MAX1681ESA+T Maxim Integrated Products, MAX1681ESA+T Datasheet - Page 7

• Manufacturer Part Number: MAX1681ESA+T
• Description: IC VOLT CONV 125MA 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Switched Capacitor (Charge Pump), Doubler, Invertingr

Specifications of MAX1681ESA+T

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -2 ~ -5.5 V, 4 ~ 11 V
• Current - Output: 125mA
• Frequency - Switching: 500kHz, 1MHz
• Voltage - Input: 2 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Power - Output: 471mW
• Function: Inverting, Step Up
• Output Voltage: - 3 V to - 5.5 V, 8 V to 11 V
• Output Current: 125 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

It is important to recognize the trade-offs between
switching frequency, power consumption, noise, cost,
and performance. Higher frequency switching reduces
capacitor size while maintaining the same output
impedance, thus saving capacitor cost and board
space. Lower frequency designs use less supply cur-
rent. Table 2 summarizes the relative trade-offs.
Table 2. Switching-Frequency Trade-Offs
The MAX1680/MAX1681 are tested with capacitor val-
ues of 10µF and 2.2µF, respectively. Capacitor size
and switching speed determine output resistance.
Larger C1 values decrease the output resistance until
the internal switch resistance (3.5Ω typ) becomes the
dominant term. Low-ESR capacitors minimize output
resistance and ripple voltage. The entire circuit’s output
resistance can be approximated by the following equa-
tion:
R
[1 / (f
where R
tance and f
Table 3. Low-ESR Capacitor Suppliers
OUT
Output Ripple
C1, C2 Values
Supply Current
AVX
Marcon/United Chemi-Con
Matsuo
Nichicon
Sanyo
Sprague
TDK
United Chemi-Con
Vishay/Vitramon
ATTRIBUTE
OSC
R
O
O
x C2)]
SUPPLIER
is the device’s internal effective switch resis-
+ 4 x ESR
OSC
Operating Frequency Trade-Offs
is the switching frequency. Output
_______________________________________________________________________________________
Switched-Capacitor Voltage Converters
C1
FREQUENCY
+ ESR
LOWER
Smaller
Larger
Larger
Capacitor Selection
C2
[phone]
[phone]
[phone]
[phone]
USA: [phone]
Japan: 81-7-5231-8461
USA: [phone]
Japan: 81-7-2070-6306
[phone]
[phone]
[phone]
[phone]
+ [1 / (f
PHONE
FREQUENCY
125mA, Frequency-Selectable,
OSC
HIGHER
Smaller
Smaller
Larger
x C1)] +
[phone]
[phone]
[phone]
USA: [phone]
Japan: 81-7-5256-4158
USA: [phone]
Japan: 81-7-2070-1174
[phone]
[phone]
[phone]
[phone]
resistance is a critical circuit component, as it deter-
mines the voltage drop that will occur at the output from
the ideal value of -V
To optimize performance, minimize overall resistance in
the system. In particular, equivalent series resistance
(ESR) in the capacitors produces significant losses as
large currents flow through them. Therefore, choose a
low-ESR capacitor for highest efficiency. Table 3 lists
recommended capacitors and their suppliers.
Calculate the output ripple voltage as follows:
V
where I
operating frequency, C2 is the output capacitor, and
ESR
Table 4 lists the minimum recommended capacitances
that allow for the maximum output current. The output
capacitor, C2, is normally equal to or greater than the
charge-pump capacitor, C1. Capacitor values can be
scaled directly proportional to the input voltage, fre-
quency, and load current. For example, for V
5V, I
mum capacitor is recommended. For an output of only
62.5mA, a 3.2µF capacitor is recommended. C1’s value
can be estimated as follows:
C1 = 6.4µF x (V
(I
where f
is the output current (mA) required.
RIPPLE
LOAD
C2
LOAD
FAX
is the output capacitor’s ESR.
/ 125mA)
OUT
OSC
= [(I
= 125mA at f
is the load current, f
is the switching frequency (kHz) and I
OUT
INPUT
) / (2 x f
INPUT
/ 5.0V) x (125kHz / f
Surface mount, TPS series
Ceramic capacitors
Surface mount, 267 series
Through-hole, PL series
Through-hole, OS-CON series
Surface mount, 595D series
Ceramic capacitors
Through-hole, LXF series
SMT ceramic chip capacitors
OSC
OSC
(or 2V
x C2)] + 2 x (I
= 125kHz, a 6.4µF mini-
INPUT
DEVICE TYPE
S
is the charge pump’s
when doubling).
OSC
OUT
) x
x ESR
INPUT
LOAD
C2
=
7
)