MAX1637EEE Maxim Integrated Products, MAX1637EEE Datasheet - Page 12

• Manufacturer Part Number: MAX1637EEE
• Description: IC CTRLR MINI LV STPDWN 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1637EEE

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.1 ~ 5.5 V
• Current - Output: 3A
• Frequency - Switching: Adj to 350kHz
• Voltage - Input: 3.15 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 667mW
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Miniature, Low-Voltage,
Precision Step-Down Controller
The 1.100V reference (REF) is accurate to ±2% over
temperature, making REF useful as a precision system
reference. Bypass REF to GND with a 0.22µF (min)
capacitor. REF can supply up to 50µA for external
loads. Loading REF reduces the main output voltage
slightly because of the reference load-regulation error.
The MAX1637 has two independent supply pins, V
and V
the SMPS, while V
drivers. No protection diodes or sequencing require-
ments exist between the two supplies. Isolate V
V
same supply. Bypass V
tor located directly adjacent to the pin. Use only small-
signal diodes for the boost circuit (10mA to 100mA
Schottky or 1N4148 diodes are preferred), and bypass
V
package pins. The V
to 5.5V.
Gate-drive voltage for the high-side N-channel switch is
generated by a flying-capacitor boost circuit (Figure 2).
The capacitor between BST and LX is alternately
charged from the V
the high-side MOSFET’s gate-source terminals.
On start-up, the synchronous rectifier (low-side
MOSFET) forces LX to 0V and charges the boost
capacitor to V
turns on the high-side MOSFET by closing an internal
switch between BST and DH. This provides the neces-
sary enhancement voltage to turn on the high-side
switch, an action that boosts the gate-drive signal
above the battery voltage.
Ringing at the high-side MOSFET gate (DH) in discon-
tinuous-conduction mode (light loads) is a natural oper-
ating condition. It is caused by residual energy in the
tank circuit, formed by the inductor and stray capaci-
tance at the switching node, LX. The gate-drive nega-
tive rail is referred to LX, so any ringing there is directly
coupled to the gate-drive output.
Synchronous rectification reduces conduction losses in
the rectifier by shunting the normal Schottky catch
diode with a low-resistance MOSFET switch. Also, the
synchronous rectifier ensures proper start-up of the
boost gate-driver circuit. If the synchronous power
MOSFET is omitted for cost or other reasons, replace it
with a small-signal MOSFET, such as a 2N7002.
12
CC
GG
______________________________________________________________________________________
with a 20Ω resistor if they are powered from the
to PGND with a 4.7µF capacitor directly at the
GG
. V
CC
Synchronous-Rectifier Driver (DL)
High-Side Boost Gate Drive (BST)
GG
powers the sensitive analog circuitry of
. On the second half-cycle, the SMPS
GG
REF, V
GG
CC
powers the high-current MOSFET
CC
supply and placed parallel to
and V
to GND with a 0.1µF capaci-
CC
GG
, and V
input range is 3.15V
GG
Supplies
GG
from
CC
If the circuit is operating in continuous-conduction
mode, the DL drive waveform is simply the complement
of the DH high-side-drive waveform (with controlled
dead time to prevent cross-conduction or “shoot-
through”). In discontinuous (light-load) mode, the syn-
chronous switch is turned off as the inductor current
falls through zero.
SHDN is a logic input with a threshold of about 1.5V
that, when held low, places the IC in its 0.5µA shut-
down mode. The MAX1637 has no power-on-reset cir-
cuitry, and the state of the device is not known on initial
power-up. In applications that use logic to drive SHDN,
it may be necessary to toggle SHDN to initialize the
part once V
automatic start-up, drive SHDN through an external RC
network (Figure 5). The network will hold SHDN low
until V
and 0.01µF. For slow-rising V
When cycling V
discharge the 0.01µF capacitor, otherwise the circuit
may not start. A diode may be added in parallel with
the resistor to speed up the discharge.
The current-limit circuit resets the main PWM latch and
turns off the high-side MOSFET switch whenever the
voltage difference between CSH and CSL exceeds
100mV. This limiting is effective for both current flow
directions, putting the threshold limit at ±100mV. The
tolerance on the positive current limit is ±20%, so the
external low-value sense resistor (R1) must be sized for
80mV / I
required to support the full load current. Components
must be designed to withstand continuous current
stresses of 120mV / R1.
Figure 5. Power-On Reset RC Network for Automatic Start-Up
CC
Shutdown Mode and Power-On Reset
PEAK
stabilizes. Typical values for R and C are 1MΩ
V
R = 1MΩ
C = 0.01μF
IN
C
CC
R
, where I
CC
is stable. In applications that require
Current-Limiting and Current-
, V
Sense Inputs (CSH and CSL)
CC
PEAK
must stay low long enough to
SHDN
V
is the peak inductor current
GG
CC
MAX1637
, use a larger capacitor.
V
CC