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General Description

The MAX1802 provides a complete power-supply solu-

tion for digital still cameras and video cameras by inte-

grating two high-efficiency step-down DC-DC converters

and three auxiliary step-up controllers. This complete

solution is targeted for applications that use either three

to four alkaline cells or two lithium-ion (Li+) cells.

The main step-down DC-DC controller accepts inputs

from 2.5V to 11V and regulates a resistor-adjustable out-

put from 2.7V to 5.5V. It uses a synchronous rectifier to

regulate the output with up to 94% efficiency. An

adjustable operating frequency (up to 1MHz) facilitates

designs for optimum size, cost, and efficiency.

The core step-down DC-DC converter accepts inputs

from 2.7V to 5.5V and regulates a resistor-adjustable

output from 1.25V to 5.5V. It delivers 500mA with up to

94% efficiency.

The three auxiliary step-up controllers can be used to

power the digital camera’s CCD, LCD, and backlight.

The MAX1802 also features expandability by supplying

power, an oscillator signal, and a reference to the

MAX1801, a low-cost slave DC-DC controller that sup-

ports step-up, single-ended primary inductance con-

verter (SEPIC), and fly-back configurations.

The MAX1802 is available in a space-saving 32-pin

TQFP package (5mm x 5mm body), and the MAX1801

is available in an 8-pin SOT-23 package. An evaluation

kit (MAX1802EVKIT) featuring both devices is available

to expedite designs.

________________________Applications

Digital Still Cameras

Digital Video Cameras

Hand-Held Devices

Internet Access Tablets

PDAs

DVD Players

Features

♦ 2.5V to 11V Input Voltage Range

♦ Main DC-DC Controller

94% Efficiency

+2.7V to +5.5V Adjustable Output Voltage

Up to 100% Duty Cycle

Independent Shutdown

♦ Core DC-DC Converter

94% Efficiency

Up to 500mA Load Efficiency

Output Voltage Adjustable Down to 1.25V

Independent Shutdown

♦ Three Auxiliary DC-DC Controllers

Adjustable Maximum Duty Cycle

Independent Shutdown

♦ Power, Oscillator, and Reference Outputs to Drive

External Slave Controllers (MAX1801)

♦ Up to 1MHz Switching Frequency

♦ 3µA Supply Current in Shutdown Mode

♦ Internal Soft-Start

♦ Overload Protection for All DC-DC Converters

♦ Compact 32-Pin TQFP Package

MAX1802

Digital Camera Step-Down

Power Supply

________________________________________________________________ Maxim Integrated Products 1

Typical Operating Circuit

19-1850; Rev 0; 10/00

For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

Ordering Information

Note: Refer to the separate data sheet for MAX1801EKA in an 8-

pin SOT.

Pin Configuration appears at end of data sheet.

32 TQFP

PIN-PACKAGETEMP. RANGE

-40°C to +85°CMAX1802EHJ

PART

MAX1802

MASTER

MAX1801

SLAVE

INPUT

2.5V TO 11V

OSC POWER REF

MOTOR

CORE

MAIN

CCD

CCFL

TFT

Summary of content (28 pages)

PAGE 1
9-1850; Rev 0; 10/00 Digital Camera Step-Down Power Supply The main step-down DC-DC controller accepts inputs from 2.5V to 11V and regulates a resistor-adjustable output from 2.7V to 5.5V. It uses a synchronous rectifier to regulate the output with up to 94% efficiency. An adjustable operating frequency (up to 1MHz) facilitates designs for optimum size, cost, and efficiency. The core step-down DC-DC converter accepts inputs from 2.7V to 5.5V and regulates a resistor-adjustable output from 1.25V to 5.5V.
PAGE 2
MAX1802 Digital Camera Step-Down Power Supply ABSOLUTE MAXIMUM RATINGS VDDM, VH, ONM to GND .......................................-0.3V to +12V PGNDM, PGND to GND ........................................-0.3V to +0.3V VH to VDDM .............................................................-6V to +0.3V VL to VDDM ............................................................-12V to +0.3V VL, ONC, ON1, FB_, DCON_ to GND ......................-0.3V to +6V VDDC, REF, OSC, COMP_ to GND ..............-0.
PAGE 3
Digital Camera Step-Down Power Supply (Circuit of Figure 1, VVDDM = 6V, VVDDC = 3V, PGNDM = PGND = GND, DCON1 = REF, VONM = 3V, VONC = VON1 = VDCON2 = VDCON3 = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX 1.235 UNITS REFERENCE Reference Output Voltage 1.248 1.260 V REF Load Regulation VREF IREF = 20µA 10µA < IREF < 200µA 5 9 mV REF Line Rejection 2.7V < VOUT < 5.
PAGE 4
MAX1802 Digital Camera Step-Down Power Supply ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VVDDM = 6V, VVDDC = 3V, PGNDM = PGND = GND, DCON1 = REF, VONM = 3V, VONC = VON1 = VDCON2 = VDCON3 = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 5
Digital Camera Step-Down Power Supply (Circuit of Figure 1, VVDDM = 6V, VVDDC = 3V, PGNDM = PGND = GND, DCON1 = REF, VONM = 3V, VONC = VON1 = VDCON2 = VDCON3 = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS V AUXILIARY DC-DC CONTROLLERS 1, 2, 3 (VON1 = VCON_ = 3V) INTERNAL CLOCK OSC Clock Low Trip Level OSC Clock High Trip Level OSC falling edge 0.2 0.25 0.3 VDCON _ = 0.625V 0.575 0.625 0.675 VDCON _ = 1.
PAGE 6
MAX1802 Digital Camera Step-Down Power Supply ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VVDDM = 6V, VVDDC = 3V, PGNDM = PGND = GND, DCON1 = REF, VONM = 3V, VONC = VON1 = VDCON2 = VDCON3 = 0, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 11 V VONM = 0 20 µA VFBM = 1.5V, VVDDC = 0 600 VFBM = 1.5V, VVDDC = 3V 55 Main DC-DC Converter Supply Current (from VDDC) VFBM = 1.
PAGE 7
Digital Camera Step-Down Power Supply (Circuit of Figure 1, VVDDM = 6V, VVDDC = 3V, PGNDM = PGND = GND, DCON1 = REF, VONM = 3V, VONC = VON1 = VDCON2 = VDCON3 = 0, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 0.4 V LOGIC INPUTS (ONM, ONC, ON1) Input Low Level VIL Input High Level VIH ONM 1.8 ONC, ON1 1.6 ONM: VIN = 0 or 11V; ONC, ON1: VIN = 0 or 5V Input Leakage Current V 1 µA 2.7 5.5 V VOSC = 0.
PAGE 8
MAX1802 Digital Camera Step-Down Power Supply ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VVDDM = 6V, VVDDC = 3V, PGNDM = PGND = GND, DCON1 = REF, VONM = 3V, VONC = VON1 = VDCON2 = VDCON3 = 0, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN FBC Input Leakage Current VFBC = 1.35V COMPC Minimum Output Voltage VFBC = 1.35V, COMPC open 0.3 VFBC = 1.15V, COMPC open 2.00 COMPC Maximum Output Voltage VCOMPC(MAX) TYP MAX UNITS 100 nA V 2.
PAGE 9
Digital Camera Step-Down Power Supply EFFICIENCY vs. LOAD CURRENT (MAIN CONVERTER) EFFICIENCY vs. LOAD CURRENT (MAIN CONVERTER) 50 40 50 40 20 20 10 100 1000 10,000 MAX1802 toc03 VIN = +5V 40 VOUT = +1.8V 10 0 1 10 100 1000 10,000 LOAD CURRENT (mA) 10 100 LOAD CURRENT (mA) EFFICIENCY vs. LOAD CURRENT (CORE CONVERTER) MAXIMUM DUTY CYCLE vs. VDCON_ DEFAULT MAXIMUM DUTY CYCLE vs. FREQUENCY VIN = +5V 60 50 40 30 20 DEFAULT MAXIMUM DUTY CYCLE (%) 70 80 60 40 20 VOUT = +2.
PAGE 10
Typical Operating Characteristics (continued) (Circuit of Figure 1, VVDDM = 6V, VVDDC = 3.3V, VONM = 3V, VONC = VON1 = VDCON2 = VDCON3 = 0, TA = +25°C, unless otherwise noted.) REFERENCE VOLTAGE vs. TEMPERATURE REFERENCE VOLTAGE vs. REFERENCE CURRENT 1.255 1.250 1.245 MAX1802 toc10 MAX1802 toc09 1.253 1.252 REFERENCE VOLTAGE (V) REFERENCE VOLTAGE (V) 1.260 1.251 1.250 1.249 1.248 1.240 -40 1.
PAGE 11
Digital Camera Step-Down Power Supply MAIN OUTPUT LOAD-TRANSIENT RESPONSE STARTUP SEQUENCE MAX1802 toc16 MAX1802 toc15 VONM 5V/div VOUT AC-COUPLED 100mV/div 0V VMAIN 2V/div ILOAD 200mA/div 0V VCORE 2V/div 0A 0A COUT = 100µF 1ms/div 400µs/div CORE OUTPUT LOAD-TRANSIENT RESPONSE AUXILIARY OUTPUT LOAD-TRANSIENT RESPONSE MAX1802 toc18 MAX1802 toc17 VOUT AC-COUPLED 100mV/div VOUT AC-COUPLED 200mV/div ILOAD 100mA/div ILOAD 200mA/div 0A 0A VOUT = 2.
PAGE 12
MAX1802 Digital Camera Step-Down Power Supply Pin Description PIN NAME 1 FBM Main DC-DC Converter Feedback Input. Connect a feedback resistive voltage-divider from the output to FBM to set the main output voltage. Regulation voltage is VREF (1.25V). 2 COMPM Compensation for Main Controller. Output of main transconductance error amplifier. Connect a series resistor and capacitor to GND to compensate the main control loop (see Compensation Design). 3 ONM Main Converter Enable Input.
PAGE 13
Digital Camera Step-Down Power Supply PIN 17 18 19 20 NAME FUNCTION COMP2 Compensation for Auxiliary Controller 2. Output of auxiliary controller 2 transconductance error amplifier. Connect a series resistor and capacitor from COMP2 to GND to compensate the auxiliary controller 2 control loop (see Compensation Design). DCON2 Maximum Duty Cycle Control Input for Auxiliary Controller 2. Connect DCON2 to VL to set the default maximum duty cycle.
PAGE 14
MAX1802 Digital Camera Step-Down Power Supply Detailed Description The MAX1802 typical application circuit is shown in Figure 1. It features two step-down DC-DC converters (main and core), three auxiliary step-up DC-DC controllers, and control capability for multiple external MAX1801 slave DC-DC controllers. Together, these provide a complete high-efficiency power-supply solution for digital still cameras. Figures 2 and 3 show the MAX1802 functional block diagrams.
PAGE 15
+5V MOTOR DRIVE OFF CCM 4.7nF RCM 33k 100k 464k 4.7µF 6 2 CCC 470pF RCC 90k Q1 D5 Q1, Q2, Q3: FDN337N Q4, Q5: SEE MOSFET SELECTION SECTION D1, D2, D3, D4: CMSD-4448 D5: MBR0502L ON +7V BACKLIGHT OSC MAX1801 IN 1 0.1µH 3 REF COMP 4 GND DCON 5 8 DL 7 VL CC1 1000pF RC1 10k 1µF 10 40.2k VL 32 FB2 DL2 FB1 DL1 0.
PAGE 16
MAX1802 Digital Camera Step-Down Power Supply OSC VREF CLOCK GENERATOR 100ns ONE-SHOT CLK CLK REFERENCE REF VH VH COMPM VDDM DHM MAIN CURRENT-MODE DC-DC CONTROLLER FBM LXM DLM SOFT-START PGNDM VREF VL LDO ONM VL GND 2.4V CLK COMPC VDDC FBC CORE CURRENT MODE DC-DC CONTROLLER VREF LXC SOFT-START PGND ONC Figure 2. Simplified Block Diagram, Including Main and Core Core DC-DC Converter The MAX1802 core step-down DC-DC converter generates a 1.25V to 5.
PAGE 17
Digital Camera Step-Down Power Supply MAX1802 FB_ COMP_ R LEVEL SHIFT Q DL_ S SOFTSTART REF DCON_ CLK OSC FAULT PROTECTION Figure 3. Auxiliary Controller Block Diagram trollers regulate their output voltages by modulating the pulse width of the drive signal for an external N-channel MOSFET switch. The auxiliary controllers are inactive until the main output has started. Figure 3 shows a block diagram for a MAX1802 auxiliary PWM controller.
PAGE 18
MAX1802 Digital Camera Step-Down Power Supply age lockout threshold. The internal core converter, auxiliary controllers, and MAX1801 slave controllers each sink up to 30µA REF current during startup. If multiple MAX1801 controllers are turned on simultaneously, ensure that the master voltage reference can provide sufficient current, or buffer the reference with an appropriate unity-gain amplifier.
PAGE 19
Digital Camera Step-Down Power Supply See the Typical Operating Characteristics for fOSC vs. ROSC using different values of COSC. Due to duty cycle limitation in the main controller, keep fOSC ≤ VMAIN / (VVDDM(MAX) ✕ 500ns). Setting the Output Voltages Set the MAX1802 output voltage of each converter by connecting a resistive voltage-divider from the output voltage to the corresponding FB_ input. The FB_ input bias current is <100nA, so choose RL (the low-side FB_-to-GND resistor) to be 100kΩ.
PAGE 20
MAX1802 Digital Camera Step-Down Power Supply Use discontinuous current when the step-up ratio (VOUT / VIN) is greater than 1 / (1 - DMAX).
PAGE 21
Digital Camera Step-Down Power Supply For the main converter, the external gate drive swings between the voltage at VDDM and GND. For the auxiliary controllers, the external gate drive swings between the voltage at VDDC and GND. Use a MOSFET whose on-resistance is specified at or below the minimum gate drive voltage swing, and make sure that the maximum voltage swing does not exceed the maximum gate-source voltage specification of the MOSFET.
PAGE 22
MAX1802 Digital Camera Step-Down Power Supply and the output voltage is IOUT RLOAD, which is equal to IL RLOAD. Thus, the total DC loop gain is: AVDC = RLOAD AVDV AVEA / (AVCSM RDSP) 180° or AVDC AVDC = 215 VREF RLOAD / (VOUT RDS(ON)) PC PHASE Because of the current-mode control, there is a single pole in the loop response due to the output capacitor.
PAGE 23
Digital Camera Step-Down Power Supply 1) Determine the desired crossover frequency, either 1/3 of the zero due to the output capacitor ESR: fC = ZO 1 = 3 6 π COUT ESR or 1/5 of the switching frequency: f fC = SW 5 whichever is lower.
PAGE 24
MAX1802 Digital Camera Step-Down Power Supply 3) Place the compensation zero at the same frequency as the maximum output pole frequency (in Hz): ZC = 1 2VOUT − VIN = 2πRC CC 2 π (VOUT − VIN )RLOAD(MIN) COUT 180° 80 AVDC 60 PC PHASE 40 Solving for CC:   VOUT − VIN CC = COUT VOUT    RC IOUT(MAX) (2VOUT − VIN )  90° ZC = PO GAIN (dB) PHASE 20 GAIN O Use values of CC <10nF. If the above calculation determines that the capacitor should be >10nF, use CC = 10nF, skip step 4, and go to step 5.
PAGE 25
Digital Camera Step-Down Power Supply AVDC 30 180° PC GAIN PHASE ZC = PO 20 90° GAIN (dB) PHASE 4) Since response is 2nd order (-40dB per decade) between the complex pole pair and the ESR zero, determine the desired amplitude at the complex pole pair to force the crossover frequency equal to the ESR zero frequency. Thus: A(PO ) = (Z O / PO ) = L VIN2 2 COUT ESR2 VOUT 2 10 PHASE MARGIN Z0 0 GAIN MARGIN 0° ZRHP -10 FREQUENCY 5) Determine the desired compensation pole.
PAGE 26
MAX1802 Digital Camera Step-Down Power Supply converter is the SEPIC, shown in Figure 9. Inductors L1 and L2 can be separate inductors or can be wound on a single core and coupled like a transformer. Typically, using a coupled inductor will improve efficiency since some power is transferred through the coupling, so less power passes through the coupling capacitor (C2). Likewise, C2 should have low ESR to improve efficiency.
PAGE 27
Digital Camera Step-Down Power Supply MAX1802 + OUTPUT INPUT 1 CELL Li+ D3 INPUT 1 CELL Li+ VOUTC3 D1 L Main C1 MAIN D22 - OUTPUT ON ON DCON EXT EXT VOUT+ DCON Q1 Q1 C2 R1 R1 MAX1802 FB MAX1802 FB COMP COMP R2 R2 RC RC GC GC Figure 10. Auxiliary Controller, Flyback Configuration Figure 11.
PAGE 28
Digital Camera Step-Down Power Supply 32L TQFP, 5x5x01.0.EPS MAX1802 Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.