Detailed Description
The MAX5008 charge pump provides a regulated 5V
output from a 2.95V to 5.5V input. The device delivers a
maximum of 125mA load current. Designed specifically
for compact applications, a complete regulator circuit
requires a minimum number of external components.
Adjustable Current Limit
The MAX5008 has an adjustable overcurrent protec-
tion. An external current-sense resistor is connected
from RCS to OUT to set the current limit. The current
limit is defined by:
I
LIMIT
= V
CS
/ RCS
where V
CS
is the current-sense trip level, typically 60mV.
For example, I
LIMIT
= 150mA when RCS = 0.40Ω.
When the output current limit is exceeded, the output
voltage falls and the device maintains the average out-
put current at I
LIMIT
. Upon removal of the overcurrent
condition, the part resumes normal operation.
FAULT
Indication
When I
OUT
> I
LIMIT
or V
OUT
< V
TH
, FAULT asserts.
FAULT is an open-drain output that needs to be con-
nected through a 100kΩ (typ) pullup resistor to a logic
supply voltage.
Thermal Shutdown
The MAX5008 has internal thermal shutdown circuitry,
which shuts down the device when the die temperature
exceeds +150°C. The thermal shutdown circuitry has
30°C hysteresis.
Shutdown Mode
Driving SHDN low places the device in shutdown
mode, which disables the oscillator, the control logic,
and the reference. The output goes into high-imped-
ance state and drops to ground if loaded. Placing the
device in shutdown mode reduces the supply current
to less than 0.1µA. In normal operation, SHDN is driven
high or connected to IN.
Applications Information
Capacitor Selection
The MAX5008 requires four external capacitors. Their
values depend on the required output current. Table 1
shows the capacitor values recommended for different
load currents.
Input Voltage Range
The MAX5008 maintains a regulated 5V output with
input voltages from 2.95V to 5.5V. If the input voltage
exceeds 4.25V, limit the output current to 75mA or less.
This keeps the MAX5008 within its maximum power dis-
sipation limits.
Layout Considerations
All capacitors should be located as close to the IC as
practical. Connect GND and PGND through a short,
MAX5008
Regulated 5V USB Charge Pump with
Programmable Current Limit
_______________________________________________________________________________________ 5
PIN NAME FUNCTION
1 RCS
External Current-Sense Resistor. Connect a resistor from RCS to OUT to set the overcurrent
threshold.
I
LIMIT
= 60mV / R
CS
.
2 OUT Fixed 5V Output. Bypass OUT to GND with a 4.7µF capacitor.
3 FAULT
Output Fault Indicator. FAULT is asserted when either I
OUT
> I
LIMIT
or V
OUT
< V
TH
. FAULT is an
open-drain output that is high during normal operation or during shutdown.
4 GND Ground Pin. Connect GND to PGND.
5 SHDN
Shutdown Input. When SHDN = low, the device turns off. Drive SHDN high or connect to IN for
normal operation.
6 PGND Power Ground Pin. Connect PGND to GND.
7CXN Negative Terminal of the Charge-Pump Capacitor. Connect a 0.68µF capacitor from CXN to CXP.
8INInput Supply, 2.95V to 5.5V. Bypass IN to GND with a 4.7µF ceramic capacitor.
9 CXP Positive Terminal of the Charge-Pump Capacitor. Connect a 0.68µF capacitor from CXP to CXN.
10 CEXT Charge-Pump Output. Bypass CEXT to PGND with a 6.8µF capacitor.
