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ADP3604 Datasheet(PDF) 6 Page - Analog Devices

Part No. ADP3604
Description  Switched Capacitor Voltage Converter with Regulated Output
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ADP3604 Datasheet(HTML) 6 Page - Analog Devices

   
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ADP3604
REV. 0
–6–
The output current is supplied solely by the output capacitor
C3 during one-half of the charge-pump cycle. This introduces a
peak-to-peak ripple of:
VRIPPLE =
IL
2
×120 kHz ×C3
+ I
L × ESRC3
For a nominal F pump of 120 kHz (one-half the nominal 240 kHz
oscillator frequency) and C3 = 10
µF with an ESR of 0.15 Ω,
ripple voltage is approximately 60 mV with a 120 mA load
current.
Multilayer Ceramic Capacitors (MLCC) offer great perfor-
mance and small size. Using multiple capacitors connected in
parallel yields lower ESR and a potential saving in cost. Lighter
loads require proportionally smaller capacitors. To reduce high
frequency noise, bypass the output with a 0.1
µF ceramic
capacitor.
ADP3604
8
7
3
C2
4.7µF
1
4
VIN +4.5 – +6V
VOUT –3.0V
C3
4.7µF
2
5
SENSE
INPUT
L1
10µH
C4
4.7µF
C1
4.7µF
Figure 17. Circuit with Improved Output Ripple & Noise
Voltage
Table III. Recommended Components for Circuit in Figure 17
Component
Manufacturer/Type
C2
Sprague, 293D475X0035D2W
C1, C3, C4
TOKIN, 1E475ZY5U-C205-F
L1
Coiltronics, CTX32CT
EXTERNAL INPUT FILTERING
If the ADP3604 is supplied from an high-impedance source,
connect an additional bypass capacitor from V+ to ground.
Low-ESR capacitors of up to 100
µF give best results. Place
external capacitors close to the supply pins of the device with
the ground connection made as close to the device ground as
possible. The same ground point should be used for the output
bypass capacitor.
Smaller bypass capacitors can be used in conjunction with a
π-LC filter.
ADP3604
8
7
3
C3
4.7µF
1
4
VIN +4.5 – +6V
VOUT –3.0V
C4
4.7µF
2
5
SENSE
INPUT
L2
10µH
C5
4.7µF
C2
4.7µF
L1
1µH
C1
4.7µF
Figure 18. Circuit with Reduced Input and Output Ripple
& Noise Voltage
Table IV. Recommended Components for Circuit in Figure 18
Component
Manufacturer/Type
C3
Sprague, 293D475X0035D2W
C1, C2, C4, C5
TOKIN, 1E475ZY5UC205F
L1
Coiltronics, CTX32CT-1R0
L2
Coiltronics, CTX32CT-100
SHUTDOWN MODE
ADP3604’s output can be turned off by utilizing the shutdown
pin, Pin 4. Pulling the shutdown pin high to a TTL/CMOS
logic compatible level will stop the internal oscillator and turn
OFF the output pass transistor. A digital low level will turn the
output ON. If the shutdown feature of the device is not used,
Pin 4 should be tied to the ground pin of the device.
MAXIMUM OUTPUT VOLTAGE
Maximum unregulated output voltage can be obtained by con-
necting the sense pin to ground instead of the VOUT pin as
shown in Figure 19.
Under this condition, the magnitude of the unregulated output
voltage depends on the load current. VOUT is inversely propor-
tional to the load current as shown on the graph in Figure 19.
LOAD CURRENT – mA
–5.0
–4.0
10
90
30
50
70
–3.0
ADP3604
8
7
3
1
4
VIN = 5.0V
2
5
Figure 19. Maximum Unregulated Output Voltage
Under light loads, 30 mA < ILOAD, a regulated output voltage
between –3.0 V to –VIN V is possible by inserting a resistor be-
tween the sense pin and the VOUT pin as shown in Figure 20.
The output voltage is approximated using the following formula:
VOUT = –(3 +R/5)
where VOUT is in volts and R is in k
Ωs.
LOAD CURRENT – mA
–5.0
–4.0
10
90
30
50
70
–3.0
ADP3604
8
7
3
1
4
VIN = 5.0V
2
5
VOUT
R
R = 10k
R = 5k
110
Figure 20. Maximum Regulated Output Voltage


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