MAX1700 Maxim, MAX1700 Datasheet - Page 13

• Manufacturer Part Number: MAX1700
• Description: 1-Cell to 3-Cell / High-Power 1A / Low-Noise / Step-Up DC-DC Converters
• Manufacturer: Maxim

The MAX1700/MAX1701 have an internal 1.250V, 1%
bandgap reference. Connect a 0.22µF bypass capaci-
tor to GND within 0.2in. (5mm) of the REF pin. REF can
source up to 50µA of external load current.
The MAX1701 features a power-good comparator. This
comparator’s open-drain output (POK) is pulled low
when the output voltage falls to 10% below the regula-
tion point.
Table 5. Component Selection Guide
Figure 9. Using Gain Block as a Linear Regulator
Surface Mount
Through Hole
Table 4. Component Suppliers
SUPPLIER
AVX
Coilcraft
Matsuo
Motorola
Sanyo
Sumida
PRODUCTION
REF
MAX1701
USA: [phone]
USA: [phone]
USA: [phone]
USA: [phone]
USA: [phone]
Japan: 81-7-2070-6306
USA: [phone]
Japan: 81-3-3607-5111
______________________________________________________________________________________
N
AIN
AO
LX
[phone]
Sumida CDR63B, CD73, CDR73B, CD74B series
Coilcraft DO1608, DO3308, DT3316 series
Sumida RCH654 series
Low-Noise, Step-Up DC-DC Converters
PHONE
IN
100 F
R6
Power-OK (MAX1701)
2x
R5
20k
1-Cell to 3-Cell, High-Power (1A),
INDUCTORS
[phone]
[phone]
[phone]
[phone]
[phone]
81-7-2070-1174
[phone]
81-3-3607-5144
P
Reference
FAX
47 F
The MAX1701’s gain block can function as a third com-
parator or can be used to build a linear regulator using
an external P-channel MOSFET pass device. The gain-
block output is a single-stage transconductance ampli-
fier that drives an open-drain N-channel MOSFET.
Figure 9 shows the gain block used in a linear regula-
tor. The output of an external P-channel pass element is
compared to the internal reference. The difference is
amplified and used to drive the gate of the pass ele-
ment. Use a logic-level PFET such as the Fairchild
NDS336P (R
less than 250mΩ, the linear regulator output filter
capacitance may need to be increased to above 47µF.
Set the output voltage between 2.5V and 5.5V by con-
necting a resistor voltage-divider to FB from OUT to
GND, as shown in Figure 2. The resistor values are then
as follows:
where V
1.23V. Since the input bias current into FB is less than
20nA, R2 can have a large value (such as 270kΩ or
less) without sacrificing accuracy. Connect the resistor
voltage-divider as close to the IC as possible, within
0.2in. (5mm) of the FB pin.
The MAX1700/MAX1701’s high switching frequency
allows the use of a small surface-mount inductor. A
10µH inductor should have a saturation-current rating
that exceeds the N-channel switch current limit of 1.6A.
However, it is generally acceptable to bias the inductor
current into saturation by as much as 20%, although
this will slightly reduce efficiency. For high efficiency,
choose an inductor with a high-frequency core material
(such as ferrite) to reduce core losses. To minimize
radiated noise, use a toroid, pot core, or shielded bob-
bin inductor. Connect the inductor from the battery to
the LX pin as close to the IC as possible. See Table 4
for a list of component suppliers and Table 5 for sug-
gested components.
__________________Design Procedure
Matsuo 267 series
Sprague 595D series
AVX TPS series
Sanyo OS-CON series
Nichicon PL series
FB
, the boost-regulator feedback setpoint, is
DS(ON)
CAPACITORS
R1 = R2 (V
Setting the Output Voltages
= 270m
Gain Block (MAX1701)
OUT
). If the PFET R
/V
Inductor Selection
FB
Motorola MBR0520L
1N5817
- 1)
DIODES
DS(ON)
13
is