MAX1700 Maxim, MAX1700 Datasheet - Page 15

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

low-noise power for DSP, control, and RF circuitry.
Typically, RF phones spend most of their life in standby
mode with only short periods in transmit/receive mode.
During standby, maximize battery life by setting
CLK/SEL = 0; this places the IC in low-power mode (for
the lowest quiescent power consumption).
High switching frequencies and large peak currents
make PC board layout an important part of design.
Poor design can cause excessive EMI and ground-
bounce, both of which can cause instability or regula-
tion errors by corrupting the voltage and current
feedback signals.
Power components (such as the inductor, converter IC,
filter capacitors, and output diode) should be placed as
close together as possible, and their traces should be
kept short, direct, and wide. A separate low-noise
ground plane containing the reference and signal
grounds should only connect to the power-ground
plane at one point. This minimizes the effect of power-
ground currents on the part. Consult the MAX1701 EV
kit manual for a layout example.
On multilayer boards, do not connect the ground pins
of the power components using vias through an internal
ground plane. Instead, place them close together and
route them in a star-ground configuration using compo-
nent-side copper. Then use vias to connect the star
ground to the internal ground plane.
Keep the voltage feedback network very close to the
IC, within 0.2in. (5mm) of the FB pins. Keep noisy
traces, such as from the LX pin, away from the voltage
feedback networks. Separate them with grounded
copper. Consult the MAX1700 evaluation kit for a full
PC board example.
Pin Configurations (continued)
TOP VIEW
CLK/SEL
GND
ONB
ONA
POK
______________________________________________________________________________________
LBP
LBN
REF
1
2
3
4
5
6
7
8
Low-Noise, Step-Up DC-DC Converters
MAX1701
Designing a PC Board
QSOP
1-Cell to 3-Cell, High-Power (1A),
16
15
14
13
12
11
10
9
LBO
POUT
OUT
LX
PGND
FB
AIN
AO
To implement soft-start, set CLK/SEL low on power-up;
this forces low-power operation and reduces the peak
switching current to 550mA max. Once the circuit is in
regulation and start-up transients have settled,
CLK/SEL can be set high for full-power operation.
When boosting an input supply connected with a
mechanical switch, or a battery connected with spring
contacts, input power may sometimes be intermittent
as a result of contact bounce. When operating in PFM
mode with input voltages greater than 2.5V, restarting
after such dropouts may initiate high current pulses that
interfere with the MAX1700/MAX1701 internal MOSFET
switch control. If contact or switch bounce is anticipat-
ed in the design, use one of the following solutions.
1) Connect a capacitor (C
resistor (R
(Figure 12). This RC network differentiates fast input
edges at V
settles. The appropriate value of C
total output filter capacitance (C
200µF results in C
2) Use the system microcontroller to hold the
MAX1700/MAX1701 in shut down from the time when
power is applied (or reapplied) until the output capaci-
tance (C
Power-on reset times of tens of milliseconds accom-
plish this.
3) Ensure that the IC operates, or at least powers up, in
PWM mode (CLK/SEL = high). Activate PFM mode only
after the V
on reset flags are cleared.
Figure 12. Connecting C
Battery-Contact Bounce Is Anticipated
Intermittent Supply/Battery Connections
OUT
ONB
OUT
IN
) has charged to at least the input voltage.
and momentarily holds the IC off until V
C
) from ONB to GND, and tie ONA to GND
R
2nF
has settled and all of the system’s power-
ONB
ONB
1M
ONB
7
8
= 2nF.
ONB
ONB
ONA
ONB
MAX1700
MAX1701
and R
) from ONB to V
ONB
POUT
OUT
LX
ONB
OUT
when Switch or
13
14
15
), so a C
is 10
Soft-Start
-5
IN
times the
C
200 F
, a 1M
OUT
OUT
15
IN
of