Rainbow Electronics MAX1800 - Manual (Page 8)

MAX1800
Digital Camera Step-Up
Power Supply
8 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1, 19 PGND
Power Ground. Sources of internal N-channel MOSFET power switches. Connect both PGND pins to GND as
close to the IC as possible.
2 DL1
External MOSFET Gate Drive Output for Auxiliary Controller 1. DL1 swings between POUT and GND with
typical 500mA drive current. Connect DL1 to the gate of the external switching N-channel MOSFET for
auxiliary controller 1.
3 ON1 Enable Input for Auxiliary Controller 1. Connect ON1 to POUT to automatically start auxiliary controller 1.
4 FB1
Feedback Input for Auxiliary Controller 1. Connect a feedback resistive voltage-divider from the output to FB1
to set the output voltage. Regulation voltage is V
REF (1.25V).
5 COMP1
Compensation for Auxiliary Controller 1. Output of transconductance error amplifier. Connect a series resistor
and capacitor to GND to compensate the control loop. See Compensation Design.
6 DCON1
Maximum Duty-Cycle Control Input for Auxiliary Controller 1. Connect to POUT to set the default maximum
duty cycle. Connect a resistive voltage-divider from REF to DCON1 to set the maximum duty cycle between
40% and 90%. Pull DCON1 below 400mV to turn the controller off.
7, 22
POUT Main Power Output. Source of P-channel MOSFET synchronous rectifier switch. Connect both POUT pins
together as close to the IC as possible.
8 DL2
External MOSFET Gate Drive Output for Auxiliary Controller 2. DL2 swings between POUT and GND with
typical 500mA drive current. Connect DL2 to the gate of the external switching N-channel MOSFET for
auxiliary controller 2.
9 ON2 Enable Input for Auxiliary Controller 2. Connect ON2 to POUT to automatically start auxiliary controller 2.
10 FB2
Feedback Input for Auxiliary Controller 2. Connect a feedback resistive voltage-divider from the output to FB2
to set the output voltage. Regulation voltage is V
REF (1.25V).
11 COMP2
Compensation for Auxiliary Controller 2. Output of transconductance error amplifier. Connect a series resistor
and capacitor to GND to compensate the control loop. See Compensation Design.
12 DCON2
Maximum Duty-Cycle Control Input for Auxiliary Controller 2. Connect to POUT to set the default maximum
duty cycle. Connect a resistive voltage-divider from REF to DCON2 to set the maximum duty cycle between
40% and 90%. Pull DCON2 below 400mV to turn the controller off.
13 OUT
Internal Bias Supply Input. Connect to POUT through a resistor, and bypass OUT to GND with a capacitor.
See Compensation Design.
14 REF 1.250V Reference Output. Bypass REF to GND with a 0.1µF or greater ceramic capacitor.
15 GND Analog Ground. Connect GND to PGND at a single point near the IC.
16 OSC
Oscillator Control. Connect a timing capacitor from OSC to GND and a timing resistor from OSC to POUT to
set the switching frequency between 100kHz and 1MHz. See Setting the Switching Frequency.
17 FBM
Main DC/DC Converter Feedback Input. Connect a feedback resistive voltage-divider from POUT to FBM to
set the output voltage. Regulation voltage is V
REF (1.25V).
18 COMPM
Compensation for Main Controller. Output of transconductance error amplifier. Connect a series resistor and
capacitor to GND to compensate the control loop. See Compensation Design.
20,
21
LX
Main Power Switching Node. Drains of the internal P-channel and N-channel MOSFET switches. Connect the
LX pins together as close to the IC as possible.
23 RDYM
Main Converter Ready Output. An open-drain output sinks current when V FBM < 1.125V, indicating that the
main output is more than 10% out of regulation.