
360
380
400
2.0 3.0 4.0 5.0 6.0
Supply Voltage[V]
Charge Pump Ocsillator Frequency [kHz
]
Ta=25
℃
Measure : C1P
CF=CH=2.2uF
200
220
240
260
280
300
320
340
360
380
400
-50.0 0.0 50.0 100.0
Ta [
℃
]
Charge Pump Ocsillator Frequency [kHz
]
VDD=3.3V
Measure : C1P
CF=CH=2.2uF
Technical Note
14/21
BD88400GUL,BD88410GUL,BD88415GUL,BD88420GUL
www.rohm.com
2011.03 – Rev. A
© 2011 ROHM Co., Ltd. All rights reserved.
[HEADPHONE AMP]
The headphone amplifier is driven by the internal positive voltage (+2.4V) and negative voltage (SVSS, -2.4V) based on
ground (SGND). Therefore, the headphone can be connected without the output coupling capacitor. As a result, it brings the
improved low-frequency characteristic compared with the headphone of the conventional coupling capacitor type.
・Power control
L channel and R channel of the headphone amplifier can be independently controlled by SHDNLB and SHDNRB logic.
When the SVSS voltage is -1.1V
@Typ.
or more, the headphone amplifier does not operate to protect from illegal operation.
And in addition, the overcurrent protection circuit is built in. The amplifier is shutdown when the overcurrent occurs
because of the output short-circuit etc., and IC is protected from being destroyed.
Table.2 Control of the headphone amplifier
SHDNLB SHDNRB L channel R channel
L L Power down Power down
L H Power down Power on
H L Power on Power down
H H Power on Power on
VDD
0
[V]
[time]
SHDNxB
0
[V]
[time]
SVSS
-1.1V
Amplifier
Enable
Amprilier
Disable
Fig.61 Area of headphone amplifier can operate
SVSS does not have internal connection with PVSS. Please connect SVSS with PVSS on the application board.
・Input coupling capacitor
Input DC level of BD884xxGUL is 0V (SGND). The input coupling capacitor is necessary for the connection with the
signal source device. The signal decrease happens in the low frequency because of composing the high-pass filter by
this input coupling capacitor and the input impedance of BD884xxGUL.
The input impedance of BD884xxGUL is Rin (14kΩ
@Typ.
). The cutoff frequency of this high-pass filter becomes the
following formula. (In BD88400GUL, Rin becomes external resistance Ri. )
inin
c
CRπ2
1
f (2)
* Cin is the input coupling capacitor.
Fig.62 Frequency response by the input coupling capacitor (Reference data)
-21.0
-18.0
-15.0
-12.0
-9.0
-6.0
-3.0
0.0
3.0
6.0
9.0
1 10 100
Frequency [Hz]
Gain [dB]
Rin=14k
Ω
Cin=1uF
Cin=2.2uF
Cin=4.7uF
Cin=10uF
Technical Note
15/21
BD88400GUL,BD88410GUL,BD88415GUL,BD88420GUL
www.rohm.com
2011.03 – Rev. A
© 2011 ROHM Co., Ltd. All rights reserved.
And, the degradation of THD+N happens because of the input coupling capacitor. Therefore, please consider these about
the selection of parts.
* Capacitor size: 1608
Fig.63 THD+N by the input coupling capacitor (Reference data)
・State of terminal when power down
The state of the terminal changes by the power control of the headphone amplifier. When it is shutdown, the input
impedance of the input terminal becomes 7.1kΩ
@Typ.
(In BD88400GUL, become Ri + 7.1kΩ). The time constant can be
reduced when the input coupling capacitor is charged.
The input voltage changes while charging up the input coupling capacitor. Therefore, do not operate the headphone
amplifier while charging.
Audio
Source
+
-
VDD
Vout
tim e [s]
Vs [V]
Output
Bias
0
VSS
Vs Vin
tim e [s]
Vin [V]
Output
Bias
0
Cin
Rin =7.1kΩ
Fig.64 Input voltage transition with input coupling capacitor
This charge time constant becomes the following formula (3) by using the input coupling capacitor and the input
impedance. And the calculation value of the convergence to the wait time is indicated in Fig.65.
inin
CRτ (3)
* Rin=7.1kΩ
@Typ.
. In BD88400GUL, Rin=Ri+7.1kΩ
Fig.65 Wait time and convergence (Reference)
0
10
20
30
40
50
60
70
80
90
100
0τ 1τ 2τ 3τ 4τ 5τ 6τ 7τ 8τ
Wait time [s]
Convergence [%]
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10 100 1k 10k 100k
Frequency [Hz]
THD+N [dB]
BD88415GUL
VDD=3.3V
Po=10mW
RL=16
Ω
20kHz LPF
Cin=0.22uF
Cin=0.47uF
Cin=1.0uF
Cin=2.2uF
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BD88420GUL-E2

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Audio Amplifiers Audio Amp Headphone 2-CH Stereo 0.08W Class-AB T/R
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