Rainbow Electronics MAX8562 - Manual (Page 6)

MAX8560/MAX8561/MAX8562
4MHz, 500mA Synchronous Step-Down
DC-DC Converters in SOT and TDFN
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Detailed Description
The MAX8560/MAX8561/MAX8562 step-down converters
deliver a guaranteed 500mA at output levels from 0.6V to
2.5V. They use a proprietary hysteretic-PWM control
scheme that switches up to 4MHz, allowing a trade-off
between efficiency and tiny external components. At light
loads below 100mA, the MAX8560/MAX8561/MAX8562
automatically switch to pulse-skipping mode to keep qui-
escent supply current as low as 40µA (typ).
Control Scheme
A proprietary hysteretic-PWM control scheme ensures
high efficiency, fast switching, fast transient response,
low output ripple, and physically tiny external compo-
nents. This control scheme is simple: when the output
voltage falls below the regulation threshold, the error
comparator begins a switching cycle by turning on the
high-side switch. This switch remains on until the mini-
mum on-time expires and the output voltage is in regu-
lation or the current-limit threshold is exceeded. Once
off, the high-side switch remains off until the minimum
off-time expires and the output voltage falls again,
below the regulation threshold. During this period, the
low-side synchronous rectifier turns on and remains on
until either the high-side switch turns on again or the
inductor current approaches zero. The internal syn-
chronous rectifier eliminates the need for an external
Schottky diode.
Voltage-Positioning Load Regulation
As seen in the Typical Operating Circuit, the
MAX8560/MAX8561/MAX8562 use a unique feedback
network. By taking feedback from the LX node through
R1, the usual phase lag due to the output capacitor is
removed, making the loop exceedingly stable and
allowing the use of a very small ceramic output capaci-
tor. This configuration causes the output voltage to shift
by the inductor series resistance multiplied by the load
current. This voltage-positioning load regulation greatly
reduces overshoot during load transients, which effec-
tively halves the peak-to-peak output-voltage excur-
sions compared to traditional step-down converters.
See the Load Transient Response graph in the Typical
Operating Characteristics section.
Pin Description
PIN
MAX8560
MAX8561
MAX8562 NAME FUNCTION
1 1 IN
Supply Voltage Input. 2.7V to 5.5V. Bypass with a 2.2µF ceramic capacitor as close as
possible to the IN and GND pins.
2 7 GND Analog Ground
3 8 SHDN
Active-Low Shutdown Input. Connect to IN or logic high for normal operation. Connect to
GND or logic low for shutdown mode.
4 6 FB
Voltage Feedback Input. FB regulates to 0.6V nominal. Connect FB to the center of an
external resistive divider (see the Setting the Output Voltage section).
5 2 PGND Power Ground. Must connect to GND.
6 3 LX Inductor connection to the drains of the internal P-channel and N-channel MOSFETs.
— 5 ODO Auxiliary Open-Drain Output
— 4 ODI
Digital Input for Open-Drain MOSFET. Connect to IN or logic high to internally pull ODO
low (and force the MAX8562 into 100% duty cycle). Connect to GND or logic low to force
ODO to high impedance (MAX8561) or 10k
Ω pullup from ODO to IN (MAX8562).
— EP EP Exposed Pad. Connect to GND.