Rainbow Electronics MAX8884Z - Manual (Page 9)

MAX8884Y/MAX8884Z
700mA DC-DC Step-Down Converters
with Dual 300mA LDO in 2mm x 2mm CSP
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Detailed Description
The MAX8884Y/MAX8884Z are designed to power the
subcircuits within a system. These ICs contain a high-
frequency, high-efficiency step-down converter and two
LDOs. The step-down converter delivers 700mA with
either 1.2V or 1.8V selectable output voltage using SEL.
The hysteretic PWM control scheme provides extremely
fast transient response, while 2MHz and 4MHz switch-
ing frequency options allow the trade-off between effi-
ciency and the smallest external components. The
MAX8884Y/MAX8884Z linear regulators can be used to
power loads requiring a low output noise supply.
Step-Down Converter Control Scheme
A hysteretic PWM control scheme ensures high efficien-
cy, fast switching, fast transient response, low-output
voltage ripple, and physically tiny external components.
The control scheme is simple: when the output voltage
is below the regulation threshold, the error comparator
begins a switching cycle by turning on the high-side
switch. This high-side switch remains on until the mini-
mum on-time expires and output voltage is within regu-
lation, or the inductor current is above the current-limit
threshold. Once off, the high-side switch remains off
until the minimum off-time expires and the output volt-
age falls again below the regulation threshold. During
Pin Description
PIN NAME FUNCTION
A1 REFBP
Reference Noise Bypass. Bypass REFBP to AGND with a 0.033μF ceramic capacitor to reduce noise
on the LDO outputs. REFBP is internally pulled to ground through a 1k
Ω resistor during shutdown.
A2 AGND Low-Noise Analog Ground. Connect to common ground plane.
A3 NC1 No Internal Connection. Connect NC1 to ground.
A4 PGND Power Ground for Step-Down Converter. Connect to common ground plane.
B1 LDO2
300mA LDO Regulator 2 Output. For 300mA application, bypass LDO2 with a 2.2μF ceramic capacitor
as close as possible to LDO2 and AGND. For low-output current capability, up to 10mA, an output
capacitor of 0.1μF is sufficient to keep the output voltage stable. LDO2 is internally pulled to ground
through a 100
Ω resistor when this regulator is disabled.
B2 BUCK_EN
Step-Down Converter Enable Input. Connect BUCK_EN to IN1_ or logic-high for normal operation.
Connect BUCK_EN to AGND or logic-low for step-down shutdown mode.
B3 LDO2_EN
LDO2 Enable Input. Connect LDO2_EN to IN2 or logic-high for normal operation. Connect LDO2_EN to
AGND or logic-low for LDO2 shutdown mode.
B4 LX Inductor Connection. Connect an inductor from LX to the output of the step-down converter.
C1 IN2
Supply Voltage Input for LDO1, LDO2, and Internal Reference. Connect IN2 to a battery or supply
voltage from 2.7V to 5.5V. Bypass IN2 with a 4.7μF ceramic capacitor as close as possible to IN2 and
AGND. Connect IN2 to the same source as IN1A and IN1B.
C2 SEL
Output Voltage Selection for LDO1 and Step-Down Converter. Connect to IN1_ or AGND for output
voltage selection. See Table 1.
C3, C4 IN1B, IN1A
Supply Voltage Input for Step-Down Converter. Connect IN1B and IN1A to a battery or supply voltage
from 2.7V to 5.5V. Bypass the connection of IN1B and IN1A with a 2.2μF ceramic capacitor as close as
possible to IN1B, IN1A, and PGND. IN1A
and IN1B are internally connected together. Connect IN1A
and IN1B to the same source as IN2.
D1 LDO1
300mA LDO Regulator 1 Output. For 300mA application, bypass LDO1 with a 2.2μF ceramic capacitor
as close as possible to LDO1 and AGND. For low-output current capability, up to 10mA, an output
capacitor of 0.1μF is sufficient to keep output voltage stable. LDO1 is internally pulled to AGND
through a 100
Ω resistor when this regulator is disabled.
D2 LDO1_EN
LDO1 Enable Input. Connect LDO1_EN to IN2 or logic-high for normal operation. Connect LDO1_EN to
AGND or logic-low for LDO1 shutdown mode.
D3 NC2 No Internal Connection. Connect NC2 to ground.
D4 FB FB is Connected to the Internal Feedback Network