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MAX1720EUTG

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18
MAX1720
http://onsemi.com
4
5.0
4.5
3.5
4.0
3.0
2.5
1.5
80
60
90
50
70
40
100
1.00
0
−2.0
30
−5.0
2010
V
out
, OUTPUT VOLTAGE (V)
−6.0
I
out
, OUTPUT CURRENT (mA)
Figure 8. Output Voltage vs. Output Current Figure 9. Power Conversion Efficiency vs.
Output Current
h, POWER CONVERSION EFFICIENCY (%
)
Figure 10. Output Voltage Ripple and Noise
TIME = 25 ms / Div.
Figure 11. Shutdown Supply Current vs.
Ambient Temperature
T
A
, AMBIENT TEMPERATURE (°C)
I
SHDN
, SHUTDOWN SUPPLY CURRENT (mA)
OUTPUT VOLTAGE RIPPLE AND
NOISE = 10 mV / Div. AC COUPLED
Figure 12. Supply Voltage vs. Shutdown Input
Voltage Threshold
V
th(SHND)
, SHUTDOWN INPUT VOLTAGE THRESHOLD (V)
Figure 13. Wakeup Time From Shutdown
TIME = 500 ms / Div.
V
in
, SUPPLY VOLTAGE (V)
WAKEUP TIME FROM SHUTDOWN
0.0
0.5 2.52.01.51.0 3.0
−50 50 7525010
0
−25
0.50
1.25
0.75
0.25
1.50
1.75
I
out
, OUTPUT CURRENT (mA)
−4.0
−3.0
−1.0
40 50 0 302010 40 5
0
2.0
Low State,
Device Shutdown
V
in
= 2.0 V
V
in
= 3.3 V
V
in
= 5.0 V
R
L
= 10 kW
SHDN = GND
Figure 14 Test Setup
T
A
= 25°C
V
in
= 1.5 V
V
in
= 3.3 V
V
in
= 5.0 V
V
in
= 1.5 V
V
in
= 2.0 V
V
in
= 3.3 V
Figure 14 Test Setup
V
in
= 3.3 V
I
out
= 5.0 mA
T
A
= 25°C
T
A
= 25°C
High State,
Device Operating
Figure 14 Test Setup
T
A
= 25°C
V
in
= 5.0 V
V
in
= 5.0 V
R
L
= 1.0 kW
T
A
= 25°C
V
out
= 1.0 V/Div.
SHDN = 5.0V/Div.
MAX1720
http://onsemi.com
5
6
4
2
3
1
OSC
−V
out
C
1
C
2
R
L
+
+
C
3
V
in
+
Figure 14. Test Setup/Voltage Inverter
5
C
1
= C
2
= C
3
= 10 mF
DETAILED OPERATING DESCRIPTION
The MAX1720 charge pump converter inverts the voltage
applied to the V
in
pin. Conversion consists of a two−phase
operation (Figure 15). During the first phase, switches S
2
and
S
4
are open and S
1
and S
3
are closed. During this time, C
1
charges to the voltage on V
in
and load current is supplied from
C
2
. During the second phase, S
2
and S
4
are closed, and S
1
and
S
3
are open. This action connects C
1
across C
2
, restoring
charge to C
2
.
Figure 15. Ideal Switched Capacitor Charge Pump
S3 S4
C
2
C
1
S1 S2
V
in
−V
out
From Osc
APPLICATIONS INFORMATION
Output Voltage Considerations
The MAX1720 performs voltage conversion but does not
provide regulation. The output voltage will drop in a linear
manner with respect to load current. The value of this
equivalent output resistance is approximately 26 W nominal
at 25°C with V
in
= 5.0 V. V
out
is approximately −5.0 V at light
loads, and drops according to the equation below:
V
DROP
+ I
out
R
out
V
out +
* (V
in
* V
DROP
)
Charge Pump Efficiency
The overall power conversion efficiency of the charge
pump is affected by four factors:
1. Losses from power consumed by the internal
oscillator, switch drive, etc. (which vary with input
voltage, temperature and oscillator frequency).
2. I
2
R losses due to the on−resistance of the MOSFET
switches on−board the charge pump.
3. Charge pump capacitor losses due to Equivalent
Series Resistance (ESR).
4. Losses that occur during charge transfer from the
commutation capacitor to the output capacitor when
a voltage difference between the two capacitors
exists.
Most of the conversion losses are due to factors 2, 3 and 4.
These losses are given by Equation 1.
P
LOSS(2,3,4)
+ I
out
2
R
out
^ I
out
2
ƪ
1
(f
OSC
)C
1
) 8R
SWITCH
) 4ESR
C
1
) ESR
C
2
ƫ
(eq. 1)
The 1/(f
OSC
)(C
1
) term in Equation 1 is the effective output
resistance of an ideal switched capacitor circuit (Figures 16
and 17).
The losses due to charge transfer above are also shown in
Equation 2. The output voltage ripple is given by Equation 3.
) 0.5C
2
(V
RIPPLE
2
* 2V
out
V
RIPPLE
)] f
OSC
P
LOSS
+ [0.5C
1
(V
in
2
* V
out
2
)
(eq.
2)
V
RIPPLE
+
I
out
(f
OSC
)(C
2
)
) 2(I
out
)(ESR
C
2
)
(eq. 3)
R
L
C
2
C
1
V
in
V
out
f
Figure 16. Ideal Switched Capacitor Model
R
L
C
2
V
in
V
out
R
EQUIV
R
EQUIV
+
1
f C
1
Figure 17. Equivalent Output Resistance
MAX1720
http://onsemi.com
6
Capacitor Selection
In order to maintain the lowest output resistance and
output ripple voltage, it is recommended that low ESR
capacitors be used. Additionally, larger values of C
1
will
lower the output resistance and larger values of C
2
will
reduce output voltage ripple. (See Equation 3).
Table 1 shows various values of C
1
, C
2
and C
3
with the
corresponding output resistance values at 25°C. Table 2
shows the output voltage ripple for various values of C
1
, C
2
and C
3
. The data in Tables 1 and 2 was measured not
calculated.
Table 1. Output Resistance vs. Capacitance
(C
1
= C
2
= C
3
), V
in
= 4.75 V and V
out
= −4.0 V
C
1
= C
2
= C
3
(mF)
R
out
(W)
0.7 129.1
1.4 69.5
3.3 37.0
7.3 26.5
10 25.9
24 24.1
50 24
Table 2. Output Voltage Ripple vs. Capacitance
(C
1
= C
2
= C
3
), V
in
= 4.75 V and V
out
= −4.0 V
C
1
= C
2
= C
3
(mF)
Output Voltage Ripple
(mV)
0.7 382
1.4 342
3.3 255
7.3 164
10 132
24 59
50 38
Input Supply Bypassing
The input voltage, V
in
should be capacitively bypassed to
reduce AC impedance and minimize noise effects due to the
switching internals in the device. If the device is loaded from
V
out
to GND, it is recommended that a large value capacitor
(at least equal to C
1
) be connected from V
in
to GND. If the
device is loaded from V
in
to V
out
, a small (0.7 mF) capacitor
between the pins is sufficient.
Voltage Inverter
The most common application for a charge pump is the
voltage inverter (Figure 14). This application uses two or
three external capacitors. The C
1
(pump capacitor) and C
2
(output capacitor) are required. The input bypass capacitor,
C
3
, may be necessary depending on the application. The
output is equal to −V
in
plus any voltage drops due to loading.
Refer to Tables 1 and 2 for capacitor selection. The test setup
used for the majority of the characterization is shown in
Figure 14.
Layout Considerations
As with any switching power supply circuit, good layout
practice is recommended. Mount components as close
together as possible to minimize stray inductance and
capacitance. Also, use a large ground plane to minimize noise
leakage into other circuitry.
Capacitor Resources
Selecting the proper type of capacitor can reduce switching
loss. Low ESR capacitors are recommended. The MAX1720
was characterized using the capacitors listed in Table 3. This
list identifies low ESR capacitors for the voltage inverter
application.
Table 3. Capacitor Types
Manufacturer/Contact Part Types/Series
AVX
843−448−9411
www.avxcorp.com
TPS
Cornell Dubilier
508−996−8561
www.cornell−dubilier.com
ESRD
Sanyo/Os−con
619−661−6835
www.sanyovideo.com/oscon.htm
SN
SVP
Vishay
603−224−1961
www.vishay.com
593D
594
6
4
2
3
1
OSC
Capacitors = 10 mF
+
+
V
in
5
+
−V
out
Figure 18. Voltage Inverter
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18

MAX1720EUTG

Mfr. #:
Buy MAX1720EUTG
Manufacturer:
ON Semiconductor
Description:
Switching Voltage Regulators Switched Cap Voltage Inverter w/Shutdown
Lifecycle:
New from this manufacturer.
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